Dependency of the capture of field emitted electron on the phase velocity of a high-frequency accelerating structure

Abstract

Surface electric fields within high gradient linear accelerators can exceed 200 MV/m and lead to field emitted (FE) electrons entering the structure. When the accelerating field conditions permit, these FE electrons can become captured in the RF fields and be transported through the accelerating structure as a dark current. Understanding the capture and transport of these FE currents in high frequency linear accelerators, and at accelerating gradients well above the capture threshold, is important for the operation of CERN's X-band test stands and other high gradient linear accelerators. Such dark current leads to a background radiation, which dictates shielding requirements and can damage a..