Electrostatic Ion Cyclotron Waves Research Articles

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English

Instability Caused by an Inhomogeneous Energy Density Distribution as a Possible Source of Electrostatic Broadband Noise

Plasma instability caused by an inhomogeneous energy density distribution is considered. It is shown that this instability can lead to the excitation of electrostatic ion-cyclotron and oblique ion-acoustic waves, generated in the presence of an inhomogeneous transverse electric field and a shear in the parallel drift velocity of the plasma particles. The considered physical mechanisms of the instability generation in plasma can serve as possible sources of broadband electrostatic turbulence in the auroral ionosphere.

Effects of temperature anisotropy on electrostatic ion-cyclotron (EIC) wave in multi-component plasma around polar cusp region-particle aspect approach

Particle aspect analysis is used to describe electrostatic ion-cyclotron (EIC) wave with multi-ion plasma (H+, He+ and O+) around polar cusp region. Variations of resonant energy and growth rate with general loss-cone distribution function and temperature anisotropy with perpendicular wave number are studied. The whole plasma is considered to consist of resonant and non-resonant particles. The resonant particles participate in energy exchange with wave, while non-resonant particles support the oscillatory motion of the wave. The wave is assumed to propagate obliquely to the static magnetic field. It is found that the temperature anisotropy enhances the transverse, parallel resonant energies of particles and growth rate of the wave. Distribution indices also enhance the growth rate and parallel resonant energy and reduce the perpendicular resonant energy. The study may explain the EIC waves observed in polar cusp region. The results are interpreted for the space plasma parameters appropriate to the polar cusp region in the earth’s magnetosphere.

The instability of electrostatic ion cyclotron waves in a multi-component plasma

The instability of electrostatic ion cyclotron wave in a plasma consisting of isotropic hydrogen ions (H+), oxygen ions (both positively and negatively charged and denoted by O+ and O−) and electron. ESIC waves with multi component plasma have been studied by kinetic approach at different plasma densities. The dispersion relation and growth rate of the electrostatic ion-cyclotron waves with multi-ion plasma has been investigated. The effect of different plasma densities on ESIC waves in multi-ions is to enhance the growth rate of ESIC waves. The results are interpreted for the space plasma parameters appropriate to the auroral acceleration region of earth’s magneto-plasma.

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.

Reverse flow events and small‐scale effects in the cusp ionosphere

AbstractWe report in situ measurements of plasma irregularities associated with a reverse flow event (RFE) in the cuspFregion ionosphere. The Investigation of Cusp Irregularities 3 (ICI‐3) sounding rocket, while flying through a RFE, encountered several regions with density irregularities down to meter scales. We address in detail the region with the most intense small‐scale fluctuations in both the density and in the AC electric field, which were observed on the equatorward edge of a flow shear, and coincided with a double‐humped jet of fast flow. Due to its long‐wavelength and low‐frequency character, the Kelvin‐Helmholtz instability (KHI) alone cannot be the source of the observed irregularities. Using ICI‐3 data as inputs, we perform a numerical stability analysis of the inhomogeneous energy‐density‐driven instability (IEDDI) and demonstrate that it can excite electrostatic ion cyclotron waves in a wide range of wave numbers and frequencies for the electric field configuration observed in that region, which can give rise to the observed small‐scale turbulence. The IEDDI can seed as a secondary process on steepened vortices created by a primary KHI. Such an interplay between macroprocesses and microprocesses could be an important mechanism for ion heating in relation to RFEs.

Coupling of electrostatic ion cyclotron and ion acoustic waves in the solar wind

The coupling of electrostatic ion cyclotron and ion acoustic waves is examined in three component magnetized plasma consisting of electrons, protons, and alpha particles. In the theoretical model relevant to solar wind plasma, electrons are assumed to be superthermal with kappa distribution and protons as well as alpha particles follow the fluid dynamical equations. A general linear dispersion relation is derived for such a plasma system which is analyzed both analytically and numerically. For parallel propagation, electrostatic ion cyclotron (proton and helium cyclotron) and ion acoustic (slow and fast) modes are decoupled. For oblique propagation, coupling between the cyclotron and acoustic modes occurs. Furthermore, when the angle of propagation is increased, the separation between acoustic and cyclotron modes increases which is an indication of weaker coupling at large angle of propagation. For perpendicular propagation, only cyclotron modes are observed. The effect of various parameters such as number density and temperature of alpha particles and superthermality on dispersion characteristics is examined in details. The coupling between various modes occurs for small values of wavenumber.

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.

