PROBABILISTIC MODEL OF BEAM–PLASMA INTERACTION IN RANDOMLY INHOMOGENEOUS PLASMA

International audienceWe propose a new model that describes beam–plasma interaction in the presence of random density fluctuationswith a known probability distribution. We use the property that, for the given frequency, the probabilitydistribution of the density fluctuations uniquely determines the probability distribution of the phase velocity ofwaves. We present the system as discrete and consisting of small, equal spatial intervals with a linear densityprofile. This approach allows one to estimate variations in wave energy density and particle velocity, depending onthe density gradient on any small spatial interval. Because the characteristic time for the evolution of the electrondistribution function and the wave energy is much longer than the time required for a single wave–particle resonantinteraction over a small interval, we determine the description for the relaxation process in terms of averagedquantities. We derive a system of equations, similar to the quasi-linear approximation, with the conventionalvelocity diffusion coefficient D and the wave growth rate γ replaced by the average in phase space, by making useof the probability distribution for phase velocities and by assuming that the interaction in each interval isindependent of previous interactions. Functions D and γ are completely determined by the distribution function forthe amplitudes of the fluctuations. For the Gaussian distribution of the density fluctuations, we show that therelaxation process is determined by the ratio of beam velocity to plasma thermal velocity, the dispersion of thefluctuations, and the width of the beam in the velocity space

Trapped fast MGD waves in dayside magnetosphere

We studied the dynamics of the magnetosphere response to the solar wind parameters changes using the Alfvén velocity distribution in the Earth's magnetosphere obtained from the IGRF and T89 Earth's magnetic field models and plasma density diflusive equilibrium model. We used the solution of the eigenvalue problem for trapped waves in the dayside magnetosphere cavity as the initial condition for simulation. Numerical simulation of the fast MHD wave packet propagation in 3D magnetosphere cavity shows the occurrence of two global quasi-periodic modes of the dayside magnetosphere: cavity modes at the sub-solar region and waveguide modes at the magnetosphere flanks. The periods obtained in the numerical simulation are consistent with the theoretical predictions and the THEMIS measurements

Ions Accelerated by Sounder-Plasma Interaction as Observed by Mars Express

The ion sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA-3) experiment detects accelerated ions during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express. Accelerated ions (O+2, O+, and lighter ions) are observed in an energy range up to 800 eV when MARSIS transmits at a frequency close to the plasma frequency. Individual observations consist of almost monoenergetic ion beams aligned with the MARSIS antenna or lying in the plane perpendicular to the antenna. The observed ion beams are often accompanied by a small decrease in the electron flux observed by the electron sensor of Analyzer of Space Plasmas and Energetic Atoms 3. Observations indicate that the voltage applied to the antenna causes charging of the spacecraft to several hundreds of volts by the electrons of the ambient plasma. Positively charged ions are accelerated when the spacecraft discharges

Active Experiments Beyond the Earth: Plasma Effects of Sounding Radar Operations in the Ionospheres of Venus, Mars, and the Jovian System

The operation of powerful satellite- and rocket-born sounding radars is often accompanied by a heating/acceleration of the local electrons and ions. Intense fluxes of sounder accelerated particles were detected in Earth's ionosphere when the frequency of the radar transmitter was close to one of the fundamental plasma resonances: harmonic of the electron-cyclotron frequency, plasma, or upper-hybrid frequencies. Recently it was found that running a sounder in the ionosphere of the non-magnetized Mars results in similar effects. Ion and electron sensors of the ASPERA-3 experiment (Analyzer of Space Plasma and Energetic neutral Atoms) onboard the Mars Express spacecraft discovered acceleration of the local ionospheric ions and electrons from thermal threshold energies to 100's of eV during the active sounding phase of the onboard sounder. ESA and NASA missions being studied or under development to Jupiter (JUICE- JUpiter ICy moon Explorer) in 2022, Europa Clipper in 2023 and to Venus (EnVision) in 2032 and ISRO Venus obiter in 2023 will also carry powerful sounding radars. The purpose of this study is to investigate what mechanisms can cause acceleration of the plasma particles during operations of the proposed sounding radars in the Jovian system and Venusian ionosphere. Using the results of the previous studies and characteristics of the proposed sounding radars onboard JUICE, Europa Clipper, EnVision, and ISRO Venus Obiter, we define the optimal conditions for observations of sounder accelerated particles, depending on the local conditions, such as plasma density, composition, and intensity of the magnetic field. The EnVision and ISRO Venus Obiter radar operations are expected to result in the most pronounced acceleration of ions and electrons, an effect that can be used to improve the local plasma diagnostics

