Ion heating and magnetic flux pile-up in a magnetic reconnection experiment with super-Alfvénic plasma inflows

Abstract

This work presents a magnetic reconnection experiment in which the kinetic, magnetic and thermal properties of the plasma each play an important role in the overall energy balance and structure of the generated reconnection layer. Magnetic reconnection occurs during the interaction of continuous and steady flows of super-Alfvénic, magnetized, aluminum plasma, which collide in a geometry with two-dimensional symmetry, producing a stable and long-lasting reconnection layer. Optical Thomson scattering measurements show that when the layer forms, ions inside the layer are more strongly heated than electrons, reaching temperatures of T i~Z ̅ T e ≳ 300 eVmuch greater than can be expected from strong shock and viscous heating alone. Later in time, as the plasma density in the layer increases, the electron and ion temperatures are found to equilibrate, and a constant plasma temperature is achieved through a balance of the heating mechanisms and radiative losses of the plasma. Measurements from Faraday rotation polarimetry also indicate the presence of significant magnetic field pile-up occurring at the boundary of the reconnection region, which is consistent with the super-Alfvénic velocity of the inflows.

Lower-hybrid drift instability and macroscopic flow of colliding magnetized plasmas

“…The field reconnection effects may play some role in this as the rippling is more pronounced on the anode side of the layer, where the electron current must be stronger, as they are accelerated by the reconnection electric field in y− direction. On the other hand, recent experiments specifically designed to study the reconnection layer in colliding flows do not show noticeable rippling of the reconnection layer [19].…”

Interactions of magnetized plasma flows in pulsed-power driven experiments

“…This is ideal for the accompanying laser probing diagnostics [22], as they make path integrated measurements through the plasma, which can easily be interpreted to understand the structure of the interaction and extract the plasma parameters of interest. In demonstration of this figures 2(b) and 2(c) show interferograms of the colliding plasma flows between two aluminium wire arrays [30,32]. Localized measurements of the flow velocities and electron and ion temperatures come from the optical Thomson scattering diagnostic [22].…”

“…Magnetic reconnection is a complex and multifaceted process which is an active topic of research across space, astrophysics and plasma physics [28,29]. One of the most notable applications of the inverse wire array setup therefore has been to create a platform for studying this process in the laboratory [25,[30][31][32][33]. In these experiments two identical inverse wire arrays are fielded side-by-side on the MAGPIE generator, connected in parallel and in the same polarity to each receive a 50% share of the current supply.…”

“…The heating is therefore expected to draw directly from the released magnetic energy in the reconnection current sheet. This however would require a resistivity approximately 10× greater than the Spitzer resistivity to provide heating on a fast-enough timescale to heat the plasma before it leaves the reconnection layer [31,32]. Anomalous heating has been observed in numerous other reconnection experiments (see review of [28] and references therein), and could potentially arise from the development of instabilities in the reconnection layer.…”

“…(b) Carbon wire arrays produce a layer which is unstable to the production of plasmoids. Multi-frame videos showing the dynamics of the respective layers over each experiment can be found in the references[32] and[25].…”