Core fueling and edge particle flux analysis in ohmically and auxiliary heated NSTX plasmas

Abstract

The Boundary Physics program of the National Spherical Torus Experiment (NSTX) is focusing on optimization of the edge power and particle flows in β t ⩾25% L- and H-mode plasmas of t⩽0.8 s duration heated by up to 6 MW of high harmonic fast wave and up to 5 MW of neutral beam injection (NBI). Particle balance and core fueling efficiencies of low and high field side gas fueling in L-mode ohmic and NBI-heated plasmas have been compared using an analytical zero-dimensional particle balance model and measured ion and neutral fluxes. Gas fueling efficiencies are in the range of 0.05–0.20 and do not depend on discharge magnetic configuration, density or poloidal location of the injector. The particle balance modeling indicates that the addition of a pseudo-constant high field side (HFS) fueling source results in a reversal of the wall loading rate and higher wall inventories. Initial particle source estimates obtained from neutral pressure and spectroscopic measurements indicate that the recycling flux in the divertor exceeds the main chamber ion and neutral fluxes by over an order of magnitude. Present analysis provides the basis for detailed fluid modeling of edge heat and particle flows using transport models which include both diffusion and convection.