BOOTSTRAP CURRENT AND NEOCLASSICAL TRANSPORT IN TOKAMAKS OF ARBITRARYCOLLISIONALITY AND ASPECT RATIO

A multi-species fluid model is described for the steady state parallel and radial force balance equations in axisymmetric tokamak plasmas. T he bootstrap current, electrical resistivity, and particle and heat fl uxes are evaluated in terms of the rotation velocities and friction an d viscosity coefficients. A recent formulation of the neoclassical pla sma viscosity for arbitrary shape and aspect ratio (including the unit y aspect ratio limit), arbitrary collisionality, and orbit squeezing f rom strong radial electric fields is used to illustrate features of th e model. The bootstrap current for the very low aspect ratio National Spherical Torus Experiment [J. Spitzer et al., Fusion Technol. 30, 133 7 (1996)] is compared with other models; the largest differences occur near the plasma edge from treatment of the collisional contributions. The effects of orbit squeezing on bootstrap current, thermal and part icle transport, and poloidal rotation are illustrated for an enhanced reverse shear plasma in the Tokamak Fusion Test Reactor [D. Meade and the TFTR Group, Plasma Physics and Controlled Nuclear Fusion Research, 1990 (International Atomic Energy Agency, Vienna, 1991), Vol. I, p. 9 ]. Multiple charge states of impurities are incorporated using the red uced ion charge state formalism for computational efficiency. Because the force balance equations allow for inclusion of external momentum a nd heat sources and sinks they can be used for general plasma rotation studies while retaining the multi-species neoclassical effects. (C) 1 997 American Institute of Physics.