Jason M. TenBarge

Magnetic reconnection is a highly dynamic process that excites a wide variety of kinetic waves and instabilities. Transverse current sheet instabilities such as the lower‐hybrid drift and secondary drift‐kink instabilities in particular have been shown by kinetic simulations to modify the reconnection and introduce significant turbulence and mixing to the reconnection layer. Past studies using the ten‐moment fluid model to capture important kinetic physics such as the electron inertia and full representation of the pressure tensor proved advantageous to a two‐fluid representation of reconnection, but the model struggled when using a local relaxation closure for the heat flux to replicate the current sheet instabilities and subsequent mixing seen in kinetic simulations. This work uses the Gkeyll software framework to perform simulations of asymmetric reconnection based on the 16 October 2015 MMS crossing of a diffusion region, the Burch event. An improved gradient‐based heat flux closure is implemented, showing significant improvement in secondary kinetic instabilities that grow in the current sheet. These instabilities generate turbulence which leads to growth of secondary magnetic islands and flux ropes.

A forefront research question is how energy evolves in weakly collisional plasmas for which departures from local thermodynamic equilibrium (LTE) are significant. The standard approach is studying the terms in the non-LTE energy evolution equation derived by taking the second moment of the Boltzmann equation, but the resultant fluid metrics do not retain information about which particles at which velocities drive energy evolution. A widely studied channel for internal energy density evolution is the pressure–strain interaction. Here, we employ the kinetic pressure–strain, a phase-space diagnostic whose velocity-space integral recovers the pressure–strain interaction to disambiguate the contributions to the pressure–strain interaction from disparate particle populations in composite phase-space densities. We develop phase-space analogs of the pressure–strain interaction decompositions to provide the phase-space origins of normal versus sheared flow. We introduce the “kinetic strain-rate” tensor, the phase-space analog of the strain-rate tensor, which we argue is needed to interpret the phase-space origins of the pressure–strain interaction. To demonstrate the utility of these quantities, we investigate them for composite electron distributions near the electron diffusion region in two-dimensional particle-in-cell simulations of antiparallel symmetric magnetic reconnection. We find that the phase-space-based diagnostics isolate the roles of distinct populations. These results contribute to a growing body of work providing new methods for quantifying phase-space energy evolution for a broad array of processes, from magnetic reconnection to collisionless shocks and turbulence, opening new pathways for answering longstanding problems of particle energization in weakly collisional plasmas.

The collisionless transfer of energy between fields and particles through wave–particle interactions is a fundamental process in space plasmas but remains incompletely characterized because many mechanisms operate across a wide parameter range and diverse plasma conditions. The field–particle correlation (FPC) technique reveals velocity-space signatures of particle energization by correlating measured electric field fluctuations with changes in the velocity distribution. Fully mapping these signatures across plasma parameters requires an impractically large number of kinetic simulations or observations. To address this challenge, we introduce JET-PLUME (Judging Energy Transfer in a Plasma in a Linear Uniform Magnetized Environment), an extension of the PLUME Vlasov–Maxwell dispersion solver. JET-PLUME uses PLUME's ability to model parallel drifting bi-Maxwellian distributions to examine phase-space energy transfer by adding an analytic Fourier-space formulation of the FPC. This approach isolates the contribution of individual resonances, separates degenerate entropy mode components, and allows systematic analysis of unstable, growing modes. Dimensionless expressions extend the results across a broad parameter range and highlight the role of off-diagonal elements of the susceptibility tensor in coupling electric field and current response. We show that during kinetic Alfvén wave damping, the perpendicular field can drive parallel ion currents among particles with large v⊥, reducing the net Landau damping. The resulting velocity-space signatures, accessible through JET-PLUME, demonstrate how analytic formulations of phase-space energy transfer can reveal novel physics of wave–particle interactions across diverse plasma environments.

Calibrated measurements of electron velocity distribution functions (VDFs) are necessary to characterize fluid and kinetic processes in weakly collisional and nearly collisionless plasmas such as the solar wind. Therefore, we analyzed 3,996,051 electron VDFs observed by the Wind 3DP thermal electron detector near 1 au between 2005 January 1 and 2017 November 25. The data were calibrated for each electron VDF to produce accurate velocity moments in the solar wind. This is the first full solar cycle coverage electron velocity moment dataset in the near-Earth solar wind. Herein (Paper I) we discuss the calibration process/algorithms and the velocity moment constraints, uncertainties, and resulting public dataset. In the second paper (Paper II), we statistically analyze the electron velocity moment dataset.

