First Cooldown -- Cooling from RT to 77K.

  • Dripper should be out of the transfer port on the cryostat and N/V shut. This port is used to put LN in the main bath.
  • Connect external pump to the Auxilary S/V.
  • Remove helium level probe if it isn't already out.
  • isolate main bath from helium exhaust by closing blue ball valve
  • 2 x Pump and flush the main bath with helium from the recovery using external or 1k pot pump.
    • open Aux S/V to start pumping. when finished pumping, close Aux S/V.
    • To flush, allow recovery gas to flow back into cryostat by opening blue ball valve on cryostat (you also need to bypass 1 way valve near meter). After flush close blue ball valve on cryostat.
  • While you are pumping and flushing main bath, also open 1K pot needle valve and λ-plate needle valve.
  • after the final flush of main bath, Close 1K pot needle valve and λ-plate needle valve. 1K pot full.
  • Ensure main bath bypass line is attached and ready.
  • Insert a nitrogen transfer tube into the transfer port on the cryostat ensuring tube end is screwed into the cone. Bung the tube.
  • finished flushing, so close blue ball valve to recovery, close red ball valve, and bypass S/V, and finally Aux S/V
  • Attach Bunsen valve to the Auxilary S/V and open
  • Attach LN2 dewar to nitrogen transfer tube via plastic hose.
  • Start gas/liquid flow and have recovery as open rubber tube to regulate flow (10” of ¼” diameter rubber hose).
    • Dewar pressure 0.4 bar max. (Care is needed as magnet coils are fragile under cooling.)
    • We want a cooling rate of 4-9Ω/hr on the magnet resistors. 0.2 bar is too slow, 0.3 bar is good.
    • If things go way too slow pull out of the cone and run at 0.2 bar max.
    • Keep the bypass closed early or the magnet won't cool, but later can open it to help cooling the fridge.
  • Record magnet resistance and magnet thermometers R1,2,3 every 30 min
  • Wait until magnet resistors are at 77K (R_magnet = 37.9Ω) and under LN2 level before speeding dewar up to 1 bar max and remove rubber hose and attachment from recovery.
  • When there is a liquid in the main bath the recovery outlet pressure falls and the end starts to defrost.
  • At ~20cm below IVC remove rod from cone if it isn’t already.
  • Once magnet is at 77K, transfer LN for 5 more minutes and then stop LN2 transfer by closing the liquid transfer valve on LN dewar.
  • Put bung back on bunsen valve.
  • confirm there is liquid nitrogen in the main bath: insert thin diamter dipstick (without glove on the end) into the dipping port on cryostat, and check that liquid sprays out. (You need to keep rotating dipstick if it hits the plates, to make sure it goes down far enough)
  • Warm and remove LN2 line from main bath.
  • Do not refill LN2 dewar.
Topic revision: r7 - 09 Jun 2021, MatthewRendell
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