Electrostatic Ion Cyclotron Instability Research Articles

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

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.

The electromagnetic ion cyclotron instabilities of a plasma with parallel sheared current

The electromagnetic (EM) ion cyclotron (IC) instability of a plasma with parallel sheared current is investigated analytically with numerical solutions. This instability is the electromagnetic counterpart of the electrostatic current-driven ion cyclotron instability, which is renowned as the Drummond-Rosenbluth (DR) instability. Considered is the case with the current velocity shearing rate less than the ion cyclotron frequency, which corresponds to the tokamak and space plasmas. We found two new EM DR instabilities: the modified EM DR instability by the current shear and the subcritical EM DR instability which develops above the upper and below the lower critical velocities of the EM DR instability driven by the uniform current, respectively. The modified EM DR instability by the current shear develops due to the inverse electron Landau damping, whereas the subcritical EM DR instability develops due to the coupled effect of the IC damping and the current shear jointly with the inverse electron Landau damping. We also found the shear-flow-driven EM IC instability of the current-free sheared flow which develops by virtue of the coupled action of the IC damping and flow velocity shear.

Effects of inhomogeneity on electrostatic ion cyclotron instability excited by a particle beam

Electrostatic ion cyclotron (EIC) waves excited by a particle beam are studied in a magnetized inhomogeneous collisionless plasma using linear Vlasov theory. The dispersion relation of the beam-plasma system is established based on some relevant assumptions and the numerical results are presented. The behavior of EIC waves with account of parameters such as plasma inhomogeneity, propagation angle and beam velocity is studied. In particular, mode frequencies, growth rate maxima and perpendicular wavevectors are investigated in terms of these parameters. It is shown that, for lower inhomogeneities, the growth maxima are highly affected by the value of relative beam velocity. However, for higher inhomogeneities, the system is more stable for all beam velocities. It is also shown that the beam velocity has a major effect on the growth maxima only before reaching a maximum value on the curves and after the maximum, there is a declining trend in the effect of beam velocity on the growth maxima. Furthermore, for larger propagation angles, there is a more sensitive dependency on the beam velocity. At large values of relative beam velocities, the dependency of growth maxima on beam velocity becomes very weak for all propagation angles. It is found that the perpendicular wavevector decreases with both inhomogeneity and beam velocity. The decrease is smoother at larger values of propagation angle or higher inhomogeneities. In other words, for faster beams and higher inhomogeneities, the system is unstable at larger perpendicular wavelengths. It is also found that the values of maximum instability in terms of propagation angles strictly depend on inhomogeneity. For a relatively high inhomogeneity, the maxima occur over a wide range of propagation angles at almost the same value of perpendicular wavevector. A direct relationship between the magnitudes of mode frequency and growth rate is observed, implying that a higher frequency is a prerequisite for a positive (and relatively steep) slope on the growth rate curve.

Higher harmonic instability of electrostatic ion cyclotron waves

Electrostatic ion cyclotron instability pertaining to the higher harmonics of proton and helium cyclotron modes is investigated in three-component magnetised plasma consisting of beam electrons, protons and doubly charged helium ions. The effect of different plasma parameters, namely, angle of propagation, number density and temperature of helium ions and electron beam speed, has been studied on the growth of proton and helium cyclotron harmonics. It is found that an increase in angle of propagation leads to the excitation of fewer harmonics of proton cyclotron waves with decreased growth rates and higher number of helium harmonics with decreased growth rates. Also, largely odd helium harmonics are excited, except for one particular case where the second harmonic also becomes unstable. The number density and temperature of ions have significant effect on the helium cyclotron instability compared to the proton cyclotron instability. Further, as the speed of electron beam is increased, the peak growth rate increases. Our results are relevant to laboratory and space plasmas where field-aligned currents exist.

