CONGRESSES AND CONFERENCES

CONFERENCE ON ELECTRONICS

From July 6 through July 9, 1944, in Moscow, in the conference hall of the Seismological Institute of the Academy of Sciences of the USSR, meetings were held of the Session of the Division of Physical and Mathematical Sciences of the Academy of Sciences of the USSR, conducted jointly with the All-Union Scientific Council on Radiophysics and Radio Engineering, devoted to questions of electronics.

The program of the Session included 23 reports; two additional communications were made. According to their subject matter, the reports may be divided into the following principal groups:

1. Electron optics (theoretical and applied)—2 reports.
2. Electron emission (experimental data on thermionic, photoelectric, secondary, and autoelectronic emission, as well as on the photoelectric effect and certain questions of theory)—7 principal reports and 1 additional one.
3. Electronic devices: electron multipliers, photocells, questions of theory—8 principal reports and 1 additional one.
4. Gas discharge—2 reports.
5. Theory of electricity—1 report.
6. Properties of electrovacuum materials—1 report.

Thus, quantitatively, the section on electronic devices was represented most broadly. However, in qualitative terms it was not the most significant. Thus, for example, one of the two leading reports of this section—the report by P. V. Timofeev, entitled “Surface Charges in Electronic Devices”—contained only an indication that at present charges on the walls of the bulbs of electronic devices are no longer merely an obstacle to their operation, but are used in so-called “kenotrons with cold emission” (which were the subject of a brief communication by V. V. Sorokina, “The Mechanism of Operation of Kenotrons with Cold Emission”), and a recommendation to employ surface charges on emitting electrodes in order to increase their efficiency. Since the author gave no concrete examples or description of methods for such use, the communication did not create the impression of a well-founded indication of new paths for the development of electronic devices.

In connection with this report it is appropriate to mention the communication by R. M. Aponovich, “Electronic Devices with Efficient Emitters of Secondary Electrons.” The subject of this communication was oxygen–magnesium and similar (oxygen–barium, zinc, etc.) emitters, manufactured by special methods. As is known, it had formerly been asserted that such emitters could give values of the secondary-emission coefficient of several tens of units, without exhibiting inertia, characteristic of the Molter effect, despite the fact that such high $\sigma$ was considered to be caused by surface charges. Therefore the most interesting feature of this communication was the assertion emphasized by the author that the limiting value of $\sigma$ for these emitters, permissible for use in practical devices (from the standpoint of noise and inertia), is 12.

From all this it follows that the positive role of surface charges in electronic devices is still so insignificant that, for the time being, they should rather be regarded as a negative factor.

The second of the leading reports in this section, delivered by the pioneer in the field of secondary emission, L. A. Kubetskii, and entitled “Some Results of the Expired Period in the Field of the Implementation and Application of the Principle of Secondary-Electron Conversion”*)—which, as might have been expected, was supposed to sum up the work on secondary emission in the Union (if not throughout the world)—in reality contained only an exposition of the results of the author’s laboratory, obtained chiefly as early as 1937–1938.

Of greatest interest among the reports of this section were undoubtedly the reports by V. S. Lukoshkov, “Some Electrostatic Properties of Grid Electrodes,” and S. D. Gvozdover, “On the Passage of High-Frequency Currents in Electronic Devices,” devoted to theoretical questions essential from the standpoint of the calculation and design of electronic devices.

In V. S. Lukoshkov’s report it was shown that the principle of replacing a grid electrode by a solid one is correct, provided that the constancy of the parameter \(\delta\) characterizing the grid is maintained; for the cases of plane-parallel, coaxial-cylindrical, and concentric spherical electrodes, general conditions were established for the reducibility of a triode (to a diode) for an arbitrary electrode configuration, and certain properties of irreducible triodes were investigated.

In S. D. Gvozdover’s work, the case of electron motion between the emitter and the collector was subjected to mathematical consideration under conditions in which the transit phase \(\theta\) (equal to \(\omega T\), where \(\omega\) is the frequency and \(T\) is the transit time determined by the constant potential difference imposed between the two electrodes) cannot be regarded as a small quantity.

The last and very brief communication of this section was made by N. S. Khlebnikov and A. E. Melamid on new types of photocells developed by them on the basis of a cesium-antimony cathode, one of which is intended for operation in ultraviolet radiation (down to \(\lambda = 2587\) Å and even farther toward shorter waves), while the second is a photocell that does not exhibit fatigue even when operating at high light fluxes.

The second section in number of reports was that of electron emission. In contrast to the preceding section, the reports of this section, in their considerable majority, were of interest and novelty. This section included three reports of general character, concerning field emission, secondary emission, and the photoelectric effect of complex cathodes.

The first of the listed reports, “Extraction of Electrons by a Field,” was delivered by N. I. Lukirskii. This report elucidated questions of electron emission under the action of electric fields of any strength and at any temperature, field emission from single crystals, and the study of the distribution of electrons in a metal by energy by means of analysis of the energy distribution of field-emitted electrons.

In S. Yu. Luk’yanov’s report, “Secondary Electron Emission,” of particular interest was the attempt to establish features of similarity and difference between the emission of secondary electrons caused by bombardment with electrons, on the one hand, and with positive ions (\(\mathrm{H}^+\), \(\mathrm{He}^{++}\)) on the other. It was found that the velocities of the latter are of the same order as those of primary electrons in ordinary experiments on secondary emission (i.e., approximately up to 1000).

