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.