Kinetic instability of electrostatic ion cyclotron waves in inter-penetrating plasmas

The Electrostatic Ion Cyclotron (EIC) instability that includes the effect of wave-particle interaction is studied owing to the free energy source through the flowing velocity of the inter-penetrating plasmas. It is shown that the origin of this current-less instability is different from the classical current driven EIC instability. The threshold conditions applicable to a wide range of plasma parameters and the estimate of the growth rate are determined as a function of the normalized flowing velocity (u0/vtfe), the temperature (Tf/Ts) and the density ratios (nf0/ns0) of flowing component to static one. The EIC instability is driven by either flowing electrons or flowing ions, depending upon the different Doppler shifted frequency domains. It is found that the growth rate for electron-driven instability is higher than the ion-driven one. However, in both cases, the denser (hotter) is the flowing plasma, the lesser (greater) is the growth rate. The possible applications related to the terrestrial solar plasma environment are also discussed.

Understanding Breaks in Flare X-Ray Spectra: Evaluation of a Cospatial Collisional Return-current Model

Abstract Hard X-ray (HXR) spectral breaks are explained in terms of a one-dimensional model with a cospatial return current. We study 19 flares observed by the Ramaty High Energy Solar Spectroscopic Imager with strong spectral breaks at energies around a few deka-keV, which cannot be explained by isotropic albedo or non-uniform ionization alone. We identify these breaks at the HXR peak time, but we obtain 8 s cadence spectra of the entire impulsive phase. Electrons with an initially power-law distribution and a sharp low-energy cutoff lose energy through return-current losses until they reach the thick target, where they lose their remaining energy through collisions. Our main results are as follows. (1) The return-current collisional thick-target model provides acceptable fits for spectra with strong breaks. (2) Limits on the plasma resistivity are derived from the fitted potential drop and deduced electron-beam flux density, assuming the return current is a drift current in the ambient plasma. These resistivities are typically 2–3 orders of magnitude higher than the Spitzer resistivity at the fitted temperature, and provide a test for the adequacy of classical resistivity and the stability of the return current. (3) Using the upper limit of the low-energy cutoff, the return current is always stable to the generation of ion-acoustic and electrostatic ion-cyclotron instabilities when the electron temperature is nine times lower than the ion temperature. (4) In most cases, the return current is most likely primarily carried by runaway electrons from the tail of the thermal distribution rather than by the bulk drifting thermal electrons. For these cases, anomalous resistivity is not required.

Analytical study of effects of positron density and temperature anisotropy on electrostatic ion cyclotron instability

The effects of the positron concentration and ion temperature anisotropy on the electrostatic ion cyclotron instability are studied analytically, in a magnetized electron-positron-ion plasma with temperature anisotropy, using the linear kinetic theory. Positrons and electrons are supposed to drift either in the same direction or in opposite directions relative to singly ionized stationary ions and parallel to the magnetic field. The dispersion relation of the electrostatic ion cyclotron waves is derived, and then the conditions for exciting the instability of the waves are investigated. Moreover, the condition for the marginally stable state is also studied. It is found that as the positron concentration and perpendicular ion temperature increase, the growth rate of the electrostatic ion cyclotron instability decreases, whereas the critical drift velocity increases. It is also found that for the chosen set of parameters, with electrons and positrons drifting in the same direction, the instability in the plasma is stronger than when the electrons and positrons drift in opposite directions. In addition, a comparison is made to the normal electron-ion plasma.

Electrostatic ion cyclotron instability in a plasma with q-nonextensive distributions

The general dispersion relation for electrostatic waves in magnetized plasmas is derived using the standard linear Vlasov theory and the q-distribution of Tsallis statistics. The dispersion relation is solved for a plasma that has nonextensive electrons drifting with respect to stationary ions, and satisfies the other conditions for the excitation of electrostatic ion cyclotron waves. The frequency spectrum and growth rate are obtained for the electrostatic ion cyclotron waves. The marginally stable state is investigated for the onset of instability. It is shown that decreasing the non-extensivity parameter of electrons strengthens the instability and decreases the minimum value of the critical drift velocity, whereas larger temperature anisotropy of ions weakens the instability and increases the minimum value of the critical drift velocity.

