MEETINGS AND CONFERENCES

CONFERENCE ON HIGH-ENERGY PARTICLE PHYSICS*)

FIRST SECTION

The first session of the section “Elementary Particles and Their Interactions” was devoted to questions of the production of $\pi$-mesons by nucleons. The reports by M. G. Meshcheryakov, B. S. Neganov, V. P. Zrelov, I. K. Vzorov, O. V. Savchenko, and A. F. Shabudin, “Spectra of Secondary Protons and Deuterons from $(p—p)$ Collisions at an Energy of 660 MeV” and “Energy Spectra of $\pi^{+}$-Mesons in the Reaction $p+p \to p+n+\pi^{+}$ at 556 and 657 MeV,” described the study of the meson-production process carried out at the synchrocyclotron of the Institute for Nuclear Problems. With the aid of a large magnetic spectrometer, the spectra of the products of the following reactions were measured:

\[ p+p \to p+n+\pi^{+}, \tag{1} \]

\[ p+p \to p+p+\pi^{0} \tag{2} \]

and

\[ p+p \to d+\pi^{+}. \tag{3} \]

In addition, the study of the spectrum of $\pi$-mesons in reaction (1) was carried out with the aid of a telescope of scintillation counters (by range in an absorber). The experiments were performed on a proton beam extracted from the synchrocyclotron chamber. The intensity of the extracted beam was up to $3 \cdot 10^{9}$ particles/cm$^{2}$ sec. The angular distribution of the protons arising in reactions (1) and (2) is described by the law $0.8+\cos^{2}\theta$. Protons with momenta greater than 250 MeV/$c$ are emitted predominantly forward and backward, while protons with lower energy are emitted almost isotropically. Analysis of the spectrum of $\pi^{+}$-mesons shows that the matrix element for $\pi^{+}$-meson production depends on the meson momentum. The angular distribution is close to $0.43+\cos^{2}\theta$. These facts indicate that the production of $\pi$-mesons in reaction (1) occurs mainly in a $P$-state. Further analysis of the results shows that the process of meson production is strongly affected by the interaction of mesons with nucleons in the state with total angular momentum $3/2$ and isotopic spin $3/2$. In addition, the reports presented the results of a study of the spectra of $\pi^{+}$- and $\pi^{-}$-mesons formed in the bombardment of beryllium and carbon nuclei.

In the discussion of the reports, A. I. Meshkovsky spoke, indicating that in similar work carried out by him with a group of collaborators on the study of reactions (1) and (3), an angular distribution of mesons in reaction (1) was obtained that was close to isotropic.

R. Marshak’s report (USA) was devoted to the production of charged mesons on Li$^{6}$ and Li$^{7}$ nuclei by protons with an energy of 240 MeV. The purpose of the experiments was to test a number of consequences of the charge-independence hypothesis. The ratio of the cross sections for the production of $\pi^{+}$- and $\pi^{-}$-mesons at an angle of $90^\circ$ was measured. For Li$^{6}$ this ratio is equal to 64 at a meson energy of 40 MeV and 48 at an energy of 52 MeV. In the case of a Li$^{7}$ target the ratio is equal to 9.5 at an energy of 45 MeV and 1.7 at an energy of 52 MeV. This difference can be explained by taking account of the Pauli principle. Indeed, in production on Li$^{7}$ of $\pi^{+}$-mesons, 3 protons and 5 neutrons are formed, while in production of $\pi^{-}$-mesons, conversely, 3 neutrons and 5 protons are formed. In the production of $\pi^{+}$- and $\pi^{-}$-mesons on Li$^{6}$ the combinations turn out not to be so symmetrical: 3 protons and 4 neutrons for $\pi^{+}$-mesons and 5 protons and 2 neutrons for $\pi^{-}$-mesons. Therefore, in this case the probabilities of formation of $\pi^{+}$- and $\pi^{-}$-mesons must differ greatly.

*) The Conference on High-Energy Particle Physics was held in Moscow from May 14 to May 22, 1956.

In the report by L. Riddiford (England), the results were presented of a study of proton–proton interactions at an energy of 650 MeV, carried out on the accelerator in Birmingham. The investigation was performed with a Wilson diffusion chamber 18 inches in diameter, filled with hydrogen to a pressure of 26 atm and placed in a pulsed magnetic field. In all, 317 cases of interaction with two tracks at the end were observed. They were analyzed as elastic scattering and the formation of a single \(\pi\)-meson. The results agree with those obtained in other laboratories. The speaker also presented data obtained at an energy of 950 MeV. They confirm the interpretation of the interaction of nucleons on the basis of the isotopic-spin hypothesis. In conclusion, the speaker described work now in progress. Among these are the study of \((p-p)\) and \((p-d)\) interactions at an energy of 900 MeV, experiments with a polarized proton beam of energy 950 MeV, and also the construction of a hydrogen bubble chamber.

The report by S. Z. Belen’kii was devoted to the theory of multiple particle production. In the report, the application of Fermi’s statistical theory to the energy region \(1\text{–}5\) Bev was considered. As is known, Fermi’s theory, formulated at high energies, sharply contradicts experiment in this energy region. The author modified Fermi’s theory, taking into account the strong interaction of \(\pi\)-mesons with the nucleon at an energy of \(\sim 200\) MeV in a state with total angular momentum and isotopic spin \(3/2\). The theory developed in this way agrees with the results of studying interactions between nucleons at energies of \(1\text{–}3\) Bev. In addition, the speaker presented the results of calculations on star formation in antinucleon annihilation.

The participants of the meeting listened with interest to the report by L. Smith (USA) on studies carried out at the cosmotron in Brookhaven. First of all, the speaker described the study of the angular distribution in proton–proton scattering at energies up to 3 Bev. The measurements were carried out in the region of small angles, up to \(15^\circ\), in the center-of-mass system. The angular distribution shows a sharp maximum at small angles. Attempts were made to analyze these results within the framework of an optical model. The speaker then proceeded to present data on interactions obtained with a Wilson diffusion chamber. Unfortunately, the number of observed events is small, so that it is impossible to speak about the results of comparison with theory. In addition, work was carried out on the study of interactions of \(\pi\)-mesons with an energy of 1.9 Bev. The mesons were introduced into a Wilson chamber 1 m in diameter, in which carbon and lead plates were placed. In this work the lifetimes of \(\Lambda^0\)- and \(\theta^0\)-particles were measured. The speaker also acquainted the audience with the apparatus intended for studying the lifetimes of \(K\)-particles. On the same apparatus the scattering of \(K\)-mesons was studied. Experiments showed that, within the limits of errors, all \(K\)-mesons are scattered in the same way. Then an original method was described for extracting the beam from the cosmotron chamber, making it possible to obtain a beam containing \(1/3\text{–}1/2\) of the number of accelerated particles. A liquid hydrogen target will operate on this beam.

A large number of experiments on the scattering of \(K\)-mesons was carried out with photoemulsions. Several propane bubble chambers are operating in the laboratory, and in the near future three hydrogen and bubble chambers will come into operation. In conclusion, L. Smith described a study of the relation between ionization and the density of bubbles in the chamber.

Next came the report by Yu. D. Bayukov, M. S. Kozodaev, and A. A. Tyapkin, “Energy spectra of \(\gamma\)-quanta from the decay of \(\pi^0\)-mesons formed by protons with energies of 470 and 660 MeV.” With the aid of a paired spectrometer, the energy distribution of \(\gamma\)-quanta from the decay of \(\pi^0\)-mesons generated by protons of energy 660 MeV in the carbon target of the accelerator was measured for angles \(0\) and \(180^\circ\). These spectra differ strongly from those measured earlier at an energy of 470 MeV. The \(\gamma\)-quantum spectra were recalculated by known formulas into the spectra of \(\pi^0\)-mesons. The angular distribution of \(\pi^0\)-mesons at an energy of 660 MeV turned out to be close to isotropic, while at an energy of 470 MeV the distribution has the form \((0.3 \pm 0.1)+\cos^2\theta\).

In addition, in the work the spectrum of \(\gamma\)-quanta from the decay of \(\pi^0\)-mesons generated in \((p-p)\) collisions was measured (by a difference method). In the center-of-mass system the angular distribution of \(\pi^0\)-mesons has the form \(1+(0.3 \pm 0.2)\cos^2\theta\).

In the reports by Yu. D. Prokoshkin and A. A. Tyapkin, the results were reported of a study of the production of \(\pi^0\)-mesons by protons on hydrogen and complex nuclei. The measurements were carried out with a telescope composed of scintillation and Cherenkov counters. The absolute cross sections for hydrogen and deuterium were measured by a difference method, by recording the flux of \(\gamma\)-quanta emitted at the angle

\[ \theta=\arccos\frac{1}{\sqrt{3}} \]

(in the center-of-mass system). It turned out that at an energy of 660 MeV:

\[ \sigma(p+p\to\pi^0)=(3.6\pm0.3)\,10^{-27}\ \text{cm}^2, \]

\[ \sigma(p+d\to\pi^0)=(10.6\pm1.4)\,10^{-27}\ \text{cm}^2. \]

Subtraction yielded the cross section

\[ \sigma(p+n\to\pi^0)=7.0\cdot10^{-27}\ \text{cm}^2. \]

The ratio of the cross sections for production of \(\pi^0\)-mesons on the proton and on the neutron is equal to 0.5. The authors also obtained data on the dependence of the \(\pi^0\)-meson production cross section on the energy in the range \(390\text{--}660\) MeV. The angular distribution of \(\pi^0\)-mesons at an energy of 660 MeV is close to isotropic. As the energy is decreased, a term \(\sim \cos^2\theta\) appears in the angular distribution.

In studying the production of \(\pi^0\)-mesons on complex nuclei by protons with an energy of 660 MeV, a dependence of the angular distribution of \(\pi^0\)-mesons on the mass number of the target nucleus was found. This is explained by the slowing down of the incident protons in the nuclear matter.

The report by V. P. Dzhelepov, K. O. Oganesyan, and V. B. Flyagin was devoted to the production of \(\pi^0\)-mesons under the action of neutrons with an effective energy of 580 MeV. The \(\gamma\)-quanta were recorded by a telescope consisting of Cherenkov and scintillation counters. The cross section for \(\pi^0\)-meson production in \((n-p)\) collisions proved to be equal to \((5.7\pm1.5)10^{-27}\ \text{cm}^2\). The results of the study of \(\pi^0\)-meson production on deuterium show that the cross sections of \((p-p)\) and \((n-n)\) interactions coincide within the limits of error. The yield of \(\pi^0\)-quanta was also measured for bombardment by neutrons of a number of elements. The results agree with the assumption that mesons are produced only on the surface of the nucleus. For heavy elements a deviation from the law \(A^{2/3}\) is observed.

At the following sessions, questions of the interaction of nucleons with nucleons were discussed.

With great attention the participants listened to the report by E. Segrè (USA) on the antiproton. The speaker gave a detailed account of the state of experiments on the study of antiprotons. One of the most interesting results is the fact that the interaction cross section for antiprotons is approximately twice as large as the cross section for the proton. A considerable part of the report was devoted to results obtained by the photographic method. Segrè demonstrated a number of photographs showing the mechanisms of annihilation in emulsion, including cases of annihilation only into \(\pi\)-mesons. Analysis shows that the average number of \(\pi\)-mesons per annihilation star is \(5\pm1\). The report provoked a lively discussion.

The next report, read by Ya. A. Smorodinsky, was devoted to a review of experimental data on the scattering of fast nucleons by nucleons. The speaker also made a number of comments on what conclusions can be drawn from these data and what experiments are presently lacking in order to complete this analysis. Unfortunately, the energy region below 100 MeV, where further investigations are necessary, has been very poorly studied. As is known, the principal fact established as a result of analysis of the experimental data is the difference in the \(n-p\) interaction in states with isotopic spin \(T=1\) and \(T=0\). The cross section corresponding to \(T=1\) does not depend, over a wide energy interval, either on angle or on energy. This indicates that the scattering takes place in the states \({}^{1}S_0\) and \({}^{3}P_0\). At present it is necessary to carry out a separation according to ordinary spin. For a complete separation of the singlet and triplet states it is necessary to determine five functions. The speaker considers that the most direct experiments allowing the necessary results to be obtained are experiments on polarization correlation. The existing phase analysis is ambiguous. In addition, the question arises whether, in the case of nucleon-nucleon scattering, there does not exist the phase ambiguity established for the case of meson-nucleon scattering. As R. M. Ryndin showed, such uniqueness does not exist in the case of nucleons.

The cross section corresponding to \(T=0\) is similar to that obtained in the Born approximation.

In the report by V. P. Dzhelepov the results of a study of the elastic scattering of neutrons with an energy of 580 MeV by protons and neutrons were presented. The neutrons were recorded from recoil protons by means of a scintillation telescope. In the case of hydrogen the measurements were made by the difference method. The cross section for scattering of neutrons by neutrons was determined from the cross section for scattering by deuterons in the angular region where additivity of the cross sections occurs. The cross section for elastic scattering of neutrons by neutrons at an energy of 590 MeV coincides with the cross section for elastic scattering of protons by protons at the same energy.

The angular distribution in the scattering of neutrons with an energy of 590 MeV by protons shows that the direct and exchange interactions contribute to the scattering by amounts of the same order. However, in going from energies of 300–400 MeV to an energy of 600 MeV, the picture changes. The cross section at an angle of \(0^\circ\) increases with increasing energy, while the cross section at an angle of \(180^\circ\) decreases. As L. Okun and I. Pomeranchuk indicated, this circumstance is due to an increase in the role of the inelastic processes at energies of approximately 500–600 MeV and higher. Analysis of the results on the \((n-p)\) interaction permits the following conclusions to be drawn: 1) the cross sections of the interaction in states with isotopic spin \(T=0\) and \(T=1\) strongly

differ, the difference decreasing with increasing neutron energy; 2) the behavior of the cross section for \(T=1\) is anomalous, whereas the behavior of the cross section for \(T=0\) is close to that calculated in the Born approximation; 3) the meson-production cross sections at an energy of 580 MeV differ little for states with \(T=0\) and \(T=1\). In addition, at this energy the elastic-scattering cross sections at angles \(\sim 90^\circ\) turn out to be close in states with \(T=0\) and \(T=1\). These facts call into question the conclusion about a weak interaction of nucleons in the state with \(T=0\). The speaker also indicated that, in order to explain the angular distribution in elastic scattering of neutrons by protons, it is necessary to take into account angular momenta of the incident particles up to \(l=6\).

