Landau damping of long wavelength ion acoustic waves in a collision-free plasma with a gravity field

Abstract

Ion acoustic waves propagating in a collision-free gravity-supported one-dimeiisional plasma are studied, including conditions where the wavelength is of the order of the scale height of the equilibrium plasma. It turns out that the fluid dynamic steepening tendency of waves propagating in the direction of decreasing density is overcome by Landau damping up to wavelengths of the order of the scale height or even larger, depending on the ratio of the electron and the ion temperatures.

Models for electrostatic drift waves with density variations along magnetic field lines

“…For the geometric growth discussed for the initial value problem with real wave numbers, we found that the imaginary part of the frequency approached a constant level for large k z , i.e., I { ω }/ R { ω }→0 for k z → ∞ . It was demonstrated by Parkinson and Schindler [] that for stable conditions, the ion Landau damping will dominate for large k z .…”

“…[6] The observed wave growth cannot properly be called an instability [Parkinson and Schindler, 1969;Dysthe et al, 1975;D'Angelo et al, 1975]. The amplitude increase with increasing altitude z is merely a consequence of the decreasing plasma density: For fluctuating plasma velocities u, the vertical component of the wave energy density flux is to lowest order n(r ?…”

“…1. It was demonstrated by Parkinson and Schindler [1969] that for stable conditions, the ion Landau damping will dominate for large k z .…”

Ion Acoustic Waves in a Density Gradient

“…The zero order axial density profile is obtained most easily through a measurement of the probe floating potential and the relation 4 ' 7 y.Tedn0/dx = e n0d<P0/dx (1) between density and potential gradients (we consider the electrons as isothermal i.e. Te = const).…”

The transition at a periodT∼ 1 Day in solar wind spectra

“…Detailed calculations[Parkinson and Schindler, 1969;Liu, 1970] give X, = 2•rl,•. Since the (hydrodynamic) growth distance fig is given by fig = 21,• and since the (Landau) damping distance is ba • 0.4X (when Tt • T, and little plasma drift is present), there exists a 'critical' wavelength Xc, determined by the condition that fig • ha.…”