TPI Electron Accelerators

I. P. Chuchalin

Tomsk Polytechnic Institute has made a significant contribution to the development of electron accelerators. The creation of the first Soviet betatron at TPI dates to the first postwar years (1946–1947). On the initiative and under the leadership of Professor A. A. Vorob’ev, a small group of physicists and engineers, in fact isolated from the outside world because of the conditions of that time, ventured to develop and create a complex electrophysical device. The pioneers of the first Tomsk and Soviet betatrons, together with Professor A. A. Vorob’ev, were TPI associate professors A. K. Potuzhnyi, V. N. Titov, and M. F. Filippov.

Tomsk Polytechnic Institute has developed, manufactured, and installed in various scientific institutions, higher educational institutions, industrial enterprises, and clinics in our country and abroad more than 60 betatrons bearing the TPI mark. Theoretical and experimental studies carried out by TPI staff cover a wide range of questions in the field of creating magnetic fields for betatrons [1–5], the process of capturing electrons into acceleration [6–11], the extraction of electrons from the accelerating chamber [12–14], the study of the spectral and angular characteristics of bremsstrahlung and electron beams [15–16], the development of electrical circuits for power supply, control, and stabilization of radiation [17–20], etc.

Table 1 gives the main types of betatrons developed at TPI, with their characteristics indicated.

Betatrons manufactured at TPI are widely used in the fields of nuclear and radiation physics, radiation chemistry, in medicine and biology, and in industry, especially for flaw detection of products [21–26].

Below are several examples of the application of TPI betatrons.

For the Barnaul Boiler Plant, a comprehensive betatron flaw detector BD-2 at 25 MeV was developed and introduced into production for the first time in world practice, for the inspection of thick-walled welded joints. The flaw detector makes it possible to carry out continuous automatic inspection of welds up to 350 mm thick and up to 100 mm wide, with a productivity of up to 30 km of seams in one month.

For the Angarsk Oil Refinery, a comprehensive betatron flaw detector BD-1 was developed, which makes it possible to carry out ...

carry out automatic inspection of steel forgings up to 500 mm thick with a productivity of 2 m²/h.

The use of integrated betatron flaw detectors for quality control of materials and products makes it possible to reduce the inspection time tens of times compared with radiographic methods of radiation flaw detection, while maintaining high sensitivity to detectable defects.

Table 1

Characteristics of the main types of betatrons developed at TPI

Betatrons manufactured by the institute have repeatedly been exhibited at the Exhibition of Achievements of the National Economy. For the 25 MeV and 30 MeV betatrons the institute was awarded first-degree honorary diplomas, and the leading researchers were awarded medals of the VDNKh.

At the Research Institute of Nuclear Physics, Electronics, and Automation of Tomsk Polytechnic Institute (NII YaF TPI), several types of high-current betatrons and two-chamber stereobetatrons have been developed and put into operation [27–31]. Owing to the use of a high-voltage injection system and an increase in the zone of focusing forces in high-current betatrons, more than \(10^{12}\) electrons are accelerated per pulse, which is more than 100 times greater than the accelerated currents obtained in the best betatron models of the well-known foreign firms Brown—Boveri and Siemens.

Figure 1 shows a photograph of the high-current betatron SB-25 with an accelerated-electron energy of 25 MeV. Some designs of stereobetatrons were exhibited at Soviet exhibitions in the USA and Czechoslovakia. At the Exhibition of Achievements of the National Economy they were awarded diplomas, and their creators medals.

The use of high-current betatrons for flaw detection in thick-walled metallic and nonmetallic products makes it possible to sharply reduce exposure time and improve the detectability of defects. The presence in stereobetatrons of two intersecting beams of bremsstrahlung proves very useful both for the purposes of flaw detection and for deep therapy in the treatment of malignant tumors.

Fig. 1

In Tomsk, for the first time in the Soviet Union, a betatron was used for the treatment of malignant tumors, with a preliminary experimental study of the biological action of high-energy bremsstrahlung radiation.

Tomsk physicians, under the general direction of Professor I. V. Toroptsev, provided a systematics of morphological changes in the organs and tissues of experimental animals subjected to the action of bremsstrahlung radiation from betatrons at various energies over a wide range of doses under conditions of single and repeated irradiations.

The broad development of construction in our country and the associated urgent need to monitor the quality of the work being performed call for the creation and development of new portable flaw detectors. At construction and installation sites, at stations, and under field and shop conditions, radioactive radiation sources are currently most often used for flaw detection. However, these emitters have a low utilization factor, require special storage facilities, and, at medium and high activities, have considerable container dimensions and weight and constitute a serious constant radiation hazard for operators and those nearby.

In connection with the noted shortcomings of isotope radiation sources, the Tomsk Polytechnic Institute has for several years been developing special betatron designs intended for inspection under the above-mentioned nonstationary conditions. As a result of these efforts, portable betatrons with radiation energies of 3–6 MeV have been created; they are capable of successfully competing with most isotope installations, providing higher detectability of defects and making it possible to inspect products of greater thickness.

The portable compact betatrons that have been developed [32–34] are made in the form of three or four separate units connected during operation by cables. The weight and dimensions of the units make it possible to transport them manually to hard-to-reach objects of inspection.

