Dependence of SOL widths on plasma current and density in NSTX H-mode plasmas

Abstract

The dependence of various SOL widths on the line-averaged density ( n ¯ e ) and plasma current ( I p) for the quiescent H-mode plasmas with Type-V ELMs in the National Spherical Torus Experiment (NSTX) was investigated. It is found that the heat flux SOL width ( λ q), measured by the IR camera, is virtually insensitive to n ¯ e and has a strong negative dependence on I p. This insensitivity of λ q to n ¯ e is consistent with the scaling law from JET H-mode plasmas that shows a very weak dependence on the upstream density. The electron temperature, ion saturation current density, electron density, and electron pressure decay lengths ( λ Te, λ jsat, λ ne, and λ pe, respectively) measured by the probe showed that λ Te and λ jsat have strong negative dependence on I p, whereas λ ne and λ pe revealed only a little or no dependence. The dependence of λ Te on I p is consistent with the scaling law in the literature, while λ ne and λ pe dependence shows a different trend.