Laboratory Verification of Electron‐Scale Reconnection Regions Modulated by a Three‐Dimensional Instability

Abstract

Magnetic reconnection (Dungey, 1953) is the process of changing the topology of magnetic field lines in the presence of a plasma, often permitting an explosive release of magnetic energy. Well-known examples include solar flares (Priest & Forbes, 2000) and auroral substorms in the Earth's magnetosphere (Vasyliunas, 1975). Although reconnection often governs the global dynamics of plasma systems, the reconnection process occurs in localized electron diffusion regions (EDRs), where the motion of the electron fluid decouples from the magnetic field, breaking the frozen-in law of magnetohydrodynamics. The origin of this process in the collisionless regime, where conventional resistive friction is absent, remains controversial. For example, laminar kinetic models predict that the EDRs are characterized by intense current layers with widths as narrow as the kinetic scales associated with the electron orbit motion (Pritchett, 2001;Vasyliunas, 1975). In other models, the scattering of electrons by electric field fluctuations associated with high-frequency instabilities is proposed to widen the current layers and enhance the anomalous transfer of momentum from the electrons to the ions (Hoshino, 1991;Huba et al., 1977;Papadopoulos, 1977).Significant insight into reconnection physics is provided by fully kinetic numerical models. In three-dimensional (3D) configurations, it has been argued that turbulence can cause local suppression of the effective

Laboratory Study of Collisionless Magnetic Reconnection

“…This discrepancy persisted even after incorporating finite collisions (Roytershteyn et al 2010) and 3D effects via Lower Hybrid Drift Waves (LHDW, see later) (Roytershteyn et al 2013) in the simulations when averaged over the y direction. In contrast, the EDR has been recently studied on TREX and their measured half width agrees well with the predictions by 2D PIC simulations in cylindrical geometry (Greess et al 2021), shown in Fig. 9(b).…”

“…As shown in Fig. 7, magnetic field and current structures similar to those of MRX are observed, and reproduced with remarkable agreement through matching numerical simulations (Olson et al 2021;Greess et al 2021).…”

“…2.3. It is noted that the current sheet kinking that was observed on TREX and associated simulations (Greess et al 2021) and in space (e.g. Ergun et al 2019) could result in broadened current sheets due to limited spatial and/or time resolutions.…”

“…Does anomalous resistivity exist in its conventional forms, as hinted by electrostatic LHDWs observed during guide field reconnection (Yoo et al 2023) or by IAWs observed recently during anti-parallel reconnection at low ion temperature (Zhang et al 2023)? Alternatively, do anomalous effects manifest as kinking of otherwise laminar 2D reconnecting current sheets (Greess et al 2021) or is anomalous resisitivity cancelled by anomalous viscosity leaving no wave dissipative effects in the EDR (Graham et al 2022)? Further research using well-controlled experiments with adequate diagnostics, supported by matching numerical simulations, is needed to settle this long standing question.…”

Radial drift of plasma blobs in a toroidal magnetic field with fully kinetic and reduced fluid models

“…Important additional effects include finite blob extent parallel to the magnetic field, which may place blobs in a regime where the maximum velocity is determined by sheath effects at the boundaries. This may be modeled with the cylindrical VPIC code in 3D by including a full toroidal geometry or a wedge with a finite extent in the angular θ direction [45]. The effects of collisions may also be included self-consistently in PIC codes [46], and collisional effects on blog propagation in multiple spatial dimensions may be studied in the future with VPIC or another PIC code [20].…”