The saturation of ion cyclotron Alfven turbulence excited by beam particles is investigated using resonance broadening theory. The stochastic scattering which decorrelates particles, includes both random acceleration by electric fields and a turbulent magnetic mirroring effect. Turbulent mirroring is shown to yield non-Gaussian corrections to the orbits even if the random electric and magnetic fields are Gaussian. The predicted steady-state turbulence level exhibits a peaked anglular distribution, with a maximum near Theta ~ 60 degrees.
The nonlinear dynamics of collisionless Alfven trains, including resonant particle effects is studied using the kinetic nonlinear Schroedinger (KNLS) equation model. Numerical solutions of the KNLS reveal the dynamics of Alfven waves to be sensitive to the sense of polarization as well as the angle of propagation with respect to the ambient magnetic field. The combined effects of both wave nonlinearity and Landau damping result in the evolutionary formation of stationaryOA S- and arc-polarized directional and rotational discontinuities. These waveforms are freqently observed in the interplanet…
We use a guiding center code ORBIT to study the broadening of resonances and the parametric dependence of the resonance frequency broadening width $ΔΩ$ on the nonlinear particle trapping frequency $ω_b$ of wave-particle interaction with specific examples using realistic equilibrium DIII-D shot 159243 (Collins et al. 2016 Phys. Rev. Lett. 116 095001). When the mode amplitude is small, the pendulum approximation for energetic particle dynamics near the resonance is found to be applicable and the ratio of the resonance frequency width to the deeply trapped bounce frequency $ΔΩ/ω_b$ equals 4, as p…
In this work we used Particle-In-Cell simulations to study the interaction of circularly polarised Alfvén waves with one dimensional plasma density inhomogeneities transverse to the uniform magnetic field (phase mixing) in collisionless plasmas. In our preliminary work we reported discovery of a new electron acceleration mechanism, in which progressive distortion of the Alfvén wave front, due to the differences in local Alfvén speed, generates an oblique (nearly parallel to the magnetic field) electrostatic field. The latter accelerates electrons through the Landau resonance. Here we report a …
Intermittent turbulence is key for understanding the stochastic nonlinear dynamics of space, astrophysical, and laboratory plasmas. We review the observation and theory of chaos and complexity in plasmas, and elucidate their links to intermittent plasma turbulence. First, we present evidence of magnetic reconnection and intermittent magnetic turbulence in coronal mass ejections in the solar corona and solar wind via remote and in situ observations. The signatures of turbulent magnetic reconnection, i.e., bifurcated current sheet, reconnecting jet, parallel/anti-parallel Alfvén waves, and spiky…
In the parts of the solar corona and solar wind that experience the fewest Coulomb collisions, the component proton, electron, and heavy ion populations are not in thermal equilibrium with one another. Observed differences in temperatures, outflow speeds, and velocity distribution anisotropies are useful constraints on proposed explanations for how the plasma is heated and accelerated. This paper presents new predictions of the rates of collisionless heating for each particle species, in which the energy input is assumed to come from magnetohydrodynamic (MHD) turbulence. We first created an em…
We perform a theoretical and numerical study of anti-parallel 2D magnetic reconnection with asymmetries in the density and reconnecting magnetic field strength in addition to a bulk flow shear across the reconnection site in the plane of the reconnecting fields, which commonly occurs at planetary magnetospheres. We predict the speed at which an isolated X-line is convected by the flow, the reconnection rate, and the critical flow speed at which reconnection no longer takes place for arbitrary reconnecting magnetic field strengths, densities, and upstream flow speeds, and confirm the results wi…
Evidence of energy conversion in weakly collisional plasma during an interplanetary coronal mass ejection
National Institute for Astrophysics, Institute for Space Astrophysics and Planetology（国家天体物理研究所，空间天体物理学与行星级学研究所）；Department of Physics, University of Mumbai（孟买大学物理系）；Istituto per la Scienza e Tecnologia dei Plasmi, Consiglio Nazionale delle Ricerche (ISTP-CNR)（等离子体科学与技术研究所，意大利国家研究委员会）；Center of Excellence in Space Sciences India, Indian Institute of Science Education and Research Kolkata（印度空间科学卓越中心，印度科学教育与研究学院加尔各答分校）；Center for Space Plasma and Aeronomic Research (CSPAR), The University of Alabama in Huntsville（空间等离子体与大气学研究中心，阿拉巴马大学亨茨维尔分校）；Indian Institute of Geomagnetism (IIG)（印度地磁研究所）
