An 800 mK helium sorption cooler for the HUBS mission

The refrigeration system of the Hot Universe Baryon Surveyor (HUBS) mission intends to use the FAA paramagnetic salt adiabatic demagnetization refrigerator (ADR) to obtain temperatures below 100 mK. In order to obtain the 1 K pre-cooling temperature required by the FAA stage, one option is to use a GGG paramagnetic salt ADR, and the other option is to use a helium sorption cooler. A helium sorption cooler and the corresponding helium gas gap heat switch have been developed, and a cooling temperature of 800 mK has been obtained. This paper gives a detailed introduction to the prototype's structure, cooling performance, existing problems, and the next optimization measures.