Cathode ion bombardment in rf photoguns

Abstract

We use the ponderomotive potential of the rf field to accurately describe the motion of ions in an rf gun. We apply the method to the BNL 1/2-cell superconducting radio-frequency photogun and demonstrate that a significant portion of ions produced in the gun can reach the cathode if no special precautions are taken. Also, we propose simple mitigation techniques that can reduce the rate of ion bombardment.