Ion Beam Instability Research Articles

A comparative study of ion beam and velocity shear driven resonant instability of kinetic Alfvén waves with [formula omitted]-electrons

A comparative analysis is carried out between the ion beam and velocity shear as the possible source of free energy in the generation of kinetic Alfvén waves (KAWs) through a three-component theoretical model. The model consists of Kappa electrons, Maxwellian background ions, and drifting-Maxwellian beam ions as the constituent species. The ion beam and velocity shear-driven resonant instabilities of KAWs are investigated and the results are compared on a one-to-one basis. In the presence of κ-electrons, velocity shear is found to be a more effective source of free energy as compared to ion beam in the generation of KAWs. The threshold value of both energy sources in the excitation of KAWs is found numerically for a fixed set of plasma parameters. The characteristics of KAWs such as real frequency, parallel and perpendicular wavelength range, wave unstable region, growth rate, etc. are examined for both cases and the results are compared with the observed values relevant to Earth’s magnetotail.

Upstream Plasma Waves and Downstream Magnetic Reconnection at a Reforming Quasi-parallel Shock

With the help of a two-dimensional particle-in-cell simulation model, we investigate the long-time evolution (near 100Ωi0−1 , where Ω i0 is the ion gyrofrequency in the upstream) of a quasi-parallel shock. Some of the upstream ions are reflected by the shock front, and their interactions with the incident ions excite low-frequency magnetosonic waves in the upstream. Detailed analyses have shown that the dominant wave mode is caused by the resonant ion–ion beam instability, and the wavelength can reach tens of ion inertial lengths. Although these plasma waves are directed toward the upstream in the upstream plasma frame, they are brought by the incident plasma flow toward the shock front, and their amplitude is enhanced during the approaching. The interaction of the upstream plasma waves with the shock leads to the cyclic reformation of the shock front, and the reformation period is slightly larger than 10 Ωi0−1 . When crossing the shock front, these large-amplitude plasma waves are compressed and evolve into current sheets in the transition region of the shock. At last, magnetic reconnection occurs in these current sheets, accompanying the generation of magnetic islands. Simultaneously, there still exist plasma waves of another kind, with the wavelength of several ion inertial lengths in the ramp of the shock, which are excited by the nonresonant ion–ion beam instability. The current sheets in the transition region are distorted and broken into several segments when the plasma waves of this kind are transmitted into the downstream, where magnetic reconnection and the generated islands have a much smaller size. No obvious ion flow can be observed around some X-lines produced in the magnetic reconnection, and this implies that electron-only reconnection may occur.

Electromagnetic Ion Beam Instability in the Solar Corona

Remote-sensing measurements indicate that heavy ions in the corona undergo an anisotropic and mass-charge dependent energization. A popular explanation to this phenomenon is the damping of the Alfvén/ion cyclotron waves. In this paper, we propose that the ion beam instability can be an important source of the Alfvén/ion cyclotron waves, and we study the excitation of the ion beam instability in the corona at the heliocentric distance ∼3R ⊙ and the corresponding energy transfer process therein based on plasma kinetic theory. The results indicate that the existence of the motionless heavy ions inhibits the ion beam instability. However, the anisotropic beams of heavy ions promote the excitation of the ion beam instability. Besides, the existence of α beams can provide a second energy source for exciting beam instability. However, when both the proton beam and the α beam reach the instability excitation threshold, the proton beam driven instability excites preferentially. Moreover, the excitation threshold of the Alfvén/ion cyclotron instability driven by ion beam is of the local Alfvén speed or even less in the corona.

