5 High Q's from DC Magnetic Flux Expulsion
5.1 Trapped Flux Losses, Sensitivity
When a superconducting cavity is cooled below Tc, there is the potential to trap local ambient dc magnetic flux at defects, preventing the Meissner effect from expelling the flux. As a result, cryostat and cryomodule designers make strong efforts to lower ambient dc magnetic fields by adding magnetic shields in cryomodules and test dewars to achieve ambient dc field values typically in the range of 5–10 mGauss. The achieved values become occasionally higher due to residual magnetization of assembly components, some left inside accidentally.
Trapped flux losses are especially relevant to high-duty cycle accelerators based on SRF, such as LCLS-II and SHINE, which ...
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