Tokamak equilibrium reconstruction using Faraday rotation measurements

A new equilibrium reconstruction procedure using magnetic, line integrated electron density and Faraday rotation measurements has been developed. The method has been applied to a number of elongated tokamak equilibria which were computed by using a free-boundary MHD equilibrium code. Typical errors in four global plasma parameters (βp, ℓi, μ and q0) are evaluated as functions of the measurement errors and the number of source function parameters. Assuming realistic random perturbations in the measurements, the method allows source functions with up to six independent parameters to be reconstructed. It is shown that, when electron density and Faraday rotation measurements are included, the accuracy in the determination of q0 is increased by at least a factor of two, compared with cases without Faraday rotation data. The effects of adding a diamagnetic probe and of varying the plasma elongation are also investigated.