An evaluation of kinetic eects in the DIII-D divertor

Under certain conditions, high temperature electrons di€using across the separatrix 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 ®eld using measurements from divertor Thomson scattering and compare temperature measurements 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, electronion, electron-neutral, and charge exchange interactions is used to estimate the size of the high energy tail. For the cases considered, we found less than 1% of non-thermal particles near the target plate at typical densities and power levels for the DIII-D scrape-o€ layer plasma. ELMs violate our kinetic criterion. Ó 1999 Elsevier Science B.V. All rights reserved.