Evaluation of thermal helium beam and line-ratio fast diagnostic on the National Spherical Torus Experiment-Upgrade

A 1-D kinetic collisional radiative model with state-of-the-art atomic data is developed and employed to simulate line emission to evaluate the Thermal Helium Beam (THB) diagnostic on NSTX-U. This diagnostic is currently in operation on RFX-mod, and it is proposed to be installed on NSTX-U. The THB system uses the intensity ratios of neutral helium lines 667.8, 706.5, and 728.1 nm to derive electron temperature (eV) and density (cm−3) profiles. The purpose of the present analysis is to evaluate the applications of this diagnostic for determining fast ( ∽4 μs) electron temperature and density radial profiles on the scrape-off layer and edge regions of NSTX-U that are needed in turbulence studies. The diagnostic is limited by the level of detection of the 728.1 nm line, which is the weakest of the three. This study will also aid in future design of a similar 2-D diagnostic system on the divertor.