OrangeCryostatCooldownProcedure

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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

  1. 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 20 mbar (30 on a maxi cryostat). In SEA, this could be done by switching the needla valce control to automatic and set 20 - 30 for the flow maximum.
  2. Put a setpoint of 10 K on the heat exchanger.
  3. 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. With SEA, the regulation of the needle valve is done automatically, but the value for "flow set" should be optimized if not known form an earlier run.
  4. Put the temperature setpoint to zero. The cryostat should cool to 1.6 K within 10 minutes. If the base temperature can not be reached or the "nv_Set" is oscillating, most probably the value for "flow set" was not determined properly, and must be increased slighly.

Cool Down with warm valve In principle there is the possibility to cool down with the use of the warm valve, without He pump. As this is not recommended, it mentioned only for information, and that it has to be made sure that the warm valve has to be closed always.

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 with a hair blower (not a hot gun!)


Attachments:  CCU.png  NeedleValveControl.png 
This particular version was published on 07-May-2012 07:27:51 UTC by MarkusZolliker.