In the report by R. Marshak (USA), results were presented that had been obtained in the study of the differential cross section for neutron scattering by protons at an energy of 180 MeV. In addition, the speaker presented data on the scattering of polarized protons at 150 MeV and data on \((n—p)\)-polarization. The polarization is positive at small angles and negative at large angles. Results of a phase analysis at an energy of 150 MeV were given.

The results of a phase analysis of data on proton scattering by protons were presented also in the report by E. Clementel (Italy). Experimental results were used in the energy range from 18 to 260 MeV. The analysis takes into account only \(S\)- and \(P\)-waves. The set of phases obtained does not coincide with the phases presented in Marshak’s report. It should be noted that, in general, the number of admissible sets of phases is large, and making any particular choice is very difficult.

The report by V. G. Solov’ev and I. E. Tamm and V. Ya. Fainberg contained an analysis of the present state of meson theory and of the results of comparison between theory and experiment. In the authors’ opinion, despite the unsatisfactory quantitative state of contemporary meson theory, it describes reality qualitatively well. For example, the existence of an isobaric state was predicted, the repulsion at small distances, and so forth. On the quantitative side, a direction is developing in theory that attempts to obtain results not from any approximations, but from general principles. As examples, dispersion relations and limiting theorems are mentioned. In this way it has been possible to establish that the coupling constant is close to 15. In addition, the report gave a brief characterization of the approximate methods of Chew–Low and Tamm—Dancoff—Dyson.

The present state of nuclear-force theory was the subject of the report by K. Brueckner (USA). The author presented theoretical results concerning the interaction between nucleons and comparison with experiment. Ya. A. Smorodinskii, who spoke in the discussion, pointed out the unfoundedness of the conclusions drawn by the speaker both in the theoretical consideration and in the comparison with experiment.

In the report by M. G. Meshcheryakov and N. P. Bogachev, results were presented of an investigation of elastic scattering of protons by protons at energies of 460–660 MeV. As is known, in the energy region 150–360 MeV the cross section for \((p—p)\)-scattering is isotropic and does not depend on energy. At an energy of 460 MeV a departure from isotropy is observed, which increases as the energy increases. Measurements at energies of 560 and 660 MeV showed that the differential cross section increases with decreasing angle. Differential scattering cross sections at large angles decrease. The total cross section in the interval 460–660 MeV remains constant.

Elastic scattering of protons with an energy of 660 MeV in the region of small angles was also studied in the work of E. G. Bogomolov, S. M. Zamkovskii, S. Ya. Nikitin, and Ya. M. Selektor. The results agree with those obtained by Meshcheryakov and Bogachev.

In the report by V. P. Dzhelepov, V. I. Moskalev, V. I. Satarov, B. M. Golovin, and S. V. Medved’, data were presented on the total cross sections for the interaction of nucleons with nucleons, deuterons, and nuclei in the energy interval 370–660 MeV. The total cross sections were determined from the attenuation of the beam under conditions of good geometry. Thanks to meson production, the total cross section for \((p—p)\)-interaction increases with energy. The total cross section for \((n—p)\)-interaction remains approximately constant in the same energy interval. This is due to a decrease in the cross section for the elastic interaction of nucleons in the state with isotopic spin \(T=0\). The cross sections for \((n—d)\)- and \((p—d)\)-interactions are close to one another.

The final report in this group of reports was the report by L. I. Lapidus, “On the Theory of Exchange Collisions of Fast Nucleons with Deuterons.”

The meeting then proceeded to discuss problems of the interaction of \(\pi\)-mesons with nucleons.

V. Weisskopf (USA) reported on the results of an investigation of the scattering of \(\gamma\)-quanta with energy 140 MeV by hydrogen and complex nuclei at the Massachusetts Institute of Technology. The measurements were carried out below the threshold for production of \(\pi^0\)-mesons, using scintillation counters that made it possible to determine the energy of the scattered \(\gamma\)-quantum. Preliminary results obtained for hydrogen show that the scattering is close to Thomson scattering. The theoretical interpretation takes into account the Thomson mechanism, as well as resonance scattering by the meson cloud, described by a formula of the Breit–Wigner type.

The report by K. Brueckner (USA), “Meson-nucleon and nucleon-nucleon elastic and inelastic scattering in the energy interval up to 1.5 Bev,” contained an analysis and interpretation of experimental data on the basis of crude models. The maxima in the cross sections of meson-nucleon interaction are due to a strong interaction in the state with total angular momentum and isotopic spin \(3/2\) (the first) and the production of additional mesons (the subsequent ones). The angular distribution in elastic scattering at an energy of 1 Bev, which exhibits a strong forward directionality, confirms the presence of an inelastic interaction.

For the nucleon-nucleon interaction, a rapid increase of the cross section in the energy region of 500 Mev is characteristic, accompanied by a deformation of the angular distribution in forward-angle scattering. From an analysis of the data, the speaker concludes that the inelastic processes are, for the most part, associated with the state with isotopic spin \(T = 1\). It should be noted that such a conclusion is not in agreement with the conclusions from the work of Dzhelepov and co-workers. If, however, this is so, then the simplest explanation can be obtained on the basis of the isobar model, according to which mesons are produced through an intermediate state with isotopic spin \(3/2\).

In the report by E. L. Grigor’ev and N. A. Mitin, results were presented from a study of the scattering of \(\pi^+\)-mesons by protons at an energy of 310 Mev. The angular distribution was studied with the aid of nuclear emulsions. The experimental results can be described by a series of Legendre polynomials in which terms of zeroth, first, and second order are present. In addition, with the aid of an electronic computer a phase analysis was carried out. Taking account of the \(S\)- and \(P\)-waves, the following phase shifts were obtained: \(\alpha_3 = 22.7^\circ\), \(\alpha_{33} = 130.9^\circ\), and \(\alpha_{31} = -11.2^\circ\). Inclusion of the \(D\)-wave does not introduce large changes.

In the reports by A. I. Mukhin, E. B. Ozerov, B. Pontecorvo, I. V. Popova, and G. N. Tentyukova, results were set forth from studies of the scattering of \(\pi^+\)-mesons on protons at energies of 176, 200, 240, 270, and 307 Mev, performed with the aid of scintillation counters. The authors analyzed in detail the behavior of phase shifts with change of energy.

In the report by E. Clementel (Italy), “Phase analysis of reactions proceeding through only one channel,” the question was discussed of finding phases from experimental data on the scattering of mesons by protons and of applying an analogous analysis to nuclear reactions.

The report by L. S. Dul’kova, T. A. Romanova, I. B. Sokolova, L. V. Sukhov, K. D. Tolstoy, and M. G. Shafranova was devoted to the interaction of negative and positive \(\pi\)-mesons of energy about 300 Mev with hydrogen, deuterium, and the nuclei of photographic emulsions. The total cross section, angular distribution, and phases obtained in the analysis of the results for \(\pi^+\)-mesons agree with the results of other authors. The report also gives phases for the state with isotopic spin \(1/2\), obtained from data on the scattering of \(\pi^-\)-mesons. The angular distribution in angular scattering by deuterons has a maximum in the forward direction. The interaction cross section with the nuclei of the emulsion, according to the authors’ measurements, amounts to 87% of the geometrical cross section.

In the report by L. Rosenfeld (England), “Scattering of fast particles by nuclei,” the results were reported of theoretical studies of the scattering of electrons and \(\mu\)-mesons by nuclei*). Experiments on electron scattering can yield, and do yield, extremely interesting information on the distribution of charge in the nucleus. It was found that, in the region of energies of about 70 Mev, phase changes due to the structure of the nucleus amount to about 30%. At higher energies (where experiments have already been carried out), these changes amount to \(\sim 20\%\). In conclusion the speaker touched on the question of the scattering of fast neutrons by nuclei.

The report by R. Marshak (USA) dealt with the results of measurements of the differential scattering cross sections of \(\pi^+\)- and \(\pi^-\)-mesons of energy 40 Mev by hydrogen and of \(\pi^+\)-mesons of energy 28 Mev by carbon. The study of the scattering of \(\pi\)-mesons by nucleons at low energies is of great interest from the point of view of determining the \(S\)-phases, whose behavior is not explained by contemporary theories. In the case of hydrogen the cross section for \(\pi^+\)-mesons of energy 40 Mev proves to be much larger than the cross section for \(\pi^-\)-mesons. The experiment gives for \(\alpha_3\) a value differing from the extrapolation of Orear.

The report by M. S. Kozodaev, R. M. Sulyaev, A. I. Filippov, and Yu. A. Shcherbakov was devoted to the results of a study of the interaction of \(\pi^-\)-mesons of energy 300 Mev with helium nuclei. The study was carried out in a Wilson diffusion chamber of diameter 270 mm, filled with helium to a pressure of 14 atm. The cross section of elastic scattering \((\pi^- + \mathrm{He}^4 \to \pi^- + \mathrm{He}^4)\) and of all types of inelastic scat—

* The report was published in UFN 60, issue 4 (1956).

the cross sections turned out to be, respectively, 51 and \(99 \cdot 10^{-27}\ \text{cm}^2\). The cross section for the production of a \(\pi^+\)-meson is \(3 \cdot 10^{-27}\ \text{cm}^2\) (with an error of \(\pm 2 \cdot 10^{-27}\ \text{cm}^2\)). Analysis of the angular distribution in inelastic scattering and other factors shows that \(\pi\)-mesons interact with individual nucleons in the nucleus.

The report by V. P. Dzhelepov, V. G. Ivanov, M. S. Kozodaev, V. G. Osipenko, N. I. Petrov, and V. A. Rusakov discussed the results of a study of the interaction of \(\pi\)-mesons with carbon and lead nuclei at energies of 230–250 MeV. The measurements were carried out in a Wilson chamber placed in a magnetic field. Plates of the substance under investigation were placed in the middle of the chamber.

The work of V. V. Krivitsky and A. A. Reut was devoted to the search for cases of \(\pi^+\)-meson production on carbon by \(\pi^-\)-mesons with an energy of 308 MeV. The corresponding cross section turned out to be \(2.6(\pm 1.3) \cdot 10^{-27}\ \text{cm}^2\).

The last in this series of reports was the communication by A. E. Ignatenko, A. I. Mukhin, E. B. Ozerov, and B. Pontecorvo on the study of the dependence of the range of \(\pi\)-mesons in nuclear matter. The total cross sections for the interaction of \(\pi\)-mesons with beryllium, carbon, and oxygen nuclei were measured, as well as the cross sections for inelastic interactions for beryllium, carbon, copper, and lead nuclei in the energy interval 140–400 MeV. Although the behavior of the cross section with energy in general terms follows the dependence of the total scattering cross sections of \(\pi\)-mesons on hydrogen and deuterium, the mean free path was determined from the cross sections of inelastic interaction. Comparison of the obtained values of the mean free paths with those calculated from the cross sections of interaction with nucleons shows that \(\pi\)-mesons interact, mainly, with individual nucleons of the nucleus.

The next session was devoted to reports concerning the interaction of nucleons with nuclei.

The first to be heard was the report by O. Chamberlain (USA) on polarization experiments with high-energy nucleons. The speaker described work on proton–proton scattering. The aim of the work was to obtain the entire set of data at one energy necessary for performing a complete phase analysis (including \(F\)-waves). The experiments on triple scattering were described in detail. In addition, the speaker reported data from a preliminary phase analysis, as a result of which three sets of phases were obtained. The results of calculations on an electronic computer were also presented. The speaker pointed out that the \(S\)-phase can be obtained on the basis of a model of a potential with repulsion at small distances. The next stage of the work is an attempt to go to lower energies in order to obtain the dependence of the phases on energy.

The report by M. G. Meshcheryakov, G. D. Stoletov, and S. B. Nurushev concerned questions connected with the polarization of protons with an energy of 660 MeV. In the experiments the azimuthal asymmetry of protons in double scattering on beryllium was studied, as well as the dependence of the polarization on the atomic weight of the second scatterer. The authors found that polarization arises both in diffraction and in quasi-elastic scattering, and its sign is the same as in the case of \((p—p)\)-scattering. At the same time the degree of polarization is greatest for elastically scattered protons. When the energy is varied from 300 to 635 MeV, the polarization in elastic scattering on beryllium changes insignificantly (it remains no less than 60%). The polarization in quasi-elastic scattering increases in this energy interval by more than a factor of two and reaches values close to the magnitude of the polarization in free \((p—p)\)-scattering.

Then the participants of the conference heard the report by R. Marshak (USA), “Polarization Effects in \((p—p)\)-Scattering at 210 MeV and in Proton Scattering by Carbon and Calcium Nuclei at 215 MeV.” In addition to the data obtained, the speaker presented the results of a theoretical treatment using the optical model.

The report by I. I. Levintov, “On the Magnitude of the Nuclear Spin-Orbit Interaction,” was devoted to the analysis of experiments making it possible to determine the magnitude of the spin-orbit interaction. The speaker investigated two phenomena: polarization of nucleons in scattering by nuclei and spin-orbit splitting of single-particle levels. In both cases, close values of the interaction constant are obtained.

In the report by N. A. Guliev, the subject was the polarization of high-energy neutrons in scattering on carbon \(\mathrm{C}^{12}\), taking into account the volume of the nucleus. The calculations were made in the scalar version of meson theory for various distributions of density over the nucleus.

In the work of I. G. Lang and K. A. Ter-Martirosyan, the interaction of fast neutrons and deuterons with nonspherical odd-odd nuclei was studied theoretically. Nonsphericity leads to a change in the scattering cross section and to the appearance of a rotational spectrum. In the case of neutron scattering the authors obtained formulas for a semitransparent nucleus, and in the case of deuteron scattering—for a black nucleus. The results may prove useful in determining the sizes and shapes of nonspherical nuclei from scattering experiments.

The report by El-Nadi (Egypt) was devoted to the theoretical study of stripping reactions. The author considered inverse processes in which an incident nucleon or deuteron knocks two particles out of the nucleus, forming helium isotopes.

The report by J. Filber was devoted to the interaction of protons with energy of 1 Bev with nuclei of photographic emulsions. The work was carried out on an accelerator in Birmingham.

The last report in this section was that by N. A. Perfilov and O. V. Lozhkin, “Heavy Nuclear Fragments in Fissions Produced by Fast Protons in Nuclear Emulsions.”

A large number of reports were presented at sessions devoted to photonuclear reactions.

