An evaluation of kinetic effects in the DIII-D divertor

Under certain conditions, high temperature electrons diffusing across the s eparatrix near the midplane can propagate to the divertor without collision and produce a high energy tail in the electron distribution function near the separatrix. We evaluate a kinetic criterion along the field using measu rements from divertor Thomson scattering and compare temperature measuremen ts from target plate Langmuir probes to estimate the magnitude of the high energy tail. A Fokker-Planck kinetic model [O. Batishchev, Phys. Plasmas 4 (1998) 1672], which includes electron-electron, electron-ion, electron-neut ral, and charge exchange interactions is used to estimate the size of the h igh energy tail. For the cases considered, we found less than 1% of non-the rmal particles near the target plate at typical densities and power levels for the DIII-D scrape-off layer plasma. ELMs violate our kinetic criterion. (C) 1999 Elsevier Science B.V. All rights reserved.