The solar wind is a unique laboratory to study plasma turbulence, in particular at scales below the ion Larmor radius, thanks to the high-resolution in-situ measurements from satellites such as Magnetospheric Multiscale Mission, Cluster, and Parker Solar Probe. At sub-ion scales, understanding the spectral properties of electromagnetic fluctuations and energy dissipation of turbulence is crucial but challenging, because of the kinetic plasma effects that impact both position and velocity-space dynamics. While previous works usually studied these aspects separately, we show analytically and numerically that a self-consistent answer to the two questions lies in the entwined nature of the plasma dynamics in position- and velocity-space. I will first demonstrate that the combined effects of sheet-like, intermittent structures and the Landau damping of kinetic Alfvén waves determine the energy spectra of electromagnetic fluctuations. Second, I will show that efficient electron heating occurs around current sheets, and is primarily due to collisionless electron Landau damping, rather than Ohmic dissipation. This damping is facilitated by the local weakening of advective nonlinearities around intermittent current sheets and yields significant energy dissipation via a velocity-space cascade. These results are timely for the ongoing and future multi-spacecraft missions such as the HelioSwarm that explore the velocity-space dynamics of turbulence.
Hosted by Professor Yi-Hsin Liu
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