Transient beam-loading detection in an SNS cavity- simulations and initial measurements

Beam phase measurement based on the detection of a transient beam-loading signal in a SC cavity has the potential to become a very fast linac tune-up technique, especially for an electron linac, as it may precisely set up the cavity's synchronous phase. A large signal-to-noise ratio is critical in the development of a transient detector technique. This paper discusses the study of a transient detector in the Spallation Neutron Source proton linac and the major challenge for this method: stochastic noise in the rf system, which reduces the precision and increases the time needed for accurate phase measurement. Using simulation studies with a beam-cavity model, signal measurement with the Low-Level RF system, and the experiment with prototype detectors, we analyzed the influence of noise on phase measurement.