Scaling of Ohmic Tokamak Error-field Penetration Thresholds in the Presence of Neoclassical Toroidal Viscosity

A model for field error penetration is developed that includes non-resonant as well as the usual resonant field error effects. The non-resonant components cause a neoclassical toroidal viscous torque that tries to keep the plasma rotating at a rate comparable to the ion diamagnetic frequency. The new theory is used to examine resonant error-field penetration threshold scaling in ohmic tokamak plasmas. Compared to previous theoretical results, we find the plasma is less susceptible to error-field penetration and locking, by a factor that depends on the non-resonant error-field amplitude.