Interaction of a Highly Energetic Electron Beam with a Dense Plasma

Abstract

The interaction of an electron beam with a relatively dense background plasma was examined through numerical experiments, where the beam velocity is much greater than the thermal velocities. It is shown that the initial growth of the unstable waves is described by the two-stream instability and that the phenomena can be separated into two regions, (high and low density) depending on whether or not merging of space-averaged velocity distributions occurs during the growth of the initially most unstable wave. The occurrence of these regions is shown to follow from energy and momentum considerations. The long-time behavior of the low-density regime, where the merging does not take place during the initial growth of the instability is shown to be described quite well by quasilinear theory.

Ion acoustic instabilities excited by injection of an electron beam in space

“…Here, co•,e and co•,b are ambient and beam electron plasma frequencies, and V o is the beam drift speed. The resultant electric field accelerates beam electrons to form a high-energy tail (see, for example, Kainer et al [1972]). For an energetic beam whose injection speed is much faster than the thermal speed of the ambient electrons, V o >> V e, excitation of the low-frequency ion acoustic waves and ion acceleration cannot be expected, since such a high-energy electron beam cannot couple directly with Copyright 1988 by the American Geophysical Union.…”

Excitation of Chirping Whistler Waves in a Laboratory Plasma

“…4(a) at low n b /n 0 can be understood from linear growth rate estimates, given the dependence on the density ratio (n b /n 0 ) α (α = 1/3 for a beam, α = 1 for a bi-Maxwellian plasma). We should note that, although we launched a gyrating beam into the background plasma, the electron distribution function is redistributed to have a long tail up to the beam energy by other processes [23,[33][34][35].…”

Linear study of the beam‐plasma interaction as a source mechanism for the broadband electrostatic emissions observed in the electron foreshock

“…It is clear that the bandwidth of the resulting emission will ultimately be determined by the nonlinear mechanism which will stop the growth. Numerical simulations confirmed many years ago that for the beam-plasma interaction, a large range of wave number values can be unstable, the most unstable one in time being not always the one given by the linear theory [Kainer et al, 1972]. A first implication of our computations is that if we want to use the linear beam instability as being the source for the foreshock emissions, we have to take into account all the positive growth rate frequency bandwidth, instead of considering only the frequency of maximum growth.…”