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We sometimes need to (nearly) empty the fridge in a short time, for example;

  • To load/unload the target insert, and
  • To consume LHe in the fridge and/or the magnet fast.

Conditions

  • You have been trained by an experienced person on this procedure.
  • The nose LHe level is above 80%.  If it is below 80%, this method cannot evaporate LHe effectively, and thus you should simply wait until LHe evaporates by itself.
  • The heat tape for the turret is in operation.
  • About the roots pump, the rotary vane pump (SV630BF) is ON and the boosters (WH7000-1, 2 & 3) are OFF.
  • The gate-valve bypass is fully opened (at 0.25 turns).
  • On Fridge_Valve_Main.vi;
    • The mode of the level probe is "CONT" (not "HOLD").
    • The Interlock with Heat-Ex Top is enabled.
  • The "Voltage" knob of the Annealing Plate Control Box is fully rotated clockwise.

Procedure

  1. Turn ON the "Power Control" switch of the Annealing Plate Control Box, and turn it OFF when the top-section pressure of the roots pump reaches 10 Torr.
    1. Never leave the switch ON longer than required in this and later steps.
    2. You had better keep your finger on the switch, not to forget turning it OFF.
  2. Confirm that the main return flow increases to 100-150 SLM.  If it is higher/lower, find any difference in the conditions.
  3. Turn ON the "Power Control" switch, and turn it OFF when the top-section pressure reaches 16 Torr.
  4. Confirm that the main return flow increases to 150-250 SLM.  If it is higher/lower, find any difference in the conditions.
  5. Wait until the top-section pressure decreases to 8 Torr (or below).
  6. Repeat steps 3-5 until the nose LHe level becomes ~80%.
  7. x

  8. Change the separator flow to 20 SLM (from 7 SLM usually).

  9. Wait for 1.5 hours _if_ the nose LHe level is below 0% (i.e. warm).  If not, you need not wait.
  10. Change the separator flow to 25 SLM.

  11. Open the fridge bypass valve at 2.0 turns.  Confirm that the fridge return flow goes up.

  12. Open the bypass valve at 3.0 turns.
  13. Change the separator flow to 30 SLM.

  14. Wait until the Ann-Plate Top resistor goes up to 1400 Ohm, which indicates that the liquid started accumulating.  It usually takes 30 minutes from step #3.  If it takes longer than 40 minutes, search for unexpected conditions.

  15. Wait until the nose LHe level reaches 100%.  It usually takes 15 minutes from the previous step.
  16. Wait until the Heat-Ex Bottom resistor goes down from 1400 Ohm and then up.  It usually takes 10 minutes from the previous step.

  17. Wait until the Heat-Ex Top resistor goes up to 1400 Ohm, which indicates that the liquid is as high as Heat-Ex Top.  It usually takes 10 minutes from the previous step.

  18. Close the bypass valve.

    1. Usually the software interlock sets it at 0.5 turns automatically.
    2. Anyway you set it at 0.0 turns manually.

  19. Change the separator flow to 7 SLM.

  20. Change the setting of the gate-valve bypass as follows:
    1. The set point for the auto control is 40 Torr.
    2. The auto control is enabled.
  21. Change the level-probe mode back to "HOLD" if you changed it in step 5.
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