In the report “Complex Photocathodes,” delivered by N. S. Khlebnikov, the conception of the photoelectric effect of complex

*) Let us recall that by the term “principle of secondary-electron conversion” L. A. Kubetskii denotes the amplification of electron fluxes by means of secondary emission.

photocathodes. Further, on the basis of an analysis of the physical meaning of Schottky’s formula for thermionic emission of semiconductors, as well as data available in the literature on Sb—Cs and Cs—O—Ag cathodes, it was shown that the photoemission of these materials should be regarded as the transition into vacuum of electrons from various allowed energy levels of the semiconductor.

In D. V. Zernov’s report “On the influence of strong electric fields on secondary emission of thin dielectric films,” along with a review of the author’s experimental work, one of whose most important results is the establishment of a criterion for separating secondary emission in the proper sense of the word from the Malter effect at various stages of its development, an outline was also given of the main features of the theory of the Malter effect on the basis of modern ideas about a solid body.

The question of the Malter effect of the material classical for this phenomenon—aluminum oxide—was also touched upon in the supplementary communication, made on the instructions of I. F. Kvartskhava, by L. A. Artsimovich, concerning the study of this type of emission under the simultaneous action of two primary electron beams of different velocities.

A. M. Andrianov’s communication “Emission of an oxide cathode in the pulsed regime” was devoted to a description of the exceptionally high values of the emission-current density from the cathode observed under the indicated conditions, reaching 30 A/cm² in the author’s experiments. Unfortunately, the limited nature of the experimental arrangement did not enable the author to indicate a definite point of view on this phenomenon, which is of the highest degree interesting and useful.

One of the deepest observations, both in the breadth of the problem’s coverage and in the depth of its experimental development, was the report by M. M. Butelov and P. M. Morozov, “Physical properties of oxygen-silver-cesium cathodes.” The most important conclusion reached by the authors on the basis of investigation of the structure of the initial silver layer, which is the basis of such a cathode, of the spectral curves of sensitivity distribution and the distribution of photoelectrons by energies, is the conclusion that the photoemission of Cs—O—Ag is, as in the case of Sb—Cs cathodes, a volume effect and not a surface one, as de Boer had believed.

In A. I. Pyatnitskii’s report “Distribution of photoelectron velocities in semitransparent oxygen-cesium photocathodes,” in addition to an exposition of the results of investigation of the energy distribution of electrons, the author’s observations on the dependence of the photocurrent on the angle of incidence of light for Cs—O—Ag cathodes were also presented.

The section on electron optics, represented by four reports, was headed by the very substantial report of L. A. Artsimovich, “Electron optics of emission systems.”

Two reports on questions of calculation of electron-optical systems: “A short magnetic lens with minimal spherical aberration” and “A method for calculating the fields of the simplest electrostatic lenses,” were delivered by A. G. Vlasov.

V. N. Verntsner delivered a report “The GOI electron microscope.” This instrument, entirely designed and built at the GOI, contains a number of structural elements advantageously distinguishing it in respect to simplicity and efficiency from analogous instruments of foreign firms (for example, RCA). With an accelerating voltage of 40–60 kV it makes it possible to obtain a magnification of up to 25,000 times and, provided there is sufficient stabilization of the supply voltage, to achieve a resolution down to 50 Å.

Other thematic sections were represented by a considerably smaller number of reports. Thus, two reports were devoted to the question of gas discharge: N. A. Kaptsov’s “Change in the mobility of negative ions in strong electric fields and the role of this phenomenon in corona discharge” and G. V. Spivak’s, jointly with O. N. Repkova, “Behavior of an electron-ion plasma in a magnetic field.”

The last report directly related to questions of electronics was the extremely interesting communication by S. A. Vekshinsky, “On Certain Properties of Silver Films Obtained by Evaporation in Vacuum.” This work, which should more properly be assigned to the field of electrophysical materials science, was presented by the author with the persuasiveness characteristic of all his research, based on an impeccable formulation and execution of the experiment. Using a technique for obtaining metallic layers in vacuum that he had brought to a high degree of perfection, he explained a number of properties of the thin silver layers obtained by this method. He was also able to show that, in the process of oxidizing silver by a discharge in oxygen at low pressure (used, for example, in the manufacture of silver–oxygen–cesium photocathodes), a whole range of compounds of silver with oxygen is formed, and not only Ag₂O, as had been believed until now.

The work reported by A. A. Vlasov concerned not so much electronics as the fundamental questions of the theory of electricity. Proceeding from the kinetic equation and taking account of “weak forces,” i.e., the interaction of electrons in an electron plasma at distances greater than the mean distance, the author considered the vibrational properties of an electron gas and showed the necessity for the appearance, in such a gas, at the required values of temperature and pressure, of a crystalline structure.

Comparing this conference with the last of the conferences on the same subject—the Kiev conference, held in June 1940—it is necessary, of course, to note both the less broad representation of research institutions and the smaller volume of material presented (approximately half as many reports). Both are the result of various difficulties connected with the war, manifested in the transfer of a number of research organizations to the East, and so forth. Nevertheless, this conference unquestionably testifies to the growth of Soviet science during the years of the war in this field as well. This growth is manifested above all in the quality of the works reported, and also in the fact that a new direction has appeared among us, not represented at any of the previous conferences: electron optics, both theoretical and applied, which had previously been, so to speak, an “object of import.”

As for the quality of the works, it is no less characteristic in this respect that at this conference fewer papers were reported (not only in absolute terms, but also in percentage terms) that did not represent clearly completed stages of research and did not possess independent value. One of the most important results of the conference appears to us to be the establishment of a new view of the nature and mechanism of action of complex photocathodes.

Thus, we may note with satisfaction that workers in the field of electronics, together with all Soviet scientists, did not spend the difficult years of the war fruitlessly, but succeeded in raising their field to a new, higher level.

N. Khlebnikov.