Assessing the toroidal radiation distribution at Wendelstein 7-X by combining Gaussian Process Tomography and field line mapping

Abstract

Radiative cooling is one of the main heat dissipation channels for magnetically confined fusion plasmas. In stellarators power exhaust control is complicated by the three-dimensional radiation distribution. Using a Gaussian Process Tomography routine, the two-dimensional radiation distribution in Wendelstein 7-X is reconstructed from the line-integrated bolometer data of one poloidal cross-section. These experimental tomograms are mapped to the field of view of the newly installed divertor bolometer cameras and compared to the toroidally separated local measurements to assess the toroidal radiation distribution. We observe peaking of the plasma radiated power density in the divertor region and steep toroidal gradients, especially at low radiated power fraction (up to $\times 8$ increase in the emissivity along a $\sim 2$m long flux tube). These results suggest the presence of significant toroidal radiation asymmetries within a stellarator half-module.