Magnetic reconnection, the topological rearrangement of magnetic field lines in highly conducting plasma, comes about through microscopic processes which break the field lines on the electron dissipation scale and macroscopic dynamical processes which couple the local and global scales. Understanding the physics of the microscopic electron dissipation layer is critical to understanding magnetic reconnection and how it energizes the ambient plasma.
Detailed comparisons have now been made between laboratory observations of electron-scale dissipation layers near a reconnecting X-line in the Magnetic Reconnection Experiment (MRX) and direct two-dimensional full-particle simulations using realistic Coulomb collisions and boundary conditions relevant to the MRX. Many experimental features of the electron layers, such as insensitivity to the ion mass, are reproduced by the simulations.
All ion scale features are successfully reproduced. However, the electron layer thickness, is 3-5 times larger than the predictions. In view of the excellent agreement found for other quantities, this is a serious discrepancy.
No known 2D mechanism, including the one based on collisionless electron nongyrotropic pressure, is sufficient to explain the observed reconnection rates. These results suggest that 3D effects play an important role in electron-scale dissipation during fast reconnection. Currently, this subject is under further investigation in MRX. Top 3 panels (a-c): Experimental example taken from a hydrogen plasma with a fill pressure of 2 mTorr. Bottom panels (d-f). Results from a corresponding simulation shown in the same format as the experiment.