Wave-particle Interactions Research Articles

Estimation of Growth Rate of Electromagnetic Plasma Wave through Vlasov-Maxwell Mathematical Frame in Ionospheric Plasma

Unique forms of nonlinear wave energy exchange phenomena are observed in the Earth’sionosphere region. Energy upconversion of nonresonant plasma waves in the top ionospheric and auroral zone are noticed.Origin of these phenomena are tried to explained by linear andnonlinear theoretical approach.Wave-wave and wave-particle-wave interaction processes may be possible role takes place here.In this theoretical investigation we wish to derive probable growthrate expression of high frequency electromagnetic O-mode wave in the presence of low frequency electrostatic ion sound wave through wave-particle interaction process known as plasma maserinstability and estimate its value by using observational data.

Scaling laws in Hall inertial-range turbulence

Abstract. There is an increasing amount of observational evidence in space plasmas for the breakdown of inertial-range spectra of magnetohydrodynamic (MHD) turbulence on spatial scales smaller than the ion-inertial length. Magnetic energy spectra often exhibit a steepening, which is reminiscent of dissipation of turbulence energy, for example in wave–particle interactions. Electric energy spectra, on the other hand, tend to be flatter than those of MHD turbulence, which is indicative of a dispersive process converting magnetic into electric energy in electromagnetic wave excitation. Here we develop a model of the scaling laws and the power spectra for the Hall inertial range in plasma turbulence. In the present paper we consider a two-dimensional geometry with no wave vector component parallel to the magnetic field as is appropriate in Hall MHD. A phenomenological approach is taken. The Hall electric field attains an electrostatic component when the wave vectors are perpendicular to the mean magnetic field. The power spectra of Hall turbulence are steep for the magnetic field with a slope of -7/3 for compressible magnetic turbulence; they are flatter for the Hall electric field with a slope of -1/3. Our model for the Hall turbulence gives a possible explanation for the steepening of the magnetic energy spectra in the solar wind as an indication of neither the dissipation range nor the dispersive range but as the Hall inertial range. Our model also reproduces the shape of energy spectra in Kelvin–Helmholtz turbulence observed at the Earth's magnetopause.

Impact of induced field on the estimation of the ionospheric electric field

The ionospheric plasma electric field plays an important role in space physics and space meteorology, and it constitutes an essential physics magnitude for all phenomena occurring in the ionosphere, such as plasma convection, wave–particle interactions, and wave emissions. We used the direct measurements of DEMETER satellite which gives the total electric field, i.e., natural and induced fields, to show the effect of the induced field on the total electric field measurements. For that purpose, the induced electric field, generated by the satellite motion through the Earth’s magnetic lines, is calculated by selecting different velocity satellite and geomagnetic field components. The induced field is calculated by using two different methods: one according to the satellite different axes and the other by using the double-probe method. It is found that the calculated induced electric field dominates on the total electric measurements, therefore leadings to misestimation of the true value of ionospheric electric field.

Plasma Wave Observation in Space Via Scientific Satellites

Space plasmas are essentially collisionless. Kinetic energies of plasmas are transferred through wave-particle interactions. Since plasmas are dispersive media, plasma waves show various features depending on how and which plasma wave modes interact with particles. Plasma wave observations via scientific satellites have a key role in knowing physical processes in space. Plasma wave investigation systems on board satellites are dedicated to the observations of electric field and magnetic field components of plasma waves. They consist of sensors, receivers and an onboard digital processing unit. While dipole antennas are used for electric field sensors, search coil magnetometers or loop antennas are used for magnetic field sensors. Plasma wave receivers are a kind of sophisticated radio receivers. The recent plasma wave receiver is designed as a waveform receiver that can save its mass and size. In addition to waveforms, the waveform receiver provides frequency spectra which are calculated in the digital processing unit from the observed waveforms. The present paper introduces plasma wave observation by scientific satellites on the basis of the latest design of plasma wave investigation systems.

