Ion Cyclotron Instability Research Articles

Critical comparison of collisionless fluid models: Nonlinear simulations of parallel firehose instability

Two different fluid models for collisionless plasmas are compared. One is based on the classical Chew–Goldberger–Low (CGL) model that includes a finite Larmor radius correction and the Landau closure for the longitudinal mode. Another one takes into account the effect of cyclotron resonance in addition to Landau resonance and is referred to as the cyclotron resonance closure (CRC) model [T. Jikei and T. Amano, Phys. Plasmas 28, 042105 (2021)]. While the linear property of the parallel firehose instability is better described by the CGL model, the electromagnetic ion cyclotron instability driven unstable by the cyclotron resonance is reproduced only by the CRC model. Nonlinear simulation results for the parallel firehose instability performed with the two models are also discussed. Although the linear and quasilinear isotropization phases are consistent with theory in both models, long-term behaviors may be substantially different. The final state obtained by the CRC model may be reasonably understood in terms of the marginal stability condition. In contrast, the lack of cyclotron damping in the CGL model makes it rather difficult to predict the long-term behavior with simple physical arguments. This suggests that incorporating collisionless damping both for longitudinal and transverse modes is crucial for a nonlinear fluid simulation model of collisionless plasmas.

Electron Preacceleration at Weak Quasi-perpendicular Intracluster Shocks: Effects of Preexisting Nonthermal Electrons

Abstract Radio relics in the outskirts of galaxy clusters imply the diffusive shock acceleration (DSA) of electrons at merger-driven shocks with Mach number M s ≲ 3–4 in the intracluster medium (ICM). Recent studies have suggested that electron preacceleration and injection, prerequisite steps for DSA, could occur at supercritical shocks with M s ≳ 2.3 in the ICM, thanks to the generation of multiscale waves by microinstabilities such as the Alfvén ion cyclotron (AIC) instability, the electron firehose instability (EFI), and the whistler instability (WI). On the other hand, some relics are observed to have subcritical shocks with M s ≲ 2.3, leaving DSA at such weak shocks as an outstanding problem. Reacceleration of preexisting nonthermal electrons has been contemplated as one of possible solutions for that puzzle. To explore this idea, we perform particle-in-cell simulations for weak quasi-perpendicular shocks in high-β (β = P gas/P B ) plasmas with power-law suprathermal electrons in addition to Maxwellian thermal electrons. We find that suprathermal electrons enhance the excitation of electron-scale waves via the EFI and WI. However, they do not affect the ion reflection and the ensuing generation of ion-scale waves via the AIC instability. The presence of ion-scale waves is the key for the preacceleration of electrons up to the injection momentum; thus, the shock criticality condition for electron injection to DSA is preserved. Based on the results, we conclude that preexisting nonthermal electrons in the preshock region alone would not resolve the issue of electron preacceleration at subcritical ICM shocks.

Spontaneous Magnetic Fluctuations and Collisionless Regulation of Turbulence in the Earth’s Magnetotail

Abstract Among the fundamental and most challenging problems of laboratory, space, and astrophysical plasma physics is to understand the relaxation processes of nearly collisionless plasmas toward quasi-stationary states and the resultant states of electromagnetic plasma turbulence. Recently, it has been argued that solar wind plasma β and temperature anisotropy observations may be regulated by kinetic instabilities such as the ion cyclotron, mirror, electron cyclotron, and firehose instabilities; and it has been argued that magnetic fluctuation observations are consistent with the predictions of the fluctuation–dissipation theorem, even far below the kinetic instability thresholds. Here, using in situ magnetic field and plasma measurements by the THEMIS satellite mission, we show that such regulation seems to occur also in the Earth’s magnetotail plasma sheet at the ion and electron scales. Regardless of the clear differences between the solar wind and the magnetotail environments, our results indicate that spontaneous fluctuations and their collisionless regulation are fundamental features of space and astrophysical plasmas, thereby suggesting the processes is universal.

