ESS Cryomodule Testing Meeting
Thursday 8 Dec 2022, 14:00
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15:00
Europe/Stockholm
meeting_W49_20221207.pdf
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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
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