Numerical analysis of electrostatic ion cyclotron instability in an electron-positron-ion plasma

This paper presents a theoretical study of the effects of positron density on the electrostatic ion cyclotron instability in an electron-positron-ion plasma using the kinetic theory approach. It is supposed that positrons and electrons can drift parallel to the magnetic field either in the same or the opposite directions. The dispersion relation for the electrostatic ion cyclotron waves in an electron-positron-ion plasma is derived, and the numerical results are investigated. It is found that an increase in positron concentration increases the critical drift velocity for excitation of the instability in both configurations. It is also found that as the positron concentration increases the growth rate of instability decreases. In addition, it is shown that at low velocities the maximum instability growth rate for the unidirectional case is higher than the counter-streaming case; however, after a certain velocity, the maximum growth rate in the counter-streaming case dominates that of the unidirectional case.

Effect of dust charge fluctuations on current-driven electrostatic ion-cyclotron instability in a collisional magnetized plasma

Current-driven electrostatic ion-cyclotron (EIC) instability is studied in a collisional magnetized dusty plasma. The growth rate and unstable mode frequencies were evaluated based on existing physical parameters relevant to ion cyclotron waves in dusty plasmas. It is found that the unstable mode frequency and growth rate of current-driven EIC instability increase with δ (ion-to-electron density ratio). Moreover, the increase in electron neutral collisional frequency (νe) has no effect on the unstable mode frequency while the normalized growth rate has linear dependence on νe.

Non-traditional machining processes by means of velocity shear instability in plasma

The material removal within different machining process can be performed in distinct modalities. One of the modality is based on the effect of impact phenomenon. In this paper theoretical model of non-traditional machining process based on impact phenomenon is discussed. The material is removed from the surface due to the impact of ions. The velocity of ions is equal to the velocity at which the electrostatic ion-cyclotron instability driven by parallel flow velocity shear generated by massive ions takes place. The main ways for the material removal as consequence of the impact phenomenon are the microcracking, microcutting, melting and vaporizing of small quantities from the work-piece surface layer.

Ion-cyclotron instability in current-carrying Lorentzian (kappa) and Maxwellian plasmas with anisotropic temperatures: A comparative study

Current-driven electrostatic ion-cyclotron instability has so far been studied for Maxwellian plasma with isotropic and anisotropic temperatures. Since satellite-measured particle velocity distributions in space are often better modeled by the generalized Lorentzian (kappa) distributions and since temperature anisotropy is quite common in space plasmas, theoretical analysis of the current-driven, electrostatic ion-cyclotron instability is carried out in this paper for electron-proton plasma with anisotropic temperatures, where the particle parallel velocity distributions are modeled by kappa distributions and the perpendicular velocity distributions are modeled by Maxwellian distributions. Stability properties of the excited ion cyclotron modes and, in particular, their dependence on electron to ion temperature ratio and ion temperature anisotropy are presented in more detail. For comparison, the corresponding results for bi-Maxwellian plasma are also presented. Although the stability properties of the ion cyclotron modes in the two types of plasmas are qualitatively similar, significant quantitative differences can arise depending on the values of κe and κi. The comparative study is based on the numerical solutions of the respective linear dispersion relations. Quasilinear estimates of the resonant ion heating rates due to ion-cyclotron turbulence in the two types of plasma are also presented for comparison.

Analysis of electrostatic ion-cyclotron instability driven by parallel flow velocity shear

Analysis and study of parallel flow velocity shear and electrostatic ion cyclotron (EIC) instability performed in plasma containing massive positive ions and electron by using the method of characteristics solution and kinetic theory in the presence of homogeneous direct-current (DC) electric field perpendicular to ambient magnetic field. The calculation of growth rate and real frequency has been done by using the computational technique. The effect of many parameters like shear scale length, homogenous d.c.electric field, magnetic field, electron ion temperature ratio, angle between wave number k⊥ and k|, on growth rate and also the effect of homogenous d.c.electric field, magnetic field on real frequency has been discussed by using the experimental data. Applications to possible laboratory plasmas and industries are also analyzed.

