Arturs Vrublevskis

Equations of state in collisionless magnetic reconnection

Kinetic simulation as well as in situ measurement of reconnecting current sheets in the Earths magnetosphere show strong electron temperature anisotropy, with the parallel electron temperature becoming several times greater than the perpendicular temperature. This anisotropy is accounted for in a solution of the Vlasov equation recently derived for general reconnection geometries with magnetized electrons in the limit of fast transit time. A necessary ingredient is a magnetic field-aligned electric field extending over the ion inertial length scale. The parallel electric field maintains quasineutrality by regulating the electron density, traps a large fraction of thermal electrons, and heats electrons in the parallel direction. Based on the expression for the electron phase-space density, equations of state provide a fluid closure for the electrons that relates the parallel and perpendicular pressures to the density and magnetic field strength. The resulting fluid model agrees well with fully kinetic simulations of guide-field reconnection, accurately predicting the electron temperature anisotropy. In addition, the equations of state impose strong constraints on the electron Hall currents and magnetic fields that develop during antiparallel reconnection. The model provides scaling laws for the Hall magnetic fields and predicts the magnitude of the current in the electron layer.

Spontaneous onset of magnetic reconnection in toroidal plasma caused by breaking of 2D symmetry

Magnetic reconnection is studied in the collisionless limit at the Versatile Toroidal Facility (VTF) at MIT. Two distinct magnetic configurations are applied in the experiments; an open magnetic cusp and a closed cusp. In the open cusp configurations, the field lines intersect the the vacuum vessel walls and here axisymmetric oscillatory reconnection is observed. Meanwhile, in the closed cusp configuration, where the field lines are confined inside the experiment, the coupling between global modes and a current sheet leads to powerful bursts of 3D spontaneous reconnection. These spontaneous events start at one toroidal location, and then propagate around the toroidal direction at the Alfven speed (calculated with the strength of the dominant guide field). The three dimensional measurements include the detailed time evolution of the plasma density, current density, the magnetic flux function, the electrostatic potential, and the reconnection rate. The vastly different plasma behavior in the two configurati...