Holmboe instability beyond the Boussinesq approximation revisited

With no use of the Boussinesq approximation, the Holmboe instability is studied in sharply stratified shear flows with arbitrary monotonic and bounded velocity profiles without inflection points, including a piecewise-linear one. Particular attention is given to the separation and analysis of contributions to instability made by the wave–wave and wave–particle interactions which are the main physical mechanisms responsible for the loss of stability. It is shown that both mechanisms are equally important for understanding the instability properties and therefore should be taken into consideration simultaneously.

DIMOHA: A Time-Domain Algorithm for Traveling-Wave Tube Simulations

To simulate traveling-wave tubes (TWTs) in time domain and more generally the wave-particle interaction in vacuum devices, we developed the DIscrete MOdel with HAmiltonian approach (dimoha) as an alternative to current particle-in-cell (PIC) and frequency approaches. Indeed, it is based on a longitudinal N-body Hamiltonian approach satisfying Maxwell's equations. Advantages of dimoha comprise: (i) it allows arbitrary waveform (not just field envelope), including continuous waveform (CW), multiple carriers or digital modulations (shift keying); (ii) the algorithm is much faster than PIC codes thanks to a field discretization allowing a drastic degree-of-freedom reduction, along with a robust symplectic integrator; (iii) it supports any periodic slow-wave structure design such as helix or folded waveguides; (iv) it reproduces harmonic generation, reflection, oscillation and distortion phenomena; (v) it handles nonlinear dynamics, including intermodulations, trapping and chaos. dimoha accuracy is assessed by comparing it against measurements from a commercial Ku-band tapered helix TWT and against simulations from a sub-THz folded waveguide TWT with a staggered double-grating slow-wave structure. The algorithm is also tested for multiple-carriers simulations with success.

Do hydrodynamic models based on time-independent density functional theory misestimate exchange effects? Comparison with kinetic theory for electrostatic waves

We have extended previous quantum kinetic results to compute the exchange correction to the electrostatic electron susceptibility for arbitrary frequencies and wavenumbers in the low temperature limit. This has allowed us to make a general comparison with a much used hydrodynamic expression, based on density functional theory, for exchange effects. For low phase velocities, as for ion-acoustic waves, wave-particle interaction leads to a strong enhancement of the exchange correction and the hydrodynamic result is smaller by an order of magnitude. The hydrodynamic expression gives a useful approximation when the phase velocity is ≳2.5 times the Fermi velocity. If this condition is not fulfilled, the hydrodynamical theory gives misleading results. We discuss the implications of our results for the model choice for quantum plasmas, especially regarding particle dispersive effects.

Longitudinal wave instability due to rotating beam-plasma interaction in weakly turbulent astrophysical plasmas

ABSTRACTThe aim of this study is to highlight the temporal evolution of the longitudinal wave instability due to the interaction between a rotating electron beam and the magnetoactive plasma region in space plasma structures. The plasma structure which could be either in the solar atmosphere or any active plasma region in space is considered weakly turbulent, where the quasi-linear theory is implemented to enable analytic insight on the wave–particle interaction in the course of the event. It is found that in a weakly turbulent plasma, quasi-linear saturation of the longitudinal wave is accompanied by a significant alteration in the distribution function in the resonant region. In case of a pure electrostatic wave, the wave amplitude experiences elevation due to the energy transfer from the plasma particles. This causes flattening of the bump on tail (BOT) in the electron distribution function. If the gradient of the distribution function is positive, the chance that the beam would excite the wave is probable. In such a situation a plateau on the distribution function (∂f/∂v ≈ 0) is formed that will stop the diffusion of beam particles in the velocity space. Evolution of the electron distribution function experiences a decreases of the instability of the longitudinal wave. It is deduced that the growth rate of the wave instability is inversely proportional to the wave energy. Regarding the Sun, in addition to creating micro-turbulence due to wave–particle interaction, as the wave elevates to higher altitudes it enters a saturated energy state before releasing energy that may be a candidate for the generation of radio bursts.

