Equilibrium reconstruction of the safety factor profile in tokamaks from motional Stark effect data

The motional Stark effect (MSE) diagnostic has been used to obtain accurate measurements of the internal magnetic pitch angle tan−1(B Z /B T ) in finite‐pressure tokamaks. The MSE data, together with external magnetic probe data, are used to reconstruct self‐consistently the equilibrium safety factor (q) profile and, hence, the plasma current density, in the Tokamak Fusion Test Reactor (TFTR) [Plasma Phys. Controlled Nucl. Fusion Res. 1, 51 (1986)] and the Princeton Beta Experiment‐Modified (PBX‐M) tokamak [Phys. Fluids B 2, 1271 (1990)]. An efficient computational scheme, based on an inverse coordinate representation of the magnetic field, has been developed to solve the coupled nonlinear equations describing both the magnetohydrodynamic (MHD) equilibrium and the q profile, which best match all the experimental data.