The review report by A. M. Baldin was devoted to the photoproduction of mesons on protons and deuterons. The analysis of data on the photoproduction of \(\pi\)-mesons is based, on the one hand, on the use of general properties of the scattering matrix and, on the other hand, on very general assumptions about the physical nature of the phenomena: limitations at low energies by low partial waves, isotopic invariance, resonant interaction of mesons with nucleons in states with total angular momentum \(3/2\) and isotopic spin \(3/2\). Such an approach makes it possible to reveal the basic features of the process of meson photoproduction, which reduce to the following: in the reaction \(\gamma + p \to \pi^{+} + n\), mesons near the production threshold are produced in the \(S\)-state owing to the \(E1\) transition. At energies of 200–300 Mev, the transitions \(M1\) and \(E2\) to the state \(P_{3/2}\) play an essential role. In the reaction \(\gamma + p \to \pi^{0} + p\), the main role is played by the transitions \(M1\) and \(E2\) to the state \(P_{3/2}\). Production of \(\pi^{0}\)-mesons in the \(S\)-state is improbable. In addition, the study of the reaction \(\gamma + p \to \pi^{+} + n\) near the photoproduction threshold made it possible to determine the coupling constant by means of a limiting theorem. The study of the photoproduction of \(\pi^{-}\)-mesons on deuterium is of great interest because of the difference in the electromagnetic properties of the neutron and the proton. The speaker also listed the results available in this field.

The report by A. A. Abrikosov, “Effects in Quantum Electrodynamics at High Energies,” considered problems connected with deviations from the existing theory at ultrahigh energies.

The report by I. Ya. Pomeranchuk, “Difficulties of Electrodynamics and Meson Theory and Experiments with Weakly Interacting Particles,” aroused great interest. As is known, the success of renormalization theory in quantum electrodynamics gave hope for the successful construction of a consistent theory of meson interactions. However, in these cases, unlike electrodynamics, one is dealing with strong interactions, so that perturbation theory proves inapplicable. An attempt to find a way of solving the equations without using perturbation theory led to the conclusion that if the existing theory (electro- and mesodynamics) is valid up to indefinitely high energies, then such directly observable quantities as the electric and meson charges must be equal to zero. Thus, the modern theory is internally contradictory. The energies at which new effects may appear, in the case of meson phenomena, evidently should fall in the range \(10^{8}\)—\(10^{9}\) ev. It is assumed that new effects will also appear in processes involving weakly interacting particles (electrons, \(\mu\)-mesons, \(\gamma\)-quanta). As an example, the speaker pointed to the Compton effect and the scattering of electrons by electrons. However, the energies at which the study of these processes is of interest amount to several tens of Bev. There exist more accessible experiments, although they are also more complicated. These are cases of pair formation (at energies \(\sim 1\) Bev), in which an electron and a positron scatter with a large relative momentum (at large angles). Experiments on the formation of pairs of \(\mu\)-mesons are of similar interest.

The report by A. B. Migdal was devoted to bremsstrahlung emission and pair production in condensed matter. At high energies, large longitudinal distances are essential for these processes, which leads to a number of physical consequences: the dependence of bremsstrahlung and emission in a crystalline medium on orientation relative to the crystal axes and the influence of multiple scattering, which substantially reduces the probabilities of these processes.

V. Panofsky (USA) reported on preliminary results of a study of multiple photoproduction of \(\pi\)-mesons. The studies were carried out on the Stanford linear accelerator. The production of pairs of \(\pi\)-mesons on hydrogen was recorded by the appearance of negative \(\pi\)-mesons. In addition, a dependence of the yield of positive \(\pi\)-mesons on electron energy was observed. The results obtained indicate an asymmetric distribution of energy between \(\pi^{+}\)- and \(\pi^{-}\)-mesons. It can be shown that the \(\pi\)-meson is emitted as an \(S\)-wave, and the \(\pi^{+}\)-meson as a \(P\)-wave.

The audience listened with great attention to the report by M. Lévy (France) on work carried out at Stanford (USA) on the scattering of high-energy electrons on hydrogen and deuterium and on its theoretical interpretation. These works are of great interest, since they possibly indicate a violation of the hypothesis of charge ...

independence. To explain the experimental results it is necessary to make assumptions about the structure of nucleons. The best agreement in the case of the proton is obtained when the same form factor is used for charge and magnetic moment, with a distribution radius \(\sim 0.8 \cdot 10^{-13}\) cm. However, if this value of the radius is used in the case of the neutron, one cannot obtain the correct value of the electron–neutron interaction. This is also confirmed by the results of studies of fast-electron scattering on deuterons. To obtain agreement with experiment the neutron may be regarded as pointlike (with a radius much smaller than that of the proton). In the speaker’s opinion, the interaction of only \(\pi\)-mesons cannot give a complete explanation. The attraction of \(K\)-particles, owing to the asymmetry of their properties, leads to an increase of the proton radius and a decrease of the neutron radius. The results can also be explained on the basis of the hypothesis that the nucleon radius is small, and that at distances \(\sim 0.5 \cdot 10^{-14}\) cm Coulomb’s law is violated. However, no final conclusion can yet be drawn.

At the meeting three reports by V. Panofsky (USA) were heard on work carried out at the Stanford linear accelerator. In the first report, data were presented on direct electromagnetic production of pairs of \(\mu\)-mesons. To distinguish \(\mu\)-mesons in direct production from \(\mu\)-mesons arising in decay, use was made of the fact that the angular distribution of \(\mu\)-pairs is found to be strongly extended forward, whereas \(\pi\)-mesons formed in nuclei have, in the region of small angles, an almost isotropic distribution. The speaker described in detail the experimental procedure and demonstrated photographs of the apparatus. The obtained cross-section values for hydrogen are 30% higher than the theoretical ones. In the second series of measurements the excitation function of the process of \(\mu\)-pair production was studied. The study of \(\mu\)-pair production on lead did not reveal the existence of any anomalous effects.

The second report was devoted to the investigation of direct production of \(\pi\)-mesons by electrons. Finally, in the last report data were presented on bremsstrahlung at high energies.

In the report by N. B. Delone, the results of a study of the photodisintegration of the deuteron by \(\gamma\)-quanta with energies of 50–150 MeV were set forth. The results agree with those previously published in the literature.

Photodisintegration of the deuteron was also studied in the work of V. S. Roganov and P. S. Baranov by recording the neutrons arising in the breakup of the deuteron. The neutrons were recorded by the threshold reaction \(C^{12}(n, 2n)C^{11}\). Therefore, in measurements above the meson threshold, alongside the process of photodisintegration, neutrons arising in the photoproduction of \(\pi\)-mesons are also recorded. The results on photodisintegration of the deuteron agree with those published in the literature.

A communication by R. Wilson (USA) was devoted to a theoretical interpretation of the data on photodisintegration of the deuteron at high energies. As is known, in the energy region above 50–70 MeV an excess of experimental cross sections over the theoretical ones, calculated under the assumptions of a purely electromagnetic mechanism, is observed. The author introduced a meson mechanism and, using experimental data on photoproduction of \(\pi\)-mesons on nucleons, obtained satisfactory agreement with the experimental results.

In the report by A. N. Gorbunov, K. V. Kosyreva, and V. M. Spiridonov, “Photodisintegration of helium by high-energy \(\gamma\)-rays,” results obtained in a Wilson chamber were set forth. A study of the angular and energy distributions of protons and neutrons arising in the interaction of \(\gamma\)-quanta with helium nuclei shows that the integral absorption cross section coincides with that predicted from the dispersion relations and that the electric dipole mechanism of disintegration plays the main role. In addition, the results make it possible to estimate the ratio \(S/V_3\) in the operator of interaction of the electromagnetic field with the nucleus. This ratio is approximately 0.1.

The last session was devoted to new particles. In the report by Menon (India), results were reported on the study of \(S\)-particles by means of a Wilson chamber. The speaker then reviewed data on the interaction of fast \(\alpha\)-particles in cosmic rays with matter.

In the report by A. I. Alikhanian, the results of a study of the mass spectrum of cosmic-ray particles, performed on Mount Aragats, were set forth.

The report by Van Gan-chang and Zhu Xun-yuan (China) was devoted to preliminary results on the production of heavy mesons and hyperons in cosmic rays.

In the report by Tsu (China), a possible variant of the theory of elementary particles was reported.

R. Peierls (England) reported on the results of studies of hyperfragments including \(\Lambda^0\)-particles.

The concluding report was by J. Steinberger on a study of the production of strange particles by \(\pi\)-mesons with energy 1.3 BeV.

E. M. Leikin

SECOND SECTION

At the meetings of the second section, in more than 60 papers and communications by Soviet and foreign scientists, questions connected with the design and theory of various types of elementary-particle accelerators were examined. The subjects of individual meetings of the section were accelerators, linear accelerators, installations with strong focusing, and also methods of experimenting with high-energy particles.

The report “The Six-Meter Synchrocyclotron of the Institute for Nuclear Problems of the Academy of Sciences of the USSR” was presented at the plenary session by D. V. Efremov, M. G. Meshcheryakov, A. L. Mints, V. P. Dzhelepov, P. P. Ivanov, V. S. Katyshev, E. G. Komar, I. F. Malyshev, N. A. Monoszon, I. Kh. Nevyazhskii, B. I. Polyakov, and A. V. Chestnoi (Academy of Sciences of the USSR). It was devoted to a description of a powerful accelerator built at the Institute for Nuclear Problems in 1949 and at present transferred by the Soviet Government to the recently organized Joint Institute for Nuclear Research. The synchrocyclotron makes it possible to obtain protons with an energy of 680 MeV and is used to study the interaction of nucleons with high-energy nucleons, investigations of the properties of mesons, etc.

The diameter of the electromagnet poles is 6 m. In the gap between them, amounting to 60 cm, a magnetic field with an intensity of 16,800 oersteds is created at the center, falling to the periphery by 5%, the region of usable field being brought in radius to 278 cm. The vacuum chamber, with a volume of about 30 m³, has a sectional construction and is made of brass plates with rubber seals. Evacuation is carried out by two high-vacuum pumps with a speed of up to 30,000 l/sec. The pressure near the ion source is about \(10^{-3}\) mm Hg, the working pressure in the chamber is \(6 \cdot 10^{-6}\) mm Hg, and when the supply of hydrogen to the ion source is shut off it is \((1—2) \cdot 10^{-6}\) mm Hg.

The high-frequency accelerating field between the edge of the dee and the grounded frame is obtained by excitation of radio-frequency oscillations in a half-wave resonant system. The synchrocyclotron is equipped with apparatus which makes it possible to switch off the high-frequency supply in the course of the nonworking part of the acceleration cycle, to obtain single acceleration cycles, to control the voltage supplied to the ion source, and to switch on instruments and installations for investigations located on the extracted particle beams. All these processes are “tied” by means of a special system to the cycle of frequency variation of the high-frequency generator, which feeds the resonant system. The high-frequency voltage is switched on before each acceleration cycle by a photoelectric device, which is located in the housing of the variator in such a way that the beam of light falling on the photomultiplier is intersected by the vanes of the rotating rotor of the variator.

Control of the accelerator (including the pumps and refrigerating installations) is automated and is carried out from a special building, which is about 400 m distant from the synchrocyclotron. In addition to the power-supply units, installations for monitoring and controlling that equipment which cannot be separated from the accelerator are located there. The accelerator itself is situated in a large hall, where part of the apparatus for physical investigations is also located. The main apparatus and instruments for nuclear investigations are behind a protective concrete wall 5.5 m thick and are controlled remotely. The extraction system used on the synchrocyclotron makes it possible to release to the outside about 6% of the proton beam circulating in the chamber. In the shielding of the synchrocyclotron and in the yoke of its electromagnet there are 16 collimators, through which unpolarized and polarized beams of nucleons, beams of \(\pi^\pm\)-mesons, and beams of gamma quanta from the decay of \(\pi^0\)-mesons are extracted. The accelerating chamber is equipped with four probes, by means of which it is possible to irradiate samples of various substances with a beam of protons accelerated to the desired energy.

On the accelerator it is possible to carry out experiments simultaneously on several beams of identical or different particles.

At the synchrocyclotron of the Institute for Nuclear Problems, a number of interesting and important studies were carried out, in particular, the investigation of elastic scattering of protons by protons, of neutrons by neutrons and by protons; the investigation of the processes of formation of charged and neutral \(\pi\)-mesons in collisions of nucleons with nucleons and deuterons; and the investigation of the processes of interaction of \(\pi\)-mesons with nucleons.

In the report of A. L. Mints, I. Kh. Nevyazhskii, and B. I. Polyakov (Academy of Sciences of the USSR), “Certain Features and Basic Data of the High-Frequency System of the Six-Meter Synchrocyclotron,” it was indicated that, in order to expand the frequency range, it proved necessary to complicate the simple high-frequency circuit of the deuteron synchrocyclotron. The resonant system is designed in the form of a nonuniform line, the wave impedance of which varies in a definite manner along its length. Parallel connection of the tank capacitance entails a large inductance because the supports carrying the elements of the system are made in the form of spiral springs.

The resonant system consists of a duant with a grounded frame, a connecting line, and a frequency variator, whose weight is about 1 ton. The voltage on the duant is 15 kV. The average generator power is 50 kW; during the nonworking part of the cycle it is blocked by a modulator, and the power is reduced by half. In order to shorten the path of the current in the system, reduce the initial capacitance of the variable capacitor, and increase its overlap coefficient, the rotor of the variator is mounted on the inner stem of the connecting line. To reduce the magnitude of the high-frequency current passing through the ball bearings, the latter are shunted by a special coaxial capacitor with a capacitance of 0.2–0.3 μF. In addition, the duant, as well as the transition from the duant to the connecting line, is given a special configuration. The design features of the accelerating chamber, the duant, and the line, as well as the corresponding choice of elements of the circuit connecting the resonant system with the generator, made it possible to remove most of the resonant frequencies beyond the working range.

To eliminate excitation of the system at parasitic frequencies lying outside the working range, a new circuit of a “band” self-generator was proposed, in which self-excitation occurs only within a prescribed broad working frequency range. The circuit makes it possible to regulate the feedback coefficient over wide limits, even if the parasitic frequencies of the system lie in close proximity to the upper boundary of the working range. In the high-frequency system of the accelerator, the variable coupling with the generator provides the necessary change in the impedance of the system when the frequency of the accelerating voltage is reduced from 26.5 to 13.0 MHz.

