Collisional boundary layer analysis for neoclassical toroidal plasma viscosity in tokamaks

It is demonstrated that the pitch angle integrals in the transport fluxes in the nu regime calculated in K. C. Shang [Phys. Plasmas 10, 1443 (2003)] are divergent as the trapped-circulating boundary is approached. Here, nu is the collision frequency. The origin of this divergence results from the logarithmic dependence in the bounce averaged radial drift velocity. A collisional boundary layer analysis is developed to remove the singularity. The resultant pitch angle integrals now include not only the original physics of the nu regime but also the boundary layer physics. The transport fluxes, caused by the particles inside the boundary layer, scale as root nu. (C) 2008 American Institute of Physics.