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Pump Out Nitrogen Exchange Gas

Once the temperature is at a satisfactory level (> 77 mK and < 80 mK), exchange gas needs to be pumped out. We don't want any gas in there as we cool further because it will freeze inside of the IVC. The pressure will be greater than 10E-2 mbar, so we use the scroll pump rst to pump out exchange gas before switching to the turbo pump. If the scroll pump is not available, then we have to use the turbo pump on the pumping manifold and proceed delicately with pumping out exchange gas. Methods with both pumps are described below.

  1. Scroll pump
    1. Isolate the scroll pump from the pumping manifold (if not already)
    2. Turn on the scroll pump
    3. Open line from scroll pump to IVC - the scroll pump will be evacuating exchange gas
    4. When the gauge on the pumping manifold reads 10E-2 mbar, open the valve to the turbo pump. The two pumps are now pumping in parallel.
    5. Isolate the scroll pump and turn it o. The turbo pump will take over evacuating the IVC
    6. The IVC has been suciently evacuated when the pressure gauge reads < 10E-6 mbar. This might take 2-4 hours, depending on the amount of exchange gas in the IVC
  2. Turbo pump
    1. Make sure turbo pump is on and isolated from the IVC
    2. VERY slowly start to open the valve that leads to the turbo pump. At pressures greater than 10E-2 mbar, the turbo pump can be easily overwhelmed.
    3. If the turbo pump does get overwhelmed, it will shut off. If that happens:
      1. Don't panic!
      2. Close the valve to the turbo pump
      3. Switch off the turbo pump (green switch)
      4. Turn the turbo pump back on - wait for it to warm up.
      5. When turbo pump is fully on, open the valve to the turbo pump SLOWLY, as before. Make sure to cycle through the display on the pumping manifold to find the pressure reading.
    4. Once the pressure gauge reaches 10E-2 mbar, you can open the valve to the turbo pump all the way.
    5. The IVC has been sufficiently evacuated when the pressure gauge reads < 10E-6 mbar. This might take 2-4 hours, depending on the amount of exchange gas in the IVC Note that if the pressure gauge is not displaying the pressure properly, then have the IVC pumped on for 5 hours. This should be sufficient to evacuate it.