Toward laboratory torsional spine magnetic reconnection

Abstract

Magnetic reconnection is a fundamental energy conversion mechanism in nature. Major attempts to study this process in controlled settings on Earth have largely been limited to reproducing approximately two-dimensional (2-D) reconnection dynamics. Other experiments describing reconnection near three-dimensional null points are non-driven, and do not induce any of the 3-D modes of spine fan, torsional fan or torsional spine reconnection. In order to study these important 3-D modes observed in astrophysical plasmas (e.g. the solar atmosphere), laboratory set-ups must be designed to induce driven reconnection about an isolated magnetic null point. As such, we consider the limited range of fundamental resistive magnetohydrodynamic (MHD) and kinetic parameters of dynamic laboratory plasmas that are necessary to induce the torsional spine reconnection (TSR) mode characterized by a driven rotational slippage of field lines – a feature that has yet to be achieved in operational laboratory magnetic reconnection experiments. Leveraging existing reconnection models, we show that within a ${\lesssim}1~\text{m}^{3}$ apparatus, TSR can be achieved in dense plasma regimes (${\sim}10^{24}~\text{m}^{-3}$) in magnetic fields of ${\sim}10^{-1}~\text{T}$. We find that MHD and kinetic parameters predict reconnection in thin ${\lesssim}20~\unicode[STIX]{x03BC}\text{m}$ current sheets on time scales of ${\lesssim}10~\text{ns}$. While these plasma regimes may not explicitly replicate the plasma parameters of observed astrophysical phenomena, studying the dynamics of the TSR mode within achievable set-ups signifies an important step in understanding the fundamentals of driven 3-D magnetic reconnection and the self-organization of current sheets. Explicit control of this reconnection mode may have implications for understanding particle acceleration in astrophysical environments, and may even have practical applications to fields such as spacecraft propulsion.

Test particle acceleration in resistive torsional fan magnetic reconnection using laboratory plasma parameters

“…Lundquist number S > 1, see § 3.2). Here, we investigate a well-studied plasma condition that is applied to satisfy such conditions in a unique configuration (Chesny et al 2017), including the feasibility for enabling reconnection, as shown by the computed plasma parameters and their resulting particle acceleration profiles. Of particular interest to the plasma physics community would be the exploration of plasma drifting into a 3-D null point region waiting for the plasma to envelope it and feasibly resulting in a moving reconnection site (Lukin & Linton 2011;Chesny et al 2021).…”

“…The initial study of Chesny et al (2017) described a feasible apparatus that achieved both of the previous conditions, but stopped short of demonstrating particle response to reconnection. Numerous authors (Dalla & Browning 2005Stanier, Browning & Dalla 2012;Hosseinpour, Mehdizade & Mohammadi 2014;Gascoyne 2015;Threlfall et al 2015;Pallister, Pontin & Wyper 2019) have employed a test particle approach to demonstrate relativistic particle acceleration in torsional reconnection under collisionless solar plasma conditions.…”

An Alfvenic reconnecting plasmoid thruster

“…Significant thrust is generated in the form of plasmoids (confined plasma objects in closed magnetic loops) when helicity is injected into a cylindrical vessel to induce magnetic reconnection. Existing space-proven plasma thrusters, including the ion thruster (Stuhlinger 1964;Choueiri 2009) and the Hall-effect thruster (Morozov et al 1972;Raitses, Smirnov & Fisch 2007), electrostatically accelerate ions to exhaust velocities v e of tens of kilometres per second to produce thrust. However, for space exploration to Mars and beyond, high-thrust electromagnetic propulsion with exhaust velocities of tens to hundreds of kilometres per second is needed.…”

“…Unlike existing plasma accelerators, the thrust is generated from the acceleration of bulk fluid due to continuous formation of reconnecting plasmoids in the magnetohydrodynamic (MHD) regime. Neither external pulsing nor rotating fields (Chesny et al 2017;Bathgate et al 2018) are required here for acceleration through reconnection.…”

“…Neither external pulsing nor rotating fields (Chesny et al. 2017; Bathgate et al. 2018) are required here for acceleration through reconnection.…”