In the reports by the staff of the Institute for Nuclear Problems—V. P. Dmitrievsky, V. I. Danilov, Yu. N. Denisov, N. L. Zapatina, V. S. Katyshev, A. A. Kropin, and A. V. Chestnoi, “Extraction of a Proton Beam from the Six-Meter Synchrocyclotron by Means of Excitation of Radial Oscillations,” and V. I. Danilov, V. P. Dmitrievsky, and A. V. Chestnoi, “On One Method for Increasing the Density of a Proton Beam Extracted from the Six-Meter Synchrocyclotron,” the results of theoretical and experimental development of a new method for extracting accelerated particles from the chamber of the synchrocyclotron of the Institute for Nuclear Problems were presented.

With the aid of an artificially produced azimuthal inhomogeneity of the magnetic field, additional oscillations of the particles in the horizontal and vertical planes are excited in the accelerator. The increase in the amplitude of the radial oscillations in the region of this perturbation is used to inject the particles into the magnetic channel. The required inhomogeneity of the magnetic field is produced by means of iron masses located near the boundary of the working region of the accelerator. After the beam emerges from the magnetic channel, it is focused in the horizontal plane by a magnetic field with a constant gradient. Calculations showed that the optimum focusing action on a proton beam with an energy of 680 MeV is obtained for a magnetic-field gradient in the range 750–1000 oersted/cm over a region 45 cm long and 5–8 cm wide. This optimum value of the gradient was also found from experiments with a beam, which showed that the focusing device increases the beam density by a factor of two to three. After the application of the method described, in 1954 the extraction coefficient of protons accelerated to an energy of 680 MeV from the chamber was approximately 6%, and the beam intensity reached \(7 \cdot 10^7\) protons/sec. The authors indicated that an analogous method can be applied for the extraction and injection of particles in other accelerators with a time-constant magnetic field.

V. I. Danilov, V. P. Dmitrievsky, B. I. Zamolodchikov, V. S. Katyshev, A. A. Kropin, and A. V. Chestnoi (Institute for Nuclear Problems) presented the paper “Correction of the Median Surface of the Magnetic Field of the Six-Meter Synchrocyclotron,” which considers the influence of the position and shape of the median surface of the accelerator’s magnetic field on the character of particle motion in the vertical plane. The report describes two methods for determining the position and shape of the median surface: by means of thin loops and frames suspended in the magnetic field of the electromagnet gap. By redistributing the currents in the coils of the electromagnet and by shimming with thin steel sheets, the authors achieved a deviation of the median surface from the mean plane of the order of 1 cm.

Professor Bakker (European Organization for Nuclear Research—CERN) reported on the frequency-modulation system in the CERN synchrocyclotron,* which is designed to accelerate protons up to 600 MeV and is to be put into operation in 1957. At present, construction of the magnet and the synchrocyclotron windings is almost complete. The diameter of its poles is 5 m. The field at the center is 18,800 oersted. The frequency of the accelerating field changes from 27.6 to 16.6 MHz. This change is achieved not by means of a rotating capacitor, as in most such accelerators, but by the use of a peculiar tuning tuning fork. The plates of the tuning fork

* For a description of this accelerator, see, for example, Suppl. N. Cim., ser. X, 2, 403 (1955).

have dimensions of \(54 \times 200\ \text{cm}^2\); the thickness of the plates decreases toward the edges. The tuning fork is made of an aluminum alloy, chosen because of its good conductivity and high mechanical strength. It has been calculated that the bending stresses in the plates are \(6\ \text{kg}/\text{mm}^2\), whereas the elastic limit is \(12\ \text{kg}/\text{mm}^2\). Oscillations of the tuning fork at its natural frequency of 55 cycles are maintained by a mechanical exciter.

Tests on a model of the tuning fork one-quarter full size showed that the damping decrement is extremely small—less than \(0.25 \cdot 10^{-4}\). The power dissipated in such a system by the coils is 200 W, with water cooling being used. Prof. Bakker noted that the use of an aluminum alloy for the tuning fork simplified the solution of a number of engineering problems in comparison with a similar system used on the synchrocyclotron at Berkeley, USA. There the tuning fork is made of a special steel hardened in nitrogen, and therefore good conductivity is achieved only by coating it with a special conducting alloy; to create a constant temperature gradient it is necessary to cut the tuning-fork plates near the edges. Prof. Bakker observed that one of the main reasons for which the system he described had been chosen was the instability of the rotating capacitor, and said that now, after becoming acquainted with the synchrocyclotron of the Institute of Nuclear Problems, he was no longer very sure of the clear superiority of the tuning-fork resonator.

Corresponding Member of the USSR Academy of Sciences A. L. Mints, speaking in the discussion, stated that Professor Bakker’s report was devoted to the second direction in the development of high-frequency systems for synchrocyclotrons. When work on such a system began in the Soviet Union in 1947–1948, those designing it were very concerned by problems associated with the fact that the rotating capacitor had to be in vacuum. Analysis and experiments showed that the difficulties could be eliminated. In the synchrocyclotron of the Institute of Nuclear Problems the rotating capacitor operates no less reliably than the other units. At the same time, the variant with a tuning-fork resonator is very interesting, since it makes it possible to conduct the vacuum seal in a very simple manner.

H. Tyren (Uppsala, Sweden) devoted his communication to a description of the 185 MeV synchrocyclotron. The synchrocyclotron is located in an underground hall; the experimental room is also underground and separated from the accelerator by a two-meter concrete shield. The synchrocyclotron is controlled from a building situated on the surface of the earth to the east of the accelerator. The weight of the magnet is 650 t; the maximum magnetic field is 21,000 oersted. The diameter of the pole tips is 2 m, and the distance between them is 20 cm. A rotating capacitor is used in the accelerator. The voltage on the dees is 7 kV. The injection current is about 1 mA; the current of protons accelerated to an energy of 185 MeV is of the order of \(1\ \mu\text{A}\), with about 1% of the beam being extracted. Extraction is carried out by scattering radial oscillations according to the Tuck and Teng method used at the Institute of Nuclear Problems of the USSR Academy of Sciences. The extracted beam is focused by two strong-focusing lenses. The first of them, placed in the hall where the accelerator is located (field gradient of the lens \(1000\ \text{oersted}/\text{cm}\), aperture 12 cm, length about 50 cm, weight 600 kg), makes the beam almost parallel, with a diameter of 5 cm; the second, located in the experimental room, brings the beam cross section down to a few square millimeters. At this accelerator, in particular, studies are being carried out of the polarization of high-energy protons, elastic and inelastic scattering of protons in carbon, etc. Investigations of a medical nature are also being conducted. Tyren illustrated his report with a large number of diagrams and photographs and answered numerous questions in detail.

In the reports by staff members of the P. N. Lebedev Physical Institute of the USSR Academy of Sciences E. M. Moroz and M. S. Rabinovich, “On increasing the limiting energy and improving focusing in the cyclotron,” and A. K. Burtsev and A. A. Kolomensky, “On the theory of the ring phasotron,” questions were considered related to the use in accelerators of constant magnetic fields. The first report proposes the creation of a split magnet of the cyclotron type with homogeneous fields that have different intensities in the sectors and in the gaps between them. The region of orbital stability can be substantially widened by spirally bending the boundaries of the magnetic sectors. Under certain conditions, with the aid of such a construction it is apparently possible to accelerate protons, without passing through the most dangerous resonances, up to an energy on the order of 500 MeV.

A ring phasotron is the name given to a ring-shaped strong-focusing accelerator with a time-constant field, which in neighboring sectors is opposite in direction (proposed in 1953 by A. A. Kolomensky, V. A. Petukhov, and M. S. Rabinovich). In the report by Burtsev and Kolomensky it was shown that, with a theoretically selected variation of the closed periodic orbits (when all orbits are composed of arcs of circles), variants of this installation are possible in which the tolerances on various parameters are of the same order as in ordinary strong-focusing synchrophasotrons, but the radius of the installation exceeds the radius of curvature of the particle trajectory in the sectors by a factor of four to six. The use of the systems considered in both reports may make it possible to greatly increase—

increase the intensity of the beam of accelerated particles as compared with existing accelerators.

The communication by Dmitriev, Krasnov, and Kaprov (Moscow State University), “On the Question of Beam Deflection in a Cyclotron,” was devoted to the extraction of the internal beam from the chamber of a cyclotron designed to accelerate deuterons to an energy of 10.6 MeV. The ion source is displaced relative to the center of the chamber in such a way that the center of the ion trajectory coincides with the center of symmetry of the field. This displacement reached 60 mm, and when displaced by 15 mm a sharp increase in the intensity of the extracted beam was observed. With the aid of additional shimming, it was possible on this cyclotron to extract up to 20% of the beam.

With a brief communication on the 1.5 m cyclotron, Kalinin, Kondrashev, Naumov, Nemenov, Panasyuk (Academy of Sciences of the USSR) spoke. In 1947, from this cyclotron, a beam of 18 MeV deuterons was extracted. The maximum field of the accelerator is 18,000 oersteds, the field decrease is 1.7%, and the gap between the poles is 18 cm. The particles are extracted from a radius of 67 cm. In 1953 an arc source, developed independently of R. S. Livingston, was installed on the cyclotron. The accelerating system consists of dees and two coaxial lines. The voltage on the dees is about 180 kV. The control post is located behind a water shield, whose thickness is 1 m. The ion beam is focused by means of a sector magnet (horizontal focusing) and an electrostatic device (vertical focusing) and is extracted to a distance of 12 m from the cyclotron, which makes it possible to get rid of the background of neutrons and gamma quanta. The maximum current density on the target is 15 μA/cm², with 90% of the beam contained in a cross section of \(2 \times 1.5\) cm², and the spread of the particles in the beam in energy is 1%. At present, questions concerning the use of strong focusing are being considered, and the behavior of the particle beam is being investigated.

A large number of papers presented at the conference on accelerator topics were devoted to the synchrophasotron of the Academy of Sciences of the USSR for an energy of 10 BeV, as well as to the associated Institute for Nuclear Research. Its general description was given in a presentation at the plenary session of the conference by Corresponding Member of the Academy of Sciences of the USSR V. I. Veksler, on behalf of a group of physicists and engineers from a number of institutes of the Academy of Sciences of the USSR who took part in the development, design, and construction of this installation (V. I. Veksler, D. V. Efremov, A. L. Mints, P. M. Zeidlits, P. P. Ivanov, A. A. Kolomenskii, E. G. Komar, I. F. Malyshev, N. A. Monoszon, I. Kh. Nevyazhskii, V. A. Petukhov, M. S. Rabinovich, S. M. Rubchinskii, and K. D. Sinelnikov).

The synchrophasotron of the Academy of Sciences of the USSR for 10 BeV, now in the start-up stage, is the most powerful installation of this type. The main characteristics of the accelerator are:

Injection of particles into the synchrophasotron is performed from a linear accelerator at 7.5 MeV with a 570 kV forinjector. Control of the synchrophasotron units is remote. The accelerator installation itself and the equipment directly connected with it (vacuum system, injector, etc.) are housed in a special building, to which there adjoins a building for experimental apparatus, separated from the accelerator by an eight-meter protective concrete wall. All the remaining equipment, including the main control panel, from which remote control of all accelerator units is carried out, is located in a separate building at a distance of 100 m from the first.

In the paper by V. I. Veksler, A. A. Kolomenskii, V. A. Petukhov, and M. S. Rabinovich (Electrophysical Laboratory), “Physical Foundations of the Construction of a Synchrophasotron for 10 BeV,” the basic requirements imposed on such an accelerator were considered.

In designing the synchrophasotron in 1949–1950, the following problems were solved: on the motion of particles at various stages of the acceleration cycle (injection of parti-

MEETINGS AND CONFERENCES

particles from the preaccelerator, particle capture, motion in the accelerated regime, beam extraction), the influence of various perturbations on particle motion, and the effect of harmful resonances with betatron and synchrotron oscillations. Requirements and tolerances were considered for the parameters of the main units of the synchrophasotron (linear accelerator, injection optics, the magnet and its power-supply system, the vacuum chamber, the high-frequency system), as well as questions of protection against harmful radiation. In particular, it was found that, in the presence of technical pulsations of the rate of rise of the magnetic field, the tolerance for the resonant harmonic component with the frequency of synchrotron oscillations must not exceed 3.5%. In considering free oscillations, the so-called method of reflecting surfaces was applied. The results were reported of studies carried out on an operating model of the synchrophasotron (with proton energy of about 180 MeV), as well as the results of a comparison of the theory used in designing the 10-billion-eV synchrophasotron with experiments on this installation.

In reports by a group of staff members of the Research Institute of Electrophysical Apparatus, Ministry of Electrical Industry (E. G. Komar, G. A. Zeitlenok, I. F. Malyshev, I. M. Roife, and N. S. Streltsov) and staff members of the Electrophysical Laboratory of the USSR Academy of Sciences (L. P. Zinov’ev, V. A. Petukhov, K. D. Sinel’nikov, L. I. Bolotin, S. K. Esin, G. A. Zeitlenok, P. N. Zeidlits, V. S. Kladnitskii, I. F. Malyshev, A. M. Nekrashevich, I. M. Roife, L. S. Shushkever), questions connected with the technical implementation of particle injection into the synchrophasotron of the USSR Academy of Sciences were discussed. The reports described in detail the injector device, the injection optics, and gave data on the intensity and stability of the injected proton beam, as well as its geometrical parameters. Experimental results were presented that had been obtained on the 180 MeV accelerator model and directly on the installation under construction, concerning the passage of the beam through the injection device and its admission into the accelerator chamber. A report presented by staff members of the Research Institute of Electrophysical Apparatus, Ministry of Electrical Industry, also described a method for obtaining high-voltage, high-frequency pulses with a steep leading edge. The pulses serve to obtain a beam with a wide angular spread, which substantially facilitates adjustment work during the start-up process.

General technical problems connected with the radio-frequency system for the accelerator were considered in the report by A. L. Mints, S. M. Rubchinskii, M. M. Veisbein, F. A. Vodop’yanov, A. A. Kuz’min, and V. A. Uvarov (Academy of Sciences), “System for coupling the frequency of the accelerating field and the magnetic-field intensity of the synchrophasotron.” The necessary connection between the frequency of the accelerating and magnetic fields in a synchrophasotron must be maintained with an accuracy of the order of 0.3–0.1%. In addition, particle acceleration in a synchrophasotron imposes stringent requirements on the instant at which the various elements of the accelerator are switched on, which must correspond strictly to a definite value of the magnetic-field intensity. In particular, injection of particles into the chamber must be carried out with an accuracy of 5–10 μsec, which corresponds to a relative error in the value of the magnetic-field intensity of \(3 \cdot 10^{-4} — 6 \cdot 10^{-4}\). The report presented two methods for attaining the required accuracy in “locking” the frequency of the accelerating voltage to the magnetic field: first, by means of a system with an integrating magnetic-field sensor, a diode functional converter, and a wide-band frequency-modulated generator with negative feedback through a precision frequency detector; and second, by means of a system with an auxiliary electromagnet, through whose winding the current of the main magnet of the accelerator flows and in whose gap is placed a coil with a ferrite core of the oscillatory circuit of the driving generator.

