Instability Of Langmuir Waves Research Articles

Instability of Langmuir waves in plasma irradiated by directed gamma rays.

In this Letter we investigate the possibility of Langmuir turbulence generation by directed gamma rays penetrating a background plasma. Turbulence is generated because Compton scattering creates superthermal electrons whose distribution can be unstable to the Cherenkov radiation of Langmuir waves. Using the Klein-Nishina cross section for relativistic Compton scattering, we calculate the momentum distribution of recoil electrons and derive the increment of instability for nonmagnetized plasma. The instability appears when there is a sufficiently narrow bump, for example, annihilation line $h\ensuremath{\nu}{\phantom{\rule{0ex}{0ex}}=\phantom{\rule{0ex}{0ex}}m}_{e}{c}^{2}$ with a width less than $0.3{m}_{e}{c}^{2}$, in the gamma spectrum.

Transition in the dispersive properties of beam‐plasma and two‐stream instabilities

The linear dispersion relation and the quasi‐linear evolution of the electron beam‐plasma instability are studied in intermediate regimes between the limits of the gentle bump‐on‐tail instability of Langmuir waves and purely reactive instability. The ranges of beam and plasma parameters which correspond to narrow‐banded plasma waves, broadband waves and waves with frequencies substantially below the electron plasma frequency are determined in a systematic and practical manner. The transition between these regimes and the changes in the topology of the dispersion relation are described by analytic theory and by detailed numerical solutions. All branches of the dispersion relation, including weakly damped modes which may be important in nonlinear wave coupling, are considered. Dissipative and reactive instability mechanisms are differentiated analytically and by comparing solutions of the exact dispersion relation with hybrid models using fluid components. Consequences for observations, especially in the electron foreshock, and for the design and analysis of simulation experiments are pointed out. The theory is also applicable to instabilities with ion beams or current driven instabilities. The study of the effects of increasing bulk temperature (or decreasing drift) applies in particular to the evolution from reactive Buneman instability to kinetic ion sound instability.

Effect of finite spectral width on the modulational instability of Langmuir waves

The effect of finite spectral width on the modulational instability of Langmuir waves has been investigated applying a method developed by Alber to derive a transport equation for the spectral density. The numerical results presented show that the spectrum is stable against modulational perturbation when the spectral width exceeds some critical value. For a Gaussian spectrum, the maximum growth rate is less than that for a monochromatic wave but the domain of modulational instability is extended. For a uniform distribution the shift in the growth rate curve towards the region of shorter wavelength is more pronounced and, for a certain range of spectral width, the maximum growth rate exceeds that for a monochromatic wave.

Effect of nonlinear Landau damping on long time behaviour of modulational instability of Langmuir wave

The effect of nonlinear Landau damping on the long term behaviour of the modulational instability of a monochromatic Langmuir wave has been investigated. The growth or decay of the perturbation amplitude is oscillatory in character. Most of the time the amplitude changes approximately linearly with time. Growth occurs for negative nonlinear frequency shift while it decays when the frequency shift is positive.