Bulletin of the American Physical Society
65th Annual Meeting of the APS Division of Plasma Physics
Monday–Friday, October 30–November 3 2023; Denver, Colorado
Session TO04: Space Plasmas within the Heliosphere |
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Chair: Jason Shuster, University of New Hampshire; Jonathan Ng, University of Maryland Room: Governor's Square 11 |
Thursday, November 2, 2023 9:30AM - 9:42AM |
TO04.00001: Particle Heating and Acceleration in the Diamagnetic Cavities Katariina Nykyri, Jan Egedal, Yu-Lun Liou, Xinyu Yu, Xuanye Ma, Shiva Kavosi Magnetic reconnection is a universal process which results in changes of magnetic topology as well as conversion of magnetic energy to thermal and kinetic energy of the plasma particles. However, the heating and particle acceleration that occurs close to reconnection diffusion regions at the dayside magnetopause is localized to a small area and thus cannot explain the ~ two orders of magntitude specific entropy increase observed when transitioning from shocked solar wind into the Earth's magnetopshere. Recent spacecraft observations have revealed that in the vicinity of cusp-like geometries magnetic reconnection can lead to formation of large-scale magnetic bottle structures (diamagnetic cavities, DMCs) where significant fluxes of electrons and ions can be trapped and energized to hundreds of keV energies. Since cusp-like structures are universal, occurring at planetary magnetospheres and close to surface of magnetized stars we are motivated to study the formation of these structures in laboratory plasma device, Big Red Ball (BRB), at University of Wisconsin Madison. This presenation will discuss the formation of DMCs and particle acceleration using multi-spacecraft observations and discuss the experimental setup at BRB. We calculate the minimum B-surface and express several quantities on this surface as well as characterize MMS observations of magnetic reconneciton and DMCs in terms of dimensionless parameters which will aid in comparison with experiments in BRB. |
Thursday, November 2, 2023 9:42AM - 9:54AM |
TO04.00002: MMS statistical analysis of magnetic structures in turbulent magnetotail Rachel Wang, Hantao Ji, Kendra A Bergstedt, Carlton G Passley, Yuka Doke The Earth's magnetotail is a natural laboratory to study turbulent reconnection and their role in particle acceleration. We present a statistical study of over 1000 magnetic structures (MS) measured aboard the Magnetospheric Multiscale (MMS) spacecraft in the magnetotail, selected from regions of large magnetic turbulence and significant particle heating. The MS are detected with an automated algorithm based on previous research [1] using bipolar signatures in the magnetic field, then they are classified into plasmoids, pull current sheet, and push current sheets, typical MS during multiscale reconnection. Many of the MS exhibit magnetic energy dissipation which is dominated by perpendicular electron flow, indicating that they may be inside electron diffusion regions. Change in kinetic energy around MS is dominated by Fermi acceleration which is observed to be largest in plasmoids. There is also a weak correlation between betatron acceleration and perpendicular power law index change. These statistical results represent our continued effort to quantify the process of magnetic energy dissipation in MS and give us a glimpse into the physics of multi-scale turbulent reconnection. |
Thursday, November 2, 2023 9:54AM - 10:06AM |
TO04.00003: A Novel Method to Train Classification Models for Structure Detection in In-situ Spacecraft Data Kendra A Bergstedt, Hantao Ji We present a method for creating spacecraft-like data which can be used to train Machine Learning (ML) models to detect and classify structures in in-situ spacecraft data. First, we use the Grad-Shafranov (GS) equation to numerically solve for several magnetohydrostatic equilibria which are variations on a known analytic equilibrium. These equilibria are then used as the initial conditions for Particle-In-Cell (PIC) simulations in which the structures of interest are observed and labeled. We then take one-dimensional slices through the simulations to replicate what a spacecraft collecting data from the simulation would observe. This sliced data then can be used as training data for ML structure detection models. We demonstrate the method applied to the detection of small-scale plasmoids, which are important to understanding magnetotail reconnection dynamics. The simple 1D classifier we train is able to detect 77% of the plasmoid points in the dataset but also produces many false positives. Our further work on this problem is detailed, and additional uses of the method are discussed. |
