TUL-DMCS, Łódź, Poland
DESY, Hamburg, Germany
NCBJ, Świerk/Otwock, Poland
Higher efficiency of TESLA based free electron lasers (FLASH, XFEL) by means of increased quantity of photon bursts can be achieved using continuous wave operation mode. In order to maintain constant beam acceleration in superconducting cavities and keep short pulse to CW operation transition costs reasonably low some substantial modification of accelerator subsystems are necessary. Changes in: RF power source, cryo systems, electron beam source, etc. have to be also accompanied by adjustments in LLRF system. In this paper challenges for well established pulsed mode LLRF system are discussed (in case of CW and LP scenarios). Firmware, software modifications needed for maintaining high performance of cavities field parameters regulation (for 1Hz CW and LP cryo-module operation) are described. Results from studies of vector sum amplitude and phase control in case of resonators high Ql factor settings (Ql~1.5e7) are shown. Proposed modifications implemented in VME and microTCA (MTCA.4) based LLRF system has been tested during studies at CryoModule Test Bench (CMTB) in DESY. Results from this tests together with achieved regulation performance data are also presented and discussed.
