Beams Document 3686-v1

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The development of new techniques for SRF cavity surface research at Fermilab

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Camille M. Ginsburg
Updated by:
Camille M. Ginsburg
Document Created:
04 Oct 2010, 12:02
Contents Revised:
04 Oct 2010, 12:02
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04 Oct 2010, 12:02
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Surface defects such as pits, bumps, cracks, scratches, etc., have been identified as some of the main sources of limitations to SRF cavities, causing a significant spread in cavity gradient. Several new techniques for surface defects research have been developed at Fermilab. The surface replica technique can provide 1 micron resolution and depicts a vivid 3D shape of defects as well as a wealth of topology information. This information allows us to establish the mechanism of local electromagnetic quench at the flaws. The replica procedure was proved to be harmless to high performance cavities. Fermilab’s laser re-melting system is aimed at removing the flaws that limit cavity RF performance to below 20MV/m. We succeeded in re-melting a pit in a 1.3GHz single-cell cavity, and after just a light electropolishing we restored the gradient to 40MV/m. Using a laser welding technique to fabricate SRF cavities dramatically reduces the equator weld heat-affected zone area in comparison with the standard electron beam welding technique. The potential benefit is to decrease the probability of pit generation in the equator region.
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