Peak neoclassical toroidal viscosity at low toroidal rotation in the DIII-D tokamak

Observation of a theoretically predicted peak in the neoclassical toroidal viscous (NTV) force as a function of toroidal plasma rotation rate Ω is reported. The NTV was generated by applying n=3 magnetic fields from internal (I-)coils to low Ω plasmas produced with nearly balanced neutral beam injection. Locally, the peak corresponds to a toroidal rotation rate Ω0 where the radial electric field Er is near zero as determined by radial ion force balance.