Measurement of rf accelerator cavity field levels at high power from x-ray emissions

Energy spectroscopy measurements of x-rays from rf structures at high power provide an independent method of finding accelerating-gap voltages in the multiple-cell accelerating structures. An x-ray detector is used to measure the energy of the emitted x-rays; and the high-energy endpoint of the energy spectrum histogram corresponds with the peak-gap voltage in the rf structure. The x-ray measurements are used to provide a calibration relating peak-gap voltage to rf structure field sampling probes. The analyzed x-ray data has been compared to theoretical SUPERFISH and MAFIA3D predictions and to beam-dynamics data for the multiple-cell structures. Information about this diagnostic technique and its value for verifying accelerator modeling codes is presented