Abstract
Aiming at production of high brightness electron beams with longer pulses than several μsec for applications to free electron lasers by use of an RF gun with a thermionic cathode, the adverse effect of back-streaming electrons onto the cathode surface were studied both experimentally and numerically. Temperature rises of the thermionic cathode surface due to the back-streaming electrons were observed directly by use of an infrared thermometer. From the measured temperature rises, powers of the back-streaming electron beams were, then, evaluated by use of a 0-dimensional model taking into account heat transfer through thermal radiation and thermal contact to the gun body, and comparisons were made with numerical results by use of a 2-dimensional particle-in-cell simulation code we have developed. Both by the experimental evaluation and by the particle-in-cell simulation, the beam power onto the cathode surface was found to increase with the increasing RF input to the RF gun cavities, and reach a considerable power compared to the cathode heater power supply.
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