Multipoint Detection of GRB221009A’s Propagation through the Heliosphere

We present the results of processing the effects of the powerful gamma-ray burst GRB221009A captured by the charged particle detectors (electrostatic analyzers and solid-state detectors) on board spacecraft at different points in the heliosphere on 2022 October 9. To follow the GRB221009A propagation through the heliosphere, we used the electron and proton flux measurements from solar missions Solar Orbiter and STEREO-A; Earth’s magnetosphere and solar wind missions THEMIS and Wind; meteorological satellites POES15, POES19, and MetOp3; and MAVEN—a NASA mission orbiting Mars. GRB221009A had a structure of four bursts: the less intense Pulse 1—the triggering impulse—was detected by gamma-ray observatories at T 0 = 13:16:59 UT (near the Earth); the most intense Pulses 2 and 3 were detected on board all the spacecraft from the list; and Pulse 4 was detected in more than 500 s after Pulse 1. Due to their different scientific objectives, the spacecraft, whose data were used in this study, were separated by more than 1 au (Solar Orbiter and MAVEN). This enabled the tracking of GRB221009A as it was propagating across the heliosphere. STEREO-A was the first to register Pulse 2 and 3 of the GRB, almost 100 s before their detection by spacecraft in the vicinity of Earth. MAVEN detected GRB221009A Pulses 2, 3, and 4 at the orbit of Mars about 237 s after their detection near Earth. By processing the observed time delays, we show that the source location of the GRB221009A was at R.A. 288.°5, decl. 18.°5 ± 2° (J2000)

Electron beam relaxation in inhomogeneous plasmas

International audienceIn this work, we studied the effects of backgroundplasma density fluctuations on the relaxation of electronbeams. For the study, we assumed that the level of fluctuationswas so high that the majority of Langmuir waves generatedas a result of beam-plasma instability were trappedinside density depletions. The system can be considered as agood model for describing beam-plasma interactions in thesolar wind. Here we show that due to the effect of wave trapping,beam relaxation slows significantly. As a result, thelength of relaxation for the electron beam in such an inhomogeneousplasma is much longer than in a homogeneousplasma. Additionally, for sufficiently narrow beams, processof relaxation is accompanied by transformation of significantpart of the beam kinetic energy to energy of acceleratedparticles. They form the tail of the distribution and cancarry up to 50% of the initial beam energy flux

On Statistics of Electric Field Amplitudes in the Langmuir Turbulence

International audienceWe present a systematic study of the properties of the Langmuir wave turbulence generated by bump-on-tail instability in strongly non-homogeneous plasma. This type of turbulence occurs in numerous processes involving electrons beams in space plasmas. We analyse the synthetic data obtained in the numerical simulation based on two different approaches: the Hamiltonian model, and so-called probabilistic model. The Hamiltonian model describes in the self-consistent manner the wave-particle and wave-wave interactions in inhomogeneous magnetized plasmas. The model enables us to study the general properties of the distributions of the amplitudes of the Langmuir waves driven by the high-velocity electron beams in the fluctuating plasma. We pay special attention to the study of statistics of Languir waves under conditions when the decay instability, involving ion-sound waves, is developed. The probabilistic model, being modified version of the standard quasi-linear theory requires much less computational resources. Due to this it enables us to performed a detailed analysis of the statistics of the amplitudes of the Langmuir waves in the plasma with density fluctuations. To analyze data obtained in both numerical models, a Pearson technique was used to classify the probability distribution functions (PDF) of the logarithm of wave intensity. It was shown that core parts the PDF's belong to Pearson types I,IV and VI, depending on the spatial profiles of the density fluctuations, rather than to the normal distribution. The study also showed that the high-amplitude parts of the distributions follow power-low or exponential decay, depending on the type of core distribution

