Visible to the public Impact of Remanent Magnetic Field on the Heat Load of Original CEBAF Cryomodule

TitleImpact of Remanent Magnetic Field on the Heat Load of Original CEBAF Cryomodule
Publication TypeJournal Article
Year of Publication2017
AuthorsCiovati, G., Cheng, G., Drury, M., Fischer, J., Geng, R.
JournalIEEE Transactions on Applied Superconductivity
KeywordsCavity resonators, cold magnetic shield, cold tuner, compositionality, continuous electron beam accelerator facility, cool-down procedures, cryogenic testing, Cryomodules, cryostats, electron accelerators, five-cell cavity, flux-gate magnetometers, fluxgate magnetometers, He tank, heat load, Magnetic field measurement, magnetic fields, Magnetic Remanence, Magnetic shielding, Magnetometers, Niobium, original CEBAF cryomodule, pubcrawl, quality factor, Radio frequency, refurbished cryomodule C50-12, remanence, remanent magnetic field, residual magnetic fields, resilience, Resiliency, superconducting resonators, Temperature sensors, Tuners

The heat load of the original cryomodules for the continuous electron beam accelerator facility is 50% higher than the target value of 100 W at 2.07 K for refurbished cavities operating at an accelerating gradient of 12.5 MV/m. This issue is due to the quality factor of the cavities being 50% lower in the cryomodule than when tested in a vertical cryostat, even at low RF field. Previous studies were not conclusive about the origin of the additional losses. We present the results of a systematic study of the additional losses in a five-cell cavity from a decommissioned cryomodule after attaching components, which are part of the cryomodule, such as the cold tuner, the He tank, and the cold magnetic shield, prior to cryogenic testing in a vertical cryostat. Flux-gate magnetometers and temperature sensors are used as diagnostic elements. Different cool-down procedures and tests in different residual magnetic fields were investigated during the study. Three flux-gate magnetometers attached to one of the cavities installed in the refurbished cryomodule C50-12 confirmed the hypothesis of high residual magnetic field as a major cause for the increased RF losses.

Citation Keyciovati_impact_2017