A SCALING RELATION FOR THE ITER SCRAPE-OFF LAYER THERMAL-DIFFUSIVITY

We have generated an empirically based scaling relation for the thermal diffusivity, (s)chi(perpendicular-to), in the scrape-off layers (SOL) of tokamaks using a database of global energy confinement time versus core plasma parameters from 110 ohmically heated tokamak discharges whose core plasma parameters, viz., T(e), n(e), B, curvature, radial scale length, and Z(eff), are similar to the values expected in the SOL of tokamaks like ITER. These data were interpreted with an all-possible-regressions model/multiple-regressions analysis to obtain the best fit for tau(E) versus n(e), T(e), R, a, Z(eff) and V. A cylindrical-shell thermal transport model was used to extract (s)chi(perpendicular-to) from tau(E). Reasons for ignoring the effects on (s)chi(perpendicular-to) of sheath phenomena and parallel transport on open field lines are discussed.