Water-cooling system of the W7-X plasma facing components

The water-cooling system of the plasma facing components of the Wendelstein 7-X stellarator was originally conceived for long pulse plasma operation of up to 30 min duration based on an input plasma power of 10 MW. The cooling circuits have been adapted to the intermediate machine operation phases introduced prior to the completion of the full long pulse capability: a first phase with a plasma operation duration <1 s and 2 MW input power, a second phase with a plasma duration of 5-10 s. and up to 8 MW input power. In the first operation phase, 10 cooling circuits will be water-cooled, and in the second phase, 36 cooling circuits. The circuits which have not been completed are vacuum sealed inside the plasma vessel. During these phases, some of the first wall heat shields will be filled with air and the first wall panels with Neon gas. For the full long pulse operation with all water-cooled in-vessel components, a total of about 430 cooling circuits will need to be put into service.