Comparison of particle transport in the scrape-off layer plasmas of Alcator C-Mod and DIII-D

Scrape-off layer (SOL) data from DIII-D and C-Mod have been acquired and analysed for radial particle transport based on a particle balance model. This has allowed a detailed comparison for L-mode plasmas. The inferred radial particle flux, Γ⊥(r), is parameterized in terms of diffusive [Deff(r) ≡ Γ⊥(r)/∇n(r)] and convective particle transport [veff(r) ≡ Γ⊥(r)/n(r)]. The magnitude of the inferred Deff or veff increases across the SOL for both tokamaks. The inferred Deff or veff in the 'far' SOL (one density e-folding length from the separatrix and beyond) are essentially unchanged by changes in core density by factors of 2–3. This corresponds to changes in the far SOL density, collisionality (ν*) and radial fluxes of a factor of 10 or more. Thus ν* does not appear to be an important parameter in determining the radial particle transport in that region.