Scaling of Electron and Ion Transport in the High-Power Spherical Torus NSTX

Abstract

Dedicated $H$-mode parameter scans in the high-power National Spherical Torus Experiment have been used to establish the confinement scaling and underlying transport trends at low aspect ratio ($R/a\ensuremath{\simeq}1.3$). These scans indicate a strong dependence of the global and thermal energy confinement times on the toroidal field, ${B}_{T}^{0.9}$, while their dependence on plasma current is weaker, ${I}_{p}^{0.4}$. Local transport analysis indicates that the electrons control the ${B}_{T}$ scaling, whereas the ions control the ${I}_{p}$ scaling, with ${\ensuremath{\chi}}_{i}$ outside $r/a=0.5$ at the neoclassical level.