On the optimal conditions for alpha channelling in tokamaks

We investigate for a generic tokamak equilibrium the performance of alpha channelling driven by a mode-converted ion Bernstein wave with the effect of Alfvénic turbulence accounted for through an outward particle flux at the threshold magnetic moment for wave–particle interaction. The formal solution of the associated Fokker–Planck equation is given in the limit of large wave-induced diffusion with absorbing boundary conditions at the outer edge. By choosing a specific ITER-like equilibrium, the power flowing from alpha particles to the wave is explicitly computed and its dependence on the relevant physical parameters is discussed. In particular, alpha channelling is maximized when the outward flux equals the flux of pure wave-induced diffusion, in which case up to ∼55% of the total alpha particle energy can be extracted. The spectra of particles hitting the outer edge and crossing are also derived.

Statistical Study of Hard X-Ray Spectral Breaks in Solar Flares

The Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) provides hard X-ray spectral observations with ${\approx}\,1~\mbox{keV}$ resolution to study flare-accelerated ( ${>}\,10~\mbox{keV}$ ) electrons through their bremsstrahlung emission. Here we report on a statistical study of RHESSI flares with emission above 150 keV, focusing on the spectral shape at the hard X-ray peak. Spectral parameters are derived by fitting the photon spectrum with a broken power law and by the standard thick-target fit. Consistent with previous studies, the most common spectral shape of the photon spectrum (52 out of 65 events) is a double power law with a downward break (“knee”), with ten events showing a single power law and three events having an upward break (“ankle”). The spectral breaks occur typically around 55 keV and the difference of the spectral index above and below the break, $\gamma _{2}$ and $\gamma _{1}$ , is typically between 0.3 and 1. We show correlations between the downward break parameters. The most prominent correlation, with a rank order coefficient of $\rho =0.92$ , is between the power-law indices above and below the break: $\gamma _{1} = (0.74\pm 0.04)\gamma _{2} + (0.34 \pm 0.14)$ . Applying a thick target fit to the photon spectrum, a similar correlation is also found for the flare-accelerated electron spectra with $\delta _{1} =(0.85\pm 0.08)\delta _{2} - (0.3\pm 0.3)$ ( $\rho =0.67$ ). Spectral breaks could be a property of the acceleration mechanism itself or they could be a secondary effect produced by particle transport or wave-particle interactions. Any theoretical models should be consistent with these correlations. In addition, we find that one upward and 23 (49%) downward breaks are consistent with nonuniform ionization within the thick target.

The Storm Time Development of Source Electrons and Chorus Wave Activity During CME‐ and CIR‐Driven Storms

AbstractWhistler mode chorus waves influence the dynamics of the Earth's radiation belts and the inner magnetosphere through gyroresonant wave particle interactions. Chorus waves are generated by anisotropic hot electrons from a few to tens of keV, called source electrons, which have increased access from the nightside plasma sheet to the inner magnetosphere during geomagnetic storms. The primary drivers of geomagnetic storms are coronal mass ejections (CMEs) and corotating interaction regions (CIRs). Through differences in their characteristic physical parameters, they can each impact the nightside plasma sheet differently. Using Van Allen Probes observations, we have conducted a superposed epoch analysis of chorus wave activity and source electron development across all local times between L = 2–6 during 25 CME‐ and 35 CIR‐driven storms. The superposed epoch analysis shows that chorus wave power follows the storm phase‐dependent access of the source electron population. Chorus waves and source electrons are observed on the dawnside during the main phase, when open drift path access via eastward convective drift from the plasma sheet is enhanced. During the recovery phase, chorus waves and source electrons are observed at all magnetic local times with low intensities, exemplifying the formation of a weak symmetric, trapped electron population. A linear theory approximation for wave growth from source electron observations shows that increased wave growth follows the enhanced source electrons during each storm phase. CME and CIR storms display similar behavior and levels of average wave power; however, chorus wave activity reaches lower L‐shells during CME storms on average.

