This is version 5.
It is not the current version, and thus it cannot be edited.
[Back to current version]
[Restore this version]
Orange Cryostat Cooldown Procedure
Preparation
- Pump main vacuum through valve (V) with a turbo pump, ideally over night. If the cryostat
was cold recently a few hours will be o.k., but if water might be condensed inside,
it should be pumped for several days.
- Connect sample space, helium reservoir etc. (all volumes which will contain liquid
or gaseous helium) with a raw vacuum pump. Flush 2 times with helium gas. Check
the function of cold valve (C) and warm valve (W). Pump sample space.
- Fill in liquid nitrogen. Ideally wait one night.
- Fill in liquid helium.
OrangeCryostatTopPictures
Insert Sample
- Increase the temperature of the heat exchanger to 100 K.
- Connect a helium gas tube to the sample space and wait until 1 bar is reached inside.
- Remove cover.
- Enter the sample stick slowly and screw the top.
- Pump down and flush again with He gas, then pump down to a pressure between 10 and 50 mbar.
Cool down
There are two possibilities, each has advantages and drawbacks.
- Connect helium pump to the pumping port (P). Switch on the pump and wait until
the pressure stabilizes (should be less than a few millibars). Make sure that
the warm valve (W) is closed, open cold valve (C) a little, the pressure at the
pump should not exceed 40 mbar (20 on the ILL cold valve controller).
- Put a setpoint of 10 K on the heat exchanger.
- When the heat exchanger is at 10 K and the sample near 10 K, reduce the pressure
by closing the cold valve gradually until the heating power the temperature controller
needs to keep 10 K has reached a value between 100 and 200 mW. Wait half an hour
and check or change the cold valve setting again.
- Put the temperature setpoint to zero. The cryostat should cool to 1.6 K within 10 minutes.
- Open cold valve (C), open warm valve (W) by about 3 turns. Close the valve (R) going
to the He recovery.
- When the heat exchanger and the sample temperature have stabilized around at 4.2 K,
close the warm valve and reopen a little bit, just enough to held 4.2 K.
Remove Sample
- Increase the temperature of the heat exchanger to 100 K.
- Connect a helium gas tube to the sample space and wait until 1 bar is reached inside.
- Remove the stick slowly and put the cover.
- If no new sample is entered soon, pump down the sample space to at least 10 mbar.
- Dry the sample stick.
Attachments:
CCU.png
NeedleValveControl.png
This particular version was published on 07-May-2012 07:14:10 UTC by MarkusZolliker.
|