Thursday, November 2, 2023 10:06AM - 10:18AM |
TO04.00004: Non-ideal electric field induced by turbulence in the reconnection diffusion region Keizo Fujimoto, Richard D Sydora Most of the plasma fluid equations have employed the electrical resistivity to generate the magnetic dissipation required for magnetic reconnection to occur in collisionless plasma. However, there has been no clear evidence that such the model is indeed appropriate in the reconnection diffusion region in terms of the kinetic physics. To address this issue, the present study has performed a large-scale 3D particle-in-cell simulation for the anti-parallel and no guide field configuration as well as analytical analysis. The simulation results show that the thin current layer formed around the reconnection x-line is unstable to the flow shear instabilities, leading to intense electromagnetic turbulence in the diffusion region. It is found that the non-ideal electric field in the diffusion region is consistent with the Ohm's law based on viscosity rather than resistivity (1, 2). The effective viscosity is caused by the turbulence that gives rise to effective momentum transport of the electrons across the diffusion region. The present result suggests a fundamental modification of the fluid equations using the resistivity in the Ohm's law. Our presentation will cover the simulation results and analytical analysis to demonstrate the dissipation mechanism in the turbulent current layer to drive magnetic reconnection. 1. K. Fujimoto, and R. D. Sydora (2021), Astrophys. J. Lett., 909, L15. 2. K. Fujimoto, and R. D. Sydora (2023), Phys. Plasmas, 30, 022106. |
Thursday, November 2, 2023 10:18AM - 10:30AM |
TO04.00005: Kinetic Structure of Phase Space Density Gradients in and around the Electron Diffusion Region of Magnetopause Reconnection Jason Shuster, Harsha Gurram, Naoki Bessho, Roy Torbert, Matthew Argall, Kevin Genestreti, Charles Farrugia, Daniel Gershman, John Dorelli, Li-Jen Chen, Jonathan Ng, Julia Stawarz, Dominic Payne, Arya S Afshari, Paul Cassak, Steven Schwartz, Richard Denton, Haoming Liang, Hiroshi Hasegawa, Vadim Uritsky, Yi-Hsin Liu, James L Burch, Jaye Verniero, Jason Beedle, Steven Heuer, Tyler Metivier We present Magnetospheric Multiscale (MMS) four-spacecraft observations of the spatial gradient term in the electron Vlasov equation measured within the electron diffusion region (EDR) of magnetic reconnection occurring at Earth's magnetopause. We compare the MMS observations to particle-in-cell (PIC) simulations of asymmetric reconnection suitable for modeling dayside reconnection. A highly-structured, smile-shaped gradient distribution in ∇fe is discovered that corresponds to demagnetized electron crescent distributions specific to the central EDR. The intricate velocity-space features of the electron gradient distributions found in both the MMS data and the PIC simulations are useful for (1) distinguishing reconnection crescent signatures from non-reconnection diamagnetic crescent distributions that develop more generally at magnetized electron-scale boundary layers, (2) precisely determining the location of the MMS tetrahedron in relation to EDR sub-structures that are otherwise difficult to identify, and (3) understanding how spatial variations in the electron ensemble self-consistently support the reconnection electric field via net contributions to the bulk electron pressure divergence ∇⋅Pe. These results are relevant to recent studies of kinetic entropy and overarching questions in plasma physics research regarding how processes like Landau damping and magnetic reconnection appear to effect irreversible, dissipative phenomena even in the collisionless regime. |
Thursday, November 2, 2023 10:30AM - 10:42AM |
TO04.00006: Frequency-resolved local measurements of phase-space energization applied to MMS observations Emily R Lichko, James Juno, Sarah Conley, Gregory G Howes, Mel Abler, Kristopher G Klein In order to disentangle the competing kinetic-scale energy dissipation processes that are intrinsic to space and astrophysical plasmas it is critical to be able to diagnose the energy transfer that is occurring locally in both time and space. A relatively recent technique to resolve the local rate of energy transfer between the fields and particles is the field-particle correlation (Klein & Howes APJL 2016), which has resolved local energy transfer at a single point in space for a large variety of systems and physical processes. This work details an updated version of the field-particle correlation that includes for the first time a breakdown of the energy transfer in frequency space, as well as time and velocity space. In addition to the increase in available information, this new method more cleanly separates magnitude and phase information of the signal, resulting in an improvement of the temporal resolution. This new method is applied to Gkeyll simulations of electron Landau damping as a proof of concept, as well as Magnetospheric MultiScale (MMS) observations of solar wind turbulence. |