A second of the proposed systems was described in the report by A. L. Mints, S. M. Rubchinskii, M. M. Veisbein, and A. A. Vasil’ev (USSR Academy of Sciences), “Control systems for injection processes in synchrophasotrons.” It provides locking of the injection instants with an accuracy better than \(5 \cdot 10^{-4}\). To form control pulses not requiring high switching accuracy, phantastrons are used.

The subsequent report by F. A. Vodop’yanov (USSR Academy of Sciences) was devoted to the technical implementation of one part of the system for coupling the frequency and the magnetic field—the driving generator. Wide-band frequency modulation with a precision dependence on the modulating signal can be effected either by means of a precision driving generator, or by stabilizing the modulation characteristic, using negative feedback with an ordinary generator. In the course of development, a block diagram with negative feedback was chosen. Stability in such a scheme is provided by a precision frequency detector in the negative-feedback circuit. The results of an experimental test of the described driving generator showed that its modulation characteristic is linear to an accuracy of the order of one percent in the frequency range from 0.15 to 1.5 MHz and has a slope of the order of 70 kHz/V. The stability of the characteristic is better than 0.07% over 100 hours of operation. The level of parasitic frequency modulation

at the frequencies of the synchronous oscillations (600–2000 cps) less than \(5\cdot 10^{-7}\). The spectral density of the noise modulation in the same frequency range is less than \(0.05\ \mathrm{cps}/\mathrm{h}\).

The question of accelerating elements for a synchrophasotron and the basic problems of supplying them with high-frequency voltage were discussed in the report by Yu. M. Lebedev-Krasin (Academy of Sciences of the USSR). The need to obtain considerable high-frequency accelerating voltages with a large range of variation of the supply-voltage frequency, which reaches 10–20, is a significant difficulty, since the oscillatory power in this reaches hundreds of kilowatts, and the power consumption reaches thousands of kilowatts. The report indicated that the parameters of accelerating elements largely determine the principles of construction and the power of the supply equipment; therefore their selection is one of the important points in designing synchrophasotrons. From this point of view various types of accelerating elements and systems were considered. It was shown that the required total power of the output stages of a multichannel supply system, when the number of channels is increased, decreases inversely proportionally to their number, while the power of an individual channel decreases inversely proportionally to the square of the number of channels. The author established that, with a small frequency range (less than 10), in synchrophasotrons designed for energies below 10 Bev, it is expedient to use accelerating electrodes and periodic high-frequency power-supply systems built on the basis of transformer–electrode devices. In particular, it turned out that the use in the USSR Academy of Sciences synchrophasotron for 10 Bev of a power-supply system consisting of two accelerating electrodes reduced the required supply power by approximately a factor of two, and the amount of ferrite by 18 tons, compared with a single accelerating transformer, which was used at the cosmotron*).

For the stages of preliminary amplification of the high-frequency voltage, circuits have been developed that use a new broadband radio-frequency transformer.

The report by I. Kh. Nevyazhsky, G. M. Drabkin, V. F. Trubetsky, A. S. Temkin (Academy of Sciences of the USSR) was devoted to the use of inductances with ferrite cores in the circuits of the powerful stage of the USSR Academy of Sciences synchrophasotron. In designing the installation, the problem arose of constructing powerful stages of high-frequency generators according to a circuit with a tuned anode circuit containing inductances with ferrite cores. With the aid of the cores the frequency of the circuit is retuned to the frequency of the master oscillator, varying within the limits 0.18–1.5 Mc/s. The reactive power of the inductance coil at an accelerating-electrode capacitance of 1500 picofarads and a high-frequency-voltage amplitude of 20 kV reaches 3000 kva. All this required study of the behavior of ferrites in strong fields. Nickel-zinc ferrites with initial magnetic permeabilities from 200 to 800 were investigated, with the aim of determining the conditions under which the amplitude of oscillations is stable on the slopes of the resonance curve of a circuit containing ferrite, and questions related to magnetization were considered. It was found that, for the low-voltage bias circuit from the high-frequency field, it is expedient to use a system of two parallel inductances with a bias winding placed in the middle of the high-frequency current leads.

In the high-frequency device of the 10 Bev synchrophasotron, the variable inductance was made in the form of a section of coaxial line partly filled with ferrite. The weight of the ferrite of one circuit is 800 kg.

Questions connected with the electromagnet of the 10 Bev synchrophasotron were discussed in the reports of the staff members of the Research Institute of Electrophysical Apparatus of the Ministry of Electrical Industry of the USSR: E. G. Komar, N. A. Monoszon, N. S. Streltsov, and G. M. Fedotov, “Certain features of the design of the electromagnet of the synchrophasotron of the electrophysical laboratory for 10 Bev”; A. A. Zhuravlev, E. G. Komar, I. A. Mozalevsky, N. A. Monoszon, and A. M. Stolov, “Magnetic characteristics of the EFLAN synchrophasotron for 10 Bev”; M. A. Gashev, E. G. Komar, N. A. Monoszon, A. M. Stolov, and F. M. Slevakova, “Power-supply system of the electromagnet of the EFLAN synchrophasotron for 10 Bev”; and the staff members of the Electrophysical Laboratory: M. D. Veselov, A. A. Zhuravlev, I. A. Mozalevsky, E. A. Myae, A. M. Stolov, and S. V. Fedukov, “Methods and results of an experimental investigation of the magnetic field of the 10 Bev synchrophasotron.”

The outside diameter of the magnetic ring of the synchrophasotron is 72 m. The magnet consists of 48 C-shaped blocks weighing 800 tons each; the blocks are joined in four quadrants. The gap between the magnet poles is 40 cm, with a pole width of 2 m. In the vertical parts of the blocks there are oval cutouts: half of them are used to place elements of the vacuum system, and the other half to facilitate personnel access to the chamber when installing the apparatus and carrying out work in the chamber.

) The cosmotron is a synchrophasotron-type accelerator for an energy of 3 Bev, located at Brookhaven (USA) and put into operation in 1952. For a detailed description of this installation, see the special issue of the journal Rev. Sci. Instr. 24, No. 9 (1953); translation in the collection Problems of Modern Physics*, No. 11, 1954.

of the necessary work. The copper winding of the block, weighing 57 tons, is placed in a casing which, in the event of fire, is automatically filled with nitrogen. The magnet is made of sheets of electrical steel with a silicon content of 4% in order to reduce the coercive force; the thickness of these sheets is 4 and 1 cm. The maximum field is equal to 13,000 oersteds at a radius of 28 m, the field at injection is 150 oersteds. The regions suitable for using the value of the magnetic field occupy, in radius, 150 cm at injection and 40 cm at the end of acceleration. To compensate for distortions caused by the influence of residual magnetism, saturation of the steel, dynamic distortions, and errors in the installation of the blocks, special correction windings are used. The correction of the distortions made it possible to increase by 40–70 cm in radius the region of suitable values of the magnetic field. To study the behavior of the magnetic-field parameters, measuring coils, permalloy probes, and sensors based on the phenomenon of nuclear paramagnetic resonance are used.

A serious problem in the synchrophasotron power-supply system was the creation of converters of great power, consisting of four parallel-connected twelve-phase converters and four electrical-machine units with flywheels of large mass, with a total peak power of 140,000 kW. Special sealed ignitrons are used in the installation. Pulsations of the magnetic field are suppressed by means of negative feedback. As Comrade Strelov reported at the conference, adjustment of the power-supply system is being completed on the accelerator. The supply of two blocks connected in parallel has been tested, and a current of 6300 A has been obtained. Soon all four blocks of the power-supply system will be switched on.

The principal requirements for the vacuum chamber were set out in the report by E. G. Komar, I. F. Malyshev, Ya. L. Mikhelis, and A. V. Popkovich (Research Institute of Electrophysical Apparatus of the Ministry of Electrical Industry of the USSR), “The Vacuum Chamber of the 10-Bev JINR Synchrophasotron.” The vacuum chamber is double-walled. The corrugated chamber, whose walls are pole shoes sealed with textolite, getinaks, and technical rubber, makes it possible to maintain a pressure down to 1 mm Hg. The high-vacuum chamber is made of thin sheets of stainless steel with sealing at the joints of the sheets by a special rubber; here the pressure does not exceed \(2 \cdot 10^{-5}\) mm Hg.

All the reports connected with the construction of the 10-Bev synchrophasotron aroused great interest among both Soviet and foreign scientists. The speakers answered in detail numerous questions concerning the technique of making units and parts, methods of maintaining tolerances, and measures for combating foundation settlement, soil flow, etc.

A. L. Mints, speaking in the discussion, pointed out that the work connected with the design and construction of the USSR Academy of Sciences synchrophasotron for 10 Bev had been carried out in close contact with departmental organizations, so that a number of the reports presented at the conference are the result of joint work. As a result of prolonged common work, the stringent requirements set by the physicists before the radio engineers were fulfilled. At present the USSR Academy of Sciences synchrophasotron is at the stage of start-up work; however, the radio-engineering equipment has already been tested and has given the expected results.

At the plenary session, a report by the American scientist J. Marshall (Chicago, USA) on the project of a 10–15-Bev proton synchrotron, which is now being developed at the Argonne National Laboratory, USA, was heard with interest. The originality of the project, in which a number of measures have been adopted to reduce the weight of the magnet, attracted great attention.

Apparently, in this respect the project makes the fullest use of the possibilities of weak-focusing accelerators. In the accelerator described, with a magnetic field uniform in radius, horizontal and vertical focusing of the particles is carried out by means of a specially chosen shape of the magnetic sectors, i.e., so-called “edge” focusing is used, as applied, for example, in certain types of mass spectrometers. In the present project the edges of all eight sectors of the magnet make, with the radius of curvature of the particle trajectory, an angle of about 11°. The electromagnet yoke has no special pole shoes: it will consist only of two horizontal and two vertical parts and will have, in cross section, the shape of the letter “O.” The external dimensions of the yoke are: width about 2.3 m, height about 1.3 m. Inside the yoke two windings, each about \(30 \times 18\ \text{cm}^2\) in size, are placed, and between them the accelerating chamber (its dimensions \(64 \times 18\ \text{cm}^2\)). The magnetic flux creates, in the air gap of the yoke, a homogeneous field over the entire width of the accelerating chamber. The intensity of the magnetic field at the beginning of acceleration is about 400 oersteds, and at the end about 19,000 oersteds. The radius of curvature of the particle trajectory is equal to 24 m. The expected injection energy is 50 Mev. As the injector, a linear accelerator or a cyclotron with focusing by means of a magnetic field varying in azimuth will be used. The acceleration time is 1 sec, the duration of the acceleration cycle 3 sec. The weight of the iron of the magnet is approximately 3500 tons. The annular magnet will be surrounded by protective concrete walls, whose thickness is 12 m on the outside of the ring and 8 m on the inside.

S. A. Vekshinskii and M. S. Rabinovich (Vacuum Research Institute of the Ministry of Radio Engineering Industry of the USSR), in the report “Vacuum Pumping Units for Accelerators,” noted that, in order to improve the operation of pumps, they use a continuous trap cooled by liquid nitrogen. This trap almost completely stops the carry-over of oil vapors from the pump into the evacuated volume. The units described are convenient for use on accelerators, although the pumping speed with the trap employed is reduced from 5000 to 3000 l/sec.

Four reports constituted an experimental and theoretical study of the mechanism of capture into the betatron acceleration regime.

Staff members of the P. N. Lebedev Physical Institute and of the Second Scientific Research Institute of Physics of Moscow State University—V. I. Veksler, Yu. N. Lobanov, V. N. Logunov, E. P. Ovchinnikov, V. A. Petukhov, M. S. Rabinovich, and V. D. Rusanov (report “Physical Foundations of Electron Capture into the Betatron Acceleration Regime”), and Yu. N. Lobanov and V. A. Petukhov (report “Experimental Foundations of the Theory of Particle Capture into the Betatron Acceleration Regime”)—reported that the study of the influence of the current of injected electrons on the efficiency of capture made it possible to establish the existence of two essentially different mechanisms of capture and to determine their limits. One of them is determined only by the adiabatic compression of instantaneous orbits associated with the growth of the magnetic field of the betatron; the other is determined by the collective interaction of the electrons of the beam with the spatial-charge inhomogeneities present in the chamber.

The experiments showed that capture is always observed both on the leading and trailing fronts of the injection pulse and on its flat portion, but the contributions made by these regions are different and depend on the various injection parameters. The authors note the high efficiency of the collective capture mechanism, which, as established by experiments with a movable radial shutter, ensures contraction of the orbits by about 1 mm per revolution. In these experiments the shutter, without a substantial decrease in intensity, could be introduced into the chamber by 6–7 mm beyond the edge of the injector anode. It was found that the increase, observed when the frequency of the current feeding the magnet was increased (in these experiments from 200 to 800 cps), in the intensity is not connected with an increase in the rate of rise of the magnetic field during the injection period.

The Czechoslovak scientist M. Seidl (Research Institute of Vacuum Electrotechnics, Prague) reported that, in the betatron of the accelerator laboratory of this institute, the influence of a field gradient varying in time and in azimuth on the capture of betatron oscillations was studied. The azimuthal change of the field gradient was produced artificially with the aid of an electrostatic lens with strong focusing. A pulsed voltage was applied to the lens, which could be switched on with various delays relative to the injection pulse. It was established that the influence of the space charge of the electrons can be fully compensated by changing the field gradient in time and in radius at such small injection currents that the natural capture of electrons is practically equal to zero. The experimental results, as Seidl noted, confirm the correctness of Bardeen’s hypothesis that the change of the field gradient in azimuth and in time, created by the space charge at the moment of injection, can play a decisive role in the capture of electrons in betatrons.

In the report by P. A. Ryazin (P. N. Lebedev Physical Institute), “On the Capture of Electrons into the Betatron Acceleration Regime,” an attempt was made to explain the capture theoretically, taking into account the effect of self-induction and the adiabatic change of the parameters during acceleration.

V. I. Veksler, who spoke with a comment, noted that P. A. Ryazin’s work had been discussed at a number of seminars at the Physical Institute. It was noted that the experimental data diverge substantially from the predictions of the theory. The calculations, in the opinion of the institute’s theoreticians, are erroneous or unclear in many points. In connection with this, the picture of the capture mechanism set forth by P. A. Ryazin apparently does not correspond to reality.

