Bulletin of the American Physical Society
64th Annual Meeting of the APS Division of Plasma Physics
Volume 67, Number 15
Monday–Friday, October 17–21, 2022; Spokane, Washington
Session BM09: Mini-Conference: Heating and Non-Thermal Particle Acceleration during Magnetic Reconnection in Laboratory, Heliophysical and Astrophysical Plasmas ILive Streamed
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Chair: Li-jen Chen, NASA Goddard Space Flight Center; Fan Guo, Los Alamos National Laboratory Room: 206 AB |
Monday, October 17, 2022 9:30AM - 9:55AM |
BM09.00001: Particle Heating and Acceleration during Magnetic Reconnection James F Drake How the magnetic energy released during reconnection is transferred to |
Monday, October 17, 2022 9:55AM - 10:15AM |
BM09.00002: Radio Diagnostics of Reconnection-Driven Particle Energization in Solar Flares: Recent Progress and Future Outlook Bin Chen Radio remote-sensing observations of solar flares serve as a powerful tool for tracing and quantifying energetic particles produced in or around the magnetic reconnection region. In this talk, after a brief introduction to the diagnostic methods enabled by the novel technique of broadband radio imaging spectroscopy, I will highlight recent results pertinent to reconnection in solar flares using examples from the Expanded Owens Valley Solar Array (EOVSA). I will then discuss how such studies can be advanced to the next level with the Frequency Agile Solar Radiotelescope (FASR) – a next-generation solar radio telescope concept being proposed as a mid-scale research facility. Realistic simulations and radiation modeling will be used to demonstrate the breakthrough science that FASR is expected to bring to the community. |
Monday, October 17, 2022 10:15AM - 10:35AM |
BM09.00003: Particle Acceleration in Solar Flare Reconnection Joel T Dahlin, Spiro K Antiochos, Jiong Qiu, C. Richard DeVore Solar flares are explosive space weather events that rapidly convert stored magnetic energy into bulk motion, plasma heating, and particle acceleration via magnetic reconnection. Recent theory and modeling investigations have revealed that plasmoids, coherent magnetic structures generated by reconnection, play a key role in driving nonthermal particles via a first-order Fermi process. The efficiency of this mechanism is highly sensitive to the strength of the reconnection guide field. While direct observation of reconnection in the corona is highly challenging, key insights can be derived from ‘flare ribbons’ that trace the footpoints of reconnected field lines and ‘flare loops’, filled with hot plasma, that reveal the morphology of the reconnected magnetic field lines. We present new high-resolution MHD simulations of three-dimensional reconnection in an eruptive flare and compare to recent data. We derive analogues of flare ribbons and show that they highly structured and exhibit many ‘whorl’ patterns that are linked to turbulent plasmoids in the reconnecting current sheet. Such flare ribbon fine structure reveals crucial information about the fundamental turbulent vs. laminar nature of the reconnection. We also show that the guide field weakens more than an order of magnitude over the course of the flare, and instantaneously varies over a similar range along the three-dimensional current sheet. We demonstrate how the guide field may be inferred from observations of sheared (tilted) flare loops. Interestingly, we find that the number of plasmoids in the flare reconnecting current sheet increases with weakening guide field, underscoring the important role of the guide field in particle acceleration. We discuss the implications for understanding particle acceleration via reconnection the solar corona and throughout the universe. |
Monday, October 17, 2022 10:35AM - 10:50AM |
BM09.00004: Interchange reconnection within coronal holes powers the solar wind Stuart D Bale, James F Drake, Michael McManus, Mihir Desai, Michael M Swisdak, Samuel T Badman, Christina Cohen, Nour Raouafi, Davin Larson, David J McComas, Justin C Kasper, Marco C Velli The fast solar wind that fills the heliosphere originates from regions of open magnetic field on the Sun called 'coronal holes', driven by the pressure drop between the solar surface and the interstellar medium. The magnetic field near the solar surface within coronal holes is structured on angular scales associated with the boundaries of meso-scale supergranulation convection cells, where descending flows create intense bundles of magnetic field. The energy