We study the amplitude modulation of nonlinear kinetic Alfv{é}n waves (KAWs) in an intermediate low-beta magnetoplasma. Starting from a set of fluid equations coupled to the Maxwell's equations, we derive a coupled set of nonlinear partial differential equations (PDEs) which govern the evolution of KAW envelopes in the plasma. The modulational instability (MI) of such KAW envelopes is then studied by a nonlinear Schr{ö}dinger (NLS) equation derived from the coupled PDEs. It is shown that the KAWs can evolve into bright envelope solitons, or can undergo damping depending on whether the characte…
We present a method for studying the evolution of plasma turbulence by tracking dispersion relations in the energy spectrum in the wavenumber-frequency domain. We apply hybrid plasma simulations in a simplified two-dimensional geometry to demonstrate our method and its applicability to plasma turbulence in the ion kinetic regime. We identify four dispersion relations: ion-Bernstein waves, oblique whistler waves, oblique Alfvén/ion-cyclotron waves, and a zero-frequency mode. The energy partition and frequency broadening are evaluated for these modes. The method allows us to determine the evolut…
We discuss the physics of stochastic particle acceleration in relativistic magnetohydrodynamic (MHD) turbulence, combining numerical simulations of test-particle acceleration in synthetic wave turbulence spectra with detailed analytical estimates. In particular, we study particle acceleration in wavelike isotropic fast mode turbulence, in Alfvén and slow Goldreich-Sridhar type wave turbulence (properly accounting for anisotropy effects), including resonance broadening due to wave decay and pitch-angle randomization. At high particle rigidities, the contributions of those three modes to acceler…
Evolution of ion distribution functions in ionospheric plasmas perturbed by Alfvén waves
University of Trento（特伦托大学）；National Institute of Astrophysics-IAPS（国家天体物理研究所-IAPS）；Northumbria University（诺森比亚大学）；Imperial College London（伦敦帝国理工学院）；University of L’Aquila（拉奎拉大学）
The motivation for this study is to include the effect of plasma flow in Alfvén wave (AW) damping via phase mixing and to explore the observational implications. Our magnetohydrodynamic (MHD) simulations and analytical calculations show that, when a background flow is present, mathematical expressions for the AW damping via phase mixing are modified by the following substitution: $C_A^\prime(x) \to C_A^\prime(x)+V_0^\prime(x)$, where $C_A$ and $V_0$ are AW phase and the flow speeds, and the prime denotes a derivative in the direction across the background magnetic field. In uniform magnetic fi…
We discuss properties of Alfvénic fluctuations with large amplitude in plasmas characterised by low magnetic field compression. We note that in such systems power laws can not develop with arbitrarily steep slopes at large scales, i.e. when $|δ\bf{B}|$ becomes of the order of the background field $|\bf{B}|$. In such systems there is a scale $l_0$ at which the spectrum has to break due to the condition of weak compressibility. A very good example of this dynamics is offered by solar wind fluctuations in Alfvénic fast streams, characterised by the property of constant field magnitude. We show he…
We investigate the validity of Taylor's Hypothesis (TH) in the analysis of Alfvénic fluctuations of velocity and magnetic fields in solar wind streams measured by Parker Solar Probe (PSP)~during the first four encounters. We use PSP velocity and magnetic field measurements from 24 h intervals selected from each of the first four encounters. The applicability of TH is investigated by measuring the parameter $ε=δu_0/\sqrt{2}V_\perp$, which quantifies the ratio between the typical speed of large-scale fluctuations, $δu_0$, and the local perpendicular PSP speed in the solar wind frame, $V_\perp$. …
In this paper we apply a methodology, recently proposed by Bourouaine and Perez (2019) (BP19), to interpret solar-wind turbulent power spectra beyond Taylor approximation (TA). The turbulent power spectra were measured using \emph{Helios} spacecraft data near 0.6 au. We use the model proposed in BP19 to reproduce the field-perpendicular power spectrum $E(k_\perp)$ of anti-sunward Alfvénic fluctuations in the plasma frame (where $k_\perp$ is the field-perpendicular wavenumber) from the corresponding measured frequency power spectrum $P_{\rm sc}(ω,θ_b)$ along the sampling angle $θ_b$, which is t…
