scholarly journals Ion temperature anisotropy effects on threshold conditions of a shear-modified current driven electrostatic ion-acoustic instability in the topside auroral ionosphere

2013 ◽  
Vol 31 (3) ◽  
pp. 451-457 ◽  
Author(s):  
P. J. G. Perron ◽  
J.-M. A. Noël ◽  
K. Kabin ◽  
J.-P. St-Maurice
Keyword(s):  
Acoustic Waves ◽  
Larmor Radius ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
Finite Larmor Radius ◽  
Acoustic Instability ◽  
Preferred Direction ◽  
F Region ◽  
Threshold Conditions ◽  
Ion Acoustic

Abstract. Temperature anisotropies may be encountered in space plasmas when there is a preferred direction, for instance, a strong magnetic or electric field. In this paper, we study how ion temperature anisotropy can affect the threshold conditions of a shear-modified current driven electrostatic ion-acoustic (CDEIA) instability. In particular, this communication focuses on instabilities in the context of topside auroral F-region situations and in the limit where finite Larmor radius corrections are small. We derived a new fluid-like expression for the critical drift which depends explicitly on ion anisotropy. More importantly, for ion to electron temperature ratios typical of F-region, solutions of the kinetic dispersion relation show that ion temperature anisotropy may significantly lower the drift threshold required for instability. In some cases, a perpendicular to parallel ion temperature ratio of 2 and may reduce the relative drift required for the onset of instability by a factor of approximately 30, assuming the ion-acoustic speed of the medium remains constant. Therefore, the ion temperature anisotropy should be considered in future studies of ion-acoustic waves and instabilities in the high-latitude ionospheric F-region.

Ion temperature anisotropy effects on the dispersion relation and threshold conditions of a sheared current-driven electrostatic ion-acoustic instability with applications to the collisional high-latitude F-region

2014 ◽  
Vol 81 (1) ◽  
Author(s):  
Patrick J.G. Perron ◽  
J.-M. Noël ◽  
J.-P. St-Maurice ◽  
K. Kabin
Keyword(s):  
Dispersion Relation ◽  
Wave Vector ◽  
High Latitude ◽  
Instability Threshold ◽  
Larmor Radius ◽  
Ion Temperature ◽  
Temperature Anisotropy ◽  
F Region ◽  
Threshold Conditions ◽  
Ion Acoustic

Plasma instabilities play a important role in producing small-scale irregularities in the ionosphere. In particular, current-driven electrostatic ion-acoustic (CDEIA) instabilities contribute to high-latitude F-region electrodynamics. Ion temperature anisotropies with enhanced perpendicular temperature often exist in the high-latitude F-region. In addition to temperature anisotropies, ion velocity shears are observed near auroral arc edges, sometimes coexisting with thermal ion upflow processes and field-aligned currents (FAC). We investigated whether ion temperature anisotropy lowers the threshold conditions required for the onset of sheared CDEIA instabilities. We generalised a dispersion relation to include ion thermal anisotropy, finite Larmor radius corrections and collisions. We derived new fluid-like analytical expressions for the threshold conditions required for instability that depend explicitly on ion temperature anisotropy. We studied how the instability threshold conditions vary as a function of the wave vector direction in both fluid and kinetic regimes. We found that, despite the dampening effect of collisions on ion-acoustic waves, ion temperature anisotropy lowers in some cases the threshold drift requirements for a large range of oblique wave vector angles. More importantly, realistic ion temperature anisotropies contribute to reducing the instability threshold velocity shears that are associated with small drift thresholds, for modes propagating almost perpendicularly to the geomagnetic field. Small shear thresholds that seem to be sustainable in the ionospheric F-region are obtained for low-frequency waves. Such instabilities could play a role in the direct generation of field-aligned irregularities in the collisional F-region that could be observed with the Super Dual Auroral Radar Network (SuperDARN) array of high-frequency radars. These modes would be very sensitive to the radar probing direction since they are restricted to very narrow angular intervals. The ion temperature anisotropy is an important parameter that needs to be considered in the studies of sheared and collisional CDEIA waves and instabilities in the high-latitude F-region.

scholarly journals Velocity shear and current driven instability in a collisional F-region

