Electron Acceleration during Macroscale Magnetic Reconnection

Arnold, H.; Drake, J. F.; Swisdak, M.; Guo, Fan; Dahlin, Joel; Bin, Chen; Fleishman, G. D.; Glesener, Lindsay; Kontar, Eduard P.; Phan, T. D.; Shen, Chao

doi:10.1103/physrevlett.126.135101

Cited by 113 publications

(138 citation statements)

References 38 publications

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“…High-resolution imaging observations provide rich information about details of the reconnection process which result from its internal dynamics, especially the formation of plasmoids 21 , 22 and turbulent structures 23 , and from the complexity and three-dimensional (3D) nature of the solar magnetic field 24 , 25 . Spectral and multi-wavelength data reveal aspects of the microscopic processes, e.g., particle acceleration 26 , 27 , the nonthermal-thermal energy partition 28 , the plasmoid instability 29 , 30 , and bursty 31 or turbulent reconnection 32 , 33 , in addition to flows 34 . Finally, besides hot flare plasmas, the Sun also allows the reconnection of cool chromospheric structures to be studied 24 , 35 .…”

Section: Introductionmentioning

confidence: 99%

Fast plasmoid-mediated reconnection in a solar flare

et al. 2022

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Magnetic reconnection is a multi-faceted process of energy conversion in astrophysical, space and laboratory plasmas that operates at microscopic scales but has macroscopic drivers and consequences. Solar flares present a key laboratory for its study, leaving imprints of the microscopic physics in radiation spectra and allowing the macroscopic evolution to be imaged, yet a full observational characterization remains elusive. Here we combine high resolution imaging and spectral observations of a confined solar flare at multiple wavelengths with data-constrained magnetohydrodynamic modeling to study the dynamics of the flare plasma from the current sheet to the plasmoid scale. The analysis suggests that the flare resulted from the interaction of a twisted magnetic flux rope surrounding a filament with nearby magnetic loops whose feet are anchored in chromospheric fibrils. Bright cusp-shaped structures represent the region around a reconnecting separator or quasi-separator (hyperbolic flux tube). The fast reconnection, which is relevant for other astrophysical environments, revealed plasmoids in the current sheet and separatrices and associated unresolved turbulent motions.

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Section: Introductionmentioning

confidence: 99%

Fast plasmoid-mediated reconnection in a solar flare

et al. 2022

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“…Ions are Fermi accelerated as they scatter back and forth from the ends of the collapsing islands. A similar process is found to accelerate electrons (Arnold et al, 2021) and its efficiency depends upon the strength of the out-of-plane guide field. However, 3 He has not been discussed at all in this process, although there would seem to be abundant opportunities for mirroring ions to absorb waves.…”

Section: Acceleration Theorymentioning

confidence: 67%

“…In realistic jets, the opposing fields rarely exactly cancel, but rather leave an out-of-plane, residual "guide field." Particle acceleration occurs as particles, mainly electrons (Arnold et al, 2021), are Fermiaccelerated as they pitch-angle scatter in the evolving fields. As the SEPs and CME plasma are ejected on open field lines at the upper right in Figure 5, newly closing loops capture some SEPs in the lower left region labeled "flare" where they deposit their energy as heat.…”

Section: Flares Cmes Shocks and Jetsmentioning

confidence: 99%

Fifty Years of 3He-Rich Events

Reames

2021

Front. Astron. Space Sci.

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The early 1970s saw a new and surprising feature in the composition of solar energetic particles (SEPs), resonant enhancements up to 10,000-fold in the ratio 3He/4He that could even make 3He dominant over H in rare events. It was soon learned that these events also had enhancements in the abundances of heavier elements, such as a factor of ∼10 enhancements in Fe/O, which was later seen to be part of a smooth increase in enhancements vs. mass-to-charge ratio A/Q from H to Pb, rising by a factor of ∼1000. These events were also associated with streaming 10–100 keV electrons that produce type III radio bursts. In recent years we have found these “impulsive” SEP events to be accelerated in islands of magnetic reconnection from plasma temperatures of 2–3 MK on open field lines in solar jets. Similar reconnection on closed loops traps the energy of the particles to produce hot (>10 MK), bright flares. Sometimes impulsive SEP intensities are boosted by shock waves when the jets launch fast coronal mass ejections. No single theory yet explains both the sharp resonance in 3He and the smooth increase up to heavier elements; two processes seem to occur. Sometimes the efficient acceleration even exhausts the rare 3He in the source region, limiting its fluence.

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“…These enhancements were explained by simulations that showed the scattering of ions back and forth in the collapsing islands of magnetic reconnection [41], which predicted the power law dependence on A/Q. Similar considerations even apply to electron acceleration [42], but reconnection calculations have not yet explained 3 He.…”

Section: He-rich Eventsmentioning

confidence: 97%

The Evolution of Research on Abundances of Solar Energetic Particles

Reames

2021

Universe

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Sixty years of study of energetic particle abundances have made a major contribution to our understanding of the physics of solar energetic particles (SEPs) or solar cosmic rays. An early surprise was the observation in small SEP events of huge enhancements in the isotope 3He from resonant wave–particle interactions, and the subsequent observation of accompanying enhancements of heavy ions, later found to increase 1000-fold as a steep power of the mass-to-charge ratio A/Q, right across the elements from H to Pb. These “impulsive” SEP events have been related to magnetic reconnection on open field lines in solar jets; similar processes occur on closed loops in flares, but those SEPs are trapped and dissipate their energy in heat and light. After early controversy, it was established that particles in the large “gradual” SEP events are accelerated at shock waves driven by wide, fast coronal mass ejections (CMEs) that expand broadly. On average, gradual SEP events give us a measure of element abundances in the solar corona, which differ from those in the photosphere as a classic function of the first ionization potential (FIP) of the elements, distinguishing ions and neutrals. Departures from the average in gradual SEPs are also power laws in A/Q, and fits of this dependence can determine Q values and thus estimate source plasma temperatures. Complications arise when shock waves reaccelerate residual ions from the impulsive events, but excess protons and the extent of abundance variations help to resolve these processes. Yet, specific questions about SEP abundances remain.

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Electron Acceleration during Macroscale Magnetic Reconnection

Cited by 113 publications

References 38 publications

Fast plasmoid-mediated reconnection in a solar flare

Fast plasmoid-mediated reconnection in a solar flare

Fifty Years of 3He-Rich Events

The Evolution of Research on Abundances of Solar Energetic Particles

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