Electron-only Reconnection and Ion Heating in 3D3V Hybrid-Vlasov Plasma Turbulence

Abstract

We perform 3D3V hybrid-Vlasov simulations of turbulence with quasi-isotropic, compressible injection near ion scales to mimic the Earth’s magnetosheath plasma, and investigate the novel electron-only reconnection, recently observed by NASA’s Magnetospheric Multiscale mission, and its impact on ion heating. Retaining electron inertia in the generalized Ohm's law enables collisionless magnetic reconnection. Spectral analysis shows a shift from kinetic Alfvén waves to inertial kinetic Alfvén and inertial whistler waves near electron scales. To distinguish the roles of inertial scale and gyroradius (d i and ρ i), three ion beta (β i = 0.25, 1, 4) values are studied. Ion-electron decoupling increases with β i, as ions become less mobile when the injection scale is closer to ρ i than d i, highlighting the role of ρ i in achieving an electron magnetohydrodynamic regime at sub-ion scales. This regime promotes electron-only reconnection in turbulence with small-scale injection at β i ≳ 1. We observe significant ion heating even at large β i, with Q i/ϵ ≈ 69%, 91%, and 96% at β i = 0.25, 1, and 4, respectively. While ion heating is anisotropic at β i ≤ 1 (T i,⊥ > T i,∥), it is marginally anisotropic at β i > 1 (T i,⊥ ≳ T i,∥). Our results show ion turbulent heating in collisionless plasmas is sensitive to the separation between injection scales (λ inj) and ρ i, β i, and finite-k ∥ effects, necessitating further investigation for accurate modeling. These findings have implications for other collisionless astrophysical environments, like high-β plasmas in intracluster medium, where processes such as microinstabilities or shocks may inject energy near ion-kinetic scales.