Michael Barnes (Oxford): Bistable turbulence in magnetised toroidal plasma

Physikalisches Kolloquium

The prevailing paradigm for magnetised plasma turbulence associates a unique, stationary turbulent state with a given set of equilibrium plasma parameters. In this talk I present data from kinetic simulations of tokamak plasmas showing that bistable turbulence is possible in the presence of imposed flow shear. In particular, we show that at least two distinct, finite amplitude turbulent states can be obtained for the same input plasma parameters, with the initial condition determining the steady-state solution. We argue, with the aid of example data, that the occurrence of bistable turbulence is regulated by a competition between externally-imposed, equilibrium flow shear and `zonal’ flow shear that is generated by the turbulence itself. This competition produces an unexpected behaviour in some cases: the combination of zonal and equilibrium flow shears, each of which individually suppresses turbulence, results in an enhancement of turbulence amplitudes.


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