Feedforward Control Strategies for Rapid Phase Adjustment of Superconducting Cavities

Rapidly adjusting (or scanning) the phase of a superconducting radio frequency (SRF) cavity (on a millisecond or sub-millisecond time scale) under closed-loop control is crucial in various applications of many SRF facilities. However, the transient dynamic response of the feedback (FB) control loop is usually unsatisfactory (e.g., the cavity field amplitude is seriously disturbed) during the phase adjustment process because of the restricted closed-loop bandwidth and limited power budgets. Herein, we proposed a feedforward (FF) control strategy derived from a cavity differential equation to accelerate the control loop's regulation process, thereby improving the system's dynamic behavior. We demonstrated the validity of the FF-based strategy in the Chinese ADS Front-end (CAFe) proton facility demo SRF linac. The preliminary results showed that the combined FF + FB control strategy significantly improved the dynamic performance compared with the FB individual control. This study provides the basis for the FF scheme validation and may serve as a reference for applications requiring rapid SRF cavity phase change.