Analytical and experimental study of velocity shear instability in the presence of inhomogeneous perpendicular D.C electric field

Analysis and experimental study of parallel flow velocity shear electrostatic ion cyclotron (EIC) instability has been done in plasma containing massive positive ions and electron by using the method of characteristics solution and kinetic theory in the presence of inhomogeneous direct current (DC) electric field perpendicular to ambient magnetic field. The effect of many parameters on growth rate and real frequency has been discussed by using the experimental data. Applications to possible laboratory plasmas and industries are also discussed. Key words: Velocity shear instability with inhomogeneous D.C electric field.

Origin of ion-cyclotron turbulence in the downward Birkeland current region

Linear stability analysis of the electron velocity distributions, which are observed in the FAST satellite measurements in the downward Birkeland current region of the magnetosphere, is presented. The satellite-measured particle (electrons and protons) velocity distributions are fitted with analytic functions and the dispersion relation is derived in terms of the plasma dispersion functions associated with those distribution functions. Numerical solutions of the dispersion relation show that the bump-on-tail structure of the electron velocity distribution can excite electrostatic ion-cyclotron instabilities by the Landau resonance mechanism. Nonlinear evolution of these instabilities may explain the observed electrostatic ion-cyclotron turbulence in the Birkeland current region. Excitation of other types of instabilities by the fitted electron velocity distributions and their relevance are also discussed.

Nonlinear Effects Related to the Simultaneous Excitation of Three Instabiities in Magnetized Plasma

AbstractExperimental results are presented on the nonlinear effects related to the simultaneous excitation of three low‐frequency instabilities in the magnetized plasma column of a Q‐machine, namely the potential relaxation instability, the electrostatic ion‐cyclotron instability and the Kelvin‐Helmholtz instability. The influence of electron drift and magnetic field intensity on appearance, dynamics and mutual interaction of these instabilities was investigated (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Current-driven ion cyclotron instability of multicomponent field-aligned sheared flow

The effect of velocity shear of the magnetic field-aligned plasma flow on excitation of the current-driven electrostatic oxygen ion cyclotron instability in the presence of hydrogen ions is considered by using kinetic formalism. It is shown that an increase of velocity shear as well as relative concentration of oxygen ions lead to a decrease of the instability threshold. The influence of the relative concentration of oxygen ions and velocity shear on the growth rate is investigated. For a weak velocity shear the growth rate decreases with reducing of the oxygen concentration, however for a strong shear the growth rate due to the presence of hydrogen ions may increase.

Instability of higher harmonic electrostatic ion cyclotron waves in a negative ion plasma

AbstractWe present a kinetic theory analysis of the electrostatic ion cyclotron (EIC) instability in a plasma containing positive ions, electrons, and negative ions that are much more massive than the positive ions. Conditions are investigated for exciting the fundamental and the higher harmonic EIC waves associated with each ion species. We find that as the concentration of heavy negative ions increases, the wave frequencies increase, the unstable spectrum in general shifts to longer perpendicular wavelengths, and the growth of higher harmonic EIC waves tends to increase within certain parameter ranges. Applications to possible laboratory plasmas are discussed.

Oxygen-ion-beam-driven electrostatic ion cyclotron instability of hydrogen plasma

The electrostatic ion cyclotron instability of hydrogen plasma driven by an oxygen ion beam and resulting turbulent heating of both ion species is investigated. The instability growth rate exceeds the oxygen ion gyrofrequency, so that the oxygen ions may be considered as unmagnetized during the process of waves growth. As a result the instability is developed due to inverse Landau damping of the ion cyclotron waves caused by thermal motion of oxygen ions across the magnetic field. The quasilinear analysis of the turbulent heating of both ion species resulted from their interactions with ion cyclotron turbulence indicates that this instability may be responsible for the observed anisotropic heating of auroral outflowing oxygen O+ ions in the ionosphere.