The solar wind is a structured and complex system, in which the fields vary strongly over a wide range of spatial and temporal scales. As an example, the turbulent activity in the wind affects the evolution in the heliosphere of the integral turbulent scale or correlation length [λ], usually associated with the breakpoint in the turbulent-energy spectrum that separates the inertial range from the injection range. This large variability of the fields demands a statistical description of the solar wind. In this work, we study the probability distribution function (PDF) of the magnetic autocorrel…
Spatiotemporal Properties of Compressible Magnetohydrodynamic Turbulence from Space Plasma
Institut für Physik und Astronomie, Universität Potsdam（波茨坦大学物理与天文学研究所）；Deutsches Elektronen-Synchrotron DESY（德国电子同步辐射中心）；Institute of Science and Technology for Deep Space Exploration, Nanjing University（南京大学深空探测科学与技术研究院）；Shandong Key Laboratory of Space Environment and Exploration Technology, Institute of Space Sciences, School of Space Science and Technology, Shandong University（山东大学空间科学与技术学院空间科学研究所空间环境与探测技术山东省重点实验室）；Universität Potsdam（波茨坦大学）
Numerical simulations of waves and turbulence in coronal loops: observables and spectra
Università della Calabria（卡拉布里亚大学）；Istituto per la Scienza e Tecnologia dei Plasmi, Consiglio Nazionale delle Ricerche (CNR-ISTP)（等离子体科学与技术研究所，意大利国家研究委员会）；Goethe Universität（法兰克福歌德大学）；Istituto Nazionale di Astrofisica - INAF（意大利国家天体物理研究所）；Università di Palermo（巴勒莫大学）；National Institute for Astrophysics, Astronomical Observatory of Palermo（意大利国家天体物理研究所，巴勒莫天文台）；Harvard-Smithsonian Center for Astrophysics（哈佛-史密森尼天体物理中心）；KU Leuven（荷语鲁汶大学）；Lockheed Martin Solar & Astrophysics Laboratory（洛克希德·马丁太阳与天体物理实验室）；University of Oslo（奥斯陆大学）
There is mounting evidence in solar wind observations and in numerical simulations that kinetic and magnetic energies are not in equipartition in magnetohydrodynamic turbulence. The origin of their mismatch, the residual energy E_r=E_v-E_b, is not well understood. In the present work this effect is studied analytically in the regime of weak magnetohydrodynamic turbulence. We find that residual energy is spontaneously generated by turbulent dynamics, and it has a negative sign, in good agreement with the observations. We obtain that the residual energy condenses around k_||=0 with its k_||-spec…
Large-scale magnetic fields thread through the electrically conducting matter of the interplanetary and interstellar medium, stellar interiors, and other astrophysical plasmas, producing anisotropic flows with regions of high-Reynolds-number turbulence. It is common to encounter turbulent flows structured by a magnetic field with a strength approximately equal to the root-mean-square magnetic fluctuations. In this work, direct numerical simulations of anisotropic magnetohydrodynamic (MHD) turbulence influenced by such a magnetic field are conducted for a series of cases that have identical res…
Properties of Magnetic Switchbacks in the Near-Sun Solar Wind
Center for Astrophysics, Harvard & Smithsonian（哈佛-史密森天体物理中心）；Institut de Recherche en Astrophysique et Planétologie, CNES, CNRS, Université de Toulouse（天体物理学与行星学研究所，法国国家空间研究中心，法国国家科学研究中心，图卢兹大学）；Department of Physics, Imperial College London（帝国理工学院物理系）；Space Sciences Laboratory, University of California, Berkeley（加州大学伯克利分校空间科学实验室）；Astronomy and Space Physics Department, National Taras Shevchenko University of Kyiv（基辅塔拉斯舍甫琴科国立大学天文与空间物理系）；Department of Climate and Space Sciences and Engineering, University of Michigan（密歇根大学气候与空间科学与工程系）；LPC2E, OSUC, Univ Orleans, CNRS, CNES（奥尔良大学地球与环境过程实验室，观测与研究宇宙学与气候系统观测站，法国国家科学研究中心，法国国家空间研究中心）；International Space Science Institute（国际空间科学研究所）
As a fundamental astrophysical process, the scattering of particles by turbulent magnetic fields has its physical foundation laid by the magnetohydrodynamic (MHD) turbulence theory. In the framework of the modern theory of MHD turbulence, we derive a generalized broadened resonance function by taking into account both the magnetic fluctuations and nonlinear decorrelation of turbulent magnetic fields arising in MHD turbulence, and we specify the energy range of particles for the dominance of different broadening mechanisms. The broadened resonance allows for scattering of particles beyond the e…
In high-energy astronomical phenomena, the stochastic particle acceleration by turbulences is one of the promising processes to generate non-thermal particles. In this paper, we investigate the energy-diffusion efficiency of relativistic particles in a temporally evolving wave ensemble that consists of a single mode (Alfvén, fast or slow) of linear magnetohydrodynamic waves. In addition to the gyroresonance with waves, the transit-time damping (TTD) also contributes to the energy-diffusion for fast and slow-mode waves. While the resonance condition with the TTD has been considered to be fulfil…
