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Unraveling Particle Acceleration Mechanisms in Solar Flares

Investigating various particle acceleration mechanisms during magnetic reconnection in solar flares to better understand high-energy electron bursts and filament properties. Can high-resolution observations reveal the dominant acceleration mechanism?

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Unraveling Particle Acceleration Mechanisms in Solar Flares

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  1. Issues for a new flare/particle acceleration mission: Sorting out the various particle acceleration mechanisms during magnetic reconnection in flares J. F. Drake University of Maryland

  2. Electron acceleration by the parallel reconnection electric field • Parallel electric fields during reconnection are typically highly localized near the x-line and along separatrices • Over most of space E|| is zero – MHD is actually a fairly good model • A single x-line model can not explain the large numbers of electrons seen in flares • Parallel electric fields are too spatially localized to be a significant source of large numbers of energetic electrons • Can observations reveal whether the single x-line is viable? • Is high time variability consistent with a single x-line model? E||

  3. CA A multi-island acceleration model • Narrow current layers spawn multiple magnetic islands in reconnection • Do we need to abandon the classical single x-line picture!! • Do Trace observations of down-moving blobs confirm the multi-island picture (Sheeley et al 2004; Linton & Longcope 2005)? • Can the size distribution of magnetic islands (blobs?) in flares be determined from observations?

  4. Magnetic islands release energetic electrons in bursts • Secondary magnetic island merging with a large-scale field releases energetic electrons in narrow filaments • Source of millisecond bursts of energetic electrons? • Can high-resolution analysis of the time variability of energetic electrons reveal information about the size distribution of magnetic islands? • Electrons propagate down to the chromosphere as a filamentary web • Can evidence for the fine structure of energetic electrons be deduced from observations • Seems consistent with absence of Doppler shift of upward streaming evaporating plasma (Warren & Doschek 2005). Te

  5. Propagation of energetic electron filament Pexx • Spreading rate comparable to the high-energy electron thermal speed • What about return current? • Why structuring along the filament?

  6. Self-generated magnetic field Bz • Streaming energetic electrons produce a parallel current and associated non-co-spatial return current to produce Bz • Charge neutrality and current continuity require the filament to propagate as a wave --kinetic Alfven wave

  7. Sorting out the various mechanisms for particle acceleration • Directly probe the acceleration region: • Can observations reveal where particles are actually accelerated? • This will enable us to pin down the dominant acceleration mechanism • Direct acceleration from reconnection • Turbulence in the outflow jet • Slow shocks bounding the outflow • Outflow fast-mode shock • What is the magnetic structure of the high corona? • Can magnetic fields in the high corona be measured? • Magnetic geometry is critical for understanding reconnection • What is the spatial structure of precipitating energetic electrons and ions? • Provides information on acceleration mechanisms of the species • Can obtain more gamma-ray events be obtained with an instrument with greater sensitivity?

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