On March 24th 2010 a complex exercise called ‘Helium Processing’ was conducted to improve the performance of the SRF cavities in the ALICE-LINAC. The idea was to clean the surface of the cavities by exciting the cavities with intense RF field in the presence of a small amount of helium gas. Electrons emitted in the process ionise the helium gas, which is then streamed back onto the field-emitter, heating the surface by bombardment and generating more desorbed gas. A plasma then extends around the field-emitting site thereby cleaning the surface contamination of all surface residue.
Tom Powers from J-lab flew on a weekend specially to guide the ALICE technical team in undertaking this exercise. The 3-day processing operation was successful with a performance improvement achieved in the ALICE-LC1 SRF cavity as seen by a significant shift in the onset of the field emission from 7 MV/m to 10 MV/m.
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