KINETIC EFFECTS IN TOKAMAK SCRAPE-OFF LAYER PLASMAS

The short mean-free path expansion used in fluid modeling of scrape-of f layer plasmas is often violated for typical discharge parameters, es pecially by the superthermal particles, which carry most of the heat f lux. Thus, the tail of the distribution function can strongly depart f rom Maxwellian due to nonlocal mean-free path effects, which can modif y plasma transport, impurity radiation, and plasma-neutral gas interac tions. These nonlocal effects become particularly pronounced for detac hed plasma conditions that are characterized by sharp gradients in the plasma parameters along the magnetic field. These problems are being addressed by developing one spatial dimension and two velocity variabl es, fully kinetic, collisional, and time-dependent particle-in-cell co de, W1 [Contrib. Plasma Phys. 34, 436 (1994)], and its parallel-comput er version, PW1 [Contrib. Plasma Phys. 34, 424 (1996)]. Comparisons ar e made with the Fokker-Planck code ALLA [Phys. Plasmas 3, 1634 (1996)] and with experimental results. Kinetic effects on probe measurement i nterpretation, impurity radiation, and parallel heat conductivity due to non-Maxwellian features in scrape-off layer plasmas are considered. Heat conductivity is compared with nd hoc heat flux limit models. (C) 1997 American Institute of Physics.