Between 2005 January 1 and 2017 November 25, the Wind spacecraft measured 3,996,051 electron velocity distribution functions (VDFs) in the near-Earth solar wind. The instrument was calibrated, and velocity moments were calculated up to the third moment (i.e., electron heat flux). The magnetic field and ion velocity moments have been interpolated to the midpoint time of the VDFs, where we have 3,947,607 finite electron velocity moments (most prior studies used n _{e ,int} ∼ 5.43 cm ⁻³ , ∣ V _oe ∣ ∼ 421 km s ⁻¹ , T _{e ,tot} ∼ 12.7 eV, and ∣ q _{e ,∥} ∣ ∼4.92 μ W m ⁻² . The median values for the electron-to-proton temperature ratio is T e , tot / T p , tot ∼2.55, the electron temperature anisotropy A _e = T e , ⊥ / T e , ∥ ∼ 0.89, total electron beta β _{e ,tot} ∼ 1.27, electron–electron collision frequency ν _ee ∼ 0.18 day ⁻¹ , and electron–electron Knudsen number K _{n ,ee} ∼ 2.57. The results are mostly consistent with previous studies except that K _{n ,ee} is significantly larger than some other works, which implies that the near-Earth solar wind is less collisional than may have been inferred.

We describe a new model for the study of weakly collisional, magnetised plasmas derived from exploiting the separation of the dynamics parallel and perpendicular to the magnetic field. This unique system of equations retains the particle dynamics parallel to the magnetic field while approximating the perpendicular dynamics through a spectral expansion in the perpendicular degrees of freedom, analogous to moment-based fluid approaches. In so doing, a hybrid approach is obtained that is computationally efficient enough to allow for larger-scale modelling of plasma systems while eliminating a source of difficulty in deriving fluid equations applicable to magnetised plasmas. We connect this system of equations to historical asymptotic models and discuss advantages and disadvantages of this approach, including the extension of this parallel-kinetic-perpendicular moment beyond the typical region of validity of these more traditional asymptotic models. This paper forms the first of a multi-part series on this new model, covering the theory and derivation, alongside demonstration benchmarks of this approach that include shocks and magnetic reconnection.

Collisionless magnetic reconnection is postulated to be active in many regions of the heliosphere, where the physics and formation of heliospheric structures are influenced by pickup ions (PUIs). Recent investigations suggest that the presence of PUIs may enhance the reconnection rate due to PUI-induced turbulence. Our investigation from particle-in-cell simulations with seed PUI shell velocity distributions reveals that the distributions remain quasi-stable within the reconnection exhaust region. The reconnection rate is rather suppressed as compared with non-PUI reconnection simulations. The PUI population eventually responds to the reconnection dynamics and forms a thicker current sheet layer. Both PUI and regular ion populations develop sub-ion-Alfvénic outflow jets, although PUI outflows are slower in comparison and extend beyond the separatrix surface. We predict that a future Interstellar Probe mission may encounter reconnecting current sheet layers in the outer heliosphere that demonstrate an initial slow modulation followed by a sharp rotation of the reconnecting magnetic field toward the center of the layer.

The shock-drift acceleration of ions at quasi-perpendicular shocks is a well-known kinetic mechanism for the acceleration of a small fraction of incoming ions to high energy. Here, we use a suite of sixteen hybrid simulations of quasi-perpendicular collisionless shocks over the range of Alfvén Mach number 4.3≤MA≤15.8 (corresponding to a range of fast magnetosonic Mach numbers 2.6≤Mf≤9.4) and shock-normal angle 45°≤θBn≤90° to identify the velocity-space signature of shock-drift acceleration using the field-particle correlation technique. We show that the features of the ion velocity distribution in the shock foot and ramp regions can be clearly interpreted by analysis of the single-particle trajectory of a reflected ion through the full 3D-3V phase space. The characteristic features of the velocity-space signature of shock-drift acceleration remain qualitatively robust over the full parameter range of our simulations, providing a potential means for its identification using single-point spacecraft measurements. At higher Alfvén Mach numbers MA≳8 (Mf≳5), kinetic instabilities generate fluctuations of the electromagnetic fields within the shock transition region, leading to fluctuations in and smearing out of the resulting velocity-space signatures, but the signature remains generally robust and identifiable. The results on the shock-drift acceleration of ions presented here represent a novel means to determine more completely the partitioning of upstream bulk flow kinetic energy into plasma heating, particle acceleration, and electromagnetic fields in collisionless shocks.