Particle-in-cell simulations – ion beam instabilities and the generation of Alfvén and whistler waves in low β plasma

ABSTRACT Ion beam-driven instabilities in a collisionless space plasma with low β, i.e. low plasma and magnetic pressure ratio, are investigated using particle-in-cell (PIC) simulations. Specifically, the effects of different ion drift velocities on the development of Buneman and resonant electromagnetic (EM) right-handed (RH) ion beam instabilities are studied. Our simulations reveal that both instabilities can be driven when the ion beam drift exceeds the theoretical thresholds. The Buneman instability, which is weakly triggered initially, dissipates only a small fraction of the kinetic energy of the ion beam while causing significant electron heating, owing to the small electron-ion mass ratio. However, we find that the ion beam-driven Buneman instability is quenched effectively by the resonant EM RH ion beam instability. Instead, the resonant EM RH ion beam instability dominates when the ion drift velocity is larger than the Alfvén speed, leading to the generation of RH Alfvén waves and RH whistler waves. We find that the intensity of Alfvén waves decreases with decrease of ion beam drift velocity, while the intensity of whistler waves increases. Our results provide new insights into the complex interplay between ion beams and plasma instabilities in low β collisionless space plasmas.

The ion acoustic instability during collisionless two-ion-species plasma expansion

A hypothesis of the electrostatic field for the expansion of a plasma composed of two ion species into a vacuum is proposed. The solution for expansion is derived analytically and verified by numerical simulations. The expansion region is predicted to exhibit a constant velocity difference between the two ion components, which could result in ion beam instability and, thus, an increase in ion temperature. The instability, which occurs in CH plasma, is also verified theoretically and examined by particle-in-cell simulations.

Faraday detector uranium isotope ratio measurement: Insights from solution- and laser ablation-based sampling methodologies on the Neoma MC-ICP-MS

In this study we utilize an all-faraday cup detector configuration on the Neoma MC-ICP-MS to perform uranium isotope ratio determinations from certified reference materials and a nuclear fuel precursor material via solution and laser ablation based sampling methodologies. The goal in performing these measurements is primarily to demonstrate that the all-faraday cup method can produce highly precise and accurate isotope ratios even at relatively low signal intensity levels while also developing a preliminary understanding of how the complex interplay between different amplifier resistor levels (e.g. 1011 vs 1013 Ω) and integration times impacts the precision and accuracy of different types of measurements. Our results show that the faraday cups with 1013 Ω resistors in their amplifier feedback loops can be used to produce accurate and relatively precise isotope ratios for ion beams down to ∼5 K cps. However, at the lower end of the signal intensities observed in this study, longer integration times are necessary to mitigate the impact of ion beam instability that can occur during laser ablation based sampling. Despite this potential limitation, the all-faraday cup method is highly versatile as exemplified by the analysis of a collection of uranium reference materials with highly variable uranium isotopic compositions.

The Radial Distribution of Ion-scale Waves in the Inner Heliosphere

Determining the mechanism responsible for plasma heating and particle acceleration is a fundamental problem in the study of the heliosphere. Due to efficient wave–particle interactions of ion-scale waves with charged particles, these waves are widely believed to be a major contributor to ion energization, and their contribution considerably depends on the wave occurrence rate. By analyzing the radial distribution of quasi-monochromatic ion-scale waves observed by the Parker Solar Probe, this work shows that the wave occurrence rate is significantly enhanced in the near-Sun solar wind, specifically 21%–29% below 0.3 au, in comparison to 6%–14% beyond 0.3 au. The radial decrease of the wave occurrence rate is not only induced by the sampling effect of a single spacecraft detection, but also by the physics relating to the wave excitation, such as the enhanced ion beam instability in the near-Sun solar wind. This work also shows that the wave normal angle θ, the absolute value of ellipticity ϵ, the wave frequency f normalized by the proton cyclotron frequency f cp, and the wave amplitude δ B normalized by the local background magnetic field B 0 slightly vary with the radial distance. The median values of θ, ∣ϵ∣, f, and δ B are about 9°, 0.73, 3f cp, and 0.01B 0, respectively. Furthermore, this study proposes that the wave mode natures of the observed left-handed and right-handed polarized waves correspond to the Alfvén ion cyclotron mode wave and the fast magnetosonic whistler mode wave, respectively.

