ESS Cryomodule Testing Meeting

Thursday 8 Dec 2022, 14:00 → 15:00 Europe/Stockholm

meeting_W49_20221207.pdf

• Akira showed the cavity performance of CM09 (2nd) and further tests of helium signal appearing at 13 K
  • The cavity RF performance seems promising so far
  • Mysha reported that both cavities reached 12 MV/m without having strong field emission
• The helium signal is still under debate but a couple of things were understood
  • The vacuum jump at 13 K is a release of helium adsorbed by cavities surface or "cold pocket" and the mount of helium at 13 K is not a true leak rate
    • According to the data, it is NOT from a leak opening up at this particular temperature
  • The ultimate source of helium is still not known, either a very small leak inside the module or back flow from outside
    • The angle valves were close for the latest cold test to separate these two possibilities
    • Artur mentioned that opening the angle valves before the thermal cycle would generate some mount of helium and may mess up the measurement
    • Akira answered that Penning gauges read-out may be sufficient without opening the angle valves to compare with literature (Rao 1993 and 1996)
  • Nuno pointed out that the absorbed helium would be saturated by the size of cold pockets
  • Nuno proposed thermal cycles with narrower range than 12-20 K to avoid absorption of helium at all
    • Akira answered that this can be done tomorrow (2022-12-09)
    • Konrad answered that this may be technically feasible
    • Artur pointed out that the maximum temperature must be lower than some value where other gas species coming up and trap helium
    • Akira answered that 15-20 K would be the optimal cycle range
  • Akira reported that the leak is so small that it may not be an issue for ESS operation even if it is really a leak
• UU will pack ESS' leak detector tomorrow and will transport it back to ESS on next Monday (2022-12-08)
  • Akira mentioned that we had an issue with transport company last time but he will do his best this time