3-D simulation study for a thermionic RF gun using an FDTD method

Beam dynamics in a thermionic RF gun for a new pre-injector in a future synchrotron radiation facility at Tohoku university has been studied by developing a 3-D Maxwellʹs equation solver. Backbombardment (BB) effect on a cathode, which is a crucial problem for performance of the thermionic RF gun, has been investigated. It is found that an external dipole magnetic field applying around the cathode is effective to reduce high-energy backstreaming electrons from the accelerating cell. However, the low-energy electrons coming back from the first cell inevitably hit the cathode, so that characteristics of the cathode material seems to be crucial for reduction of the BB effect.