On statistics of electric field amplitudes in Langmuir turbulence

International audienceA systematic study of the properties of Langmuir wave turbulence generated by electron beams via bump-on-tail instabilities in strongly non-homogeneous plasmas is presented. A statistical analysis of the Langmuir waves' fields' amplitudes using numerical simulations based on two different theoretical models is performed : a probabilistic one and a dynamical one. The former describes the self-consistent dynamics of wave-particle and wave-wave interactions in inhomogeneous plasmas. The latter is a modified version of the standard quasi-linear theory which requires much less computational resources. To analyze the simulation data provided by the probabilistic model, a Pearson technique is used to classify the calculated probability distribution functions (PDFs) of the logarithm of the wave fields' intensities. It is demonstrated that the core parts of the PDFs belong to the Pearson types I, IV and VI distributions, depending on the spatial profiles of the density fluctuations, rather than to the normal distribution. Moreover it is shown that the high-amplitude parts of the PDFs follow power-law or exponential decay distributions, depending on the type of the corresponding cores' distributions. The PDFs of the fields' amplitudes calculated using the numerical simulations based on the dynamical model are in the whole consistent with those provided by the probabilistic model. Moreover, these simulations lead to a series of additional results. First, in the small fields' amplitudes' parts of the PDFs (i.e. in the linear stage of the system's evolution), an universal scaling parameter is found, with a value not depending on the average levels of the density fluctuations and of the Langmuir turbulence. Second, the PDFs are obtained in the presence of wave 28 decay processes, which are not taken into account in the probabilistic model. When those are weak, the PDFs show at large fields' amplitudes an exponential asymptotic behavior; during the time evolution, the corresponding scaling parameter decreases until a universal probability distribution is reached, what is realized when the wave decay processes are sufficiently strong. This distribution is analogous to that obtained for a quasi-homogeneous plasma. Such exponential type of distribution is a specific signature of transition states in the Langmuir turbulence. Third, the square of the statistical field amplitude maximum is found to be proportional to the average energy of the Langmuir waves

On the mechanism of radio emission in type III Solar Radiobursts

International audienceSolar radio emissions of the type III are between the most intense in the solar system. It is known that they are generated by intense fluxes of energetic electrons ejected by the Sun into heliosphere during periods of the of the solar activity. It is accepted that the process of generation of radiowaves occurs in two steps. First, electron beams generate electrostatic Langmuir waves and then these waves due to some, supposed to be non-linear, process generate electromagnetic emissions. Recent studies showed that the level of density fluctuations in the solar wind is so high and they significantly affect beam plasma interaction. The effect of random density fluctuations for Langmuir waves propagating in a solar wind consists in strong variations of their phase velocity. These variations suggest that wave resonate with particles having different velocities. This results in significant decrease of the instability increment and an increase of the relaxation length of a beam. These processes were studied analytically and using computer simulations. The results of modelling were shown to reproduce the majoriity of waveforms observed on satellites Wind and Stereo. Statistical characteristics of wave amplitudes in simulations are very similar with observations. We show here that intense density fluctuations not only crucially influence the beam plasma interaction but also change the mechanism of energy transformation from electrostatic waves into electromagnetic. It is known that reflection of Langmuir waves from the density inhomogeneities under certain conditions may result in partial transformation of thergy of electrostatic wave into electromagnetic. This effect was studied in application to laser-plasma interaction and in ionospheric heating. We consider this same effect of linear wave energy transformation in application to generation of type III Solar radio bursts. We use the probability distribution of density fluctuations to evaluate an efficiency of this process and to determine its statistical characteristics. We show that for the level of fluctuations of the order of 1% the mechanism of linear transformation of electrostatic waves energy into electromagnetic may be significantly more efficient than the process of nonlinear conversion of Langmuir waves by means of coupling with the ion-sound waves

On the mechanism of radio emission in type III Solar Radiobursts

International audienceSolar radio emissions of the type III are between the most intense in the solar system. It is known that they are generated by intense fluxes of energetic electrons ejected by the Sun into heliosphere during periods of the of the solar activity. It is accepted that the process of generation of radiowaves occurs in two steps. First, electron beams generate electrostatic Langmuir waves and then these waves due to some, supposed to be non-linear, process generate electromagnetic emissions. Recent studies showed that the level of density fluctuations in the solar wind is so high and they significantly affect beam plasma interaction. The effect of random density fluctuations for Langmuir waves propagating in a solar wind consists in strong variations of their phase velocity. These variations suggest that wave resonate with particles having different velocities. This results in significant decrease of the instability increment and an increase of the relaxation length of a beam. These processes were studied analytically and using computer simulations. The results of modelling were shown to reproduce the majoriity of waveforms observed on satellites Wind and Stereo. Statistical characteristics of wave amplitudes in simulations are very similar with observations. We show here that intense density fluctuations not only crucially influence the beam plasma interaction but also change the mechanism of energy transformation from electrostatic waves into electromagnetic. It is known that reflection of Langmuir waves from the density inhomogeneities under certain conditions may result in partial transformation of thergy of electrostatic wave into electromagnetic. This effect was studied in application to laser-plasma interaction and in ionospheric heating. We consider this same effect of linear wave energy transformation in application to generation of type III Solar radio bursts. We use the probability distribution of density fluctuations to evaluate an efficiency of this process and to determine its statistical characteristics. We show that for the level of fluctuations of the order of 1% the mechanism of linear transformation of electrostatic waves energy into electromagnetic may be significantly more efficient than the process of nonlinear conversion of Langmuir waves by means of coupling with the ion-sound waves