Analysis of separatrix plasma parameters using local and multi-machine databases

The characteristics of the plasma density and temperature at the edge of a diverted tokamak are presented. The analysis is done using the edge database formed by the ITER divertor database and modeling expert group, Analysis indicates the density pro file is flatter with high density operation, i.e. the separatrix density is a larger fraction of the average density. This characteristic is found to be independent of plasma operation mode. We find the separatrix density in ITER will be approximately 6 x 10(19-) m(-3), based on scaling from the major diverted tokamaks. Scaling of the edge temperature is more problematic. A model which concludes the edge temperature is sensitive to details of the recycling process is presented. The temperature profile is analyzed to obtain the perpendicular thermal diffusivity. We find a diffusivity of 0.2 m(2)/s for ITER H-mode operation. The existing data, however, does not permit any size scaling of the diffusivity. (C) 1999 Elsevier Science B.V. All rights reserved.