Generation of ion cyclotron instability by parametric coupling of gyrating ion beam with lower hybrid wave in a complex plasma

In a two-ion species tokamak plasma, with the help of gyrating ion beam was to investigate the impact of dust charge fluctuations on the parametric up-conversion of lower hybrid wave (LHW) into an upper side band wave and an ion cyclotron wave. On the existing electrons, through an upper side band wave and lower hybrid pump, a ponderomotive force has been exerted which in turn drives the ion cyclotron decay mode. The growth rate of instability is calculated by considering typical existing D-T (Deuterium-Tritium) dusty plasma parameters and observed that with an increment in amplitude of pump waves, wave number of ion cyclotron mode, number density of dust grains and relative density of dust grains, an enhanced growth rate is reported. However, a reduction in the growth rate has been detected with enhancing dust grain size and electron cyclotron frequency. The findings of this work can play an imperative role in magnetized plasma sources used in plasma material interaction / surface processing. The tokamak operation is severely affected by the various sizes and density of dust grains, which in turn, considerably affect the choice of material requisite in tokamak.

Mach number dependence of ion-scale kinetic instability at collisionless perpendicular shock: Condition for Weibel-dominated shock

We investigate ion-scale kinetic plasma instabilities at the collisionless shock using linear theory and nonlinear particle-in-cell (PIC) simulations. We focus on the Alfvén ion cyclotron (AIC), mirror, and Weibel instabilities, which are all driven unstable by the effective temperature anisotropy induced by the shock-reflected ions within the transition layer of a strictly perpendicular shock. We conduct linear dispersion analysis with a homogeneous plasma model to mimic the shock transition layer by adopting a ring distribution with finite thermal spread to represent the velocity distribution of the reflected ions. We find that, for wave propagation parallel to the ambient magnetic field, the AIC instability at lower Alfvén Mach numbers tends to transition to the Weibel instability at higher Alfvén Mach numbers. The instability property is, however, also strongly affected by the sound Mach number. We conclude that the instability at a strong shock with Alfvén and sound Mach numbers both in excess of ∼20–40 may be considered as Weibel-like in the sense that the reflected ions behave essentially unmagnetized. Two-dimensional PIC simulations confirm the linear theory and find that, with typical parameters of young supernova remnant shocks, the ring distribution model produces magnetic fluctuations of the order of the background magnetic field, which is smaller than those observed in previous PIC simulations for Weibel-dominated shocks. This indicates that the assumption of the gyrotropic reflected ion distribution may not be adequate to quantitatively predict nonlinear behaviors of the dynamics in high Mach number shocks.

Microinstabilities in the Transition Region of Weak Quasi-perpendicular Intracluster Shocks

Abstract Microinstabilities play important roles in both entropy generation and particle acceleration in collisionless shocks. Recent studies have suggested that in the transition region of quasi-perpendicular (Q ⊥) shocks in the high-beta (β = P gas/P B) intracluster medium (ICM), the ion temperature anisotropy due to the reflected-gyrating ions could trigger the Alfvén ion cyclotron (AIC) instability and the ion-mirror instability, while the electron temperature anisotropy induced by magnetic field compression could excite the whistler instability and the electron-mirror instability. Adopting the numerical estimates for ion and electron temperature anisotropies found in the particle-in-cell (PIC) simulations of Q ⊥ shocks with sonic Mach numbers, M s = 2–3, we carry out a linear stability analysis for these microinstabilities. The kinetic properties of the microinstabilities and the ensuing plasma waves on both ion and electron scales are described for wide ranges of parameters, including β and the ion-to-electron mass ratio. In addition, the nonlinear evolution of the induced plasma waves are examined by performing 2D PIC simulations with periodic boundary conditions. We find that for β ≈ 20–100, the AIC instability could induce ion-scale waves and generate shock surface ripples in supercritical shocks above the AIC critical Mach number, M AIC * ≈ 2.3 . Also, electron-scale waves are generated primarily by the whistler instability in these high-β shocks. The resulting multiscale waves from electron to ion scales are thought to be essential in the electron injection to diffusive shock acceleration in Q ⊥ shocks in the ICM.

Upper Limit of Proton Anisotropy and Its Relation to Electromagnetic Ion Cyclotron Waves in the Inner Magnetosphere

AbstractProton anisotropy in velocity space has been generally accepted as a major parameter for exciting electromagnetic ion cyclotron (EMIC) waves. In this study, we estimate the proton anisotropy parameter as defined by the linear resonance theory using data from the Van Allen Probes mission. Our investigation uses the measurements of the inner magnetosphere (L < 6) from January 2013 to February 2018. We find that the proton anisotropy is always clearly limited by an upper bound and it well follows an inverse relationship with the parallel proton β (the ratio of the plasma pressure to the magnetic pressure) within a certain range. This upper bound exists over wide spatial regions, AE conditions, and resonance energies regardless of the presence of EMIC waves. EMIC waves occur when the anisotropy lies below but close to this upper bound within a narrow plasma β range: The lower cutoff β is due to an excessively high anisotropy threshold and the upper cutoff β is possibly due to the predominant role of a faster‐growing mirror mode instability. We also find that the anisotropy during the observed EMIC waves is unstable, leading to the linear ion cyclotron instability. This result implies that the upper bound of the anisotropy is due to nonlinear processes.

