Verification of Bifurcated Current Sheets and Their Role in Energy Conversion during Magnetic Reconnection

In the magnetic reconnection regions of both laboratory and space plasmas, we have verified that bifurcated current sheets (BCS) develop at the separatrix between the inflow and the exhaust regions generating abrupt changes of magnetic field directions. We investigate bifurcated current sheets (BCS) in the Magnetic Reconnection Experiment (MRX), NASA’s Magnetospheric Multiscale Mission (MMS), and the Parker Solar Probe (PSP). BCS are characterized by double-peaked current density, strong localized electric fields, and sharp density gradients near the separatrix. We show that the presence of BCS is accompanied with a deep electrostatic potential well that facilitates energy conversion to ions during anti-parallel magnetic reconnection. By applying a simplified electron momentum equation in the ion rest frame, we demonstrate that the depth of this potential well can be directly deduced from magnetic field variations across the BCS – a prediction that is quantitatively consistent with both MRX and MMS observations [1]. The presence of a well-defined BCS also influences ion energy partitioning, resulting in a flow energy flux that exceeds the enthalpy flux within the heliospheric current sheet. Supporting 2D open-boundary particle-in-cell simulations reveal that BCS structures persist into the downstream region only when reconnection proceeds in a quasi-steady manner, offering a possible explanation for their infrequent detection in the magnetosphere.

[1] M. Yamada. Magnetic Reconnection: A Modern Synthesis of Theory, Experiment, and Observations. Princeton University Press, Princeton, USA, 2022.