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

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Abstract
The motional Stark effect (MSE) diagnostic has been used to obtain accurate measurements of the internal magnetic pitch angle tan−1(BZ/BT) 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.