For an example of cold trap cleaning, see run diary day:
20130314 Fill the LN2 cold trap full.
Close Gate valve and condenser speedivalve. This keeps most of the mixture in the fridge while it stays cold. We won't have to re-condense the mixture later.
Close V13A/B - this cuts off circulation.
Open V5 - this will pump the remainder of the mixture behind the exhaust of the He-3 pump.
Check to make sure that V12A/B are open. To pump on cold trap 1, you need to make sure its speedivalve on the back of the IGH is open.
Remove the DCRC boards. We don't want any damage to come to them while removing the helium cold trap.
Wait 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 G1 seems to still be decreasing (looking at the pressure plots on the LabVIEW vi), do not stop pumping on it.
Once all of the mixture is behind the pump, close V6A. Then close V1, V12B, the speedivalve on cold trap 1, and then V12A. Then close V5. Ensure that all the valves on the left-hand side of the IGH are closed and that the mixture is safe behind the exhaust. Again check that the condenser and gate valves are closed.
Stop the 1 K pot by closing the large speedivalve on top of the fridge, and then close the gold needle valve. Only tighten the needle valve finger tight - no wrist strength!
Turn off V4A. Switch the yellow valve on the recovery line to “exhaust” and close the black valve on the copper recovery line.
Open valves 11A, 11B, 7, 2A and 5A on IGH to open up a route from nitrogen cold traps to He-4 pump. Start with the valves closest to the pump.
Open valves 2 and 1 to open a route from the helium cold trap to He-4 pump.
Pull out the helium cold trap. Remove the O-ring and metal knut.
Pull out the nitrogen cold traps.
You'll see that the pressure in G1 will rise. This is due to the contamination in the cold traps. Wait for this value to lower down to ~1 mbar. The cold traps should be close to room temperature at this point.
Heat the cold traps. Note: do not let the heat gun touch the cold trap directly. Make sure all around the cold traps have been heated to 100 C. This is to make sure any moisture that might have gotten inside of the cold trap is out.
After three rounds of cold trap cleaning, wait for them to cool down to room temperature. Close all the valves on the IGH when this happens.
Put the metal knut and O-ring back on the helium cold trap.
Return the He cold trap to the main bath SLOWLY. You'll hear the gas meter respond to the entry of the cold trap. The cold trap is slightly bent, so be careful not to bend it more. When the cold trap hits the G10 plate, raise it less than a quarter of an inch.
Return the LN2 cold traps to their dewar slowly. The boil-off may be fierce.
Start the 1 K pot by turning on the He4 pump (if you haven't turned it off), and open V4A. Then open the gold needle valve on the fridge very slightly (roughly allowing the hole in the needle valve to face the wall towards your right). Then open the large black speedivalve. You will hear gas fill the line and perhaps the He4 pump will cry a little.
Switch the yellow recovery valve to \He Recovery“
Monitor the 1 K pot temperature. Try to keep the temperature around 1.75 K. The 1 K pot temperature will fluctuate quite a bit as we start circulation again, so make sure it's somewhat settled before adjusting it. If it's obvious that it's too high (> 1.8 K) then close the needle valve a little bit.
If necessary, do a helium transfer. We want the helium cold trap to be as cold as possible before circulating again.
Open the Gate valve and Condenser valve.
If you want to circulate through cold trap 1 first, then open V1, V13A, cold trap 1's speedivalve, and V12A.
Open V6 up to 12.8%. Open V6 gradually from there (in increments of 1-2 %). Make sure G1 and G2 don't go above 200 mbar. Once you are above 17.5 %, open V6 by 5-10 % more. The pressures in G1 and G2 shouldn't rise much, if at all. If they seem fine, open V6 all the way.
Monitor the mixing chamber temperature. It should be lowering. Be wary that you cannot take data until the temperature has stabilized. Hopefully it's at a decent base temperature to take data.