Theoretical and numerical studies of chorus waves: A review

Theoretical and numerical models of chorus waves are reviewed in this paper. Specifically, we focus on the nonlinear wave particle interactions and the current understanding of the frequency chirping of rising tone chorus waves. Various other related topics, such as the optimal excitation condition of chorus, the formation of subpackets, and the non-adiabaticity of the nonlinear interaction are also discussed. We end this review paper with a short list of questions of chorus waves that are still under research and debate.

The strong Langmuir turbulence spectra in weakly relativistic plasma

The spectral characteristics of strong Langmuir turbulence in weakly relativistic plasma is analyzed. The temporal evolutions of the turbulence energy density spectra are obtained by perfoyming the fast Fourier transformations on weakly relativistic Zakharov equations. The relativity parameter significantly influenced the Langmuir turbulence, in that a decrease in the relativity parameter lengthened the action time of wave-wave and wave-particle interactions, which is useful for studying the particles acceleration problem.

Verification and application of resonance broadened quasi-linear (RBQ) model with multiple Alfvénic instabilities

The resonance broadened quasilinear (RBQ) model for the problem of relaxing the hot ion distribution function in constant-of-motion 3D space [Gorelenkov et al., Nucl. Fusion 58, 082016 (2018)] is presented with the self-consistent evolution of multiple Alfvén eigenmode amplitudes. The RBQ model represents the generalization of the earlier published model [Berk et al., Nucl. Fusion 35, 1661 (1995)] by carefully examining the wave particle interaction in the presence of realistic Alfvén eigenmode (AE) structures and pitch angle scattering with the help of the guiding center code ORBIT. One aspect of the generalization is that the RBQ model goes beyond the local perturbative-pendulumlike approximation for the wave particle dynamics near the resonance. An iterative procedure is introduced to account for eigenstructures varying within the resonances. It is found that a radially localized mode structure implies a saturation level 2–3 times smaller than that predicted by an earlier bump-on-tail quasilinear model that employed uniform mode structures. We apply the RBQ code to a DIII-D plasma with an elevated q-profile where the beam ion profiles exhibit stiff transport properties [Collins et al., Phys. Rev. Lett. 116, 095001 (2016)]. The properties of AE driven fast ion distribution relaxation are studied for validations of the applied RBQ model in DIII-D discharges. Initial results show that the model is robust, is numerically efficient, and can predict fast ion relaxation in present and future burning plasma experiments.

Amplification of Plasma Wave through non-linear wave-particle interaction in ionospheric plasma

Amplification of Plasma Wave through non-linear wave-particle interaction in ionospheric plasma

Auto-resonant stimulated Brillouin backscattering in supersonic flowing plasmas by fully kinetic Vlasov simulations

The auto-resonant behavior of ion acoustic waves (IAWs) driven by stimulated Brillouin backscattering in supersonic flowing plasmas is self-consistently investigated by Vlasov simulations. Vlasov simulations show that the peak amplitude of the auto-resonant growing IAWs in the positive flow gradient is much larger than that in the negative flow gradient, which is contrary to the previous analysis (Wang et al 2018 Plasma Phys. Control. Fusion 60 025016). It is found that the IAW phase velocity remains unchanged in supersonic flowing plasmas, which significantly influences wave-particle interaction by changing the Landau damping and the coefficient of the kinetic nonlinear frequency shift in different position. As a result, the Landau damping of IAWs in the peak region in the negative case is stronger than that in the positive case, which has never been considered before. After considering its effects on particle trapping and, particularly, Landau damping of IAWs, theoretical predictions from three-wave mode equations are consistent with results by Vlasov simulations.

