Electron-Only Reconnection in Plasma Turbulence

Abstract

Hybrid-Vlasov-Maxwell simulations of magnetized plasma turbulence including non-linear electron-inertia effects in a generalized Ohm's law are presented. When fluctuation energy is injected on scales sufficiently close to ion-kinetic scales, the ions efficiently become de-magnetized and electron-scale current sheets largely dominate the distribution of the emerging current structures, in contrast to the usual picture, where a full hierarchy of structure sizes is generally observed. These current sheets are shown to be the sites of electron-only reconnection (e-rec), in which the usual electron exhausts are unaccompanied by ion outflows and which are in qualitative agreement with those recently observed by MMS in the Earth's turbulent magnetosheath, downstream of the bow shock. Some features of the e-rec phenomenology are shown to be consistent with an electron magnetohydrodynamic description. Simulations suggest that this regime of collisionless reconnection may be found in turbulent systems where plasma processes, such as micro-instabilities and/or shocks, overpower the more customary turbulent cascade by directly injecting energy close to the ion-kinetic scales.

The onset of electron-only reconnection

“…The appearance of electron-only reconnection in turbulent systems where the driving scale is relatively close to the ion scales has been observed rather clearly in the (two-dimensional) hybrid turbulence simulations of Califano et al. (2018), who observed electron-only reconnection when , but ion-coupled reconnection when . Our results therefore provide a theoretical context for these numerical results.…”

“…A similar situation has been observed in the hybrid Vlasov–Maxwell turbulence simulations of Califano et al. (2018), who observed that when energy is injected at scales much larger than the ion scales, ion-coupled reconnection is observed, while if energy is injected closer to the ion scales, only electron jets and electron-scale sheets are observed. Reconnection of current sheets with thicknesses of a few is also observed in the VINETA-II experiment (Jain et al.…”

“…Reconnection of current sheets with thicknesses of a few d e is also observed in the VINETA-II experiment (Jain et al 2017). We will follow the terminology of Califano et al (2018) and term this new regime 'electron-only' reconnection.…”

“…We will follow the terminology of Califano et al. (2018) and term this new regime ‘electron-only’ reconnection.…”

ViDA: a Vlasov–DArwin solver for plasma physics at electron scales

“…2001; Pritchett 2008; Califano et al. 2018). To reduce the computational cost of the simulation, reduced models – such as the gyro-kinetic (Howes et al.…”