2009 ◽  
Vol 27 (1) ◽  
pp. 381-394 ◽  
Author(s):  
P. J. G. Perron ◽  
J.-M. A. Noël ◽  
J.-P. St.-Maurice
Keyword(s):  
Dispersion Relation ◽  
Electron Temperature ◽  
Current Density ◽  
Threshold Current ◽  
Velocity Shear ◽  
Ion Temperature ◽  
Fluid Limit ◽  
Low Frequencies ◽  
F Region ◽  
Threshold Conditions

Abstract. We have studied how the presence of collisions affects the behavior of instabilities triggered by a combination of shears and parallel currents in the ionosphere under a variety of ion to electron temperature ratios. To this goal we have numerically solved a kinetic dispersion relation, using a relaxation model to describe the effects of ion and electron collisions. We have compared our solutions to expressions derived in a fluid limit which applied only to large electron to ion temperature ratios. We have limited our study to threshold conditions for the current density and the shears. We have studied how the threshold varies as a function of the wave-vector angle direction and as a function of frequency. As expected, we have found that for low frequencies and/or elevated ion to electron temperature ratios, the kinetic dispersion relation has to be used to evaluate the threshold conditions. We have also found that ion velocity shears can significantly lower the field-aligned threshold current needed to trigger the instability, especially for wave-vectors close to the perpendicular to the magnetic field. However the current density and shear requirements remain significantly higher than if collisions are neglected. Therefore, for ionospheric F-region applications, the effect of collisions should be included in the calculation of instabilities associated with horizontal shears in the vertical flow. Furthermore, in many situations of interest the kinetic solutions should be used instead of the fluid limit, in spite of the fact that the latter can be shown to produce qualitatively valid solutions.

Linear and nonlinear obliquely propagating ion-acoustic waves in magnetized negative ion plasma with non-thermal electrons

2013 ◽  
Vol 79 (5) ◽  
pp. 893-908 ◽  
Author(s):  
M. K. MISHRA ◽  
S. K. JAIN
Keyword(s):  
Acoustic Waves ◽  
Kdv Equation ◽  
Negative Ions ◽  
Ion Concentration ◽  
Negative Ion ◽  
Slow Mode ◽  
Ion Temperature ◽  
Ion Acoustic ◽  
Ion Acoustic Solitons ◽  
Ion Species

AbstractIon-acoustic solitons in magnetized low-β plasma consisting of warm adiabatic positive and negative ions and non-thermal electrons have been studied. The reductive perturbation method is used to derive the Korteweg–de Vries (KdV) equation for the system, which admits an obliquely propagating soliton solution. It is found that due to the presence of finite ion temperature there exist two modes of propagation, namely fast and slow ion-acoustic modes. In the case of slow-mode if the ratio of temperature to mass of positive ion species is lower (higher) than the negative ion species, then there exist compressive (rarefactive) ion-acoustic solitons. It is also found that in the case of slow mode, on increasing the non-thermal parameter (γ) the amplitude of the compressive (rarefactive) soliton decreases (increases). In fast ion-acoustic mode the nature and characteristics of solitons depend on negative ion concentration. Numerical investigation in case of fast mode reveals that on increasing γ, the amplitude of compressive (rarefactive) soliton increases (decreases). The width of solitons increases with an increase in non-thermal parameters in both the modes for compressive as well as rarefactive solitons. There exists a value of critical negative ion concentration (αc), at which both compressive and rarefactive ion-acoustic solitons appear as described by modified KdV soliton. The value of αc decreases with increase in γ.

An assessment of how a combination of shears, field-aligned currents and collisions affect F-region ionospheric instabilities

2007 ◽  
Vol 73 (1) ◽  
pp. 69-88 ◽  
Author(s):  
J.-P. ST.-MAURICE ◽  
J.-M. NOËL ◽  
P. J. PERRON
Keyword(s):  
Magnetic Field ◽  
Low Frequency ◽  
Theoretical Framework ◽  
Fluid Limit ◽  
Ambient Magnetic Field ◽  
Acoustic Instability ◽  
F Region ◽  
Ion Acoustic ◽  
Depth Study ◽  
Zero Frequency

Abstract.We present an in depth study of the fluid limit of a kinetically derived collisional, current-driven instability that includes shears in the field-aligned currents as well as collisions. We show how the theory presented here generalizes other theories, including the collisionless current-driven electrostatic ion acoustic instability and its sheared collisionless version. We offer a low-frequency generalization of the zero frequency ion shear driven instability by minimizing the relative drift magnitude as well as the shears themselves. We discuss the implication of our theoretical framework both for strongly field-aligned modes and modes where the wavevectors have arbitrary angles with respect to the ambient magnetic field. We discuss the results in terms of F-region irregularity observations of coherent echoes by ionospheric radars.

