Magnetic flux ropes are ubiquitous magnetic structures found in plasmas ranging from astrophysical to laboratory. We employ a newly-developed parallel-kinetic-perpendicular-moment (PKPM) model to simulate the 3D interaction and evolution of two line-tied flux ropes at realistic laboratory plasma parameters, while retaining essential parallel kinetic physics in the system. We find that ropes undergo a current-dependent transition from a diamagnetic to paramagnetic regime, which we quantify with a simple analytic model. Although the macroscopic structural evolution qualitatively differs significantly between these regimes, analyzing the reconnection in proper field-aligned coordinates reveals that the underlying kinetic dynamics remain similar. Using the squashing factor and quasi-potential as diagnostics of 3D magnetic reconnection, we identify the formation of a quasi-separatrix layer and show that these quantities provide consistent metrics for reconnection rate and structure.
Quasi-separatrix layers and three-dimensional reconnection diagnostics for line-tied tearing modes
在没有闭合场线或磁零点存在的等离子体的三维磁位形中，根据最严格的重联定义，不可能发生磁重联。一个具有线系边界条件的超长箍缩，其中所有的磁场线都从系统的一端开始，并延伸到另一端，就是这样一个系统的一个例子。然而，对于这种类型的长系统，电阻磁流体力学（MHD）的物理行为基本上涉及重联。这已经通过比较几何宽度和撕裂宽度[1，2]进行了解释。准分界线层[3，4]的概念是为这样的系统开发的。本文研究了一个具有不稳定撕裂模的线束缚系统模型。我们分析了这个系统的两个磁场线诊断，挤压因子[3-5]和静电电势差用于运动学重联研究[6，7]。我们讨论了这两个诊断的物理和几何意义，并比较他们的情况下，辨别撕裂样行为的线绑模式。[1]G. L. Delzanno和J.M.等离子体物理，15（3）：032904，2008. [2]Y.-- M. Huang和E. G.茨韦贝尔等离子体物理，16（4）：042102，2009。[3]E. R.牧师和P·德穆兰杰·吉奥菲斯。结果：100（A12）：23443-23463，1995. [4]P. Démoulin，JC Henoux，E. R. Priest和C. H.曼德里尼太空人。太空人，308：643-655，1996年4月。[5]V. S. Titov和G.霍尼格Advances in Space Research，29（7）：1087-1092，2002…
The relaxation of field-line tension during magnetic reconnection gives rise to a universal Fermi acceleration process involving the curvature drift of particles. However, the efficiency of this mechanism is limited by the trapping of energetic particles within flux-ropes. Using 3D fully kinetic simulations, we demonstrate that the flux-rope kink instability leads to strong field-line chaos in weak-guide-field regimes where the Fermi mechanism is most efficient, thus allowing particles to transport out of flux-ropes and undergo further acceleration. As a consequence, both ions and electrons de…
We present a 3D MHD simulation of two merging flux ropes exhibiting self-generated and self-sustaining turbulent reconnection (SGTR) that is fully 3D and fast. The exploration of SGTR is crucial for understanding the relationship between MHD turbulence and magnetic reconnection in astrophysical contexts including the solar corona. We investigate the pathway towards SGTR and apply novel tools to analyse the structure and topology of the reconnection layer. The simulation proceeds from 2.5D Sweet-Parker reconnection to 2.5D nonlinear tearing, followed by a dynamic transition to a final SGTR phas…
Magnetic Reconnection Governs the Entire Lifecycle of Solar Eruptive Magnetic Flux Rope
State Key Laboratory of Solar Activity and Space Weather, School of Aerospace, Harbin Institute of Technology, Shenzhen（哈尔滨工业大学深圳航天学院）；School of Opto-electronic Engineering, Zaozhuang University（枣庄学院光电工程学院）
Magnrtic flux ropes (MFRs) play a crucial role during magnetic reconnection. They are believed to be primarily generated by tearing mode instabilities in the electron diffusion region (EDR). However, they have never been observed inside the EDR. Here, we present the first observation of an MFR inside an EDR. The bifurcated non-force-free MFR, with a width of 27.5de in the L direction and 4.8de in the N direction, was moving away from the X-line. Inside the MFR, strong energy dissipation was detected. The MFR can modulate the electric field in the EDR. We reconstructed magnetic topology of the …
We use 3D fully kinetic particle-in-cell simulations to study the occurrence of magnetic reconnection in a simulation of decaying turbulence created by anisotropic counter-propagating low-frequency Alfvén waves consistent with critical-balance theory. We observe the formation of small-scale current-density structures such as current filaments and current sheets as well as the formation of magnetic flux ropes as part of the turbulent cascade. The large magnetic structures present in the simulation domain retain the initial anisotropy while the small-scale structures produced by the turbulent ca…
