Performance improvement of Adiabatic Demagnetization Refrigerator for HUBS

HUBS is a proposed X-ray satellite project dedicated to addressing the “missing baryon problem”. Its payload incorporates TES microcalorimeters operating at sub-100 mK, making ADR a key technology for the HUBS mission. Currently, we are in the process of improving the performance of a two-stage ADR prototype, mainly to increase the hold time at the operating temperature by reducing heat load on the cold stage. The heat load optimization steps taken include properly heat sinking the Kevlar suspension and wiring, lowering the temperature of the first (GGG) stage, and improving the performance of the gas-gap heat switch. Meanwhile, we replace the previous CPA salt pill with a new FAA salt pill containing more moles of crystals, as FAA has more cooling capacity than CPA per mole in the temperature range of interest. In this contribution, we describe the performance improvement of the ADR prototype and present the test results.