Electron-only reconnection and ion heating in 3D3V hybrid-Vlasov plasma turbulence

We perform 3D3V hybrid-Vlasov (fully kinetic ions and fluid electrons) simulations of sub-ion-scale plasma turbulence with quasi-isotropic, compressible injection close to the ion scales to investigate electron-only reconnection and its effect on ion heating. Retaining electron inertia in the generalized Ohm s law provides the mechanism for collisionless magnetic reconnection. Spectral analysis reveals a shift from kinetic Alfv\'{e}n waves (KAW) to inertial kinetic Alfv\'{e}n (IKAW) and inertial whistler waves (IWW) near electron scales. To distinguish the roles of the inertial scale and the gyroradius (dᵢ and ρᵢ), three values of ion beta (βᵢ = 0.25, 1, 4) are studied. Ion-electron decoupling increases with βᵢ, as ions become less mobile when the injection scale is closer to ρᵢ than to dᵢ, highlighting the role of ρᵢ in achieving an electron magnetohydrodynamic (EMHD) regime at sub-ion scales. The EMHD regime promotes electron-only reconnection in turbulence with small-scale injection at βᵢ 1. Despite this EMHD-favoured dynamics, we still observe significant ion heating also at large βᵢ, namely Qᵢ/ε ≈ 69, 91, and 96 at βᵢ = 0.25, 1, and 4, respectively. Moreover, while ion heating is significantly anisotropic at βᵢ ≤ 1 (namely, Ti,⊥ > Ti,∥), it becomes only marginally anisotropic at βᵢ > 1 (i.e., Ti,⊥ Ti,∥). Our results highlight that ion turbulent heating in collisionless plasmas is sensitive to the separation between injection scales λᵢₙⱼ and the ion gyroradius ρᵢ, as well as to βᵢ and finite-k∥ effects, requiring an extended investigation of these parameters for accurate modelling.