ITER edge database investigations of the SOL width

Based on the ITER edge database, comparisons among the major tokamaks (ASDE X, ASDEX-Up, COMPASS-D, C-MOD, DIII-D, JET, JFT-2M and JT-60U) with respect to systematic SOL-width behavior are presented in terms of free-form regre ssion analysis for lambda(ne) and lambda(Tc). Emphasis is placed on OH-L pl asmas as this data is most abundant and coherent. Despite differences in si ze, wall-conditioning and divertor configuration, broadly similar trends ar e found in the regimes of low- and high-recycling and partially-detached di vertor operation. In the low-recycling regime all machines appear to underl ie a size scaling: lambda(ne) (min), lambda(Te) (min) similar to const.(sur face area/I-p)(0.7). Operation at high q(95), high densities with respect t o the Greenwald limit, or high powers leads to SOL widths considerably in e xcess of the values indicated by this simple scaling, and are documented in the form of machine-specific or machine-group-specific parametric expressi ons. For ELMy II-modes there is a general, but not universal, trend of smal ler lambda(ne) and lambda(Tc) being associated with higher core confinement . On ASDEX-Up the SOL pressure e-folding length can vary as n(e) I-p(-2) fo r ELMy H-modes. (C) 1999 Elsevier Science B.V. All rights reserved.