Abstract:
Background The stability of the radio-frequency (RF) electromagnetic field in superconducting cavities is a critical factor determining energy gain and beam quality in modern particle accelerators. In pulsed operation, the interaction between RF electromagnetic pressure and cavity wall deformation causes strong dynamic Lorentz force detuning (LFD). This effect leads to rapid shifts in the cavity resonant frequency, resulting in pronounced transient “field droop” in RF amplitude during low-level RF (LLRF) control, which degrades field stability and acceleration consistency.
Purpose This study aims to mitigate the adverse effects of LFD-induced perturbations by implementing a phase feedforward compensation strategy. The goal is to counteract anticipated frequency deviations through the LLRF control system, thereby suppressing transient field perturbations and enhancing RF field stability during the cavity fill and beam acceleration phases.
Methods A quantitative characterization method for cavity detuning was developed by extracting and processing forward voltage and cavity accelerating voltage signals. Based on these signals, the time-dependent detuning frequency and the instantaneous detuning phase angle between the forward and cavity voltages were calculated. These calculated phase offsets were converted into compensation data and programmed into a field-programmable gate array (FPGA) within the LLRF controller. This setup enabled real-time, synchronized phase correction during pulsed operation.
Results The proposed method was experimentally verified at the High Intensity Heavy-Ion Accelerator Facility (HIAF). The experimental results demonstrated that the application of phase feedforward compensation significantly reduced the RF amplitude droop. The system exhibited improved field stability under high-current pulsed operation, aligning with theoretical expectations and confirming the feasibility of the FPGA-based real-time correction.
Conclusions The phase feedforward strategy provides an effective framework for managing dynamic LFD in pulsed superconducting accelerators. By integrating precise detuning calculations with real-time FPGA compensation, the approach enhances both RF stability and acceleration efficiency. This method offers a practical and robust solution for high-performance LLRF control in high-current accelerator environments.
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