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Description
Mechanical-mode characterization is essential for understanding Lorentz-force detuning (LFD) and improving field stability in superconducting RF cavities. This work presents two complementary approaches for identifying LFD-induced mechanical dynamics under LLRF control. First, a physics-informed grey-box model is estimated from LFD transients. It extracts dominant mechanical modes when stepped-sine measurements are time-consuming or compromised by ponderomotive instability, and yields low-order models that reproduce measured detuning transients. Second, a closed-loop broadband chirp method injects a perturbation through the cavity-field amplitude setpoint while amplitude and phase feedback remain active. The mechanical transfer function is reconstructed from the squared-field perturbation and detuning. Measurements on a half-wave resonator show that one chirp sweep identifies dominant modes consistent with closed-loop stepped-sine measurements and grey-box identification. The effects of excitation strength, chirp duration, feedback gains, and microphonics processing are evaluated. Together, the methods provide tools for robust mechanical-mode identification and LLRF optimization.
| Abstract Classification | System Identification |
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