V3FIT Reconstructions using Soft X-Ray and Interferometric Diagnostics on the Compact Toroidal Hybrid*

Reconstruction of three-dimensional (3D) equilibrium is important for improving the operation and understanding the physics of non-axisymmetric magnetic confinement devices. We present V3FIT[1] 3D reconstruction results from the Compact Toroidal Hybrid (CTH) experiment ($R_o = 0.75$\,m, $a_p \approx 0.2$\,m, $B \leq 0.7$\,T, $\overline{n}_e \leq 5 \times 10^{19}$\,m$^{-3}$,\, $T_e \leq 300$\,eV, $I_p \leq 80$\,kA) where we have used internal diagnostic signals as inputs to the V3FIT code. The two diagnostics, a three-channel, 1\,{mm} interferometer, and a 54-channel Soft X-ray (SXR) array, are chordal type measurements that generate signals based on the line-integrated values of the plasma density and/or temperature sampled from the interior of the plasma. We use two parameterization models for the electron density and SXR emissivity profiles: a two-power fit model capable of producing flat to centrally peaked profiles, and a line-segment model that can produce hollow profiles. Results show that SXR diagnostics are sensitive to plasma elongations caused by plasma current profile changes not detected by magnetic diagnostics.\\[4pt] [1] J.D. Hanson, S.P. Hirshman, S.F. Knowlton, L.L. Lao, E.A. Lazarus, J.M. Shields, Nucl. Fusion, \textbf{49},(2009)\,075031.