Adding He Exchange Gas

As was done for the LN2 transfer, you will now put in exchange gas into the IVC to help facilitate cooling. However, this time we are using He-4 gas. NOTE: the amount of He exchange gas put into the IVC for the first LHe transfer is smaller than the amount of nitrogen exchange gas used for the LN2 transfer. He-4 is much hard to pump out!

1. Isolate the leak checker from the IVC and turn it off.
2. Close all valves on the pumping manifold and all valves leading to the IVC. Make sure the turbo pump has been isolated.
3. Open the He gas supply from the tank by the door at the top of the stairs. You should not have to adjust the regulator valve. Make sure that the blue valve you're using on the gas line for the He gas supply source is closed.
4. Make sure a clear hose is connected from He gas supply to the pumping manifold, but keep it isolated from the pump and IVC. If the hose is not connected to the He-4 gas supply, disconnect the one that was used for the nitrogen exchange gas process and connect it to the He-4 gas supply line.
5. You are going to pump on the clear hose to evacuate any gas or air because this hose will be used to deliver He exchange gas to the IVC and we want this to be clean. You will use the scroll pump to do this. Making sure the scroll pump isolated, turn it on.
6. Open the scroll pump.
7. Open green regulator valve. You are now evacuating the clear hose. When evacuated, the little pressure gauge above the green regulator valve should read -30 in-Hg (though the pressure is actually lower than this!).
8. Close green regulator valve.
9. Open the He valve (blue) on the gas supply line to let He gas into the clear hose (still isolated). It should read 2-3 PSI on little pressure gauge.
10. Isolate scroll pump and turn it off.
11. STOP! DON'T DO ANYTHING ELSE. Here's a thinking moment… how are you going to let He-4 gas into the IVC? There are two options for doing so. One is more risky than the other. Read the options below:

This is a 1-shot method, and you have a smaller room for error because the amount of He-4 gas you're letting in is much smaller than the nitrogen exchange gas, and He-4 gas is much harder to pump out because the He-4 atoms are much smaller.

1. Open the black valve adjacent to the green regulator valve that leads to IVC line.
2. Open the IVC valve on top of the fridge platform. There should now be an open pathway into the IVC.
3. VERY SLOWLY open the regulator valve and keep an eye on the pressure reading on the pumping manifold. You should aim for 0.046 mbar to be filled into the IVC.

The volume in the IVC line is about 8x smaller than the IVC, so you will need to compensate with 8x greater the amount of He gas pressure in that line. This method is less risky because if you let in too much He-4 gas you can pump it out more easily. Do NOT forget to open valve to IVC after gas is in the line.

1. Open the black valve adjacent to the green regulator valve that leads to IVC line
2. VERY SLOWLY open the regulator valve and keep an eye on the pressure reading. Only allow 0.3-0.4 mbar into the IVC, then close the regulator valve.
3. Open the IVC valve on top of the fridge platform to let the He-4 gas into the IVC.
4. Close the He-4 gas supply on the copper line and the tank.