Janis exchange gas systems offer two main advantages to the experimenter: rapid sample exchange while the refrigerator is operating, and efficient cooling for non-conductive or irregularly shaped samples not easily clamped to a cold finger (e.g., powders, liquid solutions, etc.). These advantages are made possible by using the refrigerator to cool a column of helium exchange gas surrounding the sample. The sample is inserted, via a long rod, into a nearly isothermal region of the gas column for cooling. Sample exchange by simply removing the sample rod, switching samples on the rod, and reinserting the rod into the cryostat. The entire sequence takes only a matter of minutes and is performed while the refrigerator is operating. Thus the time to cool successive samples is greatly reduced as compared with sample in vacuum cryostats.
The cooler is mounted above the sample chamber in these cryostats. This design permits the sample region to be inserted into the sample chamber of a spectrometer or the room temperature bore of a superconducting magnet.
Optimized for experiments requiring optical access to the sample, the SHI-950 and SHI-950-5 systems include the following components:
- Isothermal static helium gas sample chamber, with exchange gas introduction valve
- Optical vacuum shroud and radiation shield
- Gold-plated OFHC copper sample holder
- Adjustable sample positioner with 8-pin and 10-pin electrical feedthroughs for thermometry and customer wiring into the sample area
- Two spare electrical access ports
- Evacuation valve and safety pressure relief
- Four-way optical access into the sample chamber
- Silicon diode thermometer and control heater
- Additional electrical feedthroughs (BNC, SMA, multipin, and others)
- Additional window ports
- O-ring or epoxy sealed windows
- Indium sealed strain relief mounted cold windows
- IR and other window materials
- Larger or smaller diameter sample chamber
- Special sample positioners, including a double rotating sample positioner for sample rotation about the optical axis (Model SHI-950)
- Non-optical configurations
- Compact configurations (for use with electromagnets)
- Custom configurations
Standard models include:
("x" indicates the cooling power of the refrigerator)
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