A μK-Level Temperature Stability Control Method for TES Energy Resolution Test

Hot Universe Baryon Surveyor (HUBS) will focus on the major scientific issue of “missing” baryons. Since the expected radiation is in the soft X-ray band (< ~ 1 keV) and is very weak, HUBS will use an X-ray microcalorimeter based on a transition-edge sensor (TES) array and an adiabatic demagnetization refrigerator (ADR) will be employed to cool the detector down to its working temperature (< 100 mK). TESs are a kind of thermal detector based on superconducting films which detect the energy of a single X-ray photon as a temperature rise. Therefore, temperature fluctuation of the ADR will influence the TES’s measurement of photon energy, so very stable temperature regulation is required to minimize this effect. In order to test the energy resolution of TES, we built a PID control system on a commercial ADR and develop the technology for temperature regulation. In this study, we are able to reduce the temperature fluctuation of the detector stage down to 3.47 μK level. This temperature stability could meet our requirements for detector resolution test at current phase.