Collider Structure Autopsies
Observed limitations to the surface field gradient in x-band structures have been speculated as being due to breakdown damage, leading to copper (mass) loss. This mass-loss theory then leads to an incorrect structure phase advance. To test this theory, sections of rf-operated structures have been sectioned cleanly for microscopic analysis by secondary electron microscopy (SEM) and for chemical analysis by energy-dispersive x-ray spectrometry (EDX). Examination of three complete structures shows that most breakdowns are not associated with particle debris but rather with a combination of 1) abrupt structural features that result in rf heating and melting, 2) subsurface defects, principally oxides and processing remnants, and 3) copper mass movement caused by high rf losses in some metal grains.
Further reading: “Surface analysis of OFE copper x-band accelerating structures and possible correlation to rf breakdown events”, AVS 50th International Symposium, in press, SLAC-PUB-10197 (2003).
