DENSITY PROFILE CONSISTENCY AND ITS RELATION TO THE TRANSPORT OF TRAPPED VERSUS PASSING ELECTRONS IN TOKAMAKS

A formal expression for the canonical steady-state density profile in a tokamak can be obtained from the Fokker-Planck-type diffusion equati on derived from the Vlasov equation in the limit of anomalous diffusio n due to strong turbulence. Here we derive an explicit expression for this canonical profile for a tokamak with arbitrary cross section and aspect ratio. The resulting profile is independent of the spatial depe ndence of the diffusion coefficient, but does depend on the relative d iffusion of trapped versus passing particles. Under conditions where o nly the trapped particles transport due to interactions with the turbu lence the profiles are considerably flatter than if both the trapped a nd passing transport the same. The steepness of the calculated profile depends on the ratio of the diffusion coefficients for passing and tr apped particles. The calculated profiles are compared with measured pr ofiles from the tokamak known as DIII-D [J.L.Luxon et al., Plasma Phys ics and Controlled Nuclear Fusion Research 1986 (International Atomic Energy Agency, Vienna, 1987), Vol. I, p. 159]. Density profiles for a typical International Thermonuclear Experimental Reactor (ITER) [R. Ay mar, Fusion Eng. Design 24, 977 (1984)] plasma are also derived. (C) 1 998 American Institute of Physics.