Chuchlin (Tomsk Polytechnic Institute) reported on a method of increasing the intensity by approximately a factor of two, used on a betatron designed for an energy of 15 Mev. The injection pulse has two maxima. The increase in intensity is apparently explained by double capture on the leading front of the pulse. The speaker noted that the optimal conditions of capture are observed with a sharp increase and a slow fall of the pulse. The possibility of capture on the flat portion of the pulse is also not excluded.

In cyclic electron accelerators for energies above 1 Bev, the principal difficulty lies in compensating radiation losses, which grow in proportion to the fourth power of the energy. The losses reach, for example, at 10 Bev about 30 Mev per revolution. Together with these radiative losses, namely the quantum, discrete character of the energy losses, affects the motion of electrons in the accelerator, leading, as calculations show, to the buildup of betatron and synchrotron oscillations.

“As V. I. Veksler noted in the discussion, this question is not abstract. It is no accident, therefore, that clarification of the degree of danger of build-up took place at the conference in an atmosphere of lively discussion.

A. A. Sokolov (Moscow State University), presenting his report “Motion of Electrons in Cyclic Accelerators with Allowance for Quantum Effects” and the report of D. D. Ivanenko, A. A. Sokolov, and I. M. Ternov (Moscow State University) “Theory of Synchrotron Electrons,” stated that, according to the quantum-mechanical calculations of these authors, the amplitude of betatron oscillations, owing to the quantum character of the radiation, grows proportionally to the square root of the acceleration time and depends strongly ($\sim E^{7/2}$) on the energy. The additional radiation damping caused by the emission, in the authors’ opinion, is small and is characterized by a damping time of the order

\[ \frac{E^3}{(mc^2)^2 W}, \]

where $W$ is the radiation intensity. In connection with this, acceleration in a weak-focusing magnet to energies greater than $2 \div 3$ Bev becomes practically impossible, and rather stringent conditions are imposed on the operating regime of strong-focusing synchrotrons.

This result was also used by A. N. Matveev (Moscow State University) in the report “Motion of Electrons in Cyclic Accelerators as a Stochastic Process.”

A. A. Kolomenskii and A. N. Lebedev (P. N. Lebedev Physical Institute, Academy of Sciences) in their report “Certain Features of High-Energy Electron Cyclic Accelerators” pointed out the erroneousness of the results of A. A. Sokolov and his collaborators. The authors, in the classical equations of motion, introduced statistical terms describing the quantum fluctuations of the radiation. In addition, the allowance for the combined action of the accelerating system of the installation and of the reaction of the radiation proved to be extremely important. The “radiation friction” thus caused in weak-focusing magnets strongly limits the growth of the amplitudes of betatron oscillations. In strong-focusing magnets, in order that the radiation reaction cause damping of the oscillations, special measures are needed, which, however, do not create additional difficulties. According to the authors’ calculations, the damping time of the betatron oscillations is approximately equal to

\[ \frac{E}{W}, \]

thanks to which the build-up of oscillations does not constitute a serious danger for accelerators.

Those who took part in the discussion, V. L. Ginzburg and M. S. Rabinovich, noted the correctness of Kolomenskii and Lebedev’s assumptions and calculations and pointed out the errors made by Sokolov and his collaborators.

The subject of the report on linear accelerators, which was presented by a group of staff members of the Institute of Chemical Physics, Academy of Sciences of the USSR (N. N. Semenov, I. L. Zelmanov, B. M. Stepanov, B. K. Shembel, and A. S. Kompaneets), was certain results in the development of high-current linear accelerators. In the course of this work, a number of important technical problems were solved, connected, for example, with the construction of an injector giving a current of the order of fractions of an ampere at a voltage of $10^5$ v, with the development of special accelerating resonators, etc. In addition, A. S. Kompaneets succeeded in carrying out an exact solution of the equations jointly for the phase and radial motion in an accelerator, taking account of Coulomb interaction. In the accelerator being developed it is proposed to obtain a current of about 50 ma in a pulse (for protons). To clarify the optimum relations between the parameters of the machine, special studies were carried out at reduced accelerating voltage on an electronic model, at whose output an average current of 0.1 a was attained. Many of the conclusions of the reported work coincide with the results of analogous American studies—this was reported to the conference by Prof. Panofsky (Stanford, U.S.A.).

In the debate on Khizhnyak’s report, Veksler made a communication about a linear proton accelerator built in Kharkov. In this accelerator, which operates on a traveling wave, the focusing of the beam is based on the difference (velocity) effect. At the output the machine gives a proton current with energy 5 Mev and strength about 10 a. It is assumed that the use of resonators loaded with dielectric will make it possible to bring the current up to 100 a.

Professor Panofsky (U.S.A.) briefly reported on American linear accelerators for high currents. In addition to proton accelerators (7 Mev, 0.1 a) and electron accelerators (15 Mev, 0.2 a), in the U.S.A. it is planned to build a strong-focusing accelerator for heavy multiply charged ions (up to neon), in which they are to acquire an energy of about 10 Mev per nucleon. The machine consists of two sections: in the first, ions with small charge are accelerated in one resonator. After this they enter the region of increased pressure, where their charge “is stripped”; the principal acceleration takes place over a path of 20 m. The problem of obtaining large currents in this machine required the construction of special ion sources. High-energy proton accelerators were not considered. Professor Panofsky also answered questions concerning the Stanford linear accelerator,”

...giving electrons with energies up to 660 MeV*), and showed a number of photographs of the main components of the installation. The operating expenses for this machine amount to approximately 50% of the total cost of the studies; the failure rate of klystrons (the average time of their operation is 1500 hours) leads to the fact that the accelerator operates about 350 hours per month. As a result, the cost of operating it is twice as high as for a synchrotron of the same energy, but the average current is about 1 μA.

The work of the staff of the Scientific Research Institute of Electrophysical Apparatus of the Ministry of Electrical Industry—I. A. Grishaev, P. M. Zeidlits, G. A. Zeitlenko, V. V. Rumyantsev, V. L. Smirnov, L. P. Fomina, and V. K. Khokhlova—was devoted to economic and technical grounds for choosing the parameters of linear accelerators for high energies, with the point being made that the question of the cost of construction is of decisive importance. In the cases considered, the most effective system proved to be a traveling-wave guide loaded with diaphragms. It is most expedient to supply the sections of such an accelerator independently from separate high-frequency generators; in this case their number is proportional to the final energy of the particles. Despite the fact that the accelerating field at present can be brought up to 300 kV/cm, it proves unprofitable to use a field greater than 140 kV/cm, since operating expenses then increase sharply.

In the report by A. D. Vlasov (Academy of Sciences of the USSR) a linear theory was set forth of strong focusing in linear proton accelerators, based on the orbital method. The theory applies to installations in which the accelerating-focusing system is divided into alternating sections, in each of which the motion is stable either in the longitudinal or in the transverse direction. It is known that by an appropriate choice of parameters one can obtain in such a system stability both for phase and for radial motion. The construction of the region of stability in the coordinates “accelerating field—gradient in the focusing lenses” is highly illustrative. Such a region of stability was given in the report for the simplest case, when the period of the accelerating-focusing system has a rectangular characteristic. From the necessity of keeping the working point in the middle of this region there follow, on the one hand, definite values for the magnetic-field gradient and, on the other hand, a limit for the intensity of the high-frequency accelerating field, which, as was explained, cannot be raised by increasing the field in the lenses. The work also obtained certain general relations pertaining to an arbitrary structure of the accelerating-focusing field.

The theory of strong focusing in linear accelerators was also the subject of the report by L. S. Solov’ev and E. L. Burshtein (Academy of Sciences of the USSR) and the work of A. A. Sharshanov and K. N. Stepanov (Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR).

Somewhat aside from the main subject matter stood the report, presented to the accelerator section, by L. N. Rozentsveig, G. L. Vysotsky, and A. A. Kresnin (Physico-Technical Institute, Academy of Sciences of the Ukrainian SSR), in which a new method was proposed for obtaining and analyzing polarized electron beams. Carrying out experiments with polarized particles can yield a number of interesting results, but the existing technique proves practically unsuitable at relativistic energies. The report proposed using the phenomenon of cold emission from a metal at low temperature. If, in doing so, so strong a magnetic field is imposed that the energy of the magnetic interaction is greater than the thermal energy, then the probability of emission will prove to depend rather strongly on the electron spin. The formula obtained in the work shows that at \(E = 10^6\) V/cm, \(H = 10^5\) oersted, and hydrogen temperatures, the beam should be polarized by approximately 10–20%.

At a special meeting, the accelerator section discussed one of the most important questions at the present time—the question of the theory and implementation of accelerators with strong focusing. It is well known that the problem of constructing ring accelerators of the usual type for energies of the order of tens of BeV runs into the necessity of greatly increasing the dimensions of the accelerating chamber and, consequently, the weight of the magnet. Although Marshall’s report (USA) at the plenary session showed that on the basis of conventional methods not all possibilities for reducing the weight had yet been exhausted, nevertheless the most promising course in the near future is apparently the transition to strong focusing, which makes it possible to reduce considerably the dimensions of the chamber.

In this connection the interest aroused at the conference by the report of R. Wilson (Ithaca, USA) on the first operating strong-focusing synchrotron of Cornell University, giving electrons with an energy of 1 BeV, is quite understandable. The use of strong focusing, i.e. of alternating large negative and positive field gradients, requires, as was explained, high precision

* For a detailed description of this accelerator, see, for example, Rev. Sci. Instr. 26, 134 (1955).

MEETINGS AND CONFERENCES

...of manufacture and installation of the machine. It is natural, therefore, that in the first accelerators of this type the magnetic-field fall-off index \(n\) is taken to be comparatively small; in particular, in this machine it is equal to 20. Such a value was determined here, in addition, by the structure of the magnet, which was originally designed as weak-focusing. The chosen parameters made it possible to obtain a rather broad region of stable operation, in which the operating point is located; its width is \(\Delta n = \pm 2\). The accuracy with which the machine is assembled may be characterized, for example, by the fact that the foundation is installed with a tolerance of \(\pm 1\) mm. The strong-focusing pole shoes of the magnet can be replaced by weak-focusing ones, and their displacement and fastening are carried out by a very simple and reliable method with the aid of compressed air. The small size of the gap, as well as the narrow track (the accelerator chamber cross section is \(3 \times 7\ \mathrm{cm}^2\)), made it possible greatly to reduce the weight of the magnet: it is only 20 tons, which is several times less than the weight of the magnet of a weak-focusing synchrotron of 300–400 MeV. Injection into the accelerator is carried out at 2 MeV from a Van de Graaff generator giving a current of 10 mA in a pulse that lasts for one revolution of the particle. \(H_z\) on the equilibrium orbit is at this moment approximately 20 oersteds.

For the chosen initial energy the electrons being accelerated still noticeably change their velocity (at injection \(\beta = 0.9\)); therefore a special design of a coupled accelerating resonator has been used. At first only one half of it operates, having a low \(Q\) and fed from a separate generator with a modulated frequency. The second half, with high \(Q\), in which the principal acceleration takes place, is switched on only at 10 MeV; moreover, as was found, there is no need to maintain precisely the moment of transition from one resonator to the other. The operating frequency, beginning from this moment, is equal to 80 MHz (the eighth harmonic of the revolution frequency). At the beginning of acceleration, when radiation losses are still negligibly small, the voltage amplitude on the resonator is only 5 kV; by the end of the cycle it rises to 24 kV.

Prof. Wilson noted that, as became clear during the adjustment of the machine, the accelerator was built with an excessively large margin, since over a large part of the acceleration cycle (at an energy greater than 100 MeV) the diameter of the transverse cross section of the beam is less than 1 mm, while the beam dimensions do not change appreciably. At an energy of about 100 MeV the beam can already be observed visually by its radiation: the vacuum chamber is made of glass. It is planned subsequently to raise the magnetic field of the accelerator to 13,000 oersteds (at present its intensity is 8800 oersteds), in order to bring the energy up to 1.5 GeV. Residual field lines during injection are compensated by four special coils, the need for which will disappear if in the future a transition is made to injection at 10 MeV; in addition, compensation of the Earth’s magnetic field is provided. The field nonlinearities are small; variations of the field index over the entire working space do not exceed 5%.

The acceleration cycle is repeated 30 times per second, and in each pulse the machine gives \(3 \cdot 10^8\) particles. In the future it is planned to raise the intensity to \(10^{10}\) particles per pulse. It is interesting that the adjustment and final tuning of the accelerator took a year and a half, whereas its assembly lasted only 6 months.

O. Wernholm (Stockholm, Sweden) reported on the construction of an electron synchrotron with strong focusing for an energy of 1.2 GeV, being built in Sweden. The radius of the sectors of this installation is 3.65 m. The maximum field is 11,000 oersteds. The magnetic-field fall-off index is 10.6. In its design and in the arrangement of the elements, the magnet of the accelerator described is practically analogous to the accelerator described by R. Wilson. The original feature of the installation is a microtron injector for an energy of 6 MeV. The microtron injector current is 20 mA. The particles make 10 revolutions in it. The energy spread of the particles at the exit from the microtron is approximately 0.5%. The high energy of the particles at injection makes it possible in this synchrotron to dispense with modulation of the frequency of the accelerating field. The accelerator chamber has dimensions \(7 \times 4\ \mathrm{cm}^2\). The accelerator will operate with particle injection at a frequency of 25 Hz. The machine is to be put into operation in 1957.

One of the largest proton strong-focusing accelerators is at present being constructed near Geneva by the international organization CERN. One of the authors of the project—M. Regenstreif—told the conference about its basic parameters. The accelerator is designed for a maximum energy of 25 GeV. In a strong-focusing magnet it is difficult to obtain a field greater than 12,000 oersteds; therefore the radius of curvature of the trajectory of protons of such energy will be 70 m. Accordingly, the ring magnet of the synchrophasotron, buried in the ground, has a mean radius of 100 m. The high value of the magnetic-field index, characterizing the focusing force, equal to 282, imposes rather severe requirements on the accuracy of installation; the authors of the project propose to maintain, throughout the entire acceleration cycle, the calculated dimensions of the magnet with an accuracy of up to 1 mm. For this purpose a special foundation has been designed and is now being constructed, consisting of a concrete ring on piles embedded in rocky ground, and certain...

measures providing compensation for possible displacement of individual sections of the magnet.

