Flux driven turbulence in tokamaks

The work presented deals with tokamak plasma turbulence in the case where fluxes are fixed and profiles are allowed to fluctuate. These systems are intermittent. In particular, radially propagating fronts are usually observed over a broad range of time and spatial scales. The existence of these fronts provides one possible way to understand the fast transport events sometimes observed in tokamaks. it is also shown that the confinement scaling law can still be of the gyro-Bohm type in spite of these large scale transport events. Some departure from the gyro-Bohm prediction is observed at low flux, i.e. when the gradients are close to the instability threshold. Finally, it is found that the diffusivity is not the same for a turbulence calculated at fixed flux as for a turbulence calculated at fixed temperature gradient, with the same time averaged profile.