Improvement of electron beam properties by reducing back-bombardment effects in a thermionic RF gun

In the Free Electron Laser (FEL) experiment, where a long beam macro-pulse is required, energy shift caused by an increase of current density at the cathode surface due to heating by back-streaming electrons is quite serious. It was numerically found that the low-energy component of the back-streaming electrons causes a serious effect. It was also found that the effect can be decreased by applying a transverse magnetic field by calculating time evolution of the cathode surface temperature with a one-dimensional thermal conduction model.