Production tests of prototypes of portable betatrons revealed their high efficiency and led to broad interest in these installations on the part of industrial enterprises.

Figure 2 shows a photograph of the compact PMB-6s betatron, which makes it possible to inspect steel products up to 250 mm thick and concrete products up to 600 mm thick. The exposure time for steel

Fig. 2

250 mm thick is 45 minutes, with a sensitivity of about 1%.

The PMB-6s betatron developed at the institute, together with industrial enterprises in Tomsk, has been prepared for serial production. Designs of this betatron were exhibited at international fairs in Vienna (1968) and Leipzig (1969), where they were sold from the stands. One of the betatrons was supplied to France on order from a firm. In July 1969 the PMB-6s betatron was demonstrated at the International Exhibition of Welding Equipment in Japan.

At the Nuclear Physics Research Institute of TPI, two types of microtrons have been developed [35–38], whose characteristics are given in Table 2.

The microtrons were developed as injectors for a 1.5 GeV synchrotron. The synchrotron operates at a frequency of 1–2 Hz, and therefore the pulse repetition rate of the microtrons is likewise 1–2 Hz. The pulse repetition rate of the microtrons can be increased to 50 or 400 Hz,

which makes it possible to obtain an average accelerated-electron current of up to 7.5 or 600 μA, respectively.

Table 2

Main characteristics of microtrons developed at the Scientific Research Institute of Nuclear Physics, TPI

Figure 3 shows a photograph of the 7.0 MeV microtron.
At the Scientific Research Institute of Nuclear Physics of TPI, direct-action accelerators are being developed. Initially, direct-action accelerators were developed as electron injectors into cyclic accelerators—betatrons and synchrotrons.

Fig. 3

Subsequently, the need arose to create direct-action accelerators for energies of 200–700 keV as independent installations for use in various fields of science and technology, such as quantum electronics, radiation chemistry, medicine, etc.

Table 3 gives the main characteristics of the high-current high-voltage accelerator SVU-1. Structurally, the accelerator is arranged in two mobile units—the emitter unit and the control console.

The radiator unit contains a pulse transformer, an electron gun, and a vacuum system with its power-supply circuit. The dimensions of the radiator unit are \(880 \times 850 \times 11070\ \mathrm{mm}^3\), and its weight is 200 kg. The control console contains the modulator with rectifier and all monitoring and control instruments. The dimensions of the control console are \(900 \times 1200 \times 1300\ \mathrm{mm}^3\), and its weight is 200 kg.

Obtaining the vacuum in the electron gun and accelerating tube of the SVU-1 accelerator, as in the vacuum chambers of the TPI betatrons, is accomplished by small-size titanium ion-sorption pumps developed at the institute.

The SVU-1 accelerator was exhibited in 1966 at the Exhibition of Achievements of the National Economy, where it was awarded a silver medal. In 1967 it was exhibited at the Soviet exhibition in Budapest.

For research in the field of quantum electronics, a nanosecond electron accelerator was developed with the following parameters: energy of accelerated electrons up to 500 keV, electron current in the pulse up to 1500 A, current-pulse duration 30–40 nsec.

Table 3

Main parameters of the SVU-1.

At the Tomsk Polytechnic Institute, A. A. Vorob’ev proposed [39–40], and under the direction of A. A. Vorob’ev and A. N. Didenko there were developed [41–42], waveguide synchrotrons combining the advantages of linear waveguide and cyclic accelerators. Being waveguide accelerators, they provide large energy increments per unit length. Being cyclic, they make it possible to accelerate particles to high energies with a comparatively small waveguide length.

Structurally, the high-frequency system of waveguide synchrotrons is some kind of slowing, bent, ring-closed system placed in the interpole space of a conventional synchrotron. The slowing system is necessary in order to reduce the phase velocity of one of the waves to the particle velocity (in the case of electrons, to the speed of light) and thereby create the condition for continuous acceleration of particles.

In order to confirm the principal theoretical propositions, in 1963 and 1964 two waveguide cyclic electron accelerators for 10 MeV were built and put into operation at the TPI Nuclear Physics Research Institute: one with an accelerating system in the form of a bent waveguide of rectangular cross section, diaphragmed along the outer bent wall, and the other with an accelerating system in the form of a smooth bent closed waveguide. In both accelerators the electrons are first accelerated to an energy of 3 MeV in the betatron mode.

Waveguide accelerating systems are one of the possible variants in the development of electron and proton accelerators for ultrahigh energies. The efficiency of such systems increases greatly if the aperture of the accelerating chamber is reduced, as occurs in cybernetic accelerators developed under the direction of Academician A. L. Mints.

At the TPI Nuclear Physics Research Institute, one of the most powerful cyclic electron accelerators has been developed, built, and put into operation.

in our country—the “Sirius” electron synchrotron with an energy of 1.5 GeV [43–50].

A large volume of scientific research has been carried out on the synchrotron, and interesting results have been obtained on the influence of quantum fluctuations of electron radiation on their motion in the accelerator chamber. Valuable results have been obtained in elementary-particle physics.

At the Tomsk Polytechnic Institute, theoretical and experimental studies are being conducted on new methods of accelerating charged particles and on the development of new types of accelerators [51–57].

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