Poloidal rotation spin-up in divertor tokamaks

Poloidal spin-up can occur in divertor tokamaks as a consequence of magnetic field geometry. The presence of a divertor X point causes poloidal variation in the diffusion of particles and heat. The resulting pressure variation on flux surfaces produces a poloidal torque. The spin-up is opposed by sound wave propagation. The physical model consists of dissipative compressional reduced magnetohydrodynamics (CRMHD), including viscous stress. Numerical computations have been carried out using an adaptive unstructured mesh method capable of good resolution near a separatrix X point. The simulations show poloidal flow spin-up increasing with pressure diffusivity. A theory is derived that is consistent with the simulations. The equilibrium poloidal E×B/B2 drift velocity is a root of a fifth-order polynomial. Bifurcations from one rotation state to another can occur at critical parameter values.