An alternative derivation of parallel viscous coefficients in the banana regime for finite aspect ratio tokamaks

An alternative derivation of the parallel viscous coefficients in the banana regime for finite aspect ratio tokamaks is presented. It is accomplished by solving the drift kinetic equation driven by plasma flows. The zero-flow constraints are imposed to complete the description of the perturbed distribution. The parallel viscous forces are calculated from their kinetic definitions using the same quadratic form that has been employed to calculate the coefficients in the large aspect ratio limit. The approach that does not utilize the elegant subtraction procedure is equivalent to the one that does, as developed in Hirshman and Sigmar [Nucl. Fusion 21, 1079 (1981)]. With this derivation, the program of calculating parallel viscous coefficients directly from the solution of the drift kinetic equation driven by flows is complete. It may be easier to adopt the approach to treat other physics problems encountered in advanced tokamak operations.