Equilibrium reconstruction improvement via Kalman-filter-based vessel current estimation at DIII-D

Equilibrium reconstruction codes calculate the distributions of flux and toroidal current density over the plasma and surrounding vacuum region that best fit the external magnetic measurements in a least square sense, and that simultaneously satisfy the MHD equilibrium equation (Grad-Shafranov equation). Although these codes often use direct measurements of the currents in the plasma and poloidal coils, they sometimes neglect the current induced in the tokamak vessel due to the fact that they cannot be directly measured. Kalman filtering theory is employed in this work to optimally estimate the current in the tokamak vessel. The real-time version of the EFIT code is modified to accept the estimated vessel currents with the goal of improving the equilibrium reconstruction for the DIII-D tokamak.