On the interplay of solar wind proton and electron instabilities: linear and quasi-linear approaches

ABSTRACT Important efforts are currently being made to understand the so-called kinetic instabilities, driven by the anisotropy of different species of plasma particles present in the solar wind and terrestrial magnetosphere. These instabilities are fast enough to efficiently convert the free energy of plasma particles into enhanced (small-scale) fluctuations, with multiple implications, regulating the anisotropy of plasma particles. In this paper we use both linear and quasi-linear (QL) frameworks to describe complex unstable regimes, which realistically combine different temperature anisotropies of electrons and ions (protons). Thus various instabilities are parametrized, for example the proton and electron firehose, electromagnetic ion cyclotron and whistler instabilities, showing that their main linear properties are markedly altered by the interplay of anisotropic electrons and protons. Linear theory may predict the strong competition of two instabilities of different natures when their growth rates are comparable. In the QL phase, wave fluctuations grow and saturate at different levels and temporal scales, in comparison to results for the individual excitation of the proton or electron instabilities. In addition, the cumulative effects of the combined proton- and electron-induced fluctuations can markedly stimulate the relaxation of their temperature anisotropies. Only whistler fluctuations inhibit the efficiency of proton firehose fluctuations in the relaxation of anisotropic protons. These results offer valuable premises for further investigations in numerical simulations to decode the full spectrum of kinetic instabilities resulting from the interplay of anisotropic electrons and protons in space plasmas.

Electromagnetic ion cyclotron instability stimulated by the suprathermal ions in space plasmas: A quasi-linear approach

In collision-poor space plasmas, protons with an excess of kinetic energy or temperature in the direction perpendicular to the background magnetic field can excite the electromagnetic ion cyclotron (EMIC) instability. This instability is expected to be highly sensitive to suprathermal protons, which enhance the high-energy tails of the observed velocity distributions and are well reproduced by the (bi-)Kappa distribution functions. In this paper, we present the results of a refined quasi-linear approach, able to describe the effects of suprathermal protons on the extended temporal evolution of EMIC instability. It is, thus, shown that suprathermals have a systematic stimulating effect on the EMIC instability, enhancing not only the growth rates and the range of unstable wavenumbers but also the magnetic fluctuating energy density reached at the saturation. In effect, the relaxation of anisotropic temperature also becomes more efficient, i.e., faster in time and closer to isotropy.

Registration of synchronous geomagnetic pulsations and proton aurora during the substorm on March 1, 2017

Data of synchronous geomagnetic pulsations and proton aurora registrations were analyzed during the substorm on March 1, 2017 at Zhigansk (L=4.5, induction magnetometer), Maimaga (L=4, all-sky imager and Yakutsk (L = 3.3, induction magnetometer) stations, simultaneously with satellite measurement of EMIC waves. Ground-based registration of proton aurora is very difficult due to the fact that their intensity is much lower than the aurora intensity caused by precipitations of electrons, but in the event of substorm activity at the zenith of Maimaga station, a narrow (1 degree in latitude) proton arc was observed. Irregular pulsations of the diminishing periods (IPDPs) in the range of Pc1 geomagnetic pulsations associated with the injection of energetic protons were recorded simultaneously at Zhigansk and Yakutsk stations. This is the first report when STEVE (Strong Thermal Emission Velocity Enhancement) was observed in the course of a substorm with the onset at 12:45 UT after the decay of Pc1-associated proton arc. It is shown that the proton arc and geomagnetic pulsations are a consequence of ion-cyclotron instability in the area of the outer plasmasphere overlapping by energetic protons.

