SOL width scaling from consideration of edge transport in tokamaks

A simple two-point representation of the tokamak scrape-off layer (SOL), ba sed on the parallel and perpendicular energy balance equations, has been us ed to develop heat flux width scalings for a wide variety of chi(perpendicu lar to) models in terms of B-phi, n(sep), q(95), P-SOL, R and a. These scal ings have been tested against databases of SOL parameters established on CO MPASS-D (which exhibits a collisionless SOL), JET Mk IIa. divertor and Alca tor C-MOD (both of which exhibit strongly collisional SOLs). The better fit scalings to the collisionless dataset all show a positive dependence of SO L width on q(95) and an inverse dependence on n(sep). Four of the better fi t scalings also show a positive dependence on P-SOL and a strong inverse de pendance on B-phi. In the collisional case a group of 5 models, each with a chi(perpendicular to) proportional to T-1/2/n dependence, provide the bett er fit scalings to both collisional datasets. The derived scalings exhibit a strong inverse dependence on P-SOL but are independent of B-phi, unlike s calings derived from the commonly used Bohm diffusion model and four of the five are also independent of n(sep). (C) 1999 Elsevier Science B.V. All ri ghts reserved.