Demonstrating the capabilities of EUV tomography as an estimator of controllable plasma parameters on the HBT-EP tokamak

This work addresses real-time optical signal processing as an alternative to magnetic pickup diagnostics for plasma feedback and control on the HBT-EP tokamak. The diagnostic used in this study collects photons in the Extreme Ultraviolet (EUV) range of 15 eV - 1 keV from four arrays of 16 channels each in a poloidal plane. Signals are processed with a 50 kHz bandwidth on a GPU, feedback is applied to the plasma via 40 internal magnetic coils. In the first phase of this work, we present results of real time feedback on plasma major radius as well as MHD 3/1 mode amplitude using a novel Maximum Likelihood algorithm. The most probable of a set of plasma emissivity profiles representing horizontal equilibria or DCON-generated mode shape is selected by minimizing the signal reconstruction residual. In the second phase, the above results are compared against offline analysis performed with a traditional tomography algorithm. Results are presented from a benchmarking of the inversion implementation is against known 2D emissivity surfaces from equilibrium reconstructions. A novel in situ calibration of the EUV sightlines is presented as well.