density in these 'network' magnetic field bundles is a likely candidate as an energy source of the wind. However, the mechanism responsible for energizing the low altitude plasma to become the solar wind is unknown. An often invoked candidate mechanism is the heating associated with Alfven waves (McKenzie et al, 1993; Axford et al, 1997). Here we report measurements from the Parker Solar Probe (PSP) spacecraft near the perihelion from encounter 10 (E10) to show that solar wind streams are phase correlated with the magnetic field at the solar footpoint of the spacecraft. The in situ measurements reveal a highly bursty radial wind with corresponding bursts of energetic ions that form powerlaw distributions at high energy. Supporting particle-in-cell simulations of interchange reconnection reveal key features of the observations, including the energetic ion spectra in the observations. Important characteristics of interchange reconnection in the low corona are inferred from the PSP data: reconnection is collisionless and the rate of energy release is sufficient to heat the ambient plasma and drive an energized wind. In this reconnection scenario of solar wind energization open magnetic flux undergoes continuous reconnection and the wind is driven both by the resulting plasma pressure and the radial Alfvenic flow bursts. Such bursty reconnection is also the likely source of the large amplitude Alfvenic 'switchback' structures observed in the inner heliosphere. |
Monday, October 17, 2022 10:50AM - 11:05AM |
BM09.00005: Ion Acceleration During Macroscale Magnetic Reconnection Michael M Swisdak, Zhiyu Yin, James F Drake, Harry Arnold The recently developed computational model kglobal, which combines an MHD backbone with self-consistent guiding-center particles has previously demonstrated self-consistent simulations of electron acceleration during magnetic reconnection in a macroscale system that produced power-law energy spectra extending over multiple decades in energy. Here we report on an expansion of kglobal that demonstrates simultaneous ion and electron acceleration and power-law production. The ion power laws also extend over multiple decades of energy and exhibit spectral indices similar to the electrons. A strong guide field weakens the Fermi drive mechanism and suppresses nonthermal particle production. For a weak guide field, the total energy content of nonthermals dominates even though their respective number densities remain small. |
Monday, October 17, 2022 11:05AM - 11:20AM |
BM09.00006: Magnetic Energy Conversion in Magnetohydrodynamics: Curvature Relaxation and Perpendicular Expansion of Magnetic Fields Senbei Du, Hui Li, Xiangrong Fu, Zhaoming Gan, Shengtai Li The mechanisms and pathways of magnetic energy conversion are an important subject for many laboratory, space, and astrophysical systems. Here, we present a perspective on magnetic energy conversion in magnetohydrodynamics through magnetic field curvature relaxation (CR) and perpendicular expansion (PE) due to magnetic pressure gradients, and quantify their relative importance in two representative cases, namely 3D magnetic reconnection and 3D kink-driven instability in an astrophysical jet. We find that the CR and PE processes have different temporal and spatial evolutions in these systems. The relative importance of the two processes tends to reverse as the system enters the nonlinear stage from the instability growth stage. Overall, the two processes make comparable contributions to magnetic energy conversion, with the PE process somewhat stronger than the CR process. We further explore how these energy conversion terms can be related to particle energization in these systems. |
Monday, October 17, 2022 11:20AM - 11:45AM |
BM09.00007: Electron energization during Earth's magnetotail reconnection Mitsuo Oka Electrons are accelerated to very high, non-thermal energies during explosive energy-release phenomena in space plasma environments. In Earth's magnetotail, it has been established that magnetic reconnection plays an important role for releasing the magnetic energy, but it remains unclear if or how magnetic reconnection can further explain electron acceleration to non-thermal energies. Here we present an overview on heating and electron acceleration in Earth's magnetotail with a particular focus on energy partition between thermal and non-thermal components. We will also discuss some implications on electron acceleration in other plasma environments, open questions, and possible future directions. |
