Divertor regimes in NSTX

Abstract The identification of divertor operating regimes is of particular importance for heat and particle control optimization in high performance plasmas of a spherical torus, because of the magnetic geometry effects and compactness of the divertor region. Recent measurements of radiated power, heat, and particle fluxes in lower single null and double null NSTX plasmas with 0.8–6 MW NBI heating suggest that the inner divertor is detached at n ¯ e ⩽ 2 – 3 × 10 19 m - 3 whereas the outer divertor is always attached. This resilient state exists in most L- and H-mode plasmas. The inner divertor transiently re-attaches in ELMy H-mode plasmas when heat pulses from type I or type III ELMs reach the divertor.