An acoustic sensor system for localizing RF breakdown in warm copper accelerating structures

X-band accelerator structures meeting the Next Linear Collider (NLC) design requirements have been found to suffer damage due to Radio Frequency (RF) breakdown when processed to high gradients [F. Le Pimpec, et al., in: LINAC 2002, Korea, SLAC-PUB-9526, 2002 [1]]. Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. Acoustic sensors attached to an accelerator structure can detect both normal and breakdown RF pulses [M. Gangeluk, et al., Acoustic monitoring system of RF breakdowns inside the electrodynamics structure at Kurchatov SR source accelerator, in: EPAC, P.1986, 1994 [2]]. Using an array of acoustic sensors, we have been able to pinpoint both the cell and azimuth location of individual breakdown events. This permits studies of breakdown in time and in space, so that underlying causes can be determined. This technique provided a significant understanding of breakdown in the structure input coupler.