On the secular density rises in NBI-heated H-mode plasmas in NSTX

Plasma–wall interaction analysis is developed at the National Spherical Torus Experiment. At present, poloidally separated recycling and neutral pressure measurements are used to characterize recycling flux trends. The causes of monotonic density increases observed in initial phases of H-mode discharges at t ⩽ 0.2 – 0.6 s appear to be the monotonically increasing source in the divertor, and particle containment time τ p ∗ long in comparison with discharge duration. The ratio of the wall flux to divertor flux is low throughout the density increase phase except in the initial segment, when dN e / dt is highest and magnitudes of the wall and divertor fluxes are similar.