K400FridgeSOPRemoval

Removing the fridge from the dewar

1. Make the sample safe

• Ground all gates, disconnect device, ground ohmics, Field @ 0T, RuOx off.
• Switch over to floating box.

2. Remove the mixture from the fridge

• Close 1k pot N/V
• Pump and flush pot to empty it:
  • Shut 1a.
  • Open 4a to pump.
  • Shut 4a.
  • Open 1a to bath. Repeat until pot comes to vacuum (gauge P2 below range).
• close 13A to stop circulation
• open 3 to connect cond/still lines
• open 9 to dump
• turn on Still heater to 50mW, and MC heater to 20mW
• put some exchange gas into IVC (make sure you are not pumping on the pot - 4A should be closed - otherwise exchange gas will condense onto pot)
• wait for G2 to go up to 525mB, and still pressure to go down to min value
• When return line pressure is stable at ~525mb after 10-15 minutes, record all values and remove thermometry. There is an offset on P1, check previous values in the log book to ensure the still is empty before pulling.
• Still and mixing chamber heaters off.
• close all valves on cabinet
• close the 3 dump valves
• Shut gate and condenser valves on top of insert. (make sure you hear the click when closing still gate valve to confirm it is closed!)
• Turn roots pump off.
• Shut off He (rotary) pump
• take out He trap, and warm to room temp with heat gun.

• Still heater off.
• Roots pump off.
• Valve 6 shut (circulation stops).
• Open valve 3 to equalise 3He sides. (Pressure will rapidly drop to zero. Don’t panic, the mixture has all just condensed back down the pumping line.)
• Open valve 4 (Allow 3He lines to dumps).
• Shut valve 12a (Close off cold trap).
• Shut pot needle valve.
• Stop pumping pot (close 4a).
• Open the pot to the main bath (open 1a).
• Check that dump valves are open (behind the gas handling cabinet)
• Pump and flush pot to empty it:1 x ~15cm balloon of He into IVC. Wait for mixture to start coming out of the fridge (You may want to do this during the final stages of pump and flush but do it when the pot isn’t being pumped otherwise the exchange gas will just condense on the pot.)
  • Shut 1a.
  • Open 4a to pump.
  • Shut 4a.
  • Open 1a to bath. Repeat until pot comes to vacuum (gauge P2 below range).
• Check lines open to dumps and pot closed and pumped.
• When pot is down and condenser line at ~300mb put 50mW on still and 20mW on mixing chamber to get mixture out.
• Shut 13a; open 12a (Switch cold trap sides).
• Shut valve 4 (close off dumps).
• Open valve 9 slowly, pressures should equalise. 3He pump sound will change (Open to back of dumps and pump mixture in).
• Open valve 6 as a throttle (500mb maximum on return line. Watch top gauge fall.) May need to go past 500mb when dumps get full. Final pressure ~525mb. Check previous values in the logbook to confirm the dumps are full and no mixutre is lost.
• Remove He trap from dewar, let it warm up
• When the P1 pressure falls to below 1mb turn roots pump on to kick it along.
• Remove fridge plate screws (holding the jacket to the dewar).
• Get heat guns set up and running.
• When return line pressure is stable at ~525mb after 10-15 minutes, record all values and remove thermometry. There is an offset on P1, check previous values in the log book to ensure the still is empty before pulling.
• Still and mixing chamber heaters off.
• Shut gate and condenser valves on top.
• Turn roots pump off.
• Shut valve 6.
• Shut all other valves on top half of cabinet.
• Shut off He (rotary) pump

3. Ensure the pot is empty

• Pump pot to vacuum (to below the gauge range on P2) - note this may have already been done.
• Shut pot line S/V on top of fridge.
• Shut 4a and stop pumping pot.Turn off the pot pump and fans

4. Raise the fridge out of the dewar

• Disconnect 3He and pot lines at the top of fridge (make sure all the valves are shut and roots pump off first, and He trap is out and warm). Cap all the lines and blank the fridge ports.
• Make sure bypass line is closed
• Disconnect thermometry and rotator lines.
• attach sample boxes to hook
• remove insulated screws holding insert to cryostat
• Raise fridge slowly, watching clearance on valves, and making sure P_dripper doesn't go negative (you can set target pressure on dripper controller to 0.20psi instead of 0.05)
• Fridge is 1.22m high. At 1.17m stop (5cm line marked), ensure insert and surrounds are warm and dry to avoid liquid dripping into the dewar.
• Pull fridge clear and insert top hat (note this is a two-person job as the fridge does not quite clear the top of the dewar and involves manouvering).
• Put in angle pieces to hold top hat in.

5. How to take the fridge apart

• Remove fibreglass jacket.
• Heat up fridge with hot air guns or let it warm up overnight. Note the hot air guns will warm up the outside of the fridge but this does not mean inner parts are warm so water may still condense on the colder parts.
• Remove all screws on IVC.
• Use the jacking screws to break the IVC seal. The IVC can comes loose quickly so be prepared to catch it!
• Remove IVC.
• Remove 2 screws on the bottom of Rotator can
• Remove device (wear nitrile gloves so you dont damage the rotators)

6. Prepare fridge for loading

• Clean IVC can and fridge where the indium seal was. The used indium is recycled.
• Pump out 3He line, the still and the condenser in fridge