FIDASIM modeling of edge current density measurements to be performed using a new high-performance spectrometer at DIII-D

Motional Stark Effect spectroscopy is a well-established technique that allows for measurement of the magnetic field structure and plasma current distribution based on the Doppler-shifted and Zeeman-split n=3-2 emission of collisionally excited hydrogenic neutral beams. We show a design study for fast edge-current density measurements based on high-throughput, high-spectral-resolution spectrometers at DIII-D. The diagnostic setup uses an existing light collection system used for BES turbulence measurements near the edge-pedestal region that offers high spatial resolution and photon throughput. Our spectrometers utilize echelle gratings which provide excellent spectral resolution for resolving the sigma and pi lines of the beam emission, and a cooled EMCCD array with high quantum efficiency and a sampling rate of up to 10kHz. FIDASIM simulations predict a spatial resolution of less than 1cm and a sensitivity to changes of the poloidal magnetic field of 3mT. This will allow studies of the edge pedestal and ELM induced current redistribution.