Study of basic physics of RF breakdown in ultra-high vacuum accelerating structures

Description
The accelerating gradient is one of the crucial parameters affecting the design, construction and cost of next generation particle accelerators. The major obstacle to higher gradient is the rf breakdown. RF breakdown limits the working power and produces irreversible surface damage in accelerating structures and other high power rf components. The recent update of the CERN based linear collider design CLIC requires 100 MV/m loaded gradient at 12 GHz in accelerating structures in contrast to the long-lived S-band SLAC linac, which has operated for decades at 17 MV/m. Here we present the study of the basic physics of the RF breakdown directed towards increase of the accelerating gradient. In this study the surface processing, geometry, and materials of the structures have been varied, one parameter at a time. The breakdown rate or alternatively, the probability of breakdown/pulse/meter has been recorded for different operating parameters. These statistical data reveal a strong dependence of breakdown probability on surface rf magnetic field, or alternatively on surface pulsed heating. This is in contrast to the classical view of electric field dependence. We will present results showing this remarkable correlation and discuss hypotheses that may offer insight into this phenomenon.
Organised by MariaGrazia Grimaldi