The Oblique Alfvén Ion Beam Instability in the Earth's Ion Foreshock

How ions evolve in the Earth’s ion foreshock is a basic problem in the heliosphere community, and the ion beam instability is usually proposed to be one major mechanism affecting the ion dynamics therein. This work will perform comprehensive analyses of the oblique ion beam instability in the Earth’s ion foreshock. We show that in addition to two well-known parallel instabilities (i.e., the parallel fast-magnetosonic whistler instability and the parallel Alfvén ion cyclotron instability), the oblique Alfvén ion beam (OA/IB) instability can also be triggered by free energy relating to the relative drift dV between the solar wind proton and reflected proton populations. For slow dV (e.g., dV ≲ 2.2V A , where V A denotes the Alfvén speed), it only triggers the OA/IB instability. When dV ≳ 2.2V A , the growth rate in the OA/IB instability can be about 0.6 times the maximum growth rate in parallel instabilities. Moreover, this work finds the existence of two types of OA/IB instabilities. The first one appears at slow dV and in the small wavenumber region at fast dV, and this instability can be described by the cold fluid model. The second one arises in large wavenumber regions at fast dV, and this instability only appears in warm plasmas. Furthermore, through the energy transfer rate method, we propose that the OA/IB instability is driven by the competition among the Landau and cyclotron wave-particle interactions of beam protons, the cyclotron wave-particle interaction of core protons, and the Landau wave-particle interaction of electrons. Because oblique waves can experience significant damping, the importance of the OA/IB instability may be the effective heating of ions in the Earth’s foreshock.

Oblique propagation and temperature effects on the resonant right-hand ion beam instability

The resonant right-hand instability (RHI) is often the dominant mode driven by reflected ions upstream of Earth’s quasi-parallel bow shock. In the tradition of Peter Gary, this paper further explores the right-hand instability using numerical solutions of the plasma dispersion relation and non-linear kinetic simulations, with parameters inspired by observations from NASA’s Magnetospheric Multiscale (MMS) mission. Agreement is found between the ion distributions in the particle-in-cell simulations and Magnetospheric Multiscale spacecraft data, which show the gyrophase bunching characteristic of the instability. The non-linear structures created by right-hand instability tend to be stronger when the plasma beta is lower. These structures have sizes of around 100 to 200 ion inertial lengths perpendicular to the magnetic field, presenting planet-sized disturbances to the magnetosphere. 2d and 3D hybrid particle-in-cell simulations show that modes with a range of propagation angles oblique to the magnetic field are excited, providing a ground to understand previous statistical studies of observed foreshock waves.

Hybrid simulations of the decay of reconnected structures downstream of the bow shock

Observations by Magnetospheric Multiscale have demonstrated that magnetic reconnection occurs at Earth's bow shock, typically at thin current sheets arising from plasma instabilities and turbulence in the shock transition region. Observational surveys of both the shock transition and the magnetosheath downstream suggest that the number of current sheets in these regions may not be strongly dependent on the shock Mach number MA or the angle between the upstream magnetic field and shock normal (θBn). This result is somewhat surprising given that quasi-parallel and high Mach number shocks tend to have a more disordered and non-stationary structure. In order to investigate how shock reconnection manifests across different parameters, we perform a series of hybrid (fluid electron, kinetic ion) particle-in-cell simulations across a range of Mach numbers and orientations. Given that hybrid simulations cannot resolve electron-scale current sheets and reconnection, these simulations isolate an ion-scale mechanism for shock reconnection driven by an ion–ion beam instability in the foot. We find that this mechanism is strongly constrained to quasi-parallel shocks across all simulated Mach numbers. By quantifying reconnection using the area occupied by plasma on closed magnetic field lines, we find the number of reconnecting structures and closed field area increase with MA and decrease with θBn in the upstream and ramp regions. Downstream of the shock, however, we find a similar result to observational surveys: within the subset of quasi-parallel shocks, the decay rate of the closed field area (and hence thin current sheets) is not strongly dependent on upstream shock parameters.

