Hybrid Low Temperature Cryostat
Figure 1: Janis special “hybrid” cryostat
Figure 2a: “Wet” superconducting solenoid
Figure 2b: Model 2K-VTI cryostat with the “wet” magnet
Figure 3: Sample holder
Figure 4: Sample positioner
Figure 5: Single shot operation
Janis Research Company has developed a new “hybrid” low temperature system; the versatile model 2K-VTI variable temperature cryogen-free (dry) system has been combined with a “wet” (LHe cooled) 9T/4T vector magnet (Figure 1: Janis special “hybrid” cryostat) to provide low temperature and high magnetic field measurements. The 2K-VTI can be integrated with either wet or dry magnets, and can be configured for sample in vacuum, sample in ultra high vacuum (UHV), sample in exchange gas or even sample in liquid.
Because the VTI can be easily removed from the magnet, different magnets and sample cooling inserts can be combined in a variety of configurations. For example, the complete system shown in Figure 1 includes two different magnets, the 2K variable temperature cryostat, and a dilution refrigerator. Thus, four different temperature/magnetic field configurations are possible.
The model 2K-VTI system is cooled by a PT (pulse tube) cryocooler, including remote motor for reduced vibration levels. The cryostat includes a vacuum insulated tail that is inserted into the cold bore of the superconducting magnet (Figure 2a: “Wet” superconducting solenoid and Figure 2b: Model 2K-VTI cryostat with the “wet” magnet). While the hybrid system uses a LHe cooled magnet, the same 2K-VTI cryostat can alternatively be combined with a cryogen-free room temperature bore magnet.
The cryostat incorporates a top loading sample chamber. The bottom of the sample chamber includes a female taper that precisely matches the male tapered shape of the sample holder (Figure 3: Sample holder) installed at the bottom of the top loading sample positioner (Figure 4: Sample positioner). This design provides positive thermal contact between the sample holders and maintains proper alignment of the sample in the center of the magnetic field at all times.
The versatile 2K-VTI cryostat can be operated in several different modes, allowing the user to optimize the cooling method for the particular sample and experimental requirement.
- Sample in static exchange gas: The sample is surrounded by helium gas at one atmosphere or less. Temperatures <5 K can be achieved.
- Single shot mode: Helium gas is allowed to condense within the heat exchanger. Pumping on the condensed LHe results in temperatures <2 K (Figure 5: Single shot operation). The operating time depends upon the duration of the condensation period.
- Sample in flowing helium gas: Helium gas is introduced to the sample chamber through a heat exchanger. The gas is cooled by the PT cryocooler before entering the sample chamber; it then enters the chamber at ~4 K, cools the sample, and vents out of the system. The main advantage of this operation mode is that the venting cold helium gas intercepts a large portion of the conductive heat leak from the sample chamber and sample support rod.
- Continuous operation <2 K: By installing an impedance near the heat exchanger, and then connecting the helium gas inlet and outlet ports to a hermetic pump, the system can be operated continuously below 2K.
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