Electromagnetic Simulations of Solar Radio Emissions

Abstract

Solar radio emissions are electromagnetic waves emitted in the solar wind as a consequence of electron beams accelerated during solar flares or interplanetary shocks such as interplanetary coronal mass ejections. Different physical mechanisms have been suggested to describe their origin. A good understanding of the emission process would enable to infer the kinetic energy transferred from accelerated electrons to radio waves. Even if the electrostatic case has been extensively studied, full electromagnetic simulations were attempted only recently. In this work, we report large-scale 2D3V electromagnetic particle-in-cell simulations that enable to identify the generation of both electrostatic and electromagnetic waves originated by a succession of plasma instabilities. They confirm that an efficient mechanism to generate solar radio emissions close to T 2f , the harmonic of the plasma frequency, is a multistage model based on a succession of nonlinear three-wave interaction processes. Through a parametric study of the electron beam parameters, we show that (i) the global efficiency of the multistep conversion mechanism from the electron beam kinetic energy to the T 2f radio wave is independent of the beam parameters, approximately 10 −5 in all tested configurations, while (ii) the directivity of the electromagnetic radio wave strongly depends on the origin electron beam. Those results represent a step forward toward the use of solar wind radio emissions, observed remotely, as a diagnostic for the properties of the electron beam located at the source of the radio emission, and therefore to eventually better characterize remotely electron acceleration mechanisms in space regions not directly accessible to in situ measurements. Key Points:• We single out the successive steps of the generation mechanisms of solar radio emissions • We quantify the energy transferred from energetic particles to radio waves and show it is independent of energetic particles parameters • We identify the directivity of the radio emissions and show its strong dependence on energetic particles parameters.

Laser-Plasma Interaction Experiment for Solar Burst Studies

“…Analytical models and numerical simulations have been developed to interpret these space observations. Recently, three-dimensional EM particle-in-cell simulations tackled several questions regarding the efficiency of the conversion process from LW to EM waves, and the emission pattern of the EM waves [8,9]. These models and simulations yet remain to be confronted with experimental data.Laboratory experiments provide a complementary and powerful method to study the fundamental mechanisms of wave coupling.…”

A Review of Recent Solar Type III Imaging Spectroscopy

“…Both studies were able to produce electrostatic and electromagnetic waves through plasma instabilities. Henri et al (2019) found weaker electron beams produced radio waves that were more forward directed at the source, whilst larger beam densities widened the Langmuir wave spectrum, leading to a larger available angular spread of radio emission. The validity of the weak turbulence approximation has been analyzed using PIC code both for 1D (Ratcliffe et al, 2014a) and 2D (Lee et al, 2019) weak turbulence codes.…”

“…When electron beams become unstable, it has been the focus of many recent theoretical works how density inhomogeneities in the background plasma influence subsequent Langmuir wave growth, electromagnetic emission and the development of the electron distribution function. Studies are typically carried out either in one spatial location (e.g., Ratcliffe and Kontar, 2014;Krafft et al, 2015;, in a small spatial box (e.g., Thurgood and Tsiklauri, 2015;Volokitin and Krafft, 2018;Henri et al, 2019;Krafft and Volokitin, 2020) or over distance comparable to the solar corona or longer (e.g., Li et al, 2012;Reid and Kontar, 2013, 2017bLoi et al, 2014;Ratcliffe et al, 2014b). Each of these different approaches has their own advantages and disadvantages and are used based upon the focus of the relevant study.…”

“…This approach is not self-consistent with the electron beam exciter but has produced comparable type III fluxes using parameters in the solar wind. The plasma emission process has also been reproduced using particle-in-cell (PIC) codes (e.g., Thurgood and Tsiklauri, 2015;Henri et al, 2019). Both studies were able to produce electrostatic and electromagnetic waves through plasma instabilities.…”

Computer Simulations of Electromagnetic Emissions Produced via Injection of Electron Beam into a Plasma with Strong Transverse Density Gradients

“…Генерация электромагнитного (ЭМ) излучения вблизи гармоник плазменной частоты в процессе коллективного взаимодействия плазмы с потоками электронов является одной из фундаментальных проблем физики плазмы, которая в настоящее время активно изучается как применительно к солнечным радио [1][2][3] и субтерагерцовым [4; 5] вспышкам, так и в связи с разработкой мощного источника терагерцового излучения [6; 7]. В терагерцовой области спектра методы, основанные на коллективном возбуждении плазменных колебаний и их дальнейшей конверсии в электромагнитные волны, имеют ряд преимуществ по сравнению со стандартными методами вакуумной электроники.…”