Localization of rf breakdowns in a standing wave cavity

• Published in: Physical review special topics. PRST-AB. Accelerators and beams 2009-04, Vol.12 (4), p.042001, Article 042001
• Main Authors: Wang, Faya, Adolphsen, Chris
• Format: Article
• Language: English
• Subjects: ACCELERATORS; Accelerators,ACCPHY; BREAKDOWN; DECAY; Decay rate; EQUIVALENT CIRCUITS; Internal energy; PARTICLE ACCELERATORS; POSITRONS; PROCESSING; SPECTRA; STANDING WAVES; STANFORD LINEAR ACCELERATOR CENTER; STORED ENERGY
• ISSN: 1098-4402; 1098-4402; 2469-9888
• DOI: 10.1103/PhysRevSTAB.12.042001

At SLAC, a five-cell, normal-conducting, L -band (1.3 GHz), standing-wave (SW) cavity was built as a prototype positron capture accelerator for the ILC. The structure met the ILC gradient goal but required extensive rf processing. When rf breakdowns occurred, a large variation was observed in the decay rate of the stored energy in the cavity after the input power was shut off. It appeared that the breakdowns were isolating sections of the cavity, and that the trapped energy in those sections was then partitioned among its natural modes, producing a distinct beating pattern during the decay. To explore this phenomenon further, an equivalent circuit model of cavity was created that reproduces well its normal operating characteristics. The model was then used to compute the spectra of trapped energy for different numbers of isolated cells. The resulting modal patterns agree well with those of the breakdown data, and thus such a comparison appears to provide a means of identifying the irises on which the breakdowns occurred.