Beam-based phase monitoring and gradient calibration of Jefferson Laboratory RF systems

Beam-based monitoring was instituted at Jefferson Lab in December of 1994 to correct the RF system phase setpoints against drifts of the master oscillator system, while running transparently to normal beam setup and delivery operations. As then implemented, the master oscillator distribution was subject to large thermal drifts, but no means existed of tracking the distribution of drifts, nor of identifying phase errors for individual cavities following maintenance activities. The background process implemented is capable of cresting each of the 312 cavities in the linacs to within approximately ±2 degrees. In addition, during dedicated system measurement operations, the RF cavity gradients have been calibrated with beam to within a tolerance of approximately ±5%. These beam-based results are in many cases more than 20% different from commissioning results using RF measurement techniques