Transport hysteresis and zonal flow stimulation in magnetized plasmas
Résumé
A hysteresis in the relationship between zonal flows and electron heating is observed numericallyby using gyrokinetic simulations in fusion plasmas. As the electron temperature increases, a firsttransition occurs, at a given electron/ion temperature ratio, above which zonal flows are muchweaker than before the transition, leading to a poorly confined plasma. Beyond this transition,even if the electron temperature is lowered to a moderate value, the plasma fails to recover adynamic state with strong zonal flows. Then, as the electron temperature decreases further, a newtransition appears, at a temperature lower than the first transition, below which the zonal flowsare stronger than they were initially. The confinement of the plasma and the heat flux are thusfound to be sensitive to the history of the magnetized plasma. These transitions are associatedwith large exchanges of energy between the modes corresponding to instabilities (m >0) and zonalflows (m= 0). We also observe that up to the first transition it is possible to use a control methodto stimulate the appearance of zonal flows and therefore the confinement of the plasma. Beyondthat transition, this control method is no longer effective.
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