Helium refrigeration system for Wendelstein 7-X

The Greifswald Branch of the Max-Planck-Institute for Plasma Physics (IPP) is currently constructing WENDELSTEIN 7-X, a new fusion experiment of the stellarator type. This paper gives an overview on the cooling requirements as well as on the refrigeration system chosen for the superconducting magnet system and cryo vacuum pumps of the experiment. A flexible refrigerator was developed which is able to run in quite different working conditions. Special features are single phase forced flow cooling with adjustable supply temperatures down to 3.4 K using cold circulators and cold compressors. The various operating modes, combined with the requirement to limit the power input, day-night load leveling, and the spatial boundary conditions for the system layout were a challenge for process and construction designers.