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

A highly precise low-level radio-frequency (LLRF) system for a 1.3 GHz continuous-wave (CW) superconducting radio-frequency (RF) cavity is required to stabilize the electromagnetic field of cavities. However, because of the high loaded quality factor and wide electromagnetic frequency band of the 1.3 GHz CW 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 cause ponderomotive instabilities in the generator driven resonator control system, eventually resulting in variations in the electromagnetic field of the cavity. In this study, a self-excited loop (SEL) control system was developed to prevent the occurrence of ponderomotive instabilities and compensate for the effects of microphonics noise. In addition, a digital 1.3 GHz RF cavity simulator, which can easily verify the designed algorithms of the LLRF system, was developed. The recorded measurements show that the SEL control system can ensure stability of the cavity field even when the RF cavity is detuned by 5 Hz. The comparison and validation have verified that the cavity simulator is a reliable platform to test the new algorithms.