Turbulence is a ubiqutious phenomenon in nature, and it is well known that turbulence couples energy input to dissipation by cascade processes. Plasma turbulence plays a critical role in tokamak confinement. Magnetized plasma turbulence is quasi-2D, anisotropic, wave -like and 2 fluid (i.e. electrons and ions) in structure. Thus, weakly collisional plasma turbulence can mediate electron-ion energy transfer.

The issue of anomalous electron-ion energy coupling is particularly important for low collisionality, electron heated plasma, such as ITER. In this work, we reconsider the classic problem of "turbulent heating " and energy transfer pathways in drift wave turbulence. The total turbulent heating, composed of quasilinear electron cooling, quasilinear ion heating, nonlinear ion heating and zonal flow frictional heating, is analyzed. The electron-ion energy exchange via linear wave-particle resonance will be computed. To address net heating, we show the turbulent heating in an annulus arises due to a wave energy flux differential across this region. We show this net heating is proportional to the Reynolds work on the zonal flow. Zonal flow friction heats ions, thus the turbulence-zonal flow interaction enters as an important energy transfer channel. Since zonal flows are nonlinearly generated, it follows that we should apply weak turbulence theory to calculate the nonlinear ion turbulent heating via the virtual mode resonance in the electron drift wave turbulence. This defines a new collisionless turbulent energy transfer channel through nonlinear Landau damping in the electron-ion energy coupling process, which is shown to be significant in a number of relevant regimes. We show that the electron turbulent energy transfer to ions in a collisionless plasma can be same order as electron heat transport loss. It is necessary to consider the influence of collisionless energy transfer to determine the total energy budget in ITER.

(This work was performed in collaboration with P. H. Diamond at UCSD)

Host: Gian Luca Delzanno