A Strong Instability in the Ion Cyclotron Frequency Range of the Upward Sheared Flow of the Oxygen Ions in Aurora

The dispersion relation of a new electrostatic ion cyclotron (IC) instability of a plasma with a sheared current of the oxygen ions along the magnetic field is investigated analytically and solved by numerical analysis. The considered case corresponds to the upward sheared flow of the oxygen ions in the aurora where the velocity shearing rate of ion current may be larger than the cyclotron frequency of O+ ion. In such a plasma, we found a new instability in the IC frequency range which develops in the sheared flow and can have a growth rate larger than O+ cyclotron frequency. This instability develops jointly with the known IC instability for the uniform current with a growth rate much less than O+ cyclotron frequency

Combined electron firehose and electromagnetic ion cyclotron instabilities: quasilinear approach

ABSTRACT Various plasma waves and instabilities are abundantly present in the solar wind plasma, as evidenced by spacecraft observations. Among these, propagating modes and instabilities driven by temperature anisotropies are known to play a significant role in the solar wind dynamics. In situ measurements reveal that the threshold conditions for these instabilities adequately explain the solar wind conditions at large heliocentric distances. This paper pays attention to the combined effects of electron firehose instability driven by excessive parallel electron temperature anisotropy (T⊥e < T∥e) at high beta conditions, and electromagnetic ion cyclotron instability driven by excessive perpendicular proton temperature anisotropy (T⊥i > T∥i). By employing quasilinear kinetic theory based upon the assumption of bi-Maxwellian velocity distribution functions for protons and electrons, the dynamical evolution of the combined instabilities and their mutual interactions mediated by the particles is explored in depth. It is found that while in some cases, the two unstable modes are excited and saturated at distinct spatial and temporal scales, in other cases, the two unstable modes are intermingled such that a straightforward interpretation is not so easy. This shows that when the dynamics of protons and electrons are mutually coupled and when multiple unstable modes are excited in the system, the dynamical consequences can be quite complex.

Role of the Outer Ionosphere in the Winter/Summer Asymmetry of Auroral Electron Precipitations

This paper analyzes the role of the outer ionosphere in the occurrence of a large difference in the frequency of accelerated electron fluxes in the auroral region in the premidnight sector for winter and summer conditions, which are associated with discrete auroras. Simulation indicates that the critical value JEIC of the longitudinal current of the Alfven wave for the development of electrostatic ion–cyclotron instability at heights around the Earth’s radius (h ~ RE) for winter almost coincides with the upper limit of average values of the stationary large-scale longitudinal current. Therefore, weak fluctuations of the longitudinal current associated with the Alfven wave are sufficient in winter for the development of processes leading to accelerated electron fluxes, which are associated with discrete auroras. The summer value of JEIC is four to five times higher than that for winter, and a stimulated precipitation of auroral electrons is likely to be possible only at high geomagnetic activity. The winter/summer asymmetry in the JEIC value is mainly associated with specific changes in the parameters of the outer ionosphere along the geomagnetic field. The difference in electron density reaches a maximum at heights h ~ RE, where the summer values of this density are five to six times higher than the winter ones, which, in turn, is associated with higher summer temperatures of electrons and ions. The important role of these temperatures in the winter/summer asymmetry in the frequency of accelerated electrons has been noted, it would seem, for the first time.

An Event Study of Simultaneous Earthward and Tailward Reconnection Exhaust Flows in the Earth's Midtail

AbstractWe report an event of two‐satellite measurements of simultaneous earthward and tailward fast flows of ~500 km/s in the midtail at X ~ −63 RE and evaluate magnetic reconnection as a responsible mechanism by comparing the observations with a particle‐in‐cell (PIC) simulation. The two satellites were near midnight separated mainly along the X direction by ~5 RE. As they moved across the current sheet from the northern to southern lobes, the one closer to the Earth crossed the x line with fast flows changing from tailward to earthward, while the other one simultaneously observed tailward flows. The observed plasma and fields showed several key reconnection signatures, including the Walén relation, the fast reconnection rate of ~0.1, the Hall magnetic and electric fields, and counterstreaming electrons in the separatrix, indicating the fast flow was the reconnection exhaust. The observed temporal variations of flow speeds and magnetic fields suggested that the x line was moving tailward to a location between the two satellites and the exhaust was moving up and down. Within the exhaust, plasma pressure was highly anisotropic, and the current sheet can be unstable to the mirror, ion cyclotron, and firehose instabilities. Current sheet flapping and enhanced compressional waves near proton's local gyro frequencies were observed around the current sheet. Comparing with the PIC simulation suggests that the waves were mainly a result of oblique firehose instability.

Acceleration of Ion Rings by Collapsing Liners

We have established the conditions for the absence of Alfven ion-cyclotron instability in the formation and subsequent acceleration of ion rings by collapsing cylindrical plasma liners.

