scholarly journals Enhanced ion acoustic lines due to strong ion cyclotron wave fields

2008 ◽  
Vol 26 (8) ◽  
pp. 2081-2095 ◽  
Author(s):  
H. Bahcivan ◽  
R. Cosgrove
Keyword(s):  
Distribution Function ◽  
Electric Fields ◽  
Near Field ◽  
Electron Distribution Function ◽  
Ion Distribution ◽  
Incoherent Scatter Radars ◽  
Ion Acoustic ◽  
Ion Cyclotron ◽  
Observational Fact ◽  
Step Mechanism

Abstract. The Fast Auroral Snapshot Explorer (FAST) satellite detected intense and coherent 5–20 m electric field structures in the high-latitude topside auroral ionosphere between the altitudes of 350 km and 650 km. These electric fields appear to belong to electrostatic ion cyclotron (EIC) waves in terms of their frequency and wavelengths. Numerical simulations of the response of an electron plasma to the parallel components of these fields show that the waves are likely to excite a wave-driven parallel ion acoustic (IA) instability, through the creation of a highly non-Maxwellian electron distribution function, which when combined with the (assumed) Maxwellian ion distribution function provides inverse Landau damping. Because the counter-streaming threshold for excitation of EIC waves is well below that for excitation of IA waves (assuming Maxwellian statistics) our results suggest a possible two step mechanism for destabilization of IA waves. Combining this simulation result with the observational fact that these EIC waves share a common phenomenology with the naturally enhanced IA lines (NEIALS) observed by incoherent scatter radars, especially that they both occur near field-aligned currents, leads to the proposition that this two-step mechanism is an alternative path to NEIALS.

Electrostatic heat flux instabilities

1978 ◽  
Vol 20 (1) ◽  
pp. 47-60 ◽  
Author(s):  
S. Peter Gary
Keyword(s):  
Heat Flux ◽  
Distribution Function ◽  
Electron Beam ◽  
Electron Distribution ◽  
Electron Distribution Function ◽  
High Energy ◽  
Electrostatic Waves ◽  
High Energy Tail ◽  
Ion Acoustic ◽  
Ion Cyclotron

The linear Vlasov dispersion relation for electrostatic waves in a homogeneous plasma is studied for instabilities driven by an electron heat flux. A two Maxwellian model of the electron distribution function gives rise to three unstable modes: the electron beam, ion-acoustic and ion cyclotron heat flux instabilities. At large Te/Ti the ion-acoustic instability has the lowest threshold; at small Te/Ti the electron beam instability is dominant; and at intermediate values of Te/Ti the ion cyclotron mode is the first to go unstable. The presence of a high energy tail on the electron distribution function raises the value of the dimensionless heat flux qe/(nemev3e) at the ion-acoustic threshold, but increasing atomic number of the ions decreases this value.

scholarly journals Spiky parallel electrostatic ion cyclotron and ion acoustic waves

2002 ◽  
Vol 9 (1) ◽  
pp. 25-29 ◽  
Author(s):  
R. V. Reddy ◽  
G. S. Lakhina ◽  
N. Singh ◽  
R. Bharuthram
Keyword(s):  
Electric Fields ◽  
Acoustic Waves ◽  
Rest Frame ◽  
Wave Form ◽  
Ion Acoustic Waves ◽  
Parallel Propagation ◽  
Wave Phase Velocity ◽  
Ion Acoustic ◽  
Ion Cyclotron ◽  
Field Aligned Current

Abstract. One of the interesting observations from the FAST satellite is the detection of strong spiky waveforms in the parallel electric field in association with ion cyclotron oscillations in the perpendicular electric fields. We report here an analytical model of the coupled nonlinear ion cyclotron and ion-acoustic waves, which could explain the observations. Using the fluid equations for the plasma consisting of warm electrons and cold ions, a nonlinear wave equation is derived in the rest frame of the propagating wave for any direction of propagation oblique to the ambient magnetic field. The equilibrium bulk flow of ions is also included in the model to mimic the field-aligned current. Depending on the wave Mach number M defined by M = V/Cs with V and Cs being the wave phase velocity and ion-acoustic speed, respectively, we find a range of solutions varying from a sinusoidal wave form for small amplitudes and low M to sawtooth and highly spiky waveforms for nearly parallel propagation. The results from the model are compared with the satellite observations.

Minority-ion distribution function of a plasma under fundamental and second-harmonic ion-cyclotron heating

1995 ◽  
Vol 53 (1) ◽  
pp. 3-23 ◽  
Author(s):  
B. Weyssow
Keyword(s):  
Distribution Function ◽  
Kinetic Equation ◽  
Second Harmonic ◽  
Hermite Polynomials ◽  
Collision Term ◽  
Algebraic Equations ◽  
Ion Temperature ◽  
Ion Distribution ◽  
Ion Cyclotron ◽  
Analytical Result

The distribution function of the minority ions during ion-cyclotron heating is calculated from a kinetic equation composed of a Landau collision term and a surface-averaged quasi-linear heating term. The kinetic equation is solved by a moment method in which the minority-ion distribution function is expanded in irreducible tensorial Hermite polynomials. The coefficients of the expansion are shown to be solutions of a system of coupled algebraic equations, and the effective minority-ion temperature is deduced from a compatibility constraint. The latter equation is in general too complicated to be solved analytically. The distribution function obtained here is therefore a semi-analytical result.

Quasilinear dynamics of ion cyclotron instability in an anisotropic plasma

1970 ◽  
Vol 4 (1) ◽  
pp. 175-186 ◽  
Author(s):  
J. Preinhaelter ◽  
J. Václavík
Keyword(s):  
Distribution Function ◽  
Magnetoactive Plasma ◽  
Ion Distribution ◽  
Magnetostatic Field ◽  
Ion Cyclotron Waves ◽  
Anisotropic Temperature ◽  
Electrons And Ions ◽  
Ion Cyclotron ◽  
Cold Electrons ◽  
Maximum Increment

It is shown that in a dense magnetoactive plasma c/cA ≫ 1 with cold electrons and ions with an anisotropic temperature the ion cyclotron waves propagating along the magnetostatic field are excited with a maximum increment. The dynamics of the quasilinear stage of this instability is investigated. It turns out that, at any moment, the ion distribution function is of the form of a step with the steep front. The speed of the front in the velocity space and the characteristic time of the relaxation process are found. It is ascertained that the distribution function arising in the course of the relaxation is stable with respect to the ion cyclotron waves propagating obliquely to the magnetostatic field.

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