Click Photo for More Images
The easiest way to quickly cool a sample to low temperature is to submerge it in a container
of liquid helium, He4. (Liquid helium is a common industrial liquid that can
be purchased from most gas suppliers.)
I designed and assembled a cryogenic
probe to characterize samples, which can be used with a standard helium storage dewar.
The probe is made of thin-walled
stainless steel and wired with manganin wires. Both of these materials are relatively poor
thermal conductors and reduce the heat leak from room temperature. A machined brass piece was
brazed on the bottom of the stainless tube to hold the fiberglass sample holder
and mount a pair of magnetic
shields. A machined brass box was brazed to the top of the stainless tube. This box has holes for
three d-subminiature connectors which contact the sample wires in the probe. At the base the
manganin wires pass thorough a set of limiting resistors and connect to a universal chip socket.
Finally, a stainless steel ultra-torr sliding fitting is welded to a flange that fits on the neck
of the storage dewar. This allows the probe to be lowered into the dewar while maintaining a
seal that keeps moisture out. This probe design allows for quick and easy
characterization of samples at cryogenic temperatures.