The frequency and damping of ion-acoustic waves

1980 ◽  
Vol 58 (4) ◽  
pp. 565-568 ◽  
Author(s):  
A. J. Barnard ◽  
C. Gulizia
Keyword(s):  
Dispersion Relation ◽  
Electron Temperature ◽  
Acoustic Waves ◽  
Ion Temperature ◽  
Ion Acoustic Waves ◽  
Ion Acoustic

The dispersion relation for a plasma with different ion and electron temperatures is solved numerically to obtain the frequency and the damping constant for ion-acoustic waves as a function of the wavenumber. It is shown that the commonly used expressions for these variables only apply if the parameter T = ziTe/Ti is larger than 20, and can lead to large errors if T is close to 1. (Here z1 is the ion charge, Te is the electron temperature, and Ti the ion temperature.) Tables and graphs of the frequency and damping as functions of the wavenumber are given for different values of T.

Effect of finite ion-temperature on ion-acoustic solitary waves in an inhomogeneous plasma

1981 ◽  
Vol 59 (6) ◽  
pp. 719-721 ◽  
Author(s):  
Bhimsen K. Shivamoggi
Keyword(s):  
Solitary Wave ◽  
Solitary Waves ◽  
Acoustic Waves ◽  
Inhomogeneous Plasma ◽  
Ion Temperature ◽  
Ion Acoustic Waves ◽  
Weakly Nonlinear ◽  
Ion Acoustic Solitary Waves ◽  
Ion Acoustic ◽  
Velocity Of Propagation

The propagation of weakly nonlinear ion–acoustic waves in an inhomogeneous plasma is studied taking into account the effect of finite ion temperature. It is found that, whereas both the amplitude and the velocity of propagation decrease as the ion–acoustic solitary wave propagates into regions of higher density, the effect of a finite ion temperature is to reduce the amplitude but enhance the velocity of propagation of the solitary wave.

Ion- and electron-acoustic waves in sheet plasmas

1989 ◽  
Vol 41 (2) ◽  
pp. 281-287
Author(s):  
M. B. Chaudhry ◽  
M. D. Tahir
Keyword(s):  
Acoustic Waves ◽  
Cyclotron Frequency ◽  
Larmor Radius ◽  
Frequency Range ◽  
Ion Temperature ◽  
Temperature Ratio ◽  
Ion Acoustic Waves ◽  
Poisson Equations ◽  
Electron Acoustic Waves ◽  
Electron Acoustic

Ion-acoustic waves in sheet plasmas, which are of thickness of order of the ion Larmor radius ρi, have been investigated numerically. The frequency range considered is less than the ion cyclotron frequency ωci. An integral equation in wavenumber space is derived from the linearized Vlasov-Poisson equations and analysed numerically. Eigenfrequencies and eigenfunctions of the wave have been studied systematically by varying the plasma thickness, plasma density, electron-to-ion temperature ratio and parallel wavenumber. Electron-acoustic waves are found when the parallel wavenumber is very small (e.g. k∥ρi = 0·005) and the electron and ion temperatures are comparable.

Weakly relativistic effect on the modulation of nonlinear ion-acoustic waves in a warm plasma

1995 ◽  
Vol 54 (3) ◽  
pp. 295-308 ◽  
Author(s):  
S. K. El-Labany
Keyword(s):  
Perturbation Theory ◽  
Acoustic Waves ◽  
Relativistic Effect ◽  
Type Equation ◽  
Oscillatory Solution ◽  
Ion Temperature ◽  
Ion Acoustic Waves ◽  
Ion Density ◽  
Ion Acoustic ◽  
Warm Plasma

The derivative expansion perturbation method is applied to investigate the modulation of nonlinear ion-acoustic waves in a weakly relativistic warm plasma. At the second order of perturbation theory, a nonlinear Schrödingertype equation for the complex amplitude of the perturbed ion density is obtained. The coefficients in this equation show that the condition of modulational stability is modified by the relativistic effect as well as by the finite ion temperature. The association between the small-wavenumber limit of the nonlinear Schrödinger-type equation and the oscillatory solution of the Korteweg-de Vries equation obtained by reductive perturbation theory is considered. Different limits are considered in order to compare with previous work.

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