A global view of Pc3 wave activity in near-Earth space: Results from hybrid-Vlasov simulations

Ultra-low frequency (ULF) waves in the Pc3 range, with periods between 10–45 s, are routinely observed in Earth’s dayside magnetosphere. They are thought to originate in the foreshock, which extends upstream of the quasi-parallel bow shock and is populated with shock-reflected particles. The foreshock is permeated with ULF waves generated by ion beam instabilities, most notably the “30-s” waves whose periods match those of the Pc3 waves and which are carried earthward by the solar wind flow. However, the global picture of Pc3 wave activity from the foreshock to the magnetosphere and its response to changing solar wind conditions is still poorly understood. In this study, we investigate the global distribution and properties of Pc3 waves across near-Earth space using global simulations performed with the hybrid-Vlasov model Vlasiator. The simulations enable us to study the waves in their global context, and compare their properties in the foreshock, magnetosheath and dayside magnetosphere, for different sets of upstream solar wind conditions. We find that in all three regions the Pc3 wave power peaks at higher frequencies when the interplanetary magnetic field (IMF) strength is larger, consistent with previous studies. The Pc3 wave power is significantly enhanced in all three regions for higher solar wind Alfvén Mach number. As this parameter is known to affect the shock properties but has little impact inside the magnetosphere, this brings further support to the magnetospheric waves originating in the foreshock. Other parameters that are found to influence the foreshock wave power are the solar wind density and the IMF cone angle. Inside the magnetosphere, the wave power distribution depends strongly on the IMF orientation, which controls the foreshock position upstream of the bow shock. The wave power is largest when the angle between the IMF and the Sun-Earth line is smallest, suggesting that wave generation and transmission are most efficient in these conditions.

Observations of Whistler-mode Waves and Large-amplitude Electrostatic Waves Associated with a Dipolarization Front in the Bursty Bulk Flow

Plasma jets and jet fronts are common phenomena in planetary magnetospheres. They are usually associated with many plasma waves and can play a key role in the energy conversion, the excitation of wave emissions, particle acceleration, and the evolution of many astrophysical phenomena, which are major issues in the study of helio-terrestrial space physics. In this paper, we carefully investigated the properties of the whistler-mode wave and large-amplitude electrostatic wave in a plasma jet (bursty bulk flow (BBF)) using the Magnetospheric Multiscale mission data on the Earth's magnetosphere. At the leading part of the BBF, intense whistler-mode waves were observed inside the ion mirror-mode structures, which should be excited by the perpendicular temperature anisotropy of trapping electrons. A small-scale dipolarization front (DF) was then observed at the center of this BBF as a boundary between the leading and trailing parts of the BBF. Behind the DF, both an ion mirror-mode structure and whistler-mode waves disappear, while a large-amplitude electrostatic wave was detected and was associated with the cold ions at the trailing part of the BBF. The electrostatic wave is supposed to be generated by ion beam instability. These results will significantly improve the understanding of the kinetic process associated with the important boundary layer DF within plasma jets. The corresponding wave–particle interaction in space and the plasma environment can be further understood.

Linear Theory of Electromagnetic Ion Beam Instabilities in the Earth’s Forshock: Peter Gary’s Contributions (1981–1991)

We discuss Peter Gary’s contributions to the understanding of the origin and properties of ultra-low frequency (ULF) waves in the Earth’s foreshock during the period when the International Sun Earth Explorer spacecraft (ISEE-1 and -2) provided unique data about the plasma and wave environment in this region. Peter’s work concerning the linear theory of electromagnetic ion beam instabilities is contained in five journal articles and then summarized in a review article, all of which are discussed here. Brief summaries of observations and theory prior to ISEE as well as to later work are also included.

