Active Microphonics Compensation for LCLS-II

Testing of early LCLS-II cryomodules showed microphonics-induced detuning levels well above specification. As part of a risk-mitigation effort, a collaboration was formed between SLAC, LBNL, and Fermilab to develop and implement active microphonics compensation into the LCLS-II LLRF system. Compensation was first demonstrated using a Fermilab FPGA-based development system compensating on single cavities, then with the LCLS-II LLRF system on single and multiple cavities simultaneously. The primary technique used for this effort is a bank of narrowband filter set using the piezo-to-detuning transfer function. Compensation automation, optimization, and stability studies were done. Details of the techniques used, firmware/software implementation, and results of these studies will be presented.