Development of a small He II cryostat with optical windows for a microgravity experiment

In order to study film-boiling phenomena in saturated superfluid helium (He IIs) under a microgravity environment, a very compact visualization setup was designed and fabricated at High Energy Accelerator Research Organization (KEK). It consists of a cryostat, a vacuum pump, a high-speed video camera and electrical circuits for measurement. The cryostat in the setup is equipped with optical windows for the visualization of film boiling in He IIs. The setup was tested to verify its thermal and safety performance under a microgravity environment using a 10 m free-drop tower at the Hokkaido Center of the National Institute of Advanced Industrial Science and Technology (AIST). Successful system operation from 1.94 to 2.05 K under microgravity conditions below 1 × 10−3 g was confirmed. The design and test results are described in this technical note.