About cleaning the traps, first switch off the heater on the still to obtain the minimum flow rate.

There are 2 ways to clean the traps, neither one needs recovering all the mixture. The best thing to do is to first do 1 and once the traps are warm, add a T-piece and a valve to them, right on top of the trap (see pictures).

1. Clean both traps simultaneously.

(only a small part of the mixture will be recovered. The fridge will probably only heat up to 100-200mK)
  • Turn still heater off.
  • Open 9 and 10 to collect the mixture .
  • Close 4,15+M4, 6 and 7. Then pump out the 3He from the traps by opening M5+5, 16 and 8. You can check the pressure in the traps by opening A9 (only possible when Auto mode is switched off) and reading P3.
  • Once the pressure is 0, close 8 and take the traps out of the LN2. When there is air inside P3 will increase.
  • Pump out any dirt using pump4 and opening A8. You can heat the traps using a heat-gun.
  • Once cleaned, close A9, A8 and switch off pump4.
  • Put the traps in to the LN2 again and recondense the 3He which was collected in Dump3.
  • Turn still heater back on.
  • Start auto mode again to protect the system.

2. Clean the traps one by one during normal circulation.

During this procedure keen an eye on P5 - if it gets too high (>850mB) briefly open 9,10 to let He3 into dump.

  • Turn still heater off and let P5 drop.
  • First clean trap1: First pump out the 3He from the trap by closing 4,16,6 (or 7) and open 8. circulation will stop and the 3He will be pumped into aux trap. You can open A9 again to read the pressure at P3.
  • Once P3 is 0, close A9, 8 and 5. Open 16, 6 (or 7) to restart normal circulation.
  • Connect a flexible hose to the valve on the trap and connect the other end to aux port 1 (or to a turbopump).
  • Open the valve on the trap and M3, read the pressure in the trap at P3 (or on an attached pump).
  • Take trap 1 out of the LN2. Record pressure of gas coming out of trap as it's warmed. You can heat the traps using a heat-gun.
  • Pump trap with S4 (or turbo).
  • Once cleaned, put trap back in N2. Open 4 (or 15) to let He into N2 trap.
  • Open 4,16,6 (or 7).
  • Turn still heater back on.
  • Start auto mode again to protect the system.

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This topic: QED > Main > QedLabStuff > VectorFieldFridge > VectorFieldFridgeCleanLNTrapsWhileRunning
Topic revision: 30 May 2013, AlexHamilton
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