Bulletin of the American Physical Society
63rd Annual Meeting of the APS Division of Plasma Physics
Volume 66, Number 13
Monday–Friday, November 8–12, 2021; Pittsburgh, PA
Session GO09: Fundamental: Magnetic ReconnectionOn Demand

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Chair: Jack Hare, MIT PSFC Room: Room 406 
Tuesday, November 9, 2021 9:30AM  9:42AM 
GO09.00001: Thin current sheet evolution in 3D via magnetic reconnection and other processes Gregory R Werner, Dmitri A Uzdensky We perform a large ensemble of 3D particleincell (PIC) simulations of thin current sheets (CSs) in relativisticallyhot electronpositron plasma, of interest for theoretical simplicity, computational tractability, and astrophysical relevance. Sandwiched in stronglysheared magnetic fields, thin CSs facilitate fast conversion of magnetic energy into plasma energy. Previous 2D simulations of CSs show a fractal hierarchy of secondary CSs and plasmoids that explains fast energy conversion via classic 2D magnetic reconnectioni.e., nonlinear interaction of tearing and plasmoid coalescence instabilities. However, our 3D PIC simulations, covering a wide range of CSs, shed new light on the interplay of multiple linear and nonlinear instabilities, including fast magnetic energy release via the nonlinear relativistic driftkink instability (RDKI). CS conditions can affect the relative prominence of instabilities (e.g., guide magnetic field and high magnetization favor 2D reconnection over RDKI), but some initiallysimilar CSs take chaoticallydiverging paths, triggering different mechanisms with varying rates of energy release. Remarkably, the accelerated particle spectrum depends robustly on ambient plasma conditions, despite various underlying processes. 
Tuesday, November 9, 2021 9:42AM  9:54AM 
GO09.00002: Study of electron exhaust jet and currentdriven instabilities in kinetic magnetic reconnection using laserpowered capacitor coils Shu Zhang, Abraham Chien, Hantao Ji, Lan Gao, Kenneth Hill, Eric Blackman, Russell K Follett, Dustin H Froula, Joseph Katz, William S Daughton, Chikang Li, Andrew Birkel, Richard Petrasso, John D Moody, Hui Chen Magnetic reconnection is a ubiquitous phenomenon in space and astrophysical plasmas that rapidly releases magnetic energy. Plasma kinetic instabilities often play an important role in the required dissipation. We conducted kilojoule laserpowered kinetic reconnection experiments with capacitorcoils [13] to study electron outflow jets using collective Thomson scattering. Thomson scattering shows the existence of electronacoustic waves (EAW) with phase velocity near the electron thermal speed, which suggests a nonMaxwellian distribution overcoming Landau damping. We also observed bursty and asymmetric ionacoustic waves (IAW), confirming the existence of the electron jet and the currentdriven ionacoustic instabilities (IAI). The amplitude of both EAW and IAW exhibits correlated bursts with a frequency that matches the lowerhybrid frequency. Specially designed local ParticleInCell simulation shows that the currentdriven IAI can form a double layer and induce electron twostream instability generating EAW that are consistent with the measurements. Our experiments and simulations demonstrate that the electron outflow jet is unstable and can dissipate energy through electronion coupling. The combination of collective Thomson scattering and the laserpowered experiments opened up a new avenue to study kinetic physics in reconnection. 
Tuesday, November 9, 2021 9:54AM  10:06AM 
GO09.00003: Experimentally Measured Stability Properties of Arched, LineTied Magnetic Flux Ropes Andrew D Alt, Hantao Ji, Jonathan M JaraAlmonte, Jongsoo Yoo, Sayak Bose, Aaron Goodman, Masaaki Yamada Coronal mass ejections occur when longlived magnetic flux ropes (MFR) anchored to the solar surface destabilize and erupt away from the Sun. One potential cause for these eruptions is an ideal MHD instability such as the kink or torus instability. These instabilities have long been studied in axisymmetric fusion devices where the instability criteria are given in terms of the edge safety factor and confining magnetic field decay index, respectively. Laboratory experiments have been performed in the Magnetic Reconnection Experiment (MRX), where the stability properties of arched, linetied MFRs were controlled via the external fields. Previous experiments revealed a class of MFRs that were torusunstable but kinkstable, which failed to erupt [Alt et al. (2021) ApJ 908 41]. These "failedtori" went through a process similar to Taylor relaxation where the toroidal current was redistributed before their eruption ultimately failed. In more recent experiments, we have investigated this behavior through additional diagnostics that measure the current distribution at the footpoints. These measurements will confirm whether the current is redistributing along the entire rope or only at the apex, which will give insight into the phenomena responsible for the failed torus events. 
