A NOVEL ROTATING TEMPERATURE AND RADIATION MAPPING SYSTEM IN SUPERFLUID He AND ITS SUCCESSFUL DIAGNOSTICS

An novel rotating temperature and radiation mapping system in He II has been developed to investigate field emission (FE) & thermal breakdown (TB) in TESLA 9-cell SRF cavities. More than 10,000 spots on a cavity surface can be analyzed in one turn with 5° stepping. 116 special surface scanning thermometers have been developed to measure surface temperature in He II. 32 photodiodes are employed to study the X-rays induced by FE electrons. Each rotating arm holds 14 thermometers and 4 photodiodes. A unique driving and suspension system is designed to gently turn the 9 arms around the cavity and uniformly press the thermometers against cavity surfaces. A moving adapter device (pancakes) is designed for rotating a large number of electronic cables which become inflexible in superfluid He.