Thursday, November 2, 2023 10:42AM - 10:54AM |
TO04.00007: Inertial-Range Energy Transfer Free from Restrictive Assumptions in Turbulent Space Plasmas Yan Yang, Bin Jiang, Francesco Pecora, Yanwen Wang, Cheng Li, Minping Wan, Sergio Servidio, William H Matthaeus In the classical energy cascade scenario, energy is transferred from large to small scales at a constant rate, until it dissipates at the smallest scales. Laws governing the behavior of third-order structure functions in the inertial range, often called third-order laws, are among the few rigorous results about cross-scale energy transfer. Limited by available spacecraft data, energy transfer is most frequently oversimplified under the assumptions of isotropy, incompressibility, homogeneity, etc. This is not altogether convincing especially for the solar wind and magnetosheath turbulence, which is typically anisotropic and inhomogeneous. As the community is presently progressing towards multi-spacecraft constellations, e.g., MMS and HelioSwarm, we revisited several crucial issues pertinent to the inertial-range energy transfer, in particular, the 3D directional dependence (or anisotropy) of energy transfer arising from large-scale magnetic field. To properly account for the full 3D dependence, we applied and further developed direction-averaging and 3D lag-space derivative methods, using both MHD simulations and in situ observations. Both of these methods refine the estimation of energy transfer rate. |
Thursday, November 2, 2023 10:54AM - 11:06AM |
TO04.00008: Turbulence and Associated Particle Acceleration and Transport in 3D Magnetic Reconnection Xiaocan Li, Fan Guo, Yan Yang, Hui Li
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Thursday, November 2, 2023 11:06AM - 11:18AM |
TO04.00009: Developing Predictive Models of Turbulent Heating in Space and Astrophysical Plasmas Gregory G Howes Turbulence plays a key role in many space and astrophysical plasmas, mediating the transport of the energy of large-scale electromagnetic fields and plasma flows down to smaller scales, where that energy is dissipated, ultimately being deposited as heat of the plasma species or acceleration of a small population of particles. The multi-scale nature of space plasmas means that this plasma heating can feedback to influence the evolution of the system at mesoscopic and macroscopic scales. A major goal of the heliophysics and astrophysics communities is to develop predictive models of the plasma heating in terms of the plasma and turbulence parameters. Here, we will identify the critical dimensionless parameters that influence the turbulent dynamics and resulting plasma heating. Determining how the proposed mechanisms of turbulent dissipation depend on these parameters, and devising means of validating those predictions using kinetic numerical simulations and spacecraft observations, is critical step in developing a predictive capability. I will present a preliminary calculation of these dependencies and outline specific avenues, in particular using the field-particle correlation technique, to validate those findings and construct improved turbulent heating models for use in large-scale modeling. |
Thursday, November 2, 2023 11:18AM - 11:30AM |
TO04.00010: 2D Kinetic Simulations of Whistler Wave Generation by Nonlinear Scattering of Lower-hybrid Waves in Turbulent Plasmas. * Rualdo Soto-Chavez, Chris E Crabtree, Guru Ganguli, Alex Fletcher Turbulent plasmas in space, laboratory experiments, and astrophysical domains can be described by weak turbulence theory which can be characterized as a broad spectrum of incoherent interacting waves. We investigate a fundamental nonlinear kinetic mechanism of weak turbulence that can explain the generation of whistler waves in homogeneous plasmas by nonlinear scattering of short wavelength electrostatic lower-hybrid (LH) waves. Two particle-in-cell (PIC) simulations with different mass ratios in two dimensions (2D) were performed to study the phenomenon of nonlinear scattering. We use a ring ion velocity distribution to excite broadband LH waves, which are converted to whistler waves and evolve in time, frequency, and