High Power CADRs and Associated Mechanisms for Next Generation CMB Experiments (Final Summary Report)
- High Precision Devices, Inc., Boulder, CO (United States)
Continuous Adiabatic Demagnetization Refrigerators (CADR) have been used successfully as refrigerators with base temperatures below 0.1 Kelvin. Successful applications are rare however, until recently only major government space agencies able to produce them. The are valued for their high thermodynamic efficiency, lack of fluids, and gravity independence, giving them an edge in some applications (like spaceflight) over dilution refrigerator (DR) technology. This effort started as a proposal to make a CADR optimized for terrestrial use in some applications where the same benefits would be appreciated. Observation of the Cosmic Microwave Background with cryogenic receivers was the initial target application where the above-mentioned benefits would also be appreciated. Phase I was a research effort showing the path to an optimized design. Phase II was the effort to build such a prototype and the required attendant controlling hardware. Year one of this effort was devoted to developing the many ingredients which comprise a CADR. Each of which is a challenge in and of itself, and many of which have at some point been the subject of an SBIR effort on its own account. These ingredients, magnets, magnetocaloric units ("pills"), heat switches, thermal isolations, and power supplies all required significant investment of time and effort. At the end of year one we have created useful pills, novel heat switches (the subject of a pending patent), novel isolation structures, and had started in earnest on the power-supplies required to drive the system. Year two was focused on the gradual integration of these subcomponents into larger systems. The first CADR we constructed was a single stage CADR based on a GGG refrigerant. This CADR operated at extremely high frequency, capable of cycle times of less than 1 minute. This CADR could provide up to 1mW of cooling power at 1 Kelvin. At this point we focused on integration of the lower temperature elements of the systems as we moved towards a complete CADR. Here we began to encounter some challenges. The first few pills of CPA we grew in our pill growth system had significant porosity defects, which requires redesign of the pill growing machine. We later found issues in moving to lower current, higher amperage magnets. These proved far more prone to quenching than the first generation magnets we wound. The software used to drive the system also proved slow to develop and test, for want of functioning hardware. The issues with the power supply system motivated us to seek a no-cost extension of the project. We used this extra time to debug our software and move to integration and testing of a complete system. For this final integration effort we created a complete CADR, using new magnets, pills and suspension we developed. This CADR is what is visible in the pictures that follow. Our SBIR funding expired at about this point and we continued with internal funding, hoping to reach a complete system demonstration in time for unveiling at APS march meeting. In the build up to the meeting we experienced significant issues with our high-Tc leads to the 8 magnets in the system. Repeated unintentional incandescence caused significant delay and some redevelopment. Just before APS march meeting we achieved a base temperature of about 130mK, however significant unresolved issues lingered in the system, large heat leaks at the first stage for example and electrical noise problems. At this time, the COVID pandemic exploded to the scale we're now familiar with, halting progress. We are still working on the final testing effort to better characterized the technology that we have built to date. There remains significant customer interest, however it is no longer heavily focused on the CMB community. The CMB-S4 effort (the original target customer) is in the process of making technology down selects and an unproved CADR at this point is too risky an adoption to make in their effort. Additionally, the CMB effort has shifted to architectures where the power load at 1K far more than can be provided by a CADR. This shift effectively makes Dilution Refrigerators the only deployable option for now. The market for CADR which has emerged in the growing Quantum Electronics community. Potential future applications in Quantum Communications, Quantum Computing and Quantum Sensors (Quantum Information Systems or QIS informally) are creating a lot of interest is very low SWAP ultra-low temperature cryogenics. CADR is much better suited to enable the miniaturization and ruggedization these applications will require than DR technology. The application space for CADR remains quite promising. The DOE’s investment has directly enabled this challenging research. We are extremely grateful for the help and are continuing our efforts to bring this technology to the market.
- Research Organization:
- High Precision Devices, Inc., Boulder, CO (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC), High Energy Physics (HEP)
- DOE Contract Number:
- SC0015974
- OSTI ID:
- 1632810
- Type / Phase:
- SBIR (Phase II)
- Report Number(s):
- DOE-HPD-15974-1; 3034472558
- Country of Publication:
- United States
- Language:
- English
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