Plasma shape control on the National Spherical Torus Experiment (NSTX) using real-time equilibrium reconstruction

Plasma shape control using real-time equilibrium reconstruction has been implemented on the National Spherical Torus Experiment.The rtEFIT code originally developed for use on DIII-D was adapted for use on NSTX.The real-time equilibria provide calculations of the flux at points on the plasma boundary, which is used as input to a shape control algorithm known as isoflux control.The flux at the desired boundary location is compared to a reference flux value, and this flux error is used as the basic feedback quantity for the poloidal 1 field coils on NSTX.The hardware that comprises the control system is described, as well as the software infrastructure.Examples of precise boundary control are also presented.