Laboratory investigation of particle acceleration and magnetic field compression in collisionless colliding fast plasma flows

In many natural phenomena in space (cosmic-rays, fast winds), non-thermal ion populations are produced, with wave-particle interactions in self-induced electromagnetic turbulence being suspected to be mediators. However, the processes by which the electromagnetic energy is bestowed upon the particles is debated, and in some cases requires field compression. Here we show that laboratory experiments using high-power lasers and external strong magnetic field can be used to infer magnetic field compression in the interpenetration of two collisionless, high-velocity (0.01–0.1c) quasi-neutral plasma flows. This is evidenced through observed plasma stagnation at the flows collision point, which Particle-in-Cell (PIC) simulations suggest to be the signature of magnetic field compression into a thin layer, followed by its dislocation into magnetic vortices. Acceleration of protons from the plasma collision is observed as well. As a possible scenario, with 1D and 2D PIC simulations we consider a compression of the vortices against dense plasma remnants.

Transport Barrier Triggered by Resonant Three-Wave Processes Between Trapped-Particle-Modes and Zonal Flow

We address the mechanisms underlying low-frequency zonal flow generation in a turbulent system through the parametric decay of collisionless trapped particle modes and its feedback on the stabilization of the system. This model is in connection with the observation of barrier transport in reduced gyrokinetic simulations (A. Ghizzo et al., Euro. Phys. Lett. 119(1), 15003 (2017)). Here the analysis is extended with a detailed description of the resonant mechanism. A key role is also played by an initial polarisation source that allows the emergence of strong initial shear flow. The parametric decay leads to the growth of a zonal flow which differs from the standard zero frequency zonal flow usually triggered by the Reynolds stress in fluid drift-wave turbulence. The resulting zonal flow can oscillate at low frequency close to the ion precession frequency, making it sensitive to strong amplification by resonant kinetic processes. The system becomes then intermittent. These new findings, obtained from numerical experiments based on reduced semi-Lagrangian gyrokinetic simulations, shed light on the underlying physics coming from resonant wave-particle interactions for the formation of transport barriers. Numerical simulations are based on a Hamiltonian reduction technique, including magnetic curvature and interchange turbulence, where both fastest scales (cyclotron and bounce motions) are gyro-averaged.

Guiding-centre theory for kinetic-magnetohydrodynamic modes in strongly flowing plasmas

A kinetic-magnetohydrodynamic model with kinetic pressure closure is derived from a consistent guiding-centre framework. Higher-order (gyroviscous) corrections to the pressure tensor are derived in complex geometry from a reduced kinetic equation. The proposed model allows for flows of the order of the thermal ion velocity, taking into account important centrifugal effects due to the E × B flow, as well as the effects of diamagnetic flows associated with finite Larmor radius corrections to both ion fluid inertia and long mean-free path contributions. Wave–particle interactions, such as toroidal drift-resonance, are retained. Furthermore, the linearised model includes a quasi-neutrality equation, allowing the effects of a parallel electric field to be studied in fast rotating tokamak plasmas.

Test charge response and correlations in multi-ion plasmas

The interaction potentials caused by a pair of moving test charges are studied in collisionless unmagnetized multi-ion plasmas, containing the electrons, singly ionized positive ions, and two negative ions. Starting from the Vlasov-Poisson coupled equations, a generalized electrostatic potential is obtained for a pair of test charges moving with constant velocities along the z-axis. Based on the speeds and correlations of test charges, the cases of slow, fast, and resonating test charge response are specifically studied and analyzed. If the test charges move with velocities much slower than the thermal speeds of all plasma species in multi-ion plasmas, then a short-range Debye-Hückel (DH) shielding potential appears to decay exponentially with the distance, whereas the long-range far-field (FF) potential varies as the inverse cube of the distance from test charges. The shielding phenomenon does not occur if the test charges move much faster than the plasma thermal speeds. However, the oscillatory wakefield (WF) potentials only exist behind the test charges when their speeds resonate with the speed of ion-acoustic waves. Numerically, it is revealed that the profiles of DH, FF, and WF potentials are significantly affected by the multi-ion plasma parameters and correlation effects. The results might be helpful for understanding the shielding phenomena, particle-particle and wave-particle interactions in multi-ion laboratory plasmas.