Theory for Neoclassical Toroidal Plasma Viscosity in Tokamaks

Abstract. Error fields and resistive magnetohydrodynamic (MHD) modes are ubiquitous in real tokamaks. They break the toroidal symmetry in |B| in tokamaks. Here, B is the magnetic field. The broken toroidal symmetry leads to enhanced neoclassical toroidal plasma viscosity and consequently the rate of the toroidal flow damping. The neoclassical toroidal plasma viscosity also results in a steady state toroidal plasma flow even without toroidal momentum sources. The same physics mechanisms and phenomena are also applicable and can be observed in the vicinity of the magnetic islands. All these physics consequences are of interests to tokamak devices such as International Thermonuclear Experimental Reactor (ITER). ITER is expected to have low toroidal rotation. Thus, understanding viscosity becomes crucial in predicting rotation in ITER.