Influences of shear in the ion parallel drift velocity and of inhomogeneous perpendicular electric field on generation of oblique ion acoustic waves

AbstractIt is well known that the broadband electrostatic turbulence observed in the topside auroral ionosphere can be identified with electrostatic ion cyclotron and/or oblique ion acoustic waves. Under certain conditions generation of the ion cyclotron modes is inhibited, so that the oblique ion acoustic waves become the prevailing part of the broadband noise. While generation of ion cyclotron waves by the inhomogeneous distribution of energy density (IEDD) instability has been actively studied in recent years, much less attention was paid to the excitation of ion acoustic waves by means of the IEDD instability. In this work, influence of shear in the ion parallel drift velocities and of inhomogeneous perpendicular electric field on generation of nonlocal oblique ion acoustic mode is studied. It is demonstrated that the shear of the ion parallel drift velocities can generate ion acoustic waves. It is shown that this mechanism of instability development provides broadband spectrum in the frequency range around 0.1 of ion gyrofrequency, and thus, this instability can be invoked to explain the observed broadband electrostatic turbulence in the auroral region. Effect of the main background plasma parameters on excitation of oblique ion acoustic waves is analyzed.

Features of wave excitation of the electrostatic ion cyclotron type in the auroral ionosphere

Broadband electrostatic noise in the auroral ionosphere can be identified as a version of waves of an electrostatic ion cyclotron type, excited by plasma instability resulting from an inhomogeneous distribution of wave energy density. Broadband waves are generated due to both electric field inhomogeneities and plasma density inhomogeneities. The effect of the form of the distribution of electric field and plasma density inhomogeneities on the excitation of instabilities is studied. Also there is shown the role of the characteristic scale of inhomogeneities in the generation of electrostatic ion cyclotron waves due to the development of instability of this kind. The study of these issues, which are important for understanding the processes in the auroral region, is the subject of this paper. The work presents also a comparison of numerical results obtained using both satellite data and model approximations.

THEMIS observations of electrostatic ion cyclotron waves and associated ion heating near the Earth's dayside magnetopause

AbstractWe present the first observations of large‐amplitude electrostatic ion cyclotron (EIC) waves near the Earth's dayside magnetopause at MLT of ∼14 using data from Time History of Events and Macroscale Interactions during Substorms (THEMIS) satellites. The EIC waves were identified in a boundary layer in the magnetosphere adjacent to the magnetopause where reconnection was occurring. The EIC wave power was primarily at 2fcH (where fcH is the hydrogen cyclotron frequency) and simultaneously observed with perpendicular ion heating. The EIC waves had electric field amplitudes as large as 30 mV/m peak to peak with significant power both perpendicular and parallel to the magnetic field. These amplitudes were greater than those of previously observed ion cyclotron harmonics at the nightside magnetopause. The EIC waves occurred during an interval of enhancements in the quasi‐static electric field and fluctuations in the background magnetic field, plasma density, and temperatures. The observations indicate that a plasma density gradient is a possible source of free energy for the EIC waves. The observed flow shears are not large enough to drive the waves. Whistler mode waves were identified near the EIC wave region but closer to the magnetopause in a region with slightly higher ion and electron temperatures.

Inhomogeneities of plasma density and electric field as sources of electrostatic turbulence in the auroral region

Inhomogeneities of plasma density and non-uniform electric fields are compared as possible sources of a sort of electrostatic ion cyclotron waves that can be identified with broadband extremely low frequency electrostatic turbulence in the topside auroral ionosphere. Such waves are excited by inhomogeneous energy-density-driven instability. To gain a deeper insight in generation of these waves, computational modeling is performed with various plasma parameters. It is demonstrated that inhomogeneities of plasma density can give rise to this instability even in the absence of electric fields. By using both satellite-observed and model spatial distributions of plasma density and electric field in our modeling, we show that specific details of the spatial distributions are of minor importance for the wave generation. The solutions of the nonlocal inhomogeneous energy-density-driven dispersion relation are investigated for various ion-to-electron temperature ratios and directions of wave propagation. The relevance of the solutions to the observed spectra of broadband extremely low frequency emissions is shown.

INSTABILITY OF ION BEAM DRIVEN ELECTROSTATIC ION-CYCLOTRON WAVES IN COLLISIONAL MAGNETIZED TWO-ION COMPONENT PLASMA

We have studied the instability of electrostatic ion-cyclotron waves in collisional magnetized two-ion component plasma (light positive K + ions and heavy positive Cs + ions). An ion beam propagating through collisional magnetized plasma containing electrons and two positive ion components drives electrostatic ion cyclotron (EIC) waves to instability via Cerenkov interaction. Analytical expressions & numerical calculations have been carried out for the frequency and growth rate of ion cyclotron waves for two EIC wave modes for existing experimental parameters, and it is found that the unstable mode frequency does not depend on electron collision frequency, while the growth rate is increased linearly with the electron collision frequency. Moreover, as the light ion concentration is increased, the frequency of the heavy ion mode moves closer to its gyrofrequency. Similarly, the frequency of the light ion mode approaches the light ion cyclotron frequency as the heavy ion concentration is increased. It is also found that the normalized unstable mode frequencies remains unchanged with electron collision frequencies, while the growth rate is increased linearly with the electron collision frequencies. In addition, the unstable mode frequencies are found to be dependent on the magnetic field strengths.