wavenumber space. The simulations show the formation of quasi-modes, which are low frequency density perturbations driven by the ponderomotive force due to the beating of LH and whistler waves. These low frequency oscillations are damped due to resonant phase matching with thermal plasma particles. By comparing the phase and thermal speeds, we confirm the nonlinear scattering mechanism and the role of nonlinear scattering in the 2D evolution of the ring ion instability. Although the nonlinear scattering is theoretically slower in 2D than in 3D due to the absence of the vector nonlinearity, these simulations show that quasi-modes are an important diagnostic tool for PIC simulations that has not been utilized in the past. The fundamental nonlinear scattering mechanism described here plays an important role in the generation of whistler waves in active experiments such as the upcoming Space Measurement of a Rocket Release Turbulence (SMART) experiment. |
Thursday, November 2, 2023 11:30AM - 11:42AM |
TO04.00011: On the Estimation of Power Spectral Densities of Discontiguous Solar Wind Turbulence Signals Mason Dorseth, Jean C Perez, Sofiane Bourouaine, Juan Carlos Palacios Caicedo, Nour Raouafi Spectral and correlation analyses are essential tools to investigate the turbulent properties of the solar wind from in-situ spacecraft observations. Most of these statistical techniques are based on estimators of autocorrelation functions (ACF) and power spectral densities (PSD). The PSD is often estimated as the squared amplitude of the fast Fourier transform (FFT), which normally requires uniformly-spaced, contiguous data. However, spacecraft data often have missing points that need to be filled in before applying the FFT, commonly with linear interpolation. Data gaps become a bigger problem when conditioning is applied to the signal and many gaps are introduced to cover sections of the signal with undesirable properties. The PSD is also related to the ACF via the Wiener-Khinchin theorem. The advantage of the ACF is that is it possible to obtain estimators that are resilient to data gaps without the need for interpolation. In this work, we artificially introduce gaps to synthetic signals obtained from numerical simulations of steadily-driven, homogeneous Magnetohydrodynamic (MHD) turbulence and to high resolution Wind magnetic field signals to investigate the consistency (convergence to its true ensemble-averaged counterpart) of a new PSD estimator for discontiguous signals and its sensitivity to the total gap percentages (TGP). This conditioned estimator for the PSD is then applied to conditioned Wind data to study spectral and correlation properties of the slow solar wind, which allows us to use a larger statistical sample than conventional FFT methods. |
Thursday, November 2, 2023 11:42AM - 11:54AM |
TO04.00012: Scale-dependent dynamic alignment and inertial-range spectral index in solar wind turbulence Jean C Perez, Sofiane Bourouaine, Juan Carlos Palacios, Izabella Maxfield The power spectra of velocity and magnetic fluctuations in the solar wind has long been associated with an incompressible Magnetohydrodynamics (MHD) turbulent cascade mediated by Alfv'en-like fluctuations. A major development in MHD turbulence theory was Boldyrev's suggestion that as energy cascades from large to small scales in the inertial range, velocity and magnetic fluctuations develop a scale-dependent dynamic alignment (SDDA) that leads to a reduction of the nonlinear interactions and a three-dimensional anisotropy. Most phenomenological models of strong MHD turbulence have in common Goldreich and Sridhar's assumption of critical balance, i.e., that the time scale associated with linear wave propagation is comparable with the nonlinear cascade time. Broadly speaking, these models can be grouped into those that include SDDA in the critical balance condition and those that do not, resulting in different predictions for the scaling properties of turbulence spectra, SDDA and turbulence anisotropy. Although several numerical simulations to date have shown strong evidence for the existence of a SDDA, consistent with theoretical predictions for the energy spectrum, direct observational evidence of SDDA in the solar wind inertial range has been largely inconclusive. In this talk I present a brief overview of Boldyrev's SDDA phenomenology, its verification in numerical simulations as well as previous attempts to detect SDDA in solar wind observations. I will also present new results from a large statistical analysis of WIND measurements that show observational evidence of a power law scaling of the alignment angle between velocity and magnetic fluctuations, consistent with the observed scaling of the energy spectrum and Boldyrev's SDDA phenomenology. |
