Effect of neoclassical toroidal viscosity on error-field penetration thresholds

A model for error-field penetration relevant to ohmic tokamak plasmas is introduced that accounts for both resonant and non-resonant magnetic field perturbations. The non-resonant components produce neoclassical damping of the toroidal flow velocity throughout the plasma volume. For simplicity, a single resonant harmonic is considered which produces an electromagnetic torque localized on a particular resonant magnetic surface. A governing equation for the velocity profile is derived extending a recently developed drift-MHD model for error-field penetration [A.~Cole, R.~Fitzpatrick, \emph{Phys.~of Plasmas}, \textbf{13}, 032503 (2006)] by including the neoclassical physics. The model predicts a value for the critical error-field threshold. As in previous theoretical models, extrapolating a scaling of the critical threshold with engineering parameters---such as device major radius, electron density, and toroidal field strength---involves a detailed knowledge of the momentum confinement time scaling in an ohmic plasma discharge.