Thermionic RF gun with high duty factor

Back bombarding limits wide usage of thermionic RF guns. The article presents one of the possible field distribution on-axis of an RF gun, which allows to reduce back bombarding power of a cathode. Simulation predicts 20 kW of pulsed back bombarding power on the LaB₆ cathode under 0.51 A of output current and 0.908 MeV of maximum energy of the electrons. The average current can be increased until the average power of back bombarding reaches the initial filament power of a cathode. Therefore it is expected to reach at least 0.5 mA of the average output current. The energy spectrum and bunch phase length are suitable to inject the beam directly into the accelerator structure with the phase velocity equal to the velocity of light. The ramp of the cathode temperature during the RF pulse and the long time stability of the output current are discussed