Digital low-level radio frequency system and cavity simulator for 1.3 GHz continuous-wave superconducting radio-frequency cavity

Abstract

BackgroundA high precision low-level radio-frequency (LLRF) system for a superconducting radio-frequency (RF) cavity of Shanghai high-repetition-rate X-ray free-electron laser and extreme light facility (SHINE) is required to stabilize the electromagnetic field of cavities. However, due to the high loaded quality factor of the 1.3 GHz continuous-wave superconducting RF cavity, the RF cavity has a small electromagnetic bandwidth in the frequency domain. The small electromagnetic frequency mismatch between the RF power source and RF cavity can easily interlock in the generator driven resonator control system.PurposeThis study aims to develope a LLRF and a digital RF cavity simulator ensure stable electromagnetic field of 1.3 GHz continuous-wave superconducting RF cavities.MethodsA self-excited loop (SEL) control system was developed to prevent interlock, and a generator driven resonator (GDR) control system was developed to operate the RF cavity under normal working states. In addition, a digital RF cavity simulator was developed to verify the design algorithms of the LLRF system. The SEL/GDR system and RF cavity simulator were also implemented and tested based on MicroTCA.4 platform.ResultsIn the free SEL mode, the amplitude of the cavity RF field is stable at the set-point, even if the cavity is detuned for several half-bandwidths. In the locked mode, the stability of the cavity RF field in the amplitude and phase are 0.458 0% (Root Mean Square, RMS) and 0.058° (RMS) respectively, at the detuning frequency of 5 Hz.ConclusionsIt is verify that the SEL control system can stabilize the cavity RF field even when the cavity is detuning, and the cavity simulator proves to be a reliable platform for the evaluation of new algorithm.

Keywords

• digital rf cavity simulator
• high-repetition x-ray free-electron laser
• low-level rf system
• self-excited loop
• system generator