Magnetic Reconnection in a Sheared Magnetic Flux Tube: Slippage Versus Tearing

Abstract

Magnetic reconnection is a fundamental plasma process that converts magnetic energy to thermal and kinetic energy of the plasma. The earliest work of magnetic reconnection relied on a magnetic field configuration of topologically separate regions (Parker, 1957;Petschek, 1964;Sweet, 1958). Vasyliunas (1975) defined magnetic reconnection as occurring if there existed plasma flows across surfaces that separates regions containing topologically different magnetic field lines. While formally correct in two-dimensional topologies that contain an X-line type topology, this definition was shown to break down in three-dimensional situations where there exists a finite magnetic field component in the third dimension (Schindler et al., 1988). A more general definition, first introduced by Axford (1984), considered the localized breakdown of the frozen-in field (, and the resulting changes in connection as the basis of magnetic reconnection. Due to a non-ideal electric field R localized to a finite diffusion region, plasma elements which are at one time connected by a single magnetic field line are at a later time no longer connected. This concept was adapted and further developed by Schindler et al. (1988) and Hesse and Schindler (1988), who coined the term General Magnetic Reconnection (GMR). They showed that for the most general case of reconnection, where the magnetic field does not vanish inside the diffusion region, termed finite-B reconnection, a necessary condition for magnetic reconnection to be operating, and leading to large scale effects (i.e., not limited to the diffusion region) is the presence of a finite parallel electric potential drop along a set of magnetic field lines passing through the diffusion region, φ ≡∫E ‖ ds ≠ 0. The s is the arc length along this field line.Depending on the nature of this parallel electric field, the reconnection process can be both time-stationary and time-dependent (Hesse et al., 2005). In the time-stationary case, the electric field is potential and the time derivative of the magnetic field vanishes, leading to an effect like magnetic field line sections slipping relative to one another, which breaks magnetic connectivity of plasma elements. In this study, we will refer to the time-stationary case as slippage reconnection. In the time-dependent case, the electric field is inductive, and the time derivative of the magnetic field does not vanish.

Reconnection along a Separator in Shock Turbulence

“…Based on theoretical considerations, there are different forms of reconnection that can take place at magnetic nulls (Priest & Pontin 2009), or along magnetic separators (Parnell et al 2010a;. "Slippage" reconnection can also occur in sheared flux tubes (Kuniyoshi et al 2021).…”