The ion cyclotron parametric instabilities and the anomalous heating of ions in the tokamak edge plasma in the fast wave heating regime

The theory of the ion cyclotron (IC) electrostatic parametric instabilities of plasma, which are driven by the elliptically polarized fast wave (FW) of the finite wavelength, is developed. This theory provides the analytical treatment of the parametric instabilities with wavelengths comparable with the displacements of ions relative to electrons in the FW. The numerical solution of the dispersion equation for a three wave system that contains the IC mode and two beat waves with frequencies equal to the difference of the IC mode frequency and harmonics of the FW is performed. It reveals the parametric IC instability for this wave system with the maximum growth rate for the IC waves with wavelengths comparable with the thermal ion Larmor radius. The anomalous heating rates of ions resulting from the interactions of ions with parametric IC turbulence are determined employing the developed quasilinear theory for the IC quasimode decay instability. The derived results reveal that the experimentally observed anisotropic heating of cold scrape-off layer (SOL) ions may be the result of the interaction of the SOL ions with IC parametric turbulence. However, the IC parametric turbulence is unlikely to be responsible for the experimentally observed bursts of poorly confined suprathermal ions in the SOL of tokamak plasmas.

Ускорение ионных колец сжимающимися лайнерами

The conditions for the absence of Alfven ion-cyclotron instability during the creation and subsequent acceleration of ion rings by compressed cylindrical plasma liners are established

Properties of Localized Precipitation of Energetic Protons Equatorward of the Isotropic Boundary

AbstractUsing National Oceanic and Atmospheric Administration Polar Orbiting Environmental Satellite (NOAA/POES) observations of energetic protons, we for the first time investigated statistical properties of a specific type of particle precipitation—localized precipitation of energetic protons (LPEP) equatorward of the isotropy boundary. The maximum occurrence rate was found in the day‐afternoon sector at L > 6. The maximum precipitating flux is found at lower L shells (L = 4–5). The dependence of LPEP occurrence and intensity on the geomagnetic activity indices and solar wind parameters is investigated. In particular, while the precipitating proton flux increases with geomagnetic activity everywhere, the occurrence rate in the day‐afternoon sector at L > 6 decreases under the strongest activity. We conclude that revealed LPEP properties are mostly similar to those obtained for electromagnetic ion cyclotron waves on the basis of data from previous spacecraft missions. This similarity supports the suggestion on LPEP as the result of ion cyclotron instability in the magnetosphere.

Stochastic Ion Acceleration by the Ion-cyclotron Instability in a Growing Magnetic Field

Abstract Using 1D and 2D particle-in-cell simulations of a plasma with a growing magnetic field , we show that ions can be stochastically accelerated by the ion-cyclotron (IC) instability. As grows, an ion pressure anisotropy arises due to the adiabatic invariance of the ion magnetic moment ( and p ⊥,i are the ion pressures parallel and perpendicular to ). When initially β i = 0.5 ( , where p i is the ion isotropic pressure), the pressure anisotropy is limited mainly by inelastic pitch-angle scattering provided by the IC instability, which in turn produces a nonthermal tail in the ion energy spectrum. After is amplified by a factor of ∼2.7, this tail can be approximated as a power law of index ∼3.4 plus two nonthermal bumps and accounts for 2%–3% of the ions and ∼18% of their kinetic energy. On the contrary, when initially β i = 2, the ion scattering is dominated by the mirror instability, and the acceleration is suppressed. This implies that efficient ion acceleration requires that initially, β i ≲ 1. Although we focus on cases where is amplified by plasma shear, we check that the acceleration occurs similarly if grows due to plasma compression. Our results are valid in a subrelativistic regime where the ion thermal energy is ∼10% of the ion rest-mass energy. This acceleration process can thus be relevant in the inner region of low-luminosity accretion flows around black holes.

Saturation Characteristics of Parallel EMIC Waves in the Inner Magnetosphere

AbstractIn this letter, detailed evolution process of parallel electromagnetic ion cyclotron waves in the inner magnetosphere has been investigated through quasilinear theory. A new saturation has been found to occur after the usual first saturation. During the interval between these two saturations, the energy transfers from H+ band to He+ band electromagnetic ion cyclotron waves. Moreover, through a best fitting, we obtain new model parameters for the anisotropy‐beta inverse relation of hot H+, which identifies the threshold of ion cyclotron instabilities in the inner magnetosphere. In situ observations of the Van Allen Probe mission also verify these new model parameters. Therefore, our results reveal the evolution process and saturation characteristics of parallel electromagnetic ion cyclotron waves in the inner magnetosphere.