Leak Check with He Gas Spray Test

You are going to do a spray test with He gas to see if there are any obvious leaks in the flange seals. First, though, due to the flow of indium that occurs over time as it's been compressed, the screws will not be as tight as before, and so they should be tightened again. When they have been tightened to the degree that they were initially tightened before the IVC was evacuated, you can proceed with the spray test.

1. Re-tighten the screws in the bottom flange with the allen key. You want to hear the click of the screws again. However, be careful that you are not breaking the screws by overtightening because we are using larger indium wire now.
2. Connect leak checker to pumping station if it isn't already - make sure it is sealed off from the pump and IVC
3. Turn on the leak checker. It needs to warm up for 20 minutes before being used.
4. Check leak checker's calibration by doing an internal leak test (leak checker port must be sealed o). If the results aren't immediately within 0.3E-7 mbar*l/s of the internal leak rate, you will need to calibrate the leak checker.
5. Evacuate the line connecting the leak checker to the pumping manifold. First isolate the IVC. Then turn on the scroll pump.
6. Once the line from the leak checker to the pumping manifold is suffciently evacuated, isolate/turn off the scroll pump.
7. Open valve that connects the leak checker to IVC - when fully opened, wait for the leak rate to stabilize. Leak rate should be < 3E-8 mbar*l/s (note that the turbo and leak checker are pumping in parallel).
8. Isolate the turbo pump. Record the leak rate in the run diary (should be < 3E-8 mbar*l/s).
9. Open the He gas tank by the doorway at the top of the stairs.
10. Connect a clear hose to the helium gas supply on the gas line (this is NOT the hose used to put exchange gas into the IVC)
11. Connect the clear hose to the needle with the adjustable pathway for gas flow and open the helium gas supply
    • The pressure of the He gas should be ~ 3 psi. There is a brown, rectangular pressure gauge to which you can connect one end of the clear hose to check the He gas pressure. You can adjust the regulator on the helium gas tank to correct the pressure if it's not around 3 psi
12. Conduct the spray test
    1. Begin spray test at the top of the cryostat. Because He gas is light, it will rise. If you begin spraying the bottom flanges of the cryostat, the He gas will rise and might seep into higher flanges that are leaky, thus making a leak's location harder to find. Begin with the top most flange of the cryostat you wish to investigate.
    2. Press the needle with He flowing out of it in the gap between the flanges and slowly drag the needle around the circumfrence. It will take the leak checker a few moments to register if there is a leak, so the slower the movement around the flange, the easier it will be to locate the region of the leak. Make sure to complete a full circle.
    3. Progressively work from the higher flanges all the way down to the bottom IVC flange. For the bottom flange, which is most susceptible to leaks, check it twice.
13. If no leak has been detected (leak rate should be < 3E-8 mbar*l/s), then you can proceed further with the cooldown. If a leak is detected, be sure to note which flange it occurred at, for it will need to be redone. Record the leak rate in the run diary.
14. Perform another electrical check to make sure that all the connections are okay after evacuating the IVC; it's not necessary to record this data, though, if everything's the same.