2025/07/01 (Tuesday)

Status	Continue working on the fridge with the plan to cooldown tomorrow. Two tasks at hand: 1. leak check the needlevalve; 2. leak check and fix the turbo station tee
4:50	Connect the scroll pump with a Tee to the LD. Use the scroll to pump out 1K pot; close speedivalve; use the scroll to pump out main bath; completely open the needle valve to also pump it out.
5:20	Depending on the configuration (listed below), we see the following leak rate

configuration	leak rate
main bath open (pumping on both main bath and 1K pot at the same time), needlevalve open	6.7e-3
main bath closed (pumping on only 1K pot), needlevalve open	<9e-5
main bath closed (pumping on only 1K pot), needlevalve closed	5.5e-6, later 9e-6, 2e-5 (checking multiple times)

5:20	Pressure on G2 is 0.1 mbar during leak checking
5:30	We think the baseline leak rate is high because the main bath has been soaked in helium for a long time (>10 years), which created a high He background. We decided to try out luck and spray He with the lowest baseline leak rate configuration.
5:30	With main bath closed (pumping on only 1K pot), needlevalve closed, we spray He on top of the needle valve.
6:40	Wrapped plastic around pressure gauge housing, attached leak detector to turbo pump Tee; Leak rate background = 4e-8 mbarL/s. With Helium sqirting inside the plastic bag, LD 5.1e-8 L/s. It went upwards very slowly, not consistent with the type of leak we are expecting. The pressure also didn't jump when Turbo is not pumping the volume. Looks like we see it only when we blanked it off.