Estimation of Lorentz force detuning and its compensation on 650 MHz βg = 0.92 single cell SCRF cavity

Abstract

Superconducting technologies are widely used in modern radiofrequency (RF) cavities for particle accelerators in various fields of applications. The Superconducting radiofrequency (SCRF) cavities are highly sensitive to small perturbation on cavity dimensions. The operation of the superconducting cavity becomes challenging due to narrow resonance bandwidth on account of a very high-quality factor. The main perturbing source is Lorentz Force acting on the cavity wall, which detunes the cavity from resonance. Finite element (FE) analysis has an important role in Lorentz force detuning (LFD) estimation, which requires coupled-field FE analysis between the structural and RF domains of the cavity. The LFD effect can be mitigated up to a certain extent by using a proper fast tuning methodology. This paper represents the methodology for structural-high frequency electromagnetic coupled field simulation for LFD calculation of 650MHz, βg = 0.92 single-cell SCRF cavity. First, the static LFD is calculated for various voltage gradients of SCRF cavity structure and then dynamic behavior of cavity due to LFD pressure pulse is studied at different pulse widths (PW) and pulse repetition rates (PRR). A comparison of transient FE analysis of the single-cell cavity with one end fixed and another end free and cantilever beam for similar loading is done for benchmarking. To counter the detuning effect, the SCRF cavity employs a piezo tuning device. The dynamic behavior of piezo pulse response on the cavity is also studied. An experimental test of the piezo tuner system has been performed at room temperature to validate the FE coupled simulation. Further, dynamic analysis has been carried for the combined effect of LFD pressure and piezo load pulse to compensate for the LFD effect. Optimizing the piezo load for compensating the frequency shift is also discussed and based on optimum load, LFD has been mitigated for different acceleration gradients.