Improvement of beam macropulse properties using slim thermionic cathode in IAE RF gun

A long beam macropulse is strongly required for free-electron lasers. RF guns can potentially produce high brightness electron beam using a simple and compact system. However, due to a back-bombardment, a cathode surface is overheated. Thus, it is difficult to maintain a constant beam current and beam energy during a macropulse. The use of a photo cathode with a short-pulsed laser is one of the solutions, but it affects the simplicity and the compactness of the RF guns. We studied a mechanism of back-bombardment and experimentally and numerically found that a low energy component of the back-streaming electrons plays an important role in cathode surface heating.