| 1500 | Performed the leak check with the mixing chamber at 41 K and all LHe gone from the bath. Before starting I had to reattach some bellows and then pump them out. Doing so had the added benefit of resetting the external pressure sensor to a reasonable value (for the past few days it has been stuck at 1E-8 mbar). I pumped down the bellows leading up to the IVC until they were at 5.4E-3 mbar (a value that the pressure sensor often gets stuck at). I then isolated the turbo pump and the external pressure sensor rose slightly to 7.4E-3 mbar. When I opened the IVC to the external pressure sensor this value dropped to 6.3E-3 mbar, indicating that the bath was at a lower (but unfortunately unknown) pressure. I then isolated the IVC once more and started the leak checker. In the lines leading up to the IVC there was a background leak rate of 1.1E-9 mbarL/s. When I opened the IVC up to the leak checker the leak rate quickly rose to 5.6E-6 mbarL/s, and has been overtime gradually falling. Even considering the small amount of gas I let in during the pressure check, clearly there is some sort of leak. Left the system with the IVC isolated. By this time the leak rate was at 1.2E-6 mbarL/s and the external pressure sensor was back to 5.4E-3 mbar. |