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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. If you need consume LHe in the magnet, fill the fridge from the magnet.

    1. Change the separator flow to 25 SLM.

    2. If the separator flow was 7 SLM, you might wait for 0.5-1.5 hours.  To be optimized.
    3. Open the fridge bypass valve at 3.0 turns.  Confirm that the fridge return flow goes up to ~100 SLM.
    4. Monitor the LHe level probe and the chip resistors to confirm that LHe is being transferred normally.
      1. Sometimes the Heat-Ex Top resistor goes up and down independent of the LHe level.  If you are certain about the present LHe level, you can continue the filling based on the filling duration.  If not, stop the filling.
    5. Close the fridge bypass valve (i.e. set it at 0 turns) when the Heat-Ex Top resistor goes up to ~1400 Ohm.
    6. Change the separator flow to 20 SLM.

  8. Repeat steps 1-7 until the fridge and/or magnet levels reaches what you need.

  9. Change the separator flow to 7 SLM.
  10. Change the opening of the gate-valve bypass to 0.050 turns.
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