Condensing the Mixture

It is highly recommended to use the automatic condensing scripts in SEA. Click on "sorbpump", when "readyforpump", make sure that the IVC is connected to a running turbo pump, and the valve and the IVC space is open.

The automatic script is doing a sligthly different condensing procedure than described below.

• If not yet done, the IVC has to be pumped. Do not do that before the sorb T is at 4K.
• Fill the cold trap with liquid nitrogen and make sure that both traps are in the dewar
• Make sure that all tubes are connected correctly
• Cool the VTI ("1 K pot" thermometer) to a temperature below 3 K. With the Variox 2 K may be reached, with MA09 about 2.5 K. Open the needle valve to get a pressure at the 65 m3 pump of about 12 mbar.
• Open the valves in the pumping line and in the condenser line.
• Open the green valves marked "out" and "in" on the dump. The dump is the grey cylinder in the center of the gas handling system rack.
• Switch on the 3He pump (while pressing on the 3He button, press RAISE).
• Make sure that the heater on the mixing chamber is off and that the setpoint is zero. Switch off the still heater also.
• Open valve 9 (while pressing on the valve button, press RAISE).
• The reading on G2 is proportional to the amount of mixture in the dump. It should read something around 660(DIL1) or 400(DIL2) mbar.
• Open valves 1 and 6 (Valve 6 is a motor valve, while pressing the red valve button, press RAISE until a value of 99.9 is shown).
• Open valve 13A
• Open V12A a little (4 %) to allow the mixture pass the trap slowly.
• When the pressure reading on G1 stabilizes or decreases, open valve 12A completely.
• During condensation, the 1 K pot temperature might raise to more than 3 K, especially when the pressure on G1 is high. Adjusting the needle valve is only necessary, when this temperature get too high and prevents the condensation to progress.
• After some time (depends on the temperature of the mix. chamber) the mixing chamber should reach about 1 K, and then the pressure on G1 stabilizes at a low value. Now you may start to pump out the dump: close valve 9, and open valve 14 for a short time (close it when P1 raises above 50 mbar). As soon as the pressure on P1 drops down, you might open and close valve 14 again. Do that several times.
• At some stage, when opening valve 14, the pressure on P1 does no longer raise above 50 mbar. Leave the valve open until P1 drops below 1.
• The temperature in the mixing chamber goes down in steps during the condensation process. It takes some time until the temperatures start to move downwards, and goes then quickly below 1 K. Then it stays there or decreases slowly to about 0.8 K, for about half an hour or more, before going down by more than 0.01 K per minute.
• Once the temperature has stabilized in the region of 0.1 K or less, the flow on the condenser line might fall below 100 (black display below the valve panel, on DIL1 only). Setting the still heater to a power of 3-5 mW, the flow can be increased back to about 100, and the temperature should go down more. Good luck!