CW 100 keV ELECTRON RF INJECTOR FOR 40 mA AVERAGE BEAM CURRENT

CW 100 keV electron RF gun for 40 mA average beam current was developed, built, and commissioned at BINP SB RAS. The RF gun consists of normal conducting 100 MHz RF cavity with a gridded thermo cathode unit, CW 16 kW generator with GU-92A tetrode in the output stage, and a set of LLRF electronics. The gun was tested up to the design specifications at a test bench that includes a diagnostics beam line. The design features of different components of the gun are presented. Preparation and commissioning experience is discussed. The beam test results are summarized. INTRODUCKTION A 100 MHz RF electron injector was designed and manufactured at BINP for continuous wave (CW) powerful accelerator in RFNC-VNIIEF [1]. This compact accelerator, similar to the type of «RHODOTRON» [2], is designed for continuous production of short electron bunches with energy of 1.5 ÷ 7.5 MeV with power of 300 kW and higher. Each bunch passes through a single accelerating cavity of the accelerator several times. After each pass, the beam is turned in the bending magnets. In order to preserve the transverse dimensions of the electron bunches within the aperture after passing through the bends, the bunches should have small enough energy spread (<1%) and be quite short (<0.2 ns). An advantage of RF guns compared with static guns is the absence of cathode back bombardment with accelerated ions of residual gas ionized by an electron beam. This allows having a long lifetime of the cathodes and operating the gun continuously in the vacuum of 10 -6 ÷ 10 -7 Torr. Also, this enables raising the gun voltage and thus increasing the energy of the electron beam from 3040 keV to 100 keV proportionally to the beam current to the power of 2/3, in-accordance with the Poisson law. Furthermore, calculations showed that the increased voltage in the RF injector in combination with the effect of the longitudinal beam bunching therein provides a reduction in the energy spread of up to 0.3% (rms) in the first passage of the accelerator and the bunch shortening by up to 18 times.