Online Detuning Computation and Quench Detection for Superconducting Resonators

Superconducting cavities are responsible for beam acceleration in superconducting linear accelerators. Challenging cavity control specifications are necessary to reduce radio frequency (RF) costs and to maximize the availability of the accelerator. Cavity detuning and bandwidth are two critical parameters to monitor when operating particle accelerators. Cavity detuning is strongly related to the power required to generate the desired accelerating gradient. Cavity bandwidth is related to the cavity RF losses. A sudden increase in bandwidth can indicate the presence of a quench or multipacting event. Therefore, calculating these parameters in real time in the low-level RF (LLRF) system is highly desirable. A real-time estimation of the bandwidth allows for a faster response of the machine protection system in the case of quench events, whereas the estimation of cavity detuning can be used to drive piezoelectric tuner-based resonance control algorithms. In this article, a new field programmable gate array (FPGA)-based estimation component is presented. Such a component is designed to be used either in continuous wave (CW) or pulsed operation mode with loaded quality factors between 10^{6} and 10^{8} . Results of this component with free-electron LASer in Hamburg (FLASH), European X-ray free electron laser (EuXFEL), cryo module test bench (CMTB), and electron linac for beams with high brilliance and low emittance (ELBE) are presented.