Phase Scan Signature Matching for Linac Tuning

A conceptually simple method for linac tuning has been tested on the 200 MeV drift-tube linear accelerator at Fermilab. The phase of a beam-induced signal in a stripline detector is measured as tank phase is scanned over approximately 360 degrees. The stripline detector is downstream of the tuned tank. The resulting phase-scan curves have unique signatures that depend upon only a few critical parameters. By matching theoretical curves of beam phase versus tank phase to measured curves, the proper values for these parameters are determined. The parameters which are varied during curve matching are the field amplitude, the relative tank-phase offset of the phase-scan curves and the velocity of the beam as it enters the tank. The actual phase of the tank fields relative to the design phase is found by noting the position of the actual tank phase along the phase-scan curve, once a curve match is obtained.