Monday, October 17, 2022 11:45AM - 12:00PM |
BM09.00008: Multi-species Ion Acceleration in 3D Magnetic Reconnection Qile Zhang, Fan Guo, William S Daughton, Xiaocan Li, Hui Li Magnetic reconnection can efficiently accelerate particles into nonthermal energy spectra, including not only electrons and protons but also multi-species heavier ions. Multi-species nonthermal ions contain key information of the underlying particle acceleration process, but are poorly understood. Here we use 3D large-scale hybrid reconnection simulations to capture the challenging multiscale multi-species ion acceleration process. Our simulations, for the first time, achieve efficient acceleration of all ion species into nonthermal power-law spectra. We find that the 3D reconnection layers consist of fragmented kinking flux ropes, growing in size over time, as part of the reconnection-driven turbulence. Different species are injected by Fermi reflection at the Alfvenic reconnection exhausts influenced by the different initial thermal speeds, which determines the low energy bound shoulders of spectra. Then they start a universal Fermi acceleration process at different times when they are magnetized by growing magnetic flux ropes and exhausts. This gives different species similar power-law indices (p~4.5) but different maximum energy per nucleon that follows (Q/M)α (α~0.6). These results agree reasonably with the range of heliospheric current sheets and magnetotail observations. |
Monday, October 17, 2022 12:00PM - 12:15PM |
BM09.00009: Particle Acceleration in Magnetic Reconnection with Ad hoc Pitch-angle Scattering Grant R Johnson, Patrick Kilian, Fan Guo, Xiaocan Li Particle acceleration during magnetic reconnection is a long-standing topic in space, solar and astrophysical plasmas. Recent 3D particle-in-cell simulations of magnetic reconnection show that particles can leave flux ropes due to 3D field-line chaos, allowing particles to access additional acceleration sites, gain more energy through Fermi acceleration, and develop a power-law energy distribution. This 3D effect does not exist in traditional 2D simulations, where particles are artificially confined to magnetic islands due to their restricted motions across field lines. Full 3D simulations, however, are prohibitively expensive for most studies. Here, we attempt to reproduce 3D results in 2D simulations by introducing ad hoc pitch-angle scattering to a small fraction of the particles. We show that scattered particles are able to transport out of 2D islands and achieve more efficient Fermi acceleration, leading to a significant increase of energetic particle flux. We also study how the scattering frequency influences the nonthermal particle spectra. This study helps achieve a complete picture of particle acceleration in magnetic reconnection. |
Monday, October 17, 2022 12:15PM - 12:30PM |
BM09.00010: Characterizing Velocity-Space Signatures of Electron Energization in Large-Guide-Field Collisionless Magnetic Reconnection Gregory G Howes, Andrew J McCubbin, Jason M TenBarge Magnetic reconnection plays an important role in the release of magnetic energy and consequent energization of particles in collisionless plasmas. Energy transfer in collisionless magnetic reconnection is inherently a two-step process: reversible, collisionless energization of particles by the electric field, followed by collisional thermalization of that energy, leading to irreversible plasma heating. Gyrokinetic numerical simulations are used to explore the first step of electron energization, and we generate the first examples of field-particle correlation (FPC) signatures of electron energization in 2D strong-guide-field collisionless magnetic reconnection. We determine these velocity space signatures at the x-point and in the exhaust, the regions of the reconnection geometry in which the electron energization primarily occurs. Modeling of these velocity-space signatures shows that, in the strong-guide-field limit, the energization of electrons occurs through bulk acceleration of the out-of-plane electron flow by parallel electric field that drives the reconnection, a non-resonant mechanism of energization. Our analysis goes beyond the fluid picture of the plasma dynamics and exploits the kinetic features of electron energization in the exhaust region to propose a single-point diagnostic which can potentially identify a reconnection exhaust region using spacecraft observations. |
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