| 0220 | Raise dewar. |
| 0240 | IVC pressure 5.4E-4 mbar. Isolate turbo pump and open valve to leak checker. Background helium leak rate 5.5E-9 mbar l/s. Evacuate main bath and 1 K pot. Overpressurise main bath with He-4 gas. Helium leak rate rises to 2E-8 mbar l/s. Warrants further investigation. |
| 0250 | Evacuate main bath and open valve to turbo pump. Close valve to turbo pump and background helium leak rate stabilises at 6.3E-9 mbar l/s. Overpressurise main bath with He-4 gas. Helium leak rate rises to 2.5E-8 mbar l/s. It's not a gross leak, but we shouldn't see a leak of this magnitude at room temperature. |
| | It looks as though dewar has to come down and a spray test must be conducted on all the flanges. This will have to wait until the morning. Will repeat aforementioned leak test tomorrow morning. |
| 1035 | Begin pumping out main bath via 1K Pot pump. Turn on Leak checker. |
| 1145 | Perform leak check by over-pressurizing the main bath. Leak checker started with background rate of 3.2E-9 mbar*l/s. After He-4 gas was added to the main bath (G3=127 mbar), the leak rate rose to 6.5E-9 mbar*l/s and plateaued. When the main bath was brought up to higher pressures (~900 mbar) the leak rate decrease to 4.0E-9 mbar*l/s. A second leak test was performed after the main bath had been pumped out. With an initial background rate of 2.5E-9 mbar*l/s, the main bath was quickly pressurized ~900 mbar. The rate rose to the E-7 mbar*l/s range before slowly beginning to drop, suggesting that there is a leak present. |
| 1500 | Begin pumping mixture to the dump. |
| 1700 | Dewar lowered and spray test performed. Spray test began with a background leak rate of 3.0E-9 mbar*l/s. Spraying on the uppermost flange resulted in an increase of leak rate to 3.2E-9 mbar*l/s, the small flange around the striplines resulted in a leak rate increase to 3.3E-9 mbar*l/s, the upper IVC flange had a leak rate of 3.4E-9 mbar*l/s, and the lower IVC flange had a leak rate of 3.4E-9 mbar*l/s. Although there were no spikes, this does not indicate that there is not leak. To be safe, all of the flanges were tightened. |
| 1710 | Dewar was raised and another leak check performed, with a background rate of 1.5E-8 mbar*l/s. After filling the main bath with He such that G3=330 mbar, the leak rate was observed to rise to 3.4E-8 mbar*l/s. This is an somewhat acceptable leak rate, although there is fear amongst the townfolk that the leak will go larger at 77K. It has been decided to press on in hopes that the leak will either vanish, or become larger and thus more easily detected, at such temperatures. |
| 1730 | Commence Nitrogen transfer. Add 1.0mbar He exchange gas to IVC, and the main bath is filled with 1330 mbar of He. |
| 2025 | Cease nitrogen transfer. |
| 2355 | Fill N2 cold trap full. |
| | Mixing chamber temperature and IVC pressure 78.1 K & 0.4 mbar respectively. Start evacuating IVC. |