Mehul Chakraborty, Vipin K. Yadav, Rajneesh Kumar
Plasma instabilities are the non-linear processes occurring in plasmas when excess energy gets accumulated in a plasma system which is unable to hold it. There are almost 60 known plasma instabilities in nature.
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Generation of Streaming Beam-Plasma Instability in Variable Lunar Plasma around Moon
本文分析研究了月球等离子体环境中高能电子比例变化对双流不稳定性触发的影响，发现1%至25%的高能电子会改变色散关系并可能触发非线性现象。
The two-stream instability generation around Moon: Effect of Interplanetary Magnetic Field during Solar Wind - Lunar Plasma Interaction
研究太阳风与月球电子等离子体相互作用中，行星际磁场对双流不稳定性增长率的调制作用，通过理论推导和粒子模拟揭示了磁场增强导致增长率先快后慢的非线性行为。
Counter-Streaming Beams in Collisionless Pair Plasma Instability Systems I: Evolution and Parameterization of the Weibel Instability
本文利用粒子模拟的谱分析和物理场演化，研究了Weibel不稳定性在不同初始反向流束参数下的演化过程，观察到次级不稳定性、电磁波激发及丝状合并现象。
Filamentation due to the growth of a Weibel-type instability was observed in the interaction of a pair of counter-streaming, ablatively-driven plasma flows, in a supersonic, collisionless regime relevant to astrophysical collisionless shocks. The flows were created by irradiating a pair of opposing plastic (CH) foils with 1.8 kJ, 2-ns laser pulses on the OMEGA EP laser system. Ultrafast laser-driven proton radiography was used to image the Weibel-generated electromagnetic fields. The experimental observations are in good agreement with the analytical theory of the Weibel instability and with p…
Counter-Streaming Beams in Collisionless Pair Plasma Instability Systems III: Collisionless Heating, Acceleration, and Radiation
本文研究无碰撞对等离子体中韦伯不稳定性形成的大电流丝合并的能量转换与动力学效应，并探讨相关辐射过程与抖动及同步辐射的联系。
Counter-Streaming Beams in Collisionless Pair Plasma Instability Systems II: Spectral Cone and Spectral Wave Mode Analysis
本文通过粒子网格模拟的谱分析，研究无碰撞对等离子体中Weibel不稳定性的谱趋势，探讨功率对视角和频率的依赖，并关联系列首篇结果。
The solar wind wake behind the moon is studied with 1D electrostatic particle-in-cell (PIC) simulations using a physical ion to electron mass ratio (unlike prior investigations); the simulations also apply more generally to supersonic flow of dense magnetized plasma past non-magnetic objects. A hybrid electrostatic Boltzmann electron treatment is first used to investigate the ion stability in the absence of kinetic electron effects, showing that the ions are two-stream unstable for downstream wake distances (in lunar radii) greater than about three times the solar wind Mach number. Simulations…
A relativistic electron beam propagating through plasma induces a return current in the system. Such a system of counterstreaming forward and return current is susceptible to host of instabilities out of which Weibel remains a dominant mode for destabilizing the system. Weibel instability has been widely investigated in simulations, experiments, as well as, analytically using fluid and kinetic treatments. A purely growing mode like Weibel instability can also be understood by using conservation theorems and energy principle analysis. An electrostatic analog to the Weibel instability, two strea…
The Weibel instability driven by two symmetric counter-streaming relativistic electron plasmas, also referred to as current-filamentation instability, is studied in a constant and uniform external magnetic field aligned with the plasma flows. Both the linear and non linear stages of the instability are investigated using analytical modeling and Particle-In-Cell (PIC) simulations. While previous studies have already described the stabilizing effect of the magnetic field, we show here that the saturation stage is only weakly affected. The different mechanisms responsible for the saturation are d…
A non-resonant streaming instability driven by cosmic-ray currents, also called Bell's instability, is proposed as a candidate for providing the required magnetic turbulence of efficient diffusive shock accelerations. To demonstrate the saturation level and mechanism of the non-resonant streaming instability in a laboratory environment, we attempt to develop an experiment at the Photo Injector Test Facility at DESY, Zeuthen site (PITZ). As an electron beam is used to replace the proton beam to carry the cosmic-ray current in our experiment, the polarization of the non-resonant streaming instab…
Using fully-kinetic plasma simulations, we study the non-resonant (Bell) streaming instability driven by energetic leptons. We identify the necessary conditions to drive it and the differences from the standard proton-driven case in both linear and saturated stages. A simple analytic theory is presented to explain simulations. Our findings are crucial for understanding the phenomenology of astrophysical environments where only electrons may be accelerated (e.g., oblique shocks) or where relativistic pairs are produced (e.g., around pulsar wind nebulae).