Tuesday, November 9, 2021 10:06AM  10:18AM 
GO09.00004: Experimental study on ion polarization drift dynamics during fast guide field magnetic reconnection in MRX Sayak Bose, William R Fox, Hantao Ji, Jongsoo Yoo, Aaron Goodman, Andrew D Alt, Jonathan M JaraAlmonte, Masaaki Yamada We report the detection of ion polarization drift and its effects during fast guide field magnetic reconnection in the twofluid regime. The normalized guide field, b_{gn}=b_{g}/b_{up }is held at 0.7, where b_{g} is the guide field at the Xpoint and b_{up} is the upstream reconnecting field. The projection of the measured ion flow along the perpendicular electric field E_{⊥} is highly compressive and consistent with the measured quadrupolar density variation. These results are consistent with theoretical and numerical predictions [Kleva et al. Phys. Plasmas. 1995]. E_{⊥} is observed to transfer a significant amount of magnetic energy to ions in regions with enhanced plasma density, suggesting that the ion polarization drift energizes ions by compression. A limited set of ion temperature measurements show a higher ion temperature near a location where E_{⊥} is observed to transfer a significant amount of energy to ions. A study of the energy conversion process shows that the parallel electric field energizes electrons in and around the electron diffusion region (EDR). Away from the EDR, the electrons are found to work against E_{⊥}, losing energy to ions. 
Tuesday, November 9, 2021 10:18AM  10:30AM 
GO09.00005: Laboratory study of electron heating associated with lower hybrid drift waves during guide field reconnection Jongsoo Yoo, Yibo Hu, Hantao Ji, Sayak Bose, Aaron Goodman, Jonathan M JaraAlmonte, JeongYoung Ji, Andrew D Alt, Masaaki Yamada, Kendra A Bergstedt, William R Fox Lower hybrid drift waves have been observed near the electron diffusion region of the Magnetic Reconnection Experiment (MRX). In particular, the quasielectrostatic lower hybrid drift wave (ESLHDW) exists in the electron diffusion region when there is a significant guide field. Initial measurements in MRX show that there is a positive correlation between the electron temperature and density fluctuations associated with the ESLHDW. This indicates that the ESLHDW may affect electron and reconnection dynamics during reconnection with a guide field. To quantify the effects of the ESLHDW on electron heating and anomalous terms in the Ohm’s law in MRX plasmas, we have developed an insitu diagnostic that can simultaneously measure fluctuations in both the reconnection electric field and plasma density with high precision [1]. Moreover, we have also developed a local, linear model for LHDWs for plasmas with arbitrary collisionality. Results from the model show that collisional effects decrease the growth rate of both types of LHDWs but the effect is limited(<20 %) [2]. With measured amplitudes and quasilinear calculations, we will estimate the waveassociated electron heating and anomalous terms. 
Tuesday, November 9, 2021 10:30AM  10:42AM 
GO09.00006: Analytical model of energy conversion in the twofluid reconnection layer Masaaki Yamada, Jongsoo Yoo In a prototypical twodimensional antiparallel reconnection geometry, a simple quantitative analysis of the energy inventory is developed for the ion diffusion layer. As electrons and ions move into the reconnection layer with different paths, the magnetized electrons penetrate deep into the reconnection layer generating a strong potential well in the diffusion region. The shape of the well expands towards the exit of exhaust region (1). Magnetic field energy is converted to electric field potential energy through due to the motion of magnetized electrons in the background of nonmagnetized ions. While the magnetic energy is transferred to the electrons in electrondiffusion layer, ions gain their energy through electrostatic acceleration across the potential well. We have developed an analytical model based on our generalized Harris equilibrium model (2). This analytical model concludes that ½ of magnetic energy is efficiently converted to ions in a prototypical twofluid reconnection layer. Our analytical results are compared with the recent MRX data (1). 