The periodicity element of the magnetic system consists of focusing and defocusing sectors, separated in half by straight-line intervals; with this arrangement they introduce the smallest perturbations. Altogether the magnet has 100 such periodicity elements. The focusing of the particles is sufficiently strong: on each revolution the particles make about four complete oscillations around the closed orbit, and therefore the cross section of the vacuum chamber has small dimensions—\(8 \times 16\) cm. It is interesting that the operating point of the accelerator is chosen not at the center of the stability region, but somewhat to the side; thus, the well-known characteristic parameter

\[ \nu=\frac{\pi}{4}. \]

This makes it possible, at the cost of a certain increase in the amplitude of the oscillations, to ease the tolerances on the magnet parameters. Power for the magnet will be supplied by motor-generators with a total power of \(40\,000\) kW.

The accelerator was designed on the basis of linear theory. Ten different models of the magnet were built and studied; the plates of these models were made movable, which made it easy to change the configuration of the field. The nonlinear regime of the machine was checked by means of a specially designed modeling device, in which a metallized quartz ball moves in the electric field of 12 electrodes. As a result, in particular, coupling resonances of various orders were studied in detail and the most dangerous among them were identified. It was experimentally confirmed on the model that resonances of the difference type are not dangerous for operation of the machine. Numerical calculations carried out as a result of these studies give grounds to suppose that the amplitude of the oscillations under the action of nonlinearities will be somewhat greater than is predicted by perturbation theory. The design of the machine provides for the possibility of installing additional windings on the poles, as well as of introducing nonlinear lenses.

Injection into this accelerator is to be carried out at an energy of 50 MeV, which the protons will receive in a special linear accelerator with a forinjector at 600 keV. Focusing of the injected beam is carried out by means of grids and special quadrupole magnetic lenses. The injector current is 1 mA.

The frequency of the accelerating field exceeds the revolution frequency of the particles by a factor of 21 and changes during the acceleration cycle from 2.9 to 9.55 MHz. The duration of the cycle is 1 sec; the repetition frequency is one pulse every 5 sec.

At this same session a range of questions connected with the so-called critical energy was considered. From the theory of a strong-focusing accelerator it is known that in the nonrelativistic region the stable equilibrium phase has one sign, while at energies several times exceeding the rest energy it has the other. Obviously, during the acceleration cycle the equilibrium phase passes through zero. At this moment the frequency of phase oscillations also goes to zero and the phase stability is lost, i.e., arbitrarily small deviations of the parameters of the machine from ideal values will lead to loss of particles. This problem is obviously not essential in the case of electron accelerators, where the injection energy can exceed the critical one, but for the acceleration of heavy particles it is very serious.

A number of theoretical and experimental works were devoted to the problem of the critical energy. Owing to lack of time it was not possible to read all of them. Two of these works were reported at the conference—the reports of A. A. Kolomenskii and L. L. Sabovich (P. N. Lebedev Physical Institute, Academy of Sciences of the USSR), and also of V. V. Vladimirskii and E. K. Tarasov (Academy of Sciences of the USSR).

In the first report the physical picture of the transition through the critical energy was considered. In the neighborhood of the critical point the behavior of the phase was investigated with allowance for the nonlinear relation between the increment of energy and the revolution frequency, and a qualitative picture of the transition process was elucidated, clearly demonstrated on a number of diagrams. The authors pointed out the possibility of passing through the critical point with the high-frequency voltage switched off, using an accelerating field of the betatron type.

The report by Vladimirskii and Tarasov considered the possibility of eliminating the critical energy by introducing into the system special compensating magnets with a field of the opposite sign and, consequently, with an inverse curvature of the trajectory. Owing to the appropriate arrangement of these magnets (with a period close to the period of the betatron oscillations), it is possible to ensure that when the momentum deviates from the equilibrium value the orbit length does not change. One may say that in such a system the critical energy is shifted to infinity, i.e., the equilibrium phase does not change sign during the acceleration process. This is achieved at the cost of some lengthening of the magnetic system and a small increase in the amplitude of the forced oscillations.

This method has been used in two designs of Soviet strong-focusing proton accelerators, which were reported on at the plenary session of the conference

in the report by V. V. Vladimirsky, E. G. Komar, and A. L. Mints (Academy of Sciences of the USSR). The smaller of these accelerators is designed for an energy of 6–7 Bev, which, with comparatively small installation dimensions, provides a sufficient excess over the threshold for antinucleon production. In a well-known degree this accelerator can also serve as a model for an installation of 50–60 Bev, the basic parameters of which were also reported in the paper. Therefore, for both accelerators the described system of compensation for the change in orbit length is used, pushing the critical energy to infinity, although the 7 Bev accelerator can also be designed according to the usual scheme without passing through the critical energy.

The injection energy into the 7 Bev accelerator was chosen to be rather low—4 Mev—which required special consideration of the influence of space charge and scattering by the residual gas in the chamber. The report considered the influence of various perturbations on the choice of tolerances for the main parameters of the accelerator, as well as for the foundation of the installation.

Below we give a brief table of the basic parameters of both synchrophasotrons:

At the conference a report was also heard by V. V. Vladimirsky and S. V. Skachkov (Academy of Sciences of the USSR), “Calculations of Accelerator Magnets with Strong Focusing.” The results of an experimental investigation of such magnets were contained in the report by I. A. Mozalevsky and G. V. Prokhachev (Scientific-Research Electrophysical Apparatus Institute, Ministry of Electrical Industry of the USSR), in which data were given on the influence of the geometry of the gap on the distribution of the magnetic field, and various methods of measuring the field in a strongly focusing magnet were also considered.

The session at which new methods of accelerating particles were discussed began with a report by the well-known physicist Prof. M. L. Oliphant (Canberra, Australia), “An Iron-Free Proton Synchrotron of Small Dimensions for 10 Bev”*).

The main report was preceded by a brief introduction in which Prof. Oliphant noted that the construction of high-energy accelerators using electromagnets with an iron yoke leads to large dimensions and high cost of the installation. For purposes of economy, a transition to more economical iron-free magnetic systems is expedient, since they make it possible to use stronger magnetic fields and therefore have smaller dimensions and cost.

An example of such an accelerator is the proton synchrotron being built in Canberra. In this accelerator the magnetic field on the orbit is to be produced by a pulsed current flowing through a special system of conductors consisting of two groups. In transverse section both groups are two intersecting circles with a radius of about 25 cm. The common part of the section of these groups of circular conductors is removed and forms the space for particle acceleration, in which a stainless-steel vacuum chamber 22 cm in diameter is placed. The current in the circular groups of conductors has the opposite direction. Deformation of the cross section of the group makes it possible to achieve the required spatial configuration of the magnetic field with a fall-off index of about 0.51–0.60. Each group of conductors is divided into four sections, which are connected in series and thus form four turns. The mechanical forces experienced by the winding during the passage through it of the maximum current reach 16 t per centimeter of length. Therefore, to reduce the deformation of the system of conductors producing the magnetic field, it is enclosed in a tightly fitted duralumin

) A description of this accelerator is contained in Proc. Roy. Soc. 234*, 441 (1956).

housing. It is assumed that the radial deformations will not exceed 2 mm, which will have little effect on the distribution of the magnetic field. In plan, the magnetic system consists of four sectors, whose radius is 480 cm, separated by straight intervals 250 cm long. The magnetic system is designed to produce a field of 80,000 oersteds with a total current in one group of circular section of about 6 million A. The weight of copper in the installation is 80 tons (together with the lead-in conductors, which weigh twice as much as the conductors creating the magnetic field).

The magnetic system is powered by a special unipolar generator, whose rotor consists of four steel disks weighing 20 tons each and having a diameter of about 3.5 m. Before the beginning of a cycle the disks rotate with an angular velocity of 15 revolutions/sec, which corresponds to a stored kinetic energy of \(6 \cdot 10^8\) J; about half of this energy is expended in creating the magnetic field. The voltage on each disk of the unipolar generator is approximately 200 V. The generator is loaded on the magnetic system, with a voltage of 720 V, develops a current in the pulse of about 1.7 million A. A serious problem is the commutation of large currents and insulation. The current from the ribs of the disks of the unipolar generator will be taken off by “liquid brushes”—jets of a mixture of sodium–potassium melts (mercury had to be abandoned in the commutation system because of its toxicity and high resistance). The commutation system is placed in an atmosphere of nitrogen and maintained at a temperature of 100°. In one cycle about 2.5 tons of melt flow through the commutating device. Between cycles the unipolar generator is accelerated to the required speed by a mercury rectifier.

The accelerator will give one pulse of accelerated protons in 10 min. The long pause between cycles is needed to cover losses: approximately \(3/4\) of the stored energy is dissipated in the installation. However, in the future it is expected, as a result of various improvements, despite the low duty factor, to achieve the average integral intensity of ordinary accelerators. The duration of the acceleration cycle will be approximately 0.68 sec. As an injector it is proposed to use a cyclotron with an energy of about 8 MeV. In the installation it is possible to use the injector and ion source, the choice of cyclotron being dictated by the conditions of Dubna, which already has experience in this respect. It is expected that the beam of accelerated particles will be obtained in two years. At present the construction of the unipolar generator is being completed. In addition, there are models of various elements of the installation and a model of the unipolar generator, which have confirmed the calculated data. For the model of the unipolar generator a cyclotron magnet was used, which will later be employed as the injector.

Entirely new paths for the design of accelerators were indicated in the report by G. I. Budker and A. A. Naumov (Academy of Sciences of the USSR), “Theoretical and Experimental Data on an Electron Stabilized Beam,” where it is proposed to use the fields of charges inside the accelerating chamber. The so-called stabilized electron beam is a beam of relativistic electrons to which, in order to compensate the Coulomb repulsive forces, a certain quantity of positive ions has been added. Since the Coulomb interaction of the electrons in the beam is strongly weakened because of relativistic effects (by \(\gamma^2\) times, where \(\gamma = (1 - \beta^2)^{-1/2}\)), the number of compensating ions is small. The report shows that, under certain restrictions on the density of electrons and ions, the stabilized beam is stable in the transverse section, the allowable ring dimensions being of the order of 0.01 mm with beam currents of about 1000 A. Thus, inside the beam there will exist magnetic fields of the order of \(10^5\) oersteds and electric fields of the order of \(10^5\) V/cm. These fields grow with increasing distance from the beam axis and possess focusing properties. In view of the fact that the stabilized electron beam is “transparent” for ions and electromagnetic waves, and the beam “lifetime,” according to the authors, may reach several hours, it can be used as the focusing system of a cyclic resonance accelerator. To maintain a stabilized beam of ring shape, an external magnetic field with an intensity of only about 100 oersteds will be required. For this purpose the authors proposed using a magnetic field of the betatron type.

The estimates carried out show that, with a stabilized-beam current of 10,000 A, in a ring of radius 3 m one can attain a maximum energy of \(10^5\) BeV with an initial energy of 10 keV. The most difficult questions connected with the realization of a stabilized beam are questions of its stability. The authors have shown that the beam is stable in the region of currents up to 17,000 A. Perturbations of the type of constrictions do not violate the stability of the beam. Deformations of the ring lead to an instability which, however, according to the authors, is not dangerous, since the corresponding perturbations develop slowly in time.

Next the speaker G. I. Budker dwelt on the experimental work on the creation of a stabilized beam, which has already been under way for a year and a half. In order to obtain electron beams with large currents, two main directions were chosen: the accumulation of a large number of particles in the magnetic field of a beta-

...of the tron type and the use of an annular discharge in the chamber. In the latter case the idea is that an attempt is made to apply a strong vortex electric field and to achieve, in an electric discharge, the separation of electrons from ions. Here the difficulty consists in the fact that the criterion for such a separation of electrons contradicts the condition for ignition of the discharge. Somewhat apart from the first two methods stands the method of the so-called “ionic curtain,” which differs in that the space charge inside the chamber is created by means of an external ionization source. The first experiments with an ionic curtain yielded a current of about 12 A. This method appears to be one of the most promising.

In the discussion of this report, which aroused great interest, numerous questions were asked about the methods for attaining the currents needed to create a stabilized beam, about certain theoretical questions, and about methods of measurement during experiments.

In the second joint report, by Budker and Naumov, “A Pulsed Iron-Free Synchrotron,” original designs were described for iron-free pulsed accelerating installations of the synchrotron type, proposed by G. I. Budker in 1950. A feature of the magnetic system of these accelerators is the use, for producing a magnetic field, of only a single turn, the design of which is chosen so that the resultant of the mechanical forces applied to it is zero. Moreover, in these installations the problem of obtaining a magnetic field of prescribed configuration is facilitated, since the accuracy of the latter, because of the skin effect, is determined in practice only by the accuracy of the mechanical machining of the turn.

The authors examined two projects: with an orbit radius of 33 cm for an energy of 1 Bev, and with a radius of 1 m for an energy of 3 Bev. The 3-Bev installation is strongly focusing. The projects for these accelerators, according to the speakers, are extraordinarily economical. At present a model for 200–300 Mev has been built. The orbit radius in the model is 17 cm. The working region of the magnetic field, suitable for acceleration, has dimensions of \(2.5\ \text{cm} \times 5\ \text{cm}\). The index of field fall-off is \(0.57 \pm 0.02\). The weight of the model is about 150 kg; the energy supply of the magnetic system is \(9 \cdot 10^{3}\) J. The magnetic field is produced by a pulsed current of up to 400,000 A flowing around one turn of special cross section, which is placed inside a massive metallic vacuum chamber. The vacuum chamber simultaneously serves as the return conductor for the current producing the guiding magnetic field, and bears all the mechanical forces. In developing the chamber, special magnetic labyrinths were used, making it possible to weaken the magnetic fields by \(10^{4}\) times. In addition, special discharge devices have been created, controlled with an accuracy up to 0.1 μsec and at present withstanding 100–200 pulses. In the opinion of the authors, the creation of more durable discharge devices presents no serious technical difficulties.

At present all the elements of the model have been manufactured, tested, and have given reliable results. The model is in the start-up stage. It is assumed that in installations of the type described it will be easy to extract the beam, since in them there is a simple possibility of creating significant local inhomogeneities in the magnetic-field gradient.

The speaker was asked numerous questions concerning the details of the design of the proposed synchrotron projects.