The dispersion relation of kinetic Alfvén wave in inertial regime is studied in a three component non-degenerate streaming plasma. A lin- ear dispersion relation using fluid- Vlasov equation for quantum plasma is also derived. The quantum correction CQ raised due to the insertion of Bohm potential in Vlasov model causes the suppression in the Alfven wave frequency and the growth rates of instability. A number of analytical expressions are derived for various modes of propagation. It is also found that many system parameters, i.e, streaming velocity, dust charge, num- ber density and quantum co…
Magnetic field amplification by relativistic streaming plasma instabilities is central to a wide variety of high-energy astrophysical environments as well as to laboratory scenarios associated with intense lasers and electron beams. We report on a new secondary nonlinear instability which arises for relativistic dilute electron beams after the saturation of the linear Weibel instability. This instability grows due to the transverse magnetic pressure associated with the beam current filaments, which cannot be quickly neutralized due to the inertia of background ions. We show that it can amplify…
Using hybrid simulations (kinetic ions--fluid electrons), we test the linear theory predictions of the cosmic ray (CR) streaming instability. We consider two types of CR distribution functions: a "hot" distribution where CRs are represented by a drifting power law in momentum and an anisotropic "beam" of monochromatic particles. Additionally, for each CR distribution we scan over different CR densities to transition from triggering the resonant to the non-resonant (Bell) streaming instability. We determine the growth rates of these instabilities in simulations by fitting an exponential curve d…
A strong super-Alfvénic drift of energetic particles (or cosmic rays, CRs) in a magnetized plasma can amplify the magnetic field significantly through non-resonant streaming instability (NRSI). While the traditional analysis is done for an ion current, here we use kinetic particle-in-cell simulations to study how the NRSI behaves when it is driven by electrons or by a mixture of electrons and positrons. In particular, we characterize growth rate, spectrum, and helicity of the unstable modes, as well the level of magnetic field at saturation. Our results are potentially relevant for several spa…
Ion-Acoustic Waves and the Proton-Alpha Streaming Instability at Collisionless Shocks
该研究结合MMS观测与数值模拟，揭示低马赫数无碰撞激波中质子与阿尔法粒子的相对漂移引发质子-阿尔法粒子流不稳定性，产生与观测一致的离子声波，解释了电阻率来源并预测其非线性演化。
Interplay between the non-resonant streaming instability and self-generated pressure anisotropies
研究非共振流不稳定性与自生成压力各向异性之间的相互作用，揭示中性碰撞对磁场增强的影响及电离等离子体中库仑碰撞的作用。
In plasmas where the thermal energy density exceeds the magnetic energy density ($β_\parallel > 1$), the aperiodic ordinary mode (O-mode) instability is driven by an excess of parallel temperature $A = T_\perp /T_\parallel < 1$ (where $\parallel$ and $\perp$ denote directions relative to the uniform magnetic field). When stimulated by parallel plasma streams the instability conditions extend to low beta states, i.e., $β_\parallel <1$, and recent studies have proven the existence of a new regime, where the anisotropy threshold decreases steeply with lowering $β_\parallel \to 0$ if the streaming…
Alfvénic component of MHD turbulence damps Alfvénic waves. The consequences of this effect are important for many processes, from cosmic ray (CR) propagation to launching outflows and winds in galaxies and other magnetized systems. We discuss the differences in the damping of the streaming instability by turbulence and the damping of a plane parallel wave. The former takes place in the system of reference aligned with the local direction of magnetic field along which CRs stream. The latter is in the reference frame of the mean magnetic field and traditionally considered in plasma studies. We a…
Streaming cosmic rays can power the exponential growth of a seed magnetic field by exciting a non-resonant instability that feeds on their bulk kinetic energy. By generating the necessary turbulent magnetic field, it is thought to play a key role in the confinement and acceleration of cosmic rays at shocks. In this work we present hybrid-Particle-In-Cell simulations of the non-resonant mode including Monte Carlo collisions, and investigate the interplay between the pressure anisotropies produced by the instability and particle collisions in the background plasma. Simulations of poorly ionized …
From Filamentation to Stratification: Instability Dynamics in Scissors-Shaped Relativistic Beam-Plasma System
本文提出剪刀形相对论束-等离子体构型，发现其不稳定性由丝化转变为分层模式，并被磁重联快速抑制，从而以几何方式实现被动不稳定性控制。
The nonlinear development of streaming instabilities in the current layers formed during magnetic reconnection with a guide field is explored. Theory and 3-D particle-in-cell simulations reveal two distinct phases. First, the parallel Buneman instability grows and traps low velocity electrons. The remaining electrons then drive two forms of turbulence: the parallel electron-electron two-stream instability and the nearly-perpendicular lower hybrid instability. The high velocity electrons resonate with the turbulence and transfer momentum to the ions and low velocity electrons.
