LOSS OF STATIC EQUILIBRIUM, FLOW GENERATION AND THE DEVELOPMENT OF TURBULENCE AT THE EDGE OF TOKAMAKS

For three tokamaks, the local cross-field particle transport time at the edge is observed to be of the order of the local sound transit time along the magnetic field. Static equilibria as conventionally defined in magnetohydrodynamics are therefore inapplicable. It is shown that when plasma transport is poloidally asymmetric, the steady state necessarily involves parallel flows comparable to the sound speed, with significant density modulations along a given flux surface. Such sonic parallel flows can precipitate the parallel shear flow instability, with attendant large fluctuations and momentum transport. The consequences of such a loss of static equilibrium are explored.