In the report by A. A. Kolomensky (Institute of Physics, Academy of Sciences of the USSR), “New Modifications of a Ring Accelerator with a Constant Magnetic Field,” the possibility was pointed out of creating a ring cyclotron for relativistic particles—a ring strongly focusing accelerator with a time-constant field and a constant orbit perimeter. The simplest variant of such an accelerator consists of two mutually tangent ring phasotrons—a direct and a reverse one—coupled, for example, by straight-line intervals. As the energy increases, the mean radius of the orbit in one of the installations grows, while in the other it decreases, so that the orbit perimeter, and consequently the revolution frequency of the particle, remain constant. The creation of such an accelerator would make it possible to increase considerably the intensity of accelerated particles in comparison with existing accelerators. True, such an increase in intensity could be obtained at the price of tightening tolerances and increasing the dimensions of the installation.

The concluding session of the section was devoted to experimental methods. The American physicist E. Alvarez (Berkeley, USA) gave a report entitled “The Use of Counters and a Hydrogen Bubble Chamber in Experiments with High-Energy Particles.” In the first part of the report E. Alvarez discussed certain notes on the methodology of experiments with mesons, some of which have already been published. A scheme was described for staging experiments that makes it possible to select particles with a momentum of 350 Mev. Alvarez then spoke about hydrogen bubble chambers used in experiments on the bevatron. At present two chambers are in operation: a ten-centimeter chamber, with a pulsed field of 8000 oersted, made of stainless steel, and a twenty-five-centimeter chamber, the construction details of which were not described. The author presented several photographs of nuclear processes obtained with the aid of these chambers. In addition, ...

a 500-liter hydrogen chamber with a magnetic field of the order of 15,000 oersteds has been built. A schematic view of such a chamber was shown.

Álvarez was asked a number of questions concerning the experiments carried out with the aid of hydrogen chambers, and questions relating to the technical details of their design.

In the report by P. M. Morozov, B. N. Makov, and M. S. Ioffe (Academy of Sciences of the USSR), a design was proposed for a source of multiply charged nitrogen ions for a cyclotron, developed on the basis of a source for the separation of isotopes. The features of the proposed design are: distributed feeding of the working substance and a heated cathode, making it possible to control the stabilization. The greatest difficulties in setting up the source are the choice of the optimal gas flow and discharge current. The experimental results are not yet entirely satisfactory (the current of multiply charged nitrogen ions is less than 0.1 a).

Next was the report by A. A. Glazov and V. S. Katyshev (Institute for Nuclear Problems, Academy of Sciences of the USSR), “The Use of Ion Sources with a Cold Cathode for the Synchrocyclotron.” The advantages of such a source consist in the fact that it is more stable and longer-lived than an ordinary arc source. The work investigated the influence of the discharge voltage, gas flow rate, and cathode material on the operation of the source. It turned out that the most acceptable materials for cathodes are Al, Be, Cu, Mg, Ag and other metals with a large coefficient of surface ionization. It was determined that the principal factor affecting the operation of the source is the vertical component of the high-frequency field of the dee. The dependence of the ion-beam intensity on the amplitude of the accelerating voltage in such a source is stronger than in ordinary sources. The source described has been used successfully for 3 years in the synchrocyclotron of the Academy of Sciences of the USSR and gives a current of about 0.2 ma.

As is known, at present the efficiency of detecting fast (\(\sim 200\) MeV) neutrons by ordinary methods does not exceed 1–2%. In the report “A Fast-Neutron Detector with High Efficiency,” presented by Yu. K. Akimov, A. S. Kuznetsov, and T. A. Leksina (Institute for Nuclear Problems), it is proposed substantially to increase the efficiency of neutron detection by using a scintillator with a hydrogen-rich substance—the converter. The authors used a detector consisting of a liquid scintillator (a solution of terphenyl in toluene), poured into a copper container—a rectangular box measuring \(7 \times 7 \times 11\ \mathrm{cm}^3\). The converter consisted of 10 copper plates placed at a distance of 3 mm from one another. The efficiency of such a detector was 25–30%. It is indicated that increasing the converter density leads to an increase in the efficiency of neutron registration. Experiments carried out with the described detector showed that over the entire interval of neutron energies available to the experimenters (230–330 MeV), the registration efficiency was constant. The proposed detector can be used in conjunction with a telescope of scintillation counters. The detector operates with two or one photomultiplier.

In the report by I. N. Usov (Physical Institute, Academy of Sciences of the USSR), “On Measuring the Energy Flux of Bremsstrahlung by the Method of Thin Converters,” a special design of an ionization chamber was described, making it possible to reduce the experimental error in measuring the energy flux by the method of thin converters, which arises from the account taken of the contribution of photoelectrons. The error decreases with the aid of absorption of photoelectrons by aluminum foils. It turned out that the sensitivity of the proposed chamber depends strongly on its orientation in the photon beam. This circumstance was used for the rapid determination of the center of the \(\gamma\)-radiation beam with an accuracy of \(\pm 0.5\) mm at the FIAN synchrotron at 265 MeV.

In the talk by M. I. Podgoretsky (Electrophysical Laboratory), “On Determining the Moment of Occurrence of Events Recorded by Means of Photoemulsion,” a method was proposed for determining the time of an event by means of rotating plates (an emulsion chamber). The author assumes that, with a well-collimated particle beam, the resolving power of the method can be brought to \(10^{-4}\) sec. The possibility of constructing emulsion “chambers” controlled by electronics is indicated. When working with pulsed accelerators, it is proposed to use stepwise rotations of photographic plates. It is asserted that the method described can be used effectively in the study of rare events accompanied by a large background, and for accelerating the solution of problems connected with the need to view a nuclear emulsion. A shortcoming of the method is the necessity of substantially increasing the exposure time.

The report by G. M. Strakhovsky (2nd Nuclear Physics Research Institute, Moscow State University) was devoted to a description of an apparatus for studying processes with high-energy particles by means of photographic plates placed in a strong pulsed magnetic field. The apparatus makes it possible to obtain a field of the order of 100,000–150,000 oersteds in a pulse lasting 10 μsec. The pulse of the magnetic field can be synchronized with the moment when the particles strike the accelerator target with an accuracy of 1 μsec.

A. K. Burtsev, N. S. Danilkin, A. N. Lebedev

THIRD SECTION

The meetings of the third section, devoted to theoretical work on the physics of high-energy particles, were held in the conference hall of the Physics Institute of the Academy of Sciences of the USSR named after S. I. Vavilov. In addition to the four official meetings, the theoretical section also organized a number of unofficial meetings, at which papers were presented that were not included on the agenda but were of great interest to physicists working in the field of high-energy particles.

The first meeting of the theoretical section took place on the evening of May 15. All the reports at this meeting, with the exception of the first report by A. Pais (Princeton, USA), “The Variational Method in Meson Theory,” which was devoted to the problem of investigating the meson field of an infinitely heavy extended source, dealt with the question of dispersion relations in particle scattering. The dispersion relations that particle-scattering amplitudes must satisfy are a consequence of the most general physical principles, such as the causality principle, and can be obtained without the use of perturbation theory, which is especially important in studying the interaction of $\pi$-mesons and nucleons, where perturbation theory is inapplicable. The derivation and study of dispersion relations for $\pi$-mesons and nucleons have recently been given both by foreign theorists (Goldberger, Gell-Mann, Thirring, Salam, Öhme, and others) and by Soviet ones.

In the report by N. N. Bogolyubov, B. V. Medvedev, and M. K. Polivanov, “The Causality Condition as Applied to Scattering Problems,” a derivation of dispersion relations was given using a method that is essentially a generalization to many-particle states of the well-known Lehmann–Chew method. For the scattering of bosons by fermions, the derivation is carried through to the point of obtaining final dispersion relations. The scattering of mesons of different charge was considered both with and without flip of the nucleon spin.

The report by V. Ya. Fainberg and E. S. Fradkin, “A Dispersion Relation for Fermi Particles,” contained the derivation of a dispersion relation for the scattering of both charged and neutral Fermi particles. This relation includes the amplitudes for the scattering both of a fermion on a fermion and of an antifermion on a fermion.

E. S. Fradkin, in the report “On a Dispersion Relation for an Arbitrary Angle of Meson Scattering by Nucleons,” reported on a relation he had found between the imaginary and real parts of the scattering amplitude at an arbitrary angle.

The report by V. Z. Blank, “Dispersion Relations for the Scattering of Nucleons by Nucleons,” was devoted to considering the possibility of obtaining dispersion relations for the scattering of protons by protons and neutrons by protons. Approximate dispersion relations for forward scattering were obtained.

B. L. Ioffe, in the report “Dispersion Relations in Photoproduction and Scattering of $\pi$-Mesons by Nucleons,” proposed a simple and transparent derivation of dispersion relations for the production of $\pi$-mesons by photons on nucleons. Analogously, dispersion relations are obtained for the scattering of $\pi$-mesons (including at angles not equal to zero).

The report by A. A. Logunov and B. M. Stepanov, “A Dispersion Equation for the Photoproduction of $\pi$-Mesons on Nucleons,” contained a consideration of the questions of photoproduction by the method of N. N. Bogolyubov. By this method exact dispersion relations were obtained. Under the assumption that the main contribution to photoproduction is made by the $S$- and $P$-waves, approximate equations were derived. The results obtained show satisfactory agreement between the developed theory and the experimental data.

The lively discussion of the reports showed that there remain a number of unresolved and controversial questions relating to dispersion relations, and, in particular, the question of whether dispersion relations are preserved if causality is violated at small distances.

The second meeting of the theoretical section opened on the morning of May 18 with a report by R. E. Peierls (Birmingham, England), “Work Being Carried Out in Birmingham in the Field of the Theory of Phenomena Occurring at High Energies.” This report presented the results of work on the use of functional methods for the exact solution of simple problems and for the approximate solution of problems connected with the interactions of $\pi$-mesons. Some results were also presented relating to the solution of the Bethe–Salpeter equation for the interaction of a meson and a nucleon.

L. P. Gorkov and I. M. Khalatnikov devoted their report, “Quantum Electrodynamics of Charged Particles with Spin Zero,” to the study of the electrodynamics of scalar particles in the Kemmer formalism on the basis of the “smeared” interaction scheme. It was shown that, in the limit of point interaction, the physical charge in this theory goes to zero independently of the magnitude of the “bare” interaction constant.

In the report by I. T. Dyatlov, V. V. Sudakov, and K. A. Ter-Martirosyan, “Scattering of a Meson by a Meson at High Energies,” an equation found by them was reported for the total contribution of all graphs corresponding to scattering

meson on a meson. This equation is solved exactly, and it turns out that the total contribution of all diagrams is of the same order as the contribution from a single simplest diagram.

V. S. Barashenkov, in the report “On the Possibility of a Hamiltonian Formulation of a Theory with a Form Factor,” considered the difficulties arising in attempts to apply Hamilton’s method to a theory with nonlocal interaction.

The third session of the theoretical section took place on the evening of May 18. Reports were heard by M. Lévy (Paris, France), “The Present State of Research on the Theory of Nuclear Forces” and “Testing the Lévy Potential at 150 MeV,” as well as a report by W. Thirring (Bern, Switzerland), “Consequences of the Static Model in Meson Theory.”

The fourth session of the theoretical section took place on the morning of May 21. It opened with a report by D. D. Ivanenko and N. N. Kolesnikov, “On the Theory of Hypernuclei.” The authors obtain the binding energy of the \(\Lambda\)-particle in a hypernucleus by assuming that the sizes of hypernuclei coincide with the sizes of ordinary nuclei, considering the states of the \(\Lambda\)-particle in a rectangular well, and choosing the depth of this well. The consideration suggests the presence of a saturation region of the binding energy after mass numbers of order 20–30.

In the report by A. M. Brodsky and D. D. Ivanenko, “On the General Theory of Meson Scattering,” the authors’ study of the equations of symmetric pseudoscalar meson theory was reported.

The report by A. A. Sokolov and B. K. Kerimov, “The Theory of Scattering of Particles by a Fixed Center with Allowance for Damping,” was devoted to the solution of the problem of the scattering of a relativistic massless particle. Expressions for the phase shifts were found, and the condition under which damping is essential in this problem was determined.

Yu. V. Tsekhmistrenko, in the report “Theory of Scattering and Photoproduction of Charged and Neutral Mesons in the Strong-Coupling Approximation,” considered the close connection between theory and the consideration of recoil of the nucleon.

The report by I. M. Shmushkevich, “On Isotopic Invariance,” was devoted to relations between the probabilities of various processes that follow from the hypothesis of isotopic invariance. An elementary method was proposed for obtaining such relations, based on the consideration of isotopically unpolarized beams.

In the report by L. B. Okun, “Scattering of \(K\)-Mesons with Charge Exchange,” the charge exchange of \(K\)-mesons on deuterium was considered in the impulse approximation for various values of the spin and parity of \(K\)-mesons.

The report by L. B. Okun and I. M. Shmushkevich, “Capture of \(K\)-Mesons in Deuterium and Interaction of Hyperons with Nucleons,” contained a calculation, carried out in the impulse approximation, of the capture of a \(K\)-meson in deuterium with formation of a nucleon, a hyperon, and a \(\pi\)-meson.

I. Yu. Kobzarev and L. B. Okun, in the report “On the Question of the Spin of the \(\Lambda\)-Particle,” showed that from the fact of observation of the so-called \(\Lambda\)-nuclei it follows that the spin of the \(\Lambda\)-particle cannot be appreciably greater than unity.

In the report “Relations between the Probabilities of Various Processes Involving Heavy Mesons, Hyperons, and Antihyperons,” L. B. Okun reported the derivation of relations following from the hypothesis of isotopic invariance of the strong interactions of “strange” particles. The decays of these particles were also considered.

V. B. Magalinsky and Ya. P. Terletsky, in the report “On the Statistical Theory of Multiple Production of Mesons,” considered the most rigorous (from the point of view of particle statistics) scheme for calculating the statistical weights of various reaction channels for multiple production of \(\pi\)-mesons in the collision of two nucleons.

The report by A. N. Baldin and M. I. Shirokov, “On the Theory of Reactions with Polarized Particles,” was devoted to the further study of the general theory of reactions with polarized particles, developed by Simon, Belinfante, and others.

At unofficial sessions and discussions, the following reports devoted to theoretical questions of high-energy physics were heard:

L. D. Landau and I. Ya. Pomeranchuk devoted their first report to the fundamental problems of quantum electrodynamics and quantum field theory, and their second to the formation of \(\pi\)-meson pairs by high-energy \(\gamma\)-quanta and to the emission of \(\gamma\)-quanta by \(\pi\)-mesons.

E. L. Feinberg and A. I. Akhiezer reported on the theory of the interaction of fast deuterons with nuclei.

M. Gell-Mann reported on the latest research in the field of “strange” particles.

L. B. Okun