A Statistical Study of the Solar Wind Dependence of Multi‐Harmonic Toroidal ULF Waves Observed by the Arase Satellite

AbstractToroidal standing Alfvén wave is one of the ultra‐low frequency waves that are frequently observed in the terrestrial magnetosphere. They sometimes exhibit multi‐harmonic frequency spectra, indicating wide energy range input in the magnetosphere. However, their energy source has not been fully understood due to the lack of statistical studies. Here we used the data of the Arase satellite observations for ∼3.5 years and conducted a statistical analysis of the solar wind dependence of the occurrence rate, wave power, and frequency of the multi‐harmonic toroidal waves. We automatically detected the multi‐harmonic waves and categorized them into four groups according to the solar wind velocity and the cone angle of the interplanetary magnetic field. We found that the occurrence rate and wave power of the multi‐harmonic waves increase with the solar wind velocity on the flank sides. In the noon sector, the occurrence rate of the multi‐harmonic waves increases with the decrease of the cone angle. The median frequency of the multi‐harmonic waves on the dayside is positively correlated with the upstream wave frequency predicted by the theory of the ion beam instability for a small cone angle. The occurrence rate also increases with the solar wind dynamic pressure fluctuations. Therefore, we suggest that the Kelvin‐Helmholtz instability, the upstream waves, and the dynamic pressure fluctuations are possible sources of the multi‐harmonic waves. This study sheds light on the activity of the multi‐harmonic waves which can affect radiation belt electrons under various solar wind conditions.

Hybrid particle-in-cell simulations of electromagnetic coupling and waves from streaming burst debris

Various systems can be modeled as a point-like explosion of ionized debris into a magnetized, collisionless background plasma—including astrophysical examples, active experiments in space, and laser-driven laboratory experiments. Debris streaming from the explosion parallel to the magnetic field may drive multiple resonant and non-resonant ion–ion beam instabilities, some of which can efficiently couple the debris energy to the background and may even support the formation of shocks. We present a large-scale hybrid (kinetic ions + fluid electrons) particle-in-cell simulation, extending hundreds of ion inertial lengths from a 3D explosion, that resolves these instabilities. We show that the character of these instabilities differs notably from the 1D equivalent by the presence of unique transverse structure. Additional 2D simulations explore how the debris beam length, width, density, and speed affect debris–background coupling, with implications for the generation of quasi-parallel shocks.

Electromagnetic Proton Beam Instabilities in the Inner Heliosphere: Energy Transfer Rate, Radial Distribution, and Effective Excitation

Abstract Differential flows among different ion species are often observed in the solar wind, and such ion differential flows can provide the free energy to drive Alfvén/ion cyclotron and fast-magnetosonic/whistler instabilities. Previous works mainly focused on ion beam instability under the parameters representative of the solar wind nearby 1 au. In this paper we further study proton beam instability using the radial models of the magnetic field and plasma parameters in the inner heliosphere. We explore a comprehensive distribution of proton beam instability as functions of the heliocentric distance and the beam speed. We also perform a detailed analysis of the energy transfer between unstable waves and particles and quantify how much the free energy of the proton beam flows into unstable waves and other kinds of particle species (i.e., proton core, alpha particle, and electron). This work clarifies that both parallel and perpendicular electric fields are responsible for the excitation of oblique Alfvén/ion cyclotron and oblique fast-magnetosonic/whistler instabilities. Moreover, this work proposes an effective growth length to estimate whether the instability is efficiently excited or not. It shows that oblique Alfvén/ion cyclotron instability, oblique fast-magnetosonic/whistler instability, and oblique Alfvén/ion beam instability can be efficiently driven by proton beams drifting at the speed ∼600–1300 km s−1 in the solar atmosphere. In particular, oblique Alfvén/ion cyclotron waves driven in the solar atmosphere can be significantly damped therein, leading to solar corona heating. These results are helpful for understanding proton beam dynamics in the inner heliosphere and can be verified through in situ satellite measurements.

ULF Waves Observed by Lunar Prospector

AbstractWe have studied the spatial distribution of ultra‐low frequency (ULF) in the vicinity of the Moon using Lunar Prospector (LP) magnetometer data obtained at ∼100 km altitude during the period from February 20, 1998 to November 30, 1998. The lunar ULF waves are mostly identified over a broad frequency range of 10–60 mHz in the spacecraft frame. The occurrence rate of the ULF wave is high on the dayside above strong magnetic anomalies and depends on the interplanetary magnetic field orientation. We examine wave properties including the wave propagation direction and polarization. They are very similar to Kaguya observations, indicating that the ULF waves observed at LP and Kaguya are generated by the same mechanism. Although lunar ULF waves are commonly observed on the dayside above lunar magnetic anomalies, how they are established as a regular oscillation is not completely understood. In the present study, we suggest that the electromagnetic ion beam instability, driven by protons reflected from lunar magnetic anomalies, is the likely source of ULF waves observed at LP.

