Estimation of superconducting cavity bandwidth and detuning using a Luenberger observer

Enabled by progress in superconducting technology, several continuous wave linear accelerators are foreseen in the next decade. For these machines, it is of crucial importance to track the main cavity parameters, such as the resonator bandwidth and detuning. The bandwidth yields information on the superconducting state of the cavity. The detuning should be minimized to limit the required power for operation of the cavity. The estimation of these parameters is commonly implemented in the digital electronics of the low-level rf control system to minimize the computation delay. In this proceedings paper, we present a way to compute the bandwidth and detuning using a Luenberger observer. In contrast to previous methods, the state observer yields estimations at the native control system sample rate without explicitly filtering the input signals. Additionally, the error convergence properties of the estimations can be controlled intuitively by adjusting gain parameters. Implementation considerations and test results for the derived observer are presented in the manuscript.