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This is version 2.
It is not the current version, and thus it cannot be edited.
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- 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
- On the Variox or Magnet VTI, open the needle valve more than
normally in order to fill the pumping volume with some
amount of liquid helium. Put "flow" of 20 mbar until the
1 K pot temperature is stable below 3 K. Then close
the needle valve until a "flow" of about 10 mbar is reached
(the pressure decreases only slowly). Then regulate the
valve at about 10 mbar. This value must not be obeyed exactly,
the idea behind the needle valve settings is the following:
- A lower flow is better for consumption (a "flow" of more
than 10 mbar increase substatnitally the He consumption, but
during the process of condensing it might be o.k.).
- The flow should be high enough to hold the 1 K pot temperature
low (over long term: about 2 K with the Variox and about 2.5 K
with the MA09). During the condensing phase, the 1 K pot temperature
might increate to 3.5 K for a short time, when pushing the
mixture quickly.
- Open the 3 valves in the pumping line and the 2 valves in
the condenser line.
- Open the green valve marked "out" below the dump. The dump is the
grey cylinder in the center of the gas handling system rack.
- Open valve 9 (while pressing on the black valve button, press
RAISE).
- The reading on G2 is proportional to the amout of mixture in the
dump. It should read something around 660 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 a little valve 12A (4.0 % to start).
- While the pressure reading on G1 should always be below about 400 mbar,
Valve 12A can bae opened gradually, and opened completely, when the
reading on G2 drops below 350 mbar.
- After some time (about 30 min when using the Variox) the pressure on
G1 falls below 150 mbar, and it is time 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, but make sure that the pressure on G1 does
not increase above 350 mbar.
- At some stage, when opening valve 14, the pressure on P1 does no longer
raise above 50 mbar. Leave the valve open until the P1 drops below 0.1.
- 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 falls below 100 (black display below
the valve panel).
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!
This particular version was published on 29-Sep-2005 09:46:01 UTC by MarkusZolliker.
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