SECTION 2
INTRODUCTION
2.1 GENERAL DESCRIPTION
Janis closed cycle refrigerator (CCR) systems provide a convenient means of cooling
samples to temperatures below 10 K, and can be used to perform a wide variety of optical
and electrical experiments between —8 K and 325 K (475 K optional). CCR systems
require no liquid helium or liquid nitrogen as a source of cooling. Instead, a closed loop
of helium gas is compressed and expanded, based on the Gifford-McMahon (G-M)
thermodynamic cycle. During the expansion phase of each cycle, heat is removed from
the cold finger, on which the sample is mounted. (A detailed description of the G-M
cycle can be found on page C-3 in the refrigerator manual). A heater and thermometer
are installed on the cold finger and are used to precisely control the sample temperature.
2.2 SYSTEM COMPONENTS
Janis CCR systems include the following components:
1.
Compressor: This provides a supply of high-pressure helium gas to the cold head. It
can be either air cooled or water cooled, and can be configured to match the available
AC voltage and frequency.
2.
Cold Head: This expands the helium gas to cool the sample. It includes two cold
stations, the first stage (radiation shield mount) and the second stage (sample mount).
3.
Gas Lines: These lines are connected between the compressor and cold head supply
and return fittings, and transfer the helium gas between the two components. The gas
lines are flexible stainless steel and include quick disconnect fittings on both ends.
4.
Vacuum Jacket: This is bolted to the cold head. It includes an evacuation valve,
safety pressure relief, electrical feedthroughs, and a clamped vacuum seal for easy
access to the sample space.
5.
Radiation Shield: This bolts to the cold head first stage. It is used to intercept room
temperature radiation before it reaches the sample, allowing the lowest possible
sample temperature to be achieved.
6.
Optional Temperature Controller: This may be provided for use in monitoring and
controlling the sample temperature. Detailed operating procedures can be found in
the accompanying temperature controller manual.
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