Thermocathode radio-frequency gun for the Budker Institute of Nuclear Physics free-electron laser

A radio-frequency (RF) gun for a race-track microtron-recuperator injector driving the free-electron laser (FEL) (Budker Institute of Nuclear Physics) is being tested at a special stand. Electron bunches of the RF gun have an energy of up to 300 keV and a repetition rate of up to 90 MHz. The average electro-beam current can reach 100 mA in the continuous operation regime. The advantages of the new injector are as follows: long lifetime of the cathode for high average beam current; simple scheme of longitudinal beam bunching, which does not require an additional bunching resonator in the injector; absence of dark-current contamination of the injector beam; and comfortable RF gun operation due to the absence of a high potential of 300 kV at the cathode control circuits. In this study we describe the RF gun design, present the main characteristics of the injector with the RF gun, and give the results of testing.