Propagation of Ion Acoustic Waves from and to a Spherical or Cylindrical Conductor

1972 ◽  
Vol 50 (5) ◽  
pp. 506-512 ◽  
Author(s):  
L. Schott
Keyword(s):  
Phase Velocity ◽  
Acoustic Waves ◽  
Fluid Model ◽  
Debye Length ◽  
Plasma Boundary ◽  
Ion Acoustic Waves ◽  
Ion Acoustic ◽  
Analytic Expressions ◽  
Consistent Solution ◽  
Two Fluid Model

Analytic expressions for the spatial variation of the phase velocity and amplitude of ion acoustic waves propagating radially through the plasma boundary layer at a conducting sphere or cylinder are derived using the two-fluid model. The Debye length is assumed to be small compared with any relevant dimension of the problem and the wavelength small compared with the radius of the conductor. The limits of ion mean free paths small and large compared with the radius of the sphere are considered. In the cylindrical case only the collisionless limit has a self-consistent solution. It is found that both the converging and the diverging waves are damped and that the phase velocity of the wave is approximately equal to the sum of the ion acoustic velocity in a homogeneous plasma and the ion drift velocity. The contribution of Landau damping to the total damping is estimated.

Freestreaming mode excited by a pulse

1986 ◽  
Vol 64 (7) ◽  
pp. 768-772
Author(s):  
Ludwig Schott
Keyword(s):  
Acoustic Waves ◽  
Voltage Pulse ◽  
Velocity Distribution Function ◽  
Density Perturbation ◽  
Zeroth Order ◽  
Ion Acoustic Waves ◽  
Ion Acoustic Wave ◽  
Ion Acoustic ◽  
Analytic Expressions ◽  
Applied Voltage Pulse

When a voltage pulse is applied to an exciter (probe or grid) immersed in a plasma, both an ion-acoustic wave and a freestreaming (ballistic) signal are excited. It is shown that the density perturbation produced by the freestreaming signal is independent of the shape of the applied-voltage pulse for times that are large compared with the temporal width of the pulse and at distances that are large compared with the size of the sheath at the exciter, but it depends on the second derivative of the zeroth-order velocity-distribution function. Analytic expressions that are valid for all times and positions are derived for a simple sheath model. Criteria are presented that enable the experimentalist to distinguish freestreaming modes from ion-acoustic waves.

Ion-acoustic wave instability driven by drifting electrons in a generalized Lorentzian distribution

1992 ◽  
Vol 47 (3) ◽  
pp. 445-464 ◽  
Author(s):  
Zhaoyue Meng ◽  
Richard M. Thorne ◽  
Danny Summers
Keyword(s):  
Electron Temperature ◽  
Acoustic Waves ◽  
Debye Length ◽  
High Energy ◽  
Dispersion Function ◽  
Electron Drift ◽  
Kappa Distribution ◽  
Ion Acoustic Waves ◽  
High Energy Tail ◽  
Ion Acoustic

A generalized Lorentzian (kappa) particle distribution function is useful for modelling plasma distributions with a high-energy tail that typically occur in space. The modified plasma dispersion function is employed to study the instability of ion-acoustic waves driven by electron drift in a hot isotropic unmagnetized plasma modelled by a kappa distribution. The real and imaginary parts of the wave frequency ω0 + ιγ are obtained as functions of the normalized wavenumber kλD, where λD is the electron Debye length. Marginal stability conditions for instability are obtained for different ion-to-electron temperature ratios. The results for a kappa distribution are compared with the classical results for a Maxwellian. In all cases studied the ion-acoustic waves are strongly damped at short wavelengths, kλD ≫ 1, but they can be destabilized at long wavelengths. The instability for both the kappa and Maxwellian distributions can be quenched by increasing the ion-electron temperature ratio Ti/Te. However, both the marginally unstable electron drift velocities and the growth rates of unstable waves can differ significantly between a generalized Lorentzian and a Maxwellian plasma; these differences are also influenced by the value of Ti/Te.

On the Phase Velocity of Ion-Acoustic Waves

1980 ◽  
Vol 8 (3) ◽  
pp. 275-276 ◽  
Author(s):  
Noah Hershkowitz ◽  
Albert J. Lamm
Keyword(s):  
Phase Velocity ◽  
Acoustic Waves ◽  
Ion Acoustic Waves ◽  
Ion Acoustic

Long wavelength ion-acoustic waves in a magneto-plasma in a gravitational field

1970 ◽  
Vol 4 (3) ◽  
pp. 617-627 ◽  
Author(s):  
C. H. Liu
Keyword(s):  
Magnetic Field ◽  
Dispersion Relation ◽  
Static Magnetic Field ◽  
Acoustic Waves ◽  
Fluid Dynamic ◽  
Debye Length ◽  
Ion Acoustic Waves ◽  
Long Wavelength ◽  
Special Cases ◽  
Ion Acoustic

Ion-acoustic waves propagating in a collision-free, gravity-supported plasma in a static magnetic field are studied with a linearized Vlasov equation. The dispersion relation is derived in the limit of vanishing electron to ion mass ratio and wavelength much larger than the Debye length. From this dispersion relation it is shown that the well-known fluid dynamic steepening tendency of waves propagating in the direction of decreasing density is competing with the effect of Landau damping. Depending on the ratio of electron and ion temperatures, the direction of propagation and the strength of the static magnetic field, waves of wavelengths of the order of the scale height or even greater are shown to be damped. Several special cases are discussed.

scholarly journals High time resolution PFISR and optical observations of naturally enhanced ion acoustic lines

2009 ◽  
Vol 27 (4) ◽  
pp. 1457-1467 ◽  
Author(s):  
R. G. Michell ◽  
K. A. Lynch ◽  
C. J. Heinselman ◽  
H. C. Stenbaek-Nielsen
Keyword(s):  
High Resolution ◽  
Time Resolution ◽  
Acoustic Waves ◽  
Fast Moving ◽  
High Time ◽  
High Time Resolution ◽  
Ion Acoustic Waves ◽  
Raw Data ◽  
Ion Acoustic ◽  
Auroral Imaging

Abstract. Observations of naturally enhanced ion acoustic lines (NEIALs) taken with the Poker Flat Incoherent Scatter Radar (PFISR) using a mode with very high time resolution are presented. The auroral event took place over Poker Flat, Alaska on 8 February 2007 at 09:35 UT (~22:00 MLT), and the radar data are complemented by common-volume high-resolution auroral imaging. The NEIALs occurred during only one of the standard 15-s integration periods. The raw data of this time show very intermittent NEIALs which occur only during a few very short time intervals (≤1 s) within the 15-s period. The time sampling of the raw data, ~19 ms on average, allows study of the time development of the NEIALs, though there are indications that even finer time resolution would be of interest. The analysis is based on the assumption that the NEIAL returns are the result of Bragg scattering from ion-acoustic waves that have been enhanced significantly above thermal levels. The spectra of the raw data indicate that although the up- and down-shifted shoulders can both become enhanced at the same time, (within 19 ms), they are most often enhanced individually. The overall power in the up-and down-shifted shoulders is approximately equal throughout the event, with the exception of one time, when very large up-shifted power was observed with no corresponding down-shifted power. This indicates that during the 480 μs pulse, the strongly enhanced ion-acoustic waves were only traveling downward and not upward. The exact time that the NEIALs occurred was when the radar beam was on the boundary of a fast-moving (~10 km/s), bright auroral structure, as seen in the high resolution auroral imaging of the magnetic zenith. When viewed with high time resolution, the occurrence of NEIALs is associated with rapid changes in auroral luminosity within the radar field of view due to fast-moving auroral fine structures.

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