Emission Characteristics of Energetic Electrons with Crescent-shaped Velocity Distributions

TL;DR

This paper investigates how crescent-shaped electron velocity distributions in solar flares influence plasma wave emissions under various frequency ratios, revealing enhanced emission intensities and new insights into nonthermal electron effects.

Contribution

It provides the first detailed analysis of emission properties of crescent-shaped EVDFs across different plasma conditions, highlighting their impact on wave excitation and emission intensities.

Findings

Fundamental emission can reach ~10^{-4} of kinetic energy

Harmonic emission extends to ~1.5 x 10^{-5} of kinetic energy

Crescent-shaped distributions enhance wave excitation compared to other distributions

Abstract

Solar flares release magnetic energy through reconnection, accelerating electrons into nonthermal velocity distributions, including crescent-shaped electron populations. These energetic electron distributions are crucial in driving instabilities which can lead to distinct electromagnetic emissions. This study investigates the emission properties of crescent-shaped electron velocity distribution functions (EVDFs) under different frequency ratios ($\omega_{pe}/\Omega_{ce}$), critical for understanding plasma conditions in various astrophysical environments, by comparing the emissions and intensities of waves among different cases. Here, we study and analyze three distinct frequency ratio conditions (2.2, 10, and 1, designated as cases A, B, and C, respectively). We found that the beam-Langmuir (BL) and upper-hybrid (UH) modes can be efficiently excited, leading to further plasma emissions in different cases. Our study reveals that the fundamental (O/F) emission can reach a maximum value of $\sim$$10^{-4} E_{\mathrm{k}0}$, while the harmonics (H) can extend to $\sim$$1.5 \times 10^{-5} E_{\mathrm{k}0}$ depending on the frequency ratio of the environment. The intensity of the fundamental mode exceeds previous findings for pure-ring, beam, and ring-beam distributions, highlighting the impact of crescent-shaped electron velocity distributions on wave excitation and emission processes. This effect is notably influenced by different frequency ratios, offering new insights into the way that nonthermal electron distributions affect the plasma emission process.