High Power CADRs and Associated Mechanisms for Next Generation CMB Experiments

Cooling experiments to ultra-cold temperatures permits exceptionally sensitive measurements to be made. This enables the study of subjects from quantum computation to subtle variations in the cosmic microwave background (CMB). To date, there is only one practical technology which can continuously cool high power experiments below 0.2 Kelvin, the Helium Dilution Refrigerator (DR). These refrigerators are extremely expensive, complex, power intensive, orientation sensitive (with respect to gravity), and require the increasingly rare isotope Helium-3. There is another technology used to achieve these temperatures, Adiabatic Demagnetization Refrigeration (ADR). This technology relies on the demagnetization of paramagnetic solids which cool in a decreasing magnetic field. Once the field is lowered to zero, the cooling energy is depleted, and thus, typical implementations provide non-continuous refrigeration at the cold stage. Continuous cooling, as needed for CMB experimentation, requires the integration of two or more refrigerators. This has been done by NASA and a few others. However, while the resulting Continuous ADRs (CADRs) have a number of very attractive characteristics, such as cryogen-free operations, they have provided very limited load capacity – a fraction of common DRs – and therefore, have never been a commercially viable option for the laboratory researcher. We will address these shortcomings and deliver a high power CADR via innovative design and laboratory-specific optimization of each CADR sub-component and mechanism. In Phase I, a detailed mathematical model of the CADR was constructed to predict system performance and cost modeling, demonstrating feasibility. Several novel subsystem designs were built and tested. In Phase II, we propose to develop and demonstrate a prototype system. The first year will consist of detailed design and testing each of the major subsystems. The second year of Phase II will concentrate on system integration, control, and performance optimization. The commercial applications of the high power CADR include researchers in CMB astronomy, quantum computing, and other fields where more reliable and affordable access to ultra-low temperatures is desired. Ultra low temperature platforms enable cutting-edge science in astronomy, quantum computing, gamma ray spectroscopy and other research topics of national and commercial importance. A new breed of ultra-low temperature magnetic refrigerator will offer significant cost, reliability, and renewability advantages over the current use of helium dilution refrigerators.