Observational Evidence for Fast Mode Periodic Small-scale Shocks: A New Type of Plasma Phenomenon

Abstract We show observational evidence for a new form of collisionless shock in interplanetary space near Mars, small-scale shocks with periodic spacings. Pickup of new ionized hydrogen atoms in a magnetic field aligned with the solar wind direction causes the generation of a magnetosonic wave train through an ion beam instability. The waves have a frequency close to the local proton gyrofrequency. This is a similar physical process as for the formation of cometary plasma waves/turbulence. However, for the case of proton pickup near Mars, each individual magnetosonic wave cycle develops into a small-scale shock. So there is a string of fast mode shocks formed with proton gyroperiod spacings. These small-scale shocks display dissipation in the ions and dispersive whistlers. A fraction of ions trapped/reflected at the small-scale shocks are accelerated by the motional electric field. Observational results demonstrate that periodic shocks can perform the same functions as a single supercritical shock in a high-speed flow.

A new class of Ion-acoustic solitons that can exist below critical Mach number

It is commonly believed that ion-acoustic solitons can only exist above the critical Mach number in a plasma system. A new class of ion-acoustic solitons that can exist below the critical Mach number is reported for the first time in a three-component plasma consisting of hot Maxwellian electrons, and two counterstreaming ion beams. The analysis is based on the Sagdeev pseudopotential technique, and considers a simple case of two counterstreaming proton beams with equal density and streaming velocity. Linear stability analysis shows that the slow ion-acoustic modes become unstable due to ion beam instability when the beam velocity normalized with the ion acoustic speed, U0, is in the range of 0.55 ≤ U0 ≤ 1.14. It is shown that when the normalized streaming velocity is below or at a threshold value, Uth = 1.14, only the regular solitons having Mach numbers greater than critical Mach number can exist. However, when the streaming velocity exceeds the threshold value (all modes are stable), both regular and the new class of ion-acoustic solitons can exist. A special case of unequal ion densities and unequal streaming velocities of the counterstreaming beams is considered in , and similar effects are found. Hence, the new class of slow ion-acoustic solitons can exist in the parametric regime where the system is stable to counterstreaming ion beams instability. The results could be useful in the interpretation of slow electrostatic solitary waves (ESWs) observed in the magnetosphere.

Beam-ion instability and its mitigation with feedback system

The beam-ion interaction is a potential limitation of beam performance in electron accelerators, especially where the beam emittance is of a great concern in future ultra-low emittance light source. "Conventionally", the beam instability due to beam-ion interaction is attributed to two types of effects: ion trapping effect and fast ion effect, which emphasize the beam-ion dynamics in different time scales. Whereas, in accelerators, the beam suffers from a mixture of ion trapping effect and fast ion effect, leading to a more complicated process and requiring a self-consistent treatment. To evaluate the beam characteristics, as emittance growth under the influence from beam-ion effect, a new numerical simulation code based on the "quasi-strong-strong" model has been developed, including modules of ionization, beam-ion interaction, synchrotron radiation damping, quantum excitation, bunch-by-bunch feedback, etc. In the study, we do not regularly distinguish the ion trapping effect and the fast ion effect, but treat beam-ion interaction more generally and consistently. The lattice of High Energy Photon Source, a diffraction limit ring under construction in Beijing, is used as an example to show the beam-ion effect. It is found that in this low emittance ring, the beam-ion instability is not a dominant mechanism in operation mode with a high beam current, but seriously occurs in a lower beam current region. When the beam-ion instability were significantly driven and can not be damped by the synchrotron radiation damping, the simulations show the bunch-by-bunch feedback system based on the Finite Impulse Response filter technique can be adopted to mitigate it effectively.