Center for Magnetic Self Organization

in Laboratory and Astrophysical Plasmas

Effect of Magnetic Shear on Hall – Mediated Magnetic Reconnection

It has been known for many years that when electrons and ions can follow separate dynamics – the Hall regime – reversing magnetic fields can rapidly reconnect. But most instances of reconnection in nature and the laboratory involve a significant sheared, or guide field, rather than a full reversal. In magnetosphere reconnection, for example, guide fields often reach the level of the reconnecting field, while reconnection in fusion plasmas can have guide fields much larger than the reconnecting field. This is prompting the study of this type of guide field, both theoretically and numerically. It has been generally observed that reconnection of anti-parallel field lines proceeds much faster than guide field reconnection in which field lines meet with smaller angles with the effect of guide field. We are now studying the transition on MRX.

comparing E and Hall E

Reconnection electric field (E) and the “Hall Electric Field” versus normalized guide field, Bg /Brec. The reconnection electric field is normalized by x VA, where Brec is the magnitude of the reconnecting field, and VA is the Alfven speed calculated using Brec.

As shown in this figure, we observed that the addition of guide field substantially reduces the reconnection rate, and we confirm that the Hall currents in the reconnection plane determine the reconnection electric field (the reconnection rate) over a wide range of applied guide field strengths. Also we have measured quantitative dependence of the reconnection characteristics and the reconnection rate on guide field by systematically applying an external guide field using central conductor coil which creates controlled guide field. Our results will be quantitatively compared with 2-D numerical simulations in the future.

A National Science Foundation Physics Frontier Center,
established in coordination with the Department of Energy.