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

The dependence of various SOL widths on the line-averaged density ( n ¯ e ) and plasma current (Ip) 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 (λq), measured by the IR camera, is virtually insensitive to n ¯ e and has a strong negative dependence on Ip. This insensitivity of λq 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 (λTe, λjsat, λne, and λpe, respectively) measured by the probe showed that λTe and λjsat have strong negative dependence on Ip, whereas λne and λpe revealed only a little or no dependence. The dependence of λTe on Ip is consistent with the scaling law in the literature, while λne and λpe dependence shows a different trend.