We study the streaming instability of GeV$-100~$GeV cosmic rays (CRs) and its damping in the turbulent interstellar medium (ISM). We find that the damping of streaming instability is dominated by ion-neutral collisional damping in weakly ionized molecular clouds, turbulent damping in the highly ionized warm medium, and nonlinear Landau damping in the Galactic halo. Only in the Galactic halo, is the streaming speed of CRs close to the Alfvén speed. Alfvénic turbulence plays an important role in both suppressing the streaming instability and regulating the diffusion of streaming CRs via magnetic…
Plasma boundary layers are susceptible to electrostatic instabilities driven by ion flows in presheaths and, when present, these instabilities can influence transport. In plasmas with a single species of positive ion, ion-acoustic instabilities are expected under conditions of low pressure and large electron-to-ion temperature ratio ($T_e/T_i \gg 1$). In plasmas with two species of positive ions, ion-ion two-stream instabilities can also be excited. The stability phase-space is characterized using the Penrose criterion and approximate linear dispersion relations. Predictions for how these inst…
Understanding Streaming Instabilities in the Limit of High Cosmic Ray Current Density
本文利用动理学粒子模拟研究高宇宙线电流密度下Bell不稳定性的行为，发现各向异性加热导致磁场放大显著减弱，且电子尺度模式对后期演化和饱和影响有限。
The stability of two quantum counter-streaming electron beams is investigated within the quantum plasma fluid equations for arbitrarily oriented wave vectors. The analysis reveals that the two quantum two-stream unstable branches are indeed connected by a continuum of unstable modes with oblique wave vectors. Using the longitudinal approximation, the stability domain for any k is analytically explained, together with the growth rate.
Plasma refilling of the lunar wake: plasma-vacuum interactions, electrostatic shocks, and electromagnetic instabilities
本研究通过全动力学PIC模拟揭示月球尾迹填充过程：早期遵循等离子体-真空理论，后期离子束碰撞产生静电激波并激发电磁不稳定性，为理解尾迹动力学和航天器观测提供新视角。
We explore the physics of the gyro-resonant cosmic ray streaming instability (CRSI) including the effects of ion-neutral (IN) damping. This is the main damping mechanism in (partially-ionized) atomic and molecular gas, which are the primary components of the interstellar medium (ISM) by mass. Limitation of CRSI by IN damping is important in setting the amplitude of Alfvén waves that scatter cosmic rays and control galactic-scale transport. Our study employs the MHD-PIC hybrid fluid-kinetic numerical technique to follow linear growth as well as post-linear and saturation phases. During the line…
Electromagnetic emission from plasma with counter-streaming electron beams in the regime of oblique instability dominance
本研究通过粒子模拟探讨反向传播电子束注入等离子体产生电磁辐射的问题，发现激发小尺度斜等离子体振荡可实现高束辐射转换效率，辐射产生于等离子体频率二次谐波附近，且效率与光谱不依赖束厚度，系统参数可由精确线性理论确定。
In a recent work [Bret, EPL \textbf{135} (2021) 35001], quantum electrodynamic (QED) effects were evaluated for the two-stream instability. It pertains to the growth of perturbations with a wave vector oriented along the flow in a collisionless counter-streaming system. Here, the analysis is extended to every possible orientation of the wave vector. The previous result for the two-stream instability is recovered, and it is proved that even within the framework of a 3D analysis, this instability remains fundamentally 1D even when accounting for QED effects. The filamentation instability, found …
The hierarchy of unstable modes when two counter-streaming pair plasmas interact over a flow-aligned magnetic field has been recently investigated [PoP \textbf{23}, 062122 (2016)]. The analysis is here extended to the case of an arbitrarily tilted magnetic field. The two plasma shells are initially cold and identical. For any angle $θ\in [0,π/2]$ between the field and the initial flow, the hierarchy of unstable modes is numerically determined in terms of the initial Lorentz factor of the shells $γ_0$, and the field strength as measured by a parameter denoted $σ$. For $θ=0$, four different kind…