Tuesday, November 9, 2021 10:42AM  10:54AM 
GO09.00007: Entropy production and transport during magnetic reconnection Jonathan M JaraAlmonte, Hantao Ji In collisional systems, plasma entropy is produced during reconnection via heating and mixing. Recently, we have identified a thermodynamic phase transition in fully kinetic PIC simulations of magnetic reconnection, corresponding to the transition from resistive to Halllike reconnection regimes [JaraAlmonte and Ji, PRL, 2021]. Here, we extend this analysis to examine the entropy production and transport during the onset of kinetic reconnection. It is shown that viscouslike heating is the dominant source of entropy production. In fully collisionless systems, entropy is conserved and only entropy transport is present. In PIC simulations of lowβ, forcefree reconnection, it will be shown that the local distribution function is welldescribed by anisotropic κdistributions, and that the local κindex can be determined from the local entropy density. Fluid modeling of nonequilibrium entropy transport thus offers one possibility for reduced modeling of particle acceleration processes. Initial results comparing fluid simulations including nonequilibrium entropy transport with fully kinetic PIC simulations will be presented and discussed. 
Tuesday, November 9, 2021 10:54AM  11:06AM 
GO09.00008: Statistical Properties of Multiscale Magnetic Reconnection and the FLARE Project Hantao Ji, Jongsoo Yoo, Jonathan M JaraAlmonte, Kendra A Bergstedt, Stephen P Majeski, Sayak Bose, Andrew D Alt, Aaron Goodman, William R Fox, Yang Ren, Masaaki Yamada, Amitava Bhattacharjee, William S Daughton, Adam J Stanier, Ari Le Magnetic reconnection is widely recognized as a fundamental plasma process underlying many explosive and energetic phenomena observed throughout the Universe, including laboratory fusion experiments. These plasmas are characterized by their high Lundquist numbers, $S$, and large normalized system sizes, $\lambda$. Different crossscale coupling mechanisms occur during reconnection and can be organized in phase diagrams [Ji & Daughton PoP 2011; Ji et al. submitted 2021]. Statistical properties of these phases are of crucial importance in determining the energetic consequences of magnetic reconnection, such as the nonthermal acceleration of electrons. This presentation summarizes recent progress in quantifying statistical properties by analyzing magnetotail reconnection data [Bergstedt et al. GRL 2020], and theoretically predicting the effect of a guide field on plasmoid size distributions [Majeski et al. submitted 2021]. The upcoming multiscale experiment FLARE (Facility for LAboratory Reconnection Experiments) will be a DoE collaborative user facility and will provide the first experimental access to these multiscale phases. The status and plan for FLARE will be reported. 
Tuesday, November 9, 2021 11:06AM  11:18AM 
GO09.00009: Exploratory Simulations of Plasmoid Dynamics in the FLARE experiment William S Daughton, Adam J Stanier, Jonathan M JaraAlmonte, Hantao Ji In highLundquist number regimes, reconnection layers are unstable to the plasmoid instability leading to a hierarchy of magnetic islands and new current sheets that can approach kinetic scales. While this scenario offers a natural mechanism for bridging scales, it has not yet been validated experimentally, which is one major goal for the new FLARE experiment. Here we present exploratory simulations of FLARE to understand the current sheet formation and resulting onset of plasmoids in both MHD and kinetic regimes. These fully kinetic simulations are performed with a new cylindrical version of the VPIC code including the vacuum vessel, flux cores, drive coils and with a MonteCarlo treatment of Coulomb collisions. These initial 2D and 3D simulations suggest that a rich dynamical evolution may be accessible. 
Tuesday, November 9, 2021 11:18AM  11:30AM 
GO09.00010: Matching experimental reconnection to multidimensional kinetic simulations Samuel Greess, Jan Egedal, Adam J Stanier, William S Daughton, Joseph R Olson, Ari Le, Alexander MilletAyala, Mike Clark, John P Wallace, Douglass A Endrizzi, Cary B Forest

Tuesday, November 9, 2021 11:30AM  11:42AM 
GO09.00011: Thermal Energy Density Driven Magnetic Reconnection Valeria Ricci, Bruno Coppi Magnetic reconnection is usually associated with conversion of magnetic energy into particle acceleration or thermal energy. However, a specific reconnection process driven by plasma pressure gradients was identified in Ref.[1] with a consistent theory of (nonideal) MHD m^{0}=1 modes in well confined plasmas. This process, based on an Ohm's law contribution to the electron balance equations, remains the basis for the explanation of the observed sawtooth oscillations of the central plasma pressure and for the inferred magnetic field structures due to fishbone oscillations associated with injected high energy particle populations. A novel process [2] expected to have a wide range of applications concerns magnetic reconnection sustained by a significant gradient of the longitudinal electron temperature and based on the electron thermal energy balance equation rather than on an Ohm's law. 