Ion beam driven resonant ion-cyclotron instability in a magnetized dusty plasma

Electrostatic ion cyclotron waves are excited by axial ion beam in a dusty plasma via Cerenkov and slow cyclotron interaction. The dispersion relation of the instability is derived in the presence of positively/negatively charged dust grains. The minimum beam velocity needed for the excitation is estimated for different values of relative density of negatively charged dust grains. It is shown that the minimum beam velocity needed for excitation increases as the charge density carried by dust increases. Temperature of electrons and ions, charge and mass of dust grains, external static magnetic field and finite boundary of dusty plasma significantly modify the dispersion properties of these waves and play a crucial role in the growth of resonant ion cyclotron instability. The ion cyclotron modes with phase velocity comparable to the beam velocity possess a large growth rate. The maximum value of growth rate increases with the beam density and scales as the one-third power of the beam density in Cerenkov interaction and is proportional to the square root of beam density in slow cyclotron interaction.

Spiraling ion beam driven electrostatic ion cyclotron wave instabilities in collisionless dusty plasma

The numerical calculations of the growth rate in long parallel wavelength are made for a spiraling ion beam propagating through a collision less magnetized dusty plasma cylinder that drives electrostatic ion cyclotron waves to instability via cyclotron interaction. It is found that the growth rate of the instability of the electrostatic ion cyclotron waves increase in the long parallel limit with the density ratio of negatively charged dust grains to electrons. The growth rate of the unstable mode has the maximum value for the modes whose Eigen functions peak at the location of the beam and varies as the one-third power of the beam current in both the limits.

EFFECT OF DUST GRAIN PARAMETERS ON ION BEAM DRIVEN ION CYCLOTRON WAVES IN A MAGNETIZED PLASMA

Excitation of electrostatic ion cyclotron waves (EICW) in a magnetized dusty plasma by an ion beam is studied taking into account the efiect of dust particle size, dust particle charge and dust particle number density variations. The presence of dust grain charge ∞uctuations modifles the dispersion relation for ion cyclotron waves in dusty plasma. It is shown that in the absence of ion beam, the ion cyclotron mode damps due to dust charge ∞uctuations and an additional damping dust charge ∞uctuation mode is induced in plasma. The ion beam propagating parallel to the magnetic fleld drives ion cyclotron waves to instability via Cerenkov interaction. Using the analytical and numerical results the in∞uence of the relative density of negatively charged dust particles on growth rate of ion cyclotron waves is studied. The dust grain size distribution has also signiflcant contributions on the growth rate of ion cyclotron waves.

Nonlinear electron acoustic cyclotron waves in presence of uniform magnetic field

Nonlinear electron acoustic cyclotron waves (EACW) are studied in a quasineutral plasma in presence of uniform magnetic field. The fluid model is used to describe the dynamics of two temperature electron species in a stationary charge neutral inhomogeneous background. In long wavelength limit, it is shown that the linear electron acoustic wave is modified by the uniform magnetic field similar to that of electrostatic ion cyclotron wave. Nonlinear equations for these waves are solved by using Lagrangian variables. Results show that the spatial solitary wave-like structures are formed due to nonlinearities and dispersions. These structures transiently grow to larger amplitude unless dispersive effect is actively operative and able to arrest this growth. We have found that the wave dispersion originated from the equilibrium inhomogeneity through collective effect and is responsible for spatiotemporal structures. Weak dispersion is not able to stop the wave collapse and singular structures of EACW are formed. Relevance of the results in the context of laboratory and space plasmas is discussed.

The role of electromagnetic ion-cyclotron waves in solar 3He-rich events

The preferential heating of 3He by the electromagnetic ion-cyclotron waves, which propagate in the direction parallel to the magnetic fields in the solar corona, is investigated. The results obtained from this study indicate that the parallel propagating electromagnetic ion-cyclotron waves, if driven, can be efficient at heating 3He through the first harmonic resonance. This preferential heating of 3He can lead to a high temperature ratio THe3/THe4∼10–20 and thus largely increases the number of 3He to be further accelerated to high energies. Comparing to the electrostatic ion-cyclotron waves, we find that the electromagnetic ion-cyclotron waves can be even more efficient at heating 3He than the electrostatic ion-cyclotron waves if both types of waves are excited with comparable wave energy densities. Therefore, the electromagnetic ion-cyclotron waves, if generated in solar flares, should also play an important role in solar 3He-rich events along with the electrostatic ion-cyclotron waves.

Higher harmonics generation by a spiraling ion beam in collisionless magnetized plasma

AbstractA spiraling ion beam propagating through a magnetized plasma cylinder containing K+ light positive ions, electrons, and C7F14− heavy negative ions drives electrostatic ion–cyclotron waves to instability via cyclotron interaction. Higher harmonics of the beam cyclotron frequency can be generated in this way. The unstable mode frequencies and growth rates of both unstable light positive ions and heavy negative ions increase with the relative density of heavy negative ions. Moreover, the growth rate of unstable modes scales as the one-third power of the beam density. The growth rate of unstable modes increases with harmonic number. The frequencies of both unstable modes also increase with magnetic fields. In addition, the real part of both unstable modes (K+ and C7F14−) increases with the beam energy and scales as almost one-half power of the beam energy.