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SECTION 4
OPERATION
4.1 REMOVING THE VACUUM SHROUD (SEE FIGURE 4.1)
1.
Before removing the vacuum shroud, vent the vacuum space by turning the shroud
evacuation valve knob counter-clockwise.
2.
Remove the clamp located just above the evacuation valve, and carefully lift the
shroud off the refrigerator.
3.
Remove the four 6-32 screws that hold the radiation shield to the cold head, and lift
the radiation shield off the refrigerator. The cold head sample mount and sample
holder are now accessible.
4.2 SAMPLE MOUNTING
Most CCR systems are supplied with a sample holder. If the sample holder is removed, a
thin film of thermal grease (such as Crycon) or thin indium foil should be used to
enhance thermal contact when reinstalled. Grease or indium can also be used to improve
the thermal contact between the sample and sample holder.
Janis CCR systems include provisions for additional electrical feedthroughs for customer
wiring of the samples. Small gauge wires (32 AWG, 35 SWG) should be used to
minimize heat leak into the sample, and the wires should be thermally anchored in
several spots to the cold head using Stycast epoxy, GE 7031 varnish, by tying with nylon
string or floss, or by using mylar or aluminum tape (See figure 4.2). Once the sample is
mounted to the cold head, install the radiation shield and vacuum shroud. Any visible
dirt or lint on the sealing gasket is sufficient to cause a vacuum leak, so be sure the gasket
and flanges are clean and lightly greased before mounting the vacuum shroud.
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