Thursday, November 2, 2023 11:54AM - 12:06PM Withdrawn |
TO04.00013: Spatially Resolved Spectral Measurements of EIH Waves Generated by Plasma Shear Flow Layer Landry Horimbere, Bill E Amatucci, Erik M Tejero, Carl L Enloe Waves and instabilities generated by flows in plasmas due to the presence of mutually perpendicular electric and magnetic fields are of general relevance to the study of multiscale plasma dynamics and space physics. In particular, the waves generated by the shear in such flow profiles can have both stabilizing and destabilizing effects on the plasma depending on the shear's magnitude and scale length and may be the trigger of energy cascades. Over the years, laboratory experiments have been performed to simulate the broadband emissions from dipolarization fronts (highly compressed, Earth-ward propagating plasma sheets resulting from reconnection events) that energize the near-earth plasma environment, resulting in magnetospheric substorms. In this experiment, spatially scanned floating potential probes are used to conduct temporal crosscorrelation measurements of fluctuations generated by the shear at the boundary of a cylindrical flow layer in a magnetized plasma column. This 3D data set is analyzed using discrete Fourier transforms to isolate the 2D spatial structure of each mode and to reconstruct the azimuthal dispersion relation of the excited waves. Since the shear layer length scale is subLarmor radius and the minimum observed mode wavelength is greater than the plasma skin depth, these results are compared to the non-local electrostatic theory for Electron-Ion Hybrid (EIH) waves. It is shown that, in accordance with theory, the modes excited are broadly distributed around m=3 and that the waves propagate in the direction of the cross-field flow. |
Thursday, November 2, 2023 12:06PM - 12:18PM |
TO04.00014: The Effects of Shear Flow on Collisionless Magnetic Reconnection in the Heliosphere Colby C Haggerty, Michael A Shay, Carlos Giai, Paul A Cassak, Tai Phan Magnetic reconnection is an effective collisionless dissipation mechanism at current sheets, one which has been argued to be important for accelerating particles and heating plasma. However, recent observations of the current sheets made by Parker Solar Probe close to the sun do not appear to be undergoing reconnection. This suppression is correlated with the presence of a shear flow, and persists, unexpectedly for sub-Alfvénic speeds. Using kinetic particle-in-cell simulations of magnetic reconnection, we investigate this regime with a range of initial shear flows. We show that the reconnection outflow velocity is reduced by shear-dependent heating which occurs when the inflowing ions are pitch angle scattered in the exhaust. We show that while the outflow velocity and the reconnection rate are reduced by an increased shear flow, the total amount of heating generated is increased, as the reconnection process dissipates the shear flow energy. For even modest shear flows (Vshear ~ VA/2), more shear flow heating is dissipated than magnetic energy. These results have important implications for magnetic reconnection’s efficiency in energy dissipation and non-thermal particle acceleration in systems where shear flows would likely be present, such as the turbulent, weakly collisional solar wind. |
Thursday, November 2, 2023 12:18PM - 12:30PM |
TO04.00015: “Magneto-Kinetic” Reconnection Beyond Fluid Descriptions* Valeria Ricci, Bruno Coppi, Bamandas Basu As shown by previous contributions [1, 2], magnetic reconnection can be driven by the kinetic energy of particle populations in well confined plasmas. Therefore, processes are investigated where magnetic reconnection in collisionless regimes [3] is sustained by non-thermal distributions in phase space of the main components of a plasma column and, in particular, of the electron population. In this context the multifluid descriptions, that have been mostly relied upon [4] in order to find new directions for this area of investigations, are inadequate and the full kinetic kind of approach undertaken at first in Ref. [3] is needed. The simplest important case is that of unperturbed electron distributions with anisotropic temperature for which mode-particle resonances have a significant role in the evolution of the perturbed state. Relevant particle and thermal transport processes are considered in this context. *Sponsored in part by the Kavli Foundation (MIT) and by CNR of Italy. |
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