Optimal estimation of vessel currents for equilibrium reconstruction enhancement at DIII-D

A tokamak discharge requires accurate feedback control of many of the discharge parameters, including plasma shape. Real-time estimation of the plasma boundary, which is not directly measurable, is critical for shape control. One of the available methods for plasma boundary estimation is based on the equilibrium reconstruction. Equilibrium 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 use direct measurements of the currents in the plasma and poloidal coils, they usually neglect the current induced in the vessel of the tokamak due to the simple 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