Riquelme, M;
Osorio, A;
Verscharen, D;
Sironi, L;
(2022)
Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions.
Astrophysical Journal
, 924
(2)
, Article 52. 10.3847/1538-4357/ac3e67.
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Abstract
Using 2D particle-in-cell plasma simulations, we study electron acceleration by temperature anisotropy instabilities, assuming conditions typical of above-the-loop-top sources in solar flares. We focus on the long-term effect of Te,⊥ > Te,∥ instabilities by driving the anisotropy growth during the entire simulation time through imposing a shearing or a compressing plasma velocity (Te,⊥ and Te,∥ are the temperatures perpendicular and parallel to the magnetic field). This magnetic growth makes Te,⊥/Te,∥ grow due to electron magnetic moment conservation, and amplifies the ratio ωce/ωpe from ∼0.53 to ∼2 (ωce and ωpe are the electron cyclotron and plasma frequencies, respectively). In the regime ωce/ωpe ≲ 1.2–1.7, the instability is dominated by oblique, quasi-electrostatic modes, and the acceleration is inefficient. When ωce/ωpe has grown to ωce/ωpe ≳ 1.2–1.7, electrons are efficiently accelerated by the inelastic scattering provided by unstable parallel, electromagnetic z modes. After ωce/ωpe reaches ∼2, the electron energy spectra show nonthermal tails that differ between the shearing and compressing cases. In the shearing case, the tail resembles a power law of index αs ∼ 2.9 plus a high-energy bump reaching ∼300 keV. In the compressing runs, αs ∼ 3.7 with a spectral break above ∼500 keV. This difference can be explained by the different temperature evolutions in these two types of simulations, suggesting that a critical role is played by the type of anisotropy driving, ωce/ωpe, and the electron temperature in the efficiency of the acceleration.
| Type: | Article |
|---|---|
| Title: | Stochastic Electron Acceleration by Temperature Anisotropy Instabilities Under Solar Flare Plasma Conditions |
| Open access status: | An open access version is available from UCL Discovery |
| DOI: | 10.3847/1538-4357/ac3e67 |
| Publisher version: | http://dx.doi.org/10.3847/1538-4357/ac3e67 |
| Language: | English |
| Additional information: | Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. |
| Keywords: | astro-ph.SR, astro-ph.SR, astro-ph.HE |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Space and Climate Physics |
| URI: | https://discovery-pp.ucl.ac.uk/id/eprint/10142565 |
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