Within the resistive magnetohydrodynamic model, high-Lundquist number reconnection layers are unstable to the plasmoid instability, leading to a turbulent evolution where the reconnection rate can be independent of the underlying resistivity. However, the physical relevance of these results remains questionable for many applications. First, the reconnection electric field is often well above the runaway limit, implying that collisional resistivity is invalid. Furthermore, both theory and simulations suggest that plasmoid formation may rapidly induce a transition to kinetic scales, due to the f…
The Maximum Particle Energy Gain During Magnetic Reconnection
University of Maryland, College Park（马里兰大学帕克分校）；IREAP, University of Maryland, College Park（马里兰大学帕克分校综合相对论天体物理研究所）；The Johns Hopkins University Applied Physics Laboratory（约翰斯·霍普金斯大学应用物理实验室）；Institute for Physical Science and Technology, University of Maryland, College Park（马里兰大学帕克分校物理科学与技术研究所）；Joint Space Science Institute, University of Maryland, College Park（马里兰大学帕克分校联合空间科学研究所）
One "strong" magnetic cloud (MC) with the magnetic field magnitude reaching $\sim$ 40 nT at 1 au during 2012 June 16-17 is examined in association with a pre-existing magnetic flux rope (MFR) identified on the Sun. The MC is characterized by a quasi-three dimensional (3D) flux rope model based on in situ measurements from the Wind spacecraft. The magnetic flux contents and other parameters are quantified. In addition, a correlative study with the corresponding measurements of the same structure crossed by the Venus Express (VEX) spacecraft at a heliocentric distance 0.7 au and with an angular …
We show that magnetic reconnection in a magnetically-dominated fast-cooling plasma can naturally produce bright flares accompanied by rotations in the synchrotron polarization vector. With particle-in-cell simulations of reconnection, we find that flares are powered by efficient particle acceleration at the interface of merging magnetic flux ropes, or "plasmoids". The accelerated particles stream through the post-merger plasmoid towards the observer, thus progressively illuminating regions with varying plane-of-sky field direction, and so leading to a rotation in the observed polarization vect…
We review and discuss insights on ideal magnetohydrodynamic (MHD) instabilities that can play a role in destabilizing solar coronal flux rope structures. For single flux ropes, failed or actual eruptions may result from internal or external kink evolutions, or from torus unstable configurations. We highlight recent findings from 3D magnetic field reconstructions and simulations where kink and torus instabilities play a prominent role. For interacting current systems, we critically discuss different routes to coronal dynamics and global eruptions, due to current channel coalescence or to tilt-k…
In strongly magnetized astrophysical plasma systems, magnetic reconnection is believed to be a primary process during which explosive energy release and particle acceleration occur, leading to significant high-energy emission. Past years have witnessed active development of kinetic modeling of relativistic magnetic reconnection, supporting this magnetically dominated scenario. A much less explored issue is the consequence of 3D dynamics, where turbulent structures are naturally generated as various types of instabilities develop. This paper presents a series of 3D, fully-kinetic simulations of…
We report small-scale magnetic flux ropes via the Parker Solar Probe in situ measurements during the first six encounters and present additional analyses to supplement our prior work in Chen et al. 2021. These flux ropes are detected by the Grad-Shafranov-based algorithm with the duration and scale size ranging from 10 seconds to $\lesssim$1 hour and from a few hundred kilometers to 10$^{-3}$ au, respectively. They include both static structures and those with significant field-aligned plasma flows. Most structures tend to possess large cross helicity, while the residual energy distributes in …
