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Electronics | Mr. Freeze (dilution refrigerator) | Mrs. Astra

Principle of Operation | Cooling Down | Starting the Circulation | Warming Up |

Pumping the Transfer Tube and the Top Loading Stick | Loading and Unloading the Sample

 

STARTING THE 3He CIRCULATION

 

n. b. This is not a foolproof guide. It is very important that one has to know what he is doing, why he is doing it, and what’s happening in Mr. Freeze if he does it.

 

  1. In principle, one can start the circulation when the temperature in the mixing chamber is 4 K. However, condensation of the occurs when the 1 K pot is operational, i.e. the 1 K pot temperature is around 1 K. A couple of hours after starting pumping on the pot is the best time to do this procedure.

  2. Check if the following valves are closed: #4, #6, #9, #10 and #11.

  3. Close valves #8 and #1.

  4. Open valves #2, #3, #7, #5 and the DUMPS valve.

  5. Allow the condensation process to take place. When the condenser pressure (G3) is approximately 80 mbar, turn on the 3He ROTARY PUMP. During normal cold operation, the DUMP pressure and the STILL pressure are both 0 mbar.

  6. Close valve #2.

  7. Open valve #8. Open valve #1, but not fully open.

  8. Check the following:

    1. #31 is closed.

    2. #32 is open.

    3. #24 is open.

    4. #9 is closed.

    5. #5 is open.

    6. #3 is open.

    7. #7 is open.

    8. Liquid nitrogen in the cold traps has the appropriate amount

  9. Open #12 slowly and watch the pressure at T2 and G4.

  10. When #12 is fully open, control or maintain the pressure at G4 above 100 mbar using #1.

  11. When you reach T=700 mK, turn on the STILL and set it at 2 mW.

  12. When T=400 mK, switch on the 3He BOOSTER PUMP. Wait until it is warmed up. (The indication is when you hear the sound of the pump at the back of the control panel.)

  13. When the 3He BOOSTER PUMP is warmed up, open #13 and then close #12.

  14. If the backing pressure is okay, turn on the QSB valve. (Always make sure that the back pressure (G4) is at least 100 mbar, by adjusting pressure at valve #1.

  15. Do your measurements.

 

Extra Reminder:

Watch the pressure at G6. This tells something about the flow rate of liquid helium into the 1K POT. This should read zero. If it is greater than zero, it means that there is more He going into the POT than necessary. In this case, one should expect the He level in the POT to go upto 100%. To control the flow, use the C needle valve located on top of the refrigerator.

 

Updated:   August 9, 2004, Ian Jasper Agulo

 

 
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