Slow-Control Loop to Stabilize the RF Power of the FLUTE Electron Gun

The lin­ear ac­cel­er­a­tor FLUTE (Far In­frared Linac and Test Ex­per­i­ment) at KIT serves as a test fa­cil­ity for ac­cel­er­a­tor re­search and for the gen­er­a­tion of ul­tra-in­tense co­her­ent THz ra­di­a­tion. To achieve sta­ble THz pho­ton en­ergy and op­ti­mal beam tra­jec­tory, the en­ergy of the elec­trons emit­ted from the RF photo-in­jec­tor must be sta­ble. The ac­cel­er­at­ing volt­age of the RF cav­ity has been shown to be a sig­nif­i­cant in­flu­enc­ing fac­tor. Here, we re­port on the de­vel­op­ment of a slow closed-loop feed­back sys­tem to sta­bi­lize the RF power and thus the ac­cel­er­at­ing volt­age in the RF photo-in­jec­tor cav­ity. With this closed-loop feed­back sys­tem the rel­a­tive stan­dard de­vi­a­tion of the RF power in the cav­ity can be im­proved by 8.5 %.