Axisymmetric parallel velocity shear instability in the tokamak edge

The parallel velocity shear instability in an axisymmetric toroidal edge plasma is studied numerically. In the presence of a large asymmetric particle transport and a limiter, sonic parallel flows develop that are peaked at the last closed flux surface. For α=ρsqR/aLv≳1, these flows are unstable to axisymmetric modes. The associated turbulence gives order unity fluctuation levels. It is located inside the last closed flux surface (LCFS) and on the inner half of the torus. There is an up–down asymmetry of the turbulence which is due to the diamagnetic drift and poloidal rotation. These results are compared to the experimental results from the Continuous Current Tokamak (CCT) (G. R. Tynan, Ph.D. thesis, 1991).