Use of acoustic emission to diagnose breakdown in accelerator RF structures

Abstract

Accelerator structures of a wide variety have been damaged by RF breakdowns. Very little is known about the mechanisms that cause the breakdown and the damage although there has been theoretical work [1,2]. Using an array of ultrasonic acoustic emission sensors we have been able to locate and classify breakdown events more accurately than possible using microwave techniques. Data from the technique has led to improvements in the design of the NLC X-band RF structure. We report results of acoustic emission studies at the DESY TESLA Test Facility and the SLAC NLC Test Accelerator. Contributed to Particle Accelerator Conference 2003Portland, Ore., 12-16 May 2003 * Work supported by Department of Energy contract DE-AC03-76SF00515. 2 AbstractAccelerator structures of a wide variety have been damaged by RF breakdowns. Very little is known about the mechanisms that cause the breakdown and the damage although there has been theoretical work [1,2]. Using an array of ultrasonic acoustic emission sensors we have been able to locate and classify breakdown events more accurately than possible using microwave techniques.Data from the technique has led to improvements in the design of the NLC X-band RF structure. We report results of acoustic emission studies at the DESY TESLA Test Facility and the SLAC NLC Test Accelerator.

Surface Analysis of OFE-Copper X-Band Accelerating Structures and Possible Correlation to RF Breakdown Events

“…Approximate break-down position in the structure is calculated by the measurement of the the phase and timing of the reflected signal. A complementary acoustic detection method, which takes advantage of the conversion of the breakdown energy into phonons, is also used to localize the breakdown events [1]. RF-processed sections were cleanly autopsied (sectioned without adding chemical contamination or physical debris).…”

“…Improved understanding of these breakdown events is desirable for the development of structure designs, fabrication procedures, and processing techniques that minimize structure damage. RF reflected wave analysis and acoustic sensor pickup have provided breakdowns localization in RF structures [1] [2]. Particle contaminations found following clean autopsy of four RF-processed travelling wave structures, have been catalogued and analyzed.…”