Tuesday, November 9, 2021 11:42AM  11:54AM 
GO09.00012: Identifying active magnetic reconnection in simulations and in situ observations of plasma turbulence using magnetic flux transport Tak Chu Li, YiHsin Liu, Yi Qi, Christopher T Russell For decades, magnetic reconnection has been suggested to play an important role in the dynamics and energetics of plasma turbulence by spacecraft observations, numerical simulations and theory. Reliable approaches to study reconnection in turbulence are essential to advance this frontier topic of plasma physics. A new technique based on magnetic flux transport (MFT) has been recently developed to identify reconnection activity in turbulent plasmas. Applications to gyrokinetic simulations of two and threedimensional (2D and 3D) plasma turbulence, and MMS observations of reconnection events in the magnetosphere have demonstrated the capability of MFT in identifying active reconnection in turbulence. In 2D, MFT identifies three active reconnection Xlines; two of them have developed bidirectional electron and ion outflow jets, observational signatures for reconnection, while the third Xline does not have bidirectional electron or ion outflow jets, beyond the category of electrononly reconnection recently discovered in the turbulent magnetosheath [1]. In 3D, plentiful reconnection Xlines are identified through MFT, and new properties of reconnection in 3D turbulence can be studied. In space, MMS observations have demonstrated evidence for MFT signatures of active reconnection under varying conditions throughout Earth's magnetosphere [2]. MFT is applicable to in situ observations by heliospheric spacecraft missions, including PSP and Solar Orbiter, and laboratory experiments. 
Tuesday, November 9, 2021 11:54AM  12:06PM 
GO09.00013: A model for nonthermal particle acceleration in magnetic reconnection Xiaocan Li, Fan Guo, YiHsin Liu, Patrick F Kilian The past decade has seen an outstanding development of nonthermal particle acceleration in magnetic reconnection, with clear signatures of powerlaw energy distributions as an expected outcome of first principle kinetic simulations. Here we propose a model for investigating nonthermal particle acceleration in reconnection in a systematic approach. We show that particle energy distributions are well determined by particle injection, acceleration, and escape processes. Using a series of ab initio kinetic simulations, we accurately evaluate the energydependent acceleration rate, energy diffusion, and escape rate. The resulting spectral characteristics, including the spectral index, lower and upper bound of the powerlaw distribution, agree well with the simulation results. 
Tuesday, November 9, 2021 12:06PM  12:18PM 
GO09.00014: The Scaling of Asymmetric Relativistic Magnetic Reconnection: Theory and Simulations Colby C Haggerty, Rostom Mbarek, Lorenzo Sironi, Michael A Shay, Damiano Caprioli Magnetic reconnection is often invoked to explain impulsive nonthermal particle acceleration in highly magnetized astrophysical systems. However, to date, the corresponding theory for relativistic reconnection has only been developed for symmetric inflow conditions, i.e., symmetric density, temperature and field strength, despite the ubiquity of asymmetric reconnection in space and laboratory plasmas. To address this, we derive basic scaling equations for relativistic magnetic reconnection with asymmetric inflow conditions and obtain a prediction for the relativistic outflow velocity. Kinetic ParticleinCell simulations are used to verify the scaling predictions for the characteristics of the outflow jet. Additionally, we show that the spectral index of the nonthermal particles accelerated by magnetic reconnection is constrained by the inflowing plasma with the lower magnetization, in agreement with the scaling predictions. These results have important implications for the role of magnetic reconnection in astrophysical systems and for the nonthermal spectra produced by magnetic reconnection. 
Tuesday, November 9, 2021 12:18PM  12:30PM 
GO09.00015: Efficient Nonthermal Ion and Electron Acceleration Enabled by the FluxRope Kink Instability in 3D Nonrelativistic Magnetic Reconnection Qile Zhang, Fan Guo, William S Daughton, Xiaocan Li, Hui Li The relaxation of fieldline 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 fluxropes. Using 3D fully kinetic simulations, we demonstrate that the fluxrope kink instability leads to fieldline chaos in weakguidefield regimes where the Fermi mechanism is most efficient, thus allowing particles to transport out of fluxropes and undergo further acceleration. As a consequence, both ions and electrons develop clear powerlaw energy spectra which contain a significant fraction of the released energy. The lowenergy bounds are determined by the injection physics, while the highenergy cutoffs are limited only by the system size. These results have strong relevance to observations of nonthermal particle acceleration in both the magnetotail and solar corona. 
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