We show that grains streaming through a fluid are generically unstable if their velocity, projected along some direction, matches the phase velocity of a fluid wave (linear oscillation). This can occur whenever grains stream faster than any fluid wave. The wave itself can be quite general--sound waves, magnetosonic waves, epicyclic oscillations, and Brunt-Väisälä oscillations each generate instabilities, for example. We derive a simple expression for the growth rates of these "resonant drag instabilities" (RDI). This expression (i) illustrates why such instabilities are so virulent and generic…
Cosmic ray propagation in the Milky Way and other galaxies is largely diffusive, with mean free path determined primarily by pitch angle scattering from hydromagnetic waves with wavelength of order the cosmic ray gyroradius. In the theory of cosmic ray self confinement, the waves are generated by instabilities driven by the cosmic rays themselves. The dominant instability is due to bulk motion, or streaming, of the cosmic rays, parallel to the background magnetic field B, and transfers cosmic ray momentum and energy to the thermal gas as well as confining the cosmic rays. Classical arguments a…
Plasma streaming instabilities play an important role in magnetic field amplification and particle acceleration in relativistic shocks and their environments. However, in the far shock precursor region where accelerated particles constitute a highly relativistic and dilute beam, streaming instabilities typically become inefficient and operate at very small scales when compared to the gyroradii of the beam particles. We report on a plasma cavitation instability that is driven by dilute relativistic beams and can increase both the magnetic field strength and coherence scale by orders of magnitud…
The filamentation instability driven by two spatially uniform and counter-streaming beams of charged particles in plasmas is modelled by a particle-in-cell (PIC) simulation. Each beam consists of the electrons and positrons. The four species are equally dense and they have the same temperature. The one-dimensional simulation direction is orthogonal to the beam velocity vector. The magnetic field grows spontaneously and rearranges the particles in space, such that the distributions of the electrons of one beam and the positrons of the second beam match. The simulation demonstrates that as a res…
Several important mechanisms that explain the coherent pulsar radio emission rely on streaming (or beam) instabilities of the relativistic pair plasma in a pulsar magnetosphere. However, it is still not clear whether a streaming instability by itself is sufficient to explain the observed coherent radio emission. Due to the relativistic conditions that are present in the pulsar magnetosphere, kinetic instabilities could be quenched. Moreover, uncertainties regarding specific model-dependent parameters impede conclusions concerning this question. We aim to constrain the possible parameter range …
The instabilities triggered when two counter-streaming pair beams collide are analyzed. A guiding magnetic field is accounting for, while both beams are considered identical and cold. The instability analysis is conducted over the full \textbf{k}-spectrum, allowing to derive the hierarchy map of the dominant unstable modes, in terms of the initial beams energy $γ_0$ and a magnetic field strength parameter $Ω_B$. Four different regions of the $(Ω_B,γ_0)$ phase space are identified, each one governed by a different kind of mode. The analysis also unravels the existence of a "triple point", where…
Nonlinear Saturation of the Acoustic Resonant Drag Instability
研究声学共振拖曳不稳定性在非线性阶段的饱和机制，揭示其与湍流涡旋翻转时间尺度的平衡关系。
We study the stability of current filaments produced by the Weibel, or current filamentation, instability in weakly magnetized counter-streaming plasmas. It is shown that a resonance exists between the current-carrying ions and a longitudinal drift-kink mode that strongly deforms and eventually breaks the current filaments. Analytical estimates of the wavelength, growth rate and saturation level of the resonant mode are derived and validated by three-dimensional particle-in-cell simulations. Furthermore, self-consistent simulations of counter-streaming plasmas indicate that this drift-kink mod…
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