Toroidal velocity shear Kelvin-Helmholtz instabilities in strongly rotating tokamak plasmas

Strong sheared toroidal flows are predicted to drive parallel velocity shear Kelvin-Helmholtz oscillations unstable in spherical tokamak plasmas. Numerical simulations that include rotation in the equilibrium suggest that future spherical tokamaks will have an upper limit in uni-directional injected neutral beam heating in order to keep the sheared toroidal rotation below the critical level for the onset of the global parallel velocity shear Kelvin-Helmholtz instability.