Development of a Visible Bremsstrahlung Tomography System for FRC Profile Reconstruction on Helion Energy's Polaris Device

Polaris, Helion Energy's seventh generation field reversed configuration (FRC) prototype has the primary goal to demonstrate direct electricity recovery from fusion. Normalized separatrix radii of 0.4 – 0.9 are expected in the center of the compression section over the duration of a pulse. A four-view, 96-chord tomographic system monitors visible bremsstrahlung emission to reconstruct time-resolved emissivity profiles. The FRC cross-section is reconstructed using the Cormack-Granetz method and solved via Tikhonov-regularized inversion. Rigid Rotor model estimates indicate separatrix radius and emission centroid errors below 10% and 3%, respectively, across expected operating conditions. Improvements in reconstruction accuracy will focus on ring-like basis functions and edge-preserving regularization to better resolve hollow profiles and separatrix structure. Details on the optical design, build, light detection, and calibration will be presented.