300 MeV Electron Synchrotron

V. P. Anokhin, A. G. Vlasov, A. A. Vorob’ev, V. N. Eponeshnikov,
I. A. Gabrusenko, B. N. Kalinin, L. G. Kositsyn, V. A. Kochegurov,
V. N. Kuz’min, G. A. Sipailov, B. A. Solntsev, V. I. Tolmachev,
I. P. Chuchalin

The 300 MeV electron synchrotron (Fig. 1) was built as a model of a 1500 MeV electron synchrotron.

The electromagnet of the 300 MeV synchrotron is made in the form of a “racetrack,” with four straight sections and a C-shaped transverse cross section of the magnetic core (with the gap outward).

The amplitude values of the magnetic induction in the steel and of the magnetic-field strength in the orbit are taken to be, respectively, 15 kGs and 10.7 kOe. The radius of the electron orbit is 0.95 m. The length of the straight section is 0.6 m. The field falloff index in the gap of the electromagnet was chosen equal to 0.65.

To simplify fabrication and assembly, the magnetic core is composed of 24 blocks assembled from plates of transformer steel, grade E42, 0.35 mm thick. The total weight of the magnetic-core steel is 14.7 t; the weight of the copper is 1.5 t.

Excitation of the electromagnet is pulsed. The pulse repetition frequency is 1 pulse per second. The pulse shape is sinusoidal, with an equivalent frequency of 6 Hz. The operating principle of the power-supply circuit is based on the discharge of capacitors, whose charging is carried out from controlled rectifiers. The circuit provides electronic voltage stabilization (±0.5%). To reduce the required power, recharging of the capacitor banks through the electromagnet is used. The amplitude of the pulsed current through the electromagnet winding is 758 A at a voltage of 8.7 kV.

The synchrotron injector is a two-electrode accelerating tube supplied from a pulsed modulator through a step-up transformer at 260 kV. The accelerating-voltage pulse has a rectangular shape. The pulse duration is 6 μsec. The stability of the accelerating voltage is 0.07%.

The beam from the accelerating tube enters the vacuum chamber of the synchrotron through an injection channel equipped with a system of focusing magnetic lenses, deflecting coils, and devices for indicating the current and position of the beam. The electrons are introduced into the orbit by means of an electrostatic inflector in the straight section of the accelerating chamber.

¹ The articles in the present collection were presented by the scientific seminar of the laboratories of the Research Institute of Nuclear Physics, Electronics, and Automation.

Fig. 1. 300 MeV electron synchrotron.

The injection system is started by applying trigger pulses to the modulator from the synchrotron magnetic-field level sensor.

Owing to the large frequency deviation in the initial part of the acceleration cycle, it proved expedient to divide the entire high-frequency channel into two channels. The first channel operates during the synchrophasotron acceleration period, which lasts approximately 300 μsec. Here the frequency of the accelerating field varies from 28.2 to 37 MHz. The amplitude of the accelerating voltage at this stage is 500 V. The frequency variation is carried out in a self-oscillator with ferrite inductance, which serves as the driver for a 6 kW power amplifier. The second channel operates during the main part of the acceleration cycle. A 3 kW generator provides an accelerating voltage with an amplitude of 1000 V at a frequency of 37.5 MHz.

The accelerating device consists of two coupled toroidal resonators. The broadband resonator, intended for acceleration at the synchrophasotron stage, is shunted by a 35 Ω resistance and has a quality factor \(Q = 4\). The quality factor of the narrow-band resonator is 160. The switching moments of the sections of the high-frequency system are controlled by a common synchrogenerator.

The vacuum system of the synchrotron includes a vacuum chamber, a pumping system, and a control, interlock, and signaling system.

The vacuum chamber is made of separate porcelain sectors. The sectors are glued into quadrants, which in turn are connected to one another by means of flanges. The straight sections of the chamber are also made of porcelain sections. The inner surface of the chamber is coated with Aquadag with a specific resistance of 30–50 Ω/cm\(^2\).

The chamber is pumped by two VA-05-1 high-vacuum units and two titanium ion-sorption pumps. The preliminary vacuum is produced by a VN-1 pump. The pressure in the vacuum chamber is \(3\text{–}4 \cdot 10^{-6}\) mm Hg.

Startup of the accelerator was carried out with the aid of fluorescent screens and probes and a NaI crystal with an FEU-11B photomultiplier. The number of accelerated electrons was measured by ferrite sensors installed inside the vacuum chamber.