Condense Mixture

Once you've started pumping on the 1 K pot, you can begin to condense the He3-He4 mixture. The condensing stage is the process of slowly pulling out the gas mixture from the dump and cooling it within the condenser located in the 1 K pot. The mixture will be condensed through both the still and condenser lines. When condensing begins, the mixture will have its flow regulated through cold trap 1. This cold trap is used because it has a regulator valve (though a bit leaky). That's why the mixture was cleaned with cold trap 2 in previous steps- to keep the rst one clean for cool-down to base temperatures. This process can be done two ways: using the automated LabVIEW program or manually. Both processes will be described below. The manual process will describe in more detail what's happening in the automatic process. We use the manual process when we don't use the entire amount of mixture available to us. Of the total He3-He4 mixture, we sometimes only use a portion. Thus, subtract off amount we wish to use (in G2 pressure) from the total amount of mixture you've noted in the dump so that you know how much to leave in the dump for the run duration. If you condense automatically you have no control over how much mixture you leave behind in the dump.

1. Confirm that the 1 K pot is being pumped on.
2. Confirm that the mixture is isolated within the dump.
3. Make sure the LN2 cold trap dewar is suciently lled.
4. Open the gate valve and the condenser line speedivalve.
5. Open V1 and V9.
6. Open V3 to stabilize the pressure between the lines.
7. Open the speedivalve attached to cold trap 1 on the back of the IGH. We will open V13A next. You may notice boil-off in the LN2 cold trap dewar when you do so - this is due to the warm mixture flowing through the cold trap. Because V12A is leaky, opening V13A technically begins the condensation process. Before opening V12A at all, because it is leaky, we let out slowly the amount of mixture that we wish to use.
8. Open V13A to let the gas into cold trap 1. Monitor the pressure in G1. Monitor the pressure in G1 - it should stay below 200 mbar. This is to keep the 1 K pot from being overwhelmed. When G1 approaches 200 mbar, close V13A. Wait for the system to settle and for G1 to lower sufficiently such that you can open V13A. When V13A is closed, you are able to get an accurate reading of the pressure in the dump. Continue the process of opening and closing V13A to pull out mixture gradually until you have pulled out the desired amount of mix.
9. Now that you have pulled out the correct amount of mixture you wish to use, close V9.
10. Open V12A slowly, in increments of 0.2%. Keep your eye on G1 to make sure that the pressure stays below 200 mbar.
11. Continue to open V12A progressively. Once it's reached 17.5%, it's okay to open the valve all the way.
12. Once V12A is fully opened, wait until G1 and G2 have stabilized around 50-60 mbar. Close V9 and V3.

1. Confirm that the 1 K pot is being pumped on.
2. Confirm that the mixture is isolated within the dump.
3. Make sure LN2 cold trap is sufficiently filled.
4. Open the gate valve and the condenser line speedivalve.
5. Open the speedivalve attached to cold trap 1 on the back of the IGH.
6. Go to the computer controlling the DAQ and the IGH and find the Oxford Instruments Menu (OI Menu).
7. Click on \Kelvinox\ - this will bring up \KelvFrontPanel.vi\, which is the master VI for fridge operations.
8. Click on “Condense In\ - this will ask if the fridge is in the correct state to begin condensing the mixture (i.e. Are the insert valves open [gate, condenser line speedivalve], and is the mixture in the dump [manual valve is green]). When you choose to continue on from this step, the automatic process of condensing will begin.
9. Once V12A is fully opened, wait until G1 and G2 have stabilized around 70-80 mbar. Abort the program.
10. Not all of the mixture will be pulled out of the dump since it can't all be brought out, but only a little remains.

Note: Sometimes the program closes V9 prematurely, resulting in too much mixture left in the dump. If this happens and it is your intention to use all of the mixture, abort the program and open V9 again. Close V9 when G2 reaches 200 mbar. Open when G2 lowers again. Keep doing this and monitoring the pressure until you can leave V9 open without the presure rising above 200 mbar. This will ensure you are pulling more of the mixture out of the dump. After this, wait until G1 and G2 have stabilized around 70-80 mbar, and then close V9.