Dark Current Research
During the operation of an RF photo injector with high gradient, not only the photoelectron beam, but also the dark current is produced. The dark current is part of the field emission from the cavity and photocathodes, Emitted electrons are further accelerated through the gun together with the photocurrent beam. It belongs to the unwanted beam, which may eads to beam loss and facility damage, meanwgile creates additional background for primary or radiation beam users.
For CW mode operation, μA level dark current is unendurable. The studies on the dark current sources and the reduction of its effect are going on for SRF gun. A 13 MHz fast kicker is under design aiming to kick out 93.5 % of the dark current
R. Xiang, et al., Dark Current Measurements at the Rossendorf SRF Gun, FEL 2013, August 26-30, 2013, New York, USA