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Piping and Cold End Assembly (PACE) Design

The J-T cryostat assembly includes a warm contaminate filter, active valves to allow redundant operation of the coolers, four heat exchangers, an approximately 50 K charcoal filter, an approximately 30 K 0.01 micron particulate filter, a porous plug J-T expander, and three liquid reservoirs. The four tube-in-tube heat exchangers are all 6.35 mm outer diameter tubing with a 3.18 mm outer diameter inner tube. The high-pressure gas is held in the annulus. The heat exchangers are heat sunk at each thermal shield.

Contaminate trapping is done at room temperature with either a hydride getter or a resin bed (to be determined), with activated charcoal and a particulate filter at 50 K and a 0.01 micron filter at ~30 K. The J-T expansion is done through a porous plug device nearly identical to those described previously.[8] This porous plug device is highly contamination tolerant should any contamination escape past the warmer contamination traps.

The first two liquid reservoirs are designed to separate the liquid refrigerant from the two-phase fluid leaving the J-T expander. This fluid is wicked to the wall of the reservoirs. The fluid in each reservoir is at essentially the same pressure and temperature. However the heat flux into each is very different. The nominal first liquid reservoir interface temperature is approximately 17 K when providing < 230 mW of refrigeration to the HFI and the 4.5 K RAL cooler. The second reservoir has an approximately 18 K nominal interface temperature due to the higher, approximately 800 mW, heat flux from the LFI. The third reservoir is designed to vaporize any excess liquid refrigerant to ensure a stable mass flow and pressure at the cryostat. This helps to remove temperature fluctuations in the range of 1 Hz.


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