Argonne EP'd Single Cell Cavity tested on November 28th , 2007

The Large Grain single cell cavity that was electropolished at ANL was successfully tested today (an earlier attempt last month was thwarted by a cavity vacuum leak). The cavity showed good low-field Q (~2e10), however field emission began at about 14-15 MV/m. This FE processed somewhat using pulse-processing (as can be seen by the improved Q vs E curve in the attached plot), but remained the performance limitation. The maximum attained field was 22.3MV/m at a Q of 5.3e9. Maximum radiation was just under 1R/hr.

When initially tested as part of the VTS commissioning, this cavity reached a maximum gradient of about 28MV/m, but also showed FE - initially FE onset was at about 10-11MV/m and then ultimately at about 20MV/m. However the low field Q during this test was about a factor of two better than the initial commissioning test. The initial test also showed some multipacting at 5-6 MV/m - no MP was observed this time.

This cavity was equipped with thermometry, and scans of the thermometry performed during the pulse-processing did indicate heating from FE, especially on one of the equatorial sensors. Dmitri will provide a detailed analysis later.

Text and Graph Credit: Joe Ozelis, Fermilab