2-Stage GM Refrigerator Replaces LN2/LHe Dewar
We proposed a two-stage Gifford-McMahon (GM) Refrigerator which provides continuous uninterrupted operation as low as -3 K. After an accepted design study, IRTF staff dismantled and shipped the camera and cooling system to our facilities to replace the LHe/LN2 dewar with the new GM Refrigerator.
<10 K Temperature Requirement within the Same Envelope Demands Creativity
The new GM Refrigerator is larger than the existing cryogen cooler. To maintain the existing envelope, we engineered the cooling system with the cold head on its side instead of the traditional configuration of being in line with the cold plate. This configuration increased the distance from cold plate to the detector array, requiring a custom design to create separate mechanical paths to successfully meet temperatures of 55 K for stage 1 and 10 K for stage 2. The warmer temperature stage 1 was engineered to completely enclose the colder stage 2 for the entire path without touching it. Overcoming thermal resistance was achieved by an innovative path design to minimize distance and using copper to optimize thermal conductivity.
Vibration Reduction for Complex Thermal Paths
GM Refrigerators typically transmit significant vibration to the cold work surface (on the order of 10-20 μm). We design our GM systems with bellows interfaces and other vibration dampening components at any place where heat is transferred from rigid components. For this project, we designed custom thermal straps using braided copper to maintain the complex thermal path and system orientation.
Electrically Isolated Detector without Compromising Thermal Conductivity
Meeting thermal performance was complicated by the need to electrically isolate the detector mount to eliminate any noise from grounding, voltage or other sources. Electrically isolating a component also thermally isolates it. To electrically isolate the detector without compromising thermal performance, we designed a thin diamond insulator near the detector array which was enough to not break the thermal path.
For this project and many others, NASA and other clients in the scientific community rely on us to work collaboratively and solve these complex design challenges.