Measurement of voltage and power of RF cavity with capacitor probe in SC200 cyclotron

The voltage and power of the RF cavity of an accelerator were measured based on a calibration factor of the capacitor probe to assess the performance of the SC200 cavity. The calibration factor can be formulated using a low-frequency method and RF numerical simulation. Thereafter, based on it, the capacitor probe is utilized to measure the voltage and power of the RF cavity in a cool-measured and high-power platform. The cool-measured results indicated that the measured voltage was equal to 94.7% of the designed voltage at the same driver power. The decline of voltage is mainly caused by the deformation (95.9%) of the voltage profile along the Dee rather than a decrease in the quality factor. High-power experiments demonstrated that, at low reflection, the residual power may be attributed to an increase in the resistance of the RF cavity material and the dielectric loss owing to the gas desorption of cyclotron components, whereas at high reflection, the residual power is deposited by the multipactor. The steady power of the multipactor is approximately 12% of the forward power. These calculations and results could provide a reference for the measurement of the voltage and power and conditioning of the SC200-like RF cavity. (author)