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Clean LN2

  1. Fill LN2 cold trap full
  2. Pump mixture to the dump if it's not already there (refer to 'pump to dump' instructions). Make sure V12A/B and cold trap 1's speedivalve is open.
  3. Leave cold trap pumping out until G1 < 1 mbar. This will take at least an hour, most likely two. Do not rush this step. If you do, we will lose mixture. G1 has to be stable. If you think it looks like G1 is still decreasing, do not stop pumping on it.
  4. Close V6.
  5. Once closed, close gate valve and condenser line speedivalve tightly to isolate the fridge if open. You do not want any contaminants to enter when cleaning the traps.
  6. Close all valves on the IGH.
  7. Ensure vent valve on back of IGH is closed tightly. We do not want to pump on the helium gas line or introduce any contamination.
  8. Open valves 11A, 11B, 7, 2A and 5A on IGH to open a proper route from nitrogen cold traps to He-4 pump.
  9. Check that the routes between the cold traps and IGH are open. Also, check that mixture is safe in dump (ie. there is no way you can pump on it by mistake). Additionally, check that the gate valve and condenser line speedivalve are closed, as are all valves on the IGH that you do not need. This step is very important! Put every ounce of effort into this step.
  10. Turn on the He4 pump.
  11. Extract the nitrogen cold traps.
  12. Wait for nitrogen cold traps to thaw. Once nitrogen cold traps have thawed, you can start heating each one in turn
    1. To heat a cold trap, use the heat gun (located in the bottom drawer of the black tool cabinet)
    2. You must heat all sides of the cold trap and all the way up and down its length
    3. The cold trap is sufficiently heated if it is too hot to touch for more than a second. This should take 5- 10 minutes per trap.
    4. It's best to heat the cold trap in spatial increments to make it easier to test whether or not it's being heated well enough
  13. Each cold trap needs to be heated completely 3 times
  14. Leave the traps pumping for at least an hour after you're done heating it
  15. Once done, close all valves on the IGH and return cold traps to their appropriate positions. Make sure the LN2 cold trap is full.