Speaker
Description
During the preparation for the installation of the LCLS-II HE cryomodules, one previously qualified cryomodule experienced an uncontrolled vacuum event. The cavity string vacuum unexpectedly increased to 2 × 10^ (-3) Torr. Simulation showed the vacuum incident may have introduced 0.1 μm sized particulates into the cavity RF volume. Careful analysis of the particulates' path and migration indicated that the particle migration was negligible except for finer particles smaller than 0.1 μm. A repeat test of the cryomodule verified the initial analysis. The cryomodule's performance was intact. All cavities experienced no detectable x-ray as in its previous test. Particles of the smaller size may not cause harm to the cryomodule at the admin limit of the HE cavity gradients. This article describes the vacuum event, analysis, and cryomodule test results before and after the event.
Funding Agency
The work was supported by DOE contract 89243024CSC000002 for FNAL and DE-AC02-76SF00515 for SLAC
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