ISSN:
1089-7674
Source:
AIP Digital Archive
Topics:
Physics
Notes:
Simple, analytic models are developed to estimate the plasma particle fluxes to the main chamber walls of a divertor tokamak in terms of assumed values of the cross-field transport coefficients, D⊥, v⊥, and of the wall–gap size. The wall–gap size is the cross-field width of the gap between the last closed flux surface, LCFS, defined by magnetic (divertor) separatrix and the wall of the main chamber, the "wall-limiter." The neutrals recycling from the wall may be ionized at, or inboard of, the LCFS—which is a key feature of the so-called "simple SOL" and which is referred to here as the pure transport case. On the other hand, the neutrals may be ionized within the scrape-off layer, SOL, in the main chamber, with the ions returning to the wall—referred to here as the SOL ionization case. SOL ionization gives rise to a radial flux amplification effect, in the sense that the plasma flux to the walls is larger than for the "simple SOL"—all else held equal, including the separatrix density, wall–gap, and the transport coefficients. The amplification factor is found to be only modest, however, up to ∼2x. Primarily, plasma–wall contact is therefore just simply a function of cross-field plasma transport, which is strongly anomalous in the SOL, probably due to turbulence, and possibly intermittent, large-event activity in the outer regions. The experimental database for D⊥SOL, v⊥SOL is weak, particularly for the far SOL, a situation calling for increased experimental and theoretical effort. © 2002 American Institute of Physics.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.1493207
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