Metallic magnetic calorimeters based on quantum metrology: Optimal design of thermal coupling system

Abstract

Metallic Magnetic Calorimeters (MMC) are low-temperature particle detectors based on calorimetry, typically operating at ultra-low temperatures below 100 mK, and they utilize metallic paramagnetic temperature sensors to convert the temperature rise of the absorber upon absorption of high-energy particles into changes in magnetic flux detected by a superconducting quantum interference device (SQUID). Therefore, the design of the MMC heat coupling system is directly related to the signal characteristics and performance of the MMC, making it particularly important for the design of MMC heat coupling systems. This paper, based on the basic principles of MMC signal conversion and the thermal coupling characteristics of components, combines actual conditions and uses the COMSOL heat conduction module to simulate the MMC heat coupling system. Key components of the MMC heat coupling system, including the absorber, thermal bottleneck, paramagnetic sensor, and weak thermal link, have been optimized in terms of parameter design. The optimized design is proposed based on simulation results and practical considerations. Simulation results show that for the detection of the characteristic 5.9 keV gamma rays from ⁵⁵Fe, when the MMC absorber thickness is reduced to 6 μm and the paramagnetic sensor thickness is reduced to 1.5 μm, the signal amplitude of the CMG-I can be increased by more than 100 % at a working temperature of 30 mK without affecting the MMC signal response and ensuring almost 100 % stopping power; by adding four gold posts between the absorber and the paramagnetic sensor as thermal bottlenecks, with a total cross-sectional area of 5.58 % of the absorber area, the process difficulty can be significantly reduced while ensuring complete thermalization of the incident energy within the absorber and essentially eliminating position dependence; the introduction of gold thermalization strip can provide a fully metallic thermal link from the absorber-paramagnetic sensor system to the rear thermal bath, reducing the relaxation time to approximately 4.844 ms, about one-third of the original design, which can significantly increase the count rate without significantly affecting the MMC signal amplitude and reduce the negative impact on energy resolution caused by signal pile-up. The research results have a significant guide for the design of MMC heat coupling systems.