Spectra of developed Langmuir turbulence in a nonisothermal magnetized plasma

Abstract

Strong Langmuir turbulence driven by a relativistic electron beam has been investigated by the laser scattering technique. The special features of the experiments are as follows: (i) in the regime under study, Langmuir turbulence is well developed, and the temporal and spatial scales of the turbulent region far exceed those of a single caviton; (ii) the dispersion of the electron plasma waves is governed by the magnetic field, although ωpe≫ωBe; and (iii) the temperature of plasma electrons is much higher than that of ions, i.e., the damping of ion-acoustic waves is small. k-Spectra of electron plasma waves are measured in a broad spectral region by means of CO2-laser scattering. Criterion of modulational instability of observed spectra is estimated. The role of conversion and scattering of Langmuir waves by ion-acoustic waves in nonlinear energy transfer is discussed.

Nonlinear wave collapse and strong turbulence

“…Magnetized beam-plasma experiments were carried out by Vyacheslavov et al (1995) in a regime with p Ͼ⍀ e , but where the magnetic term in Eq. (9.7) greatly exceeded the thermal one.…”

“…The values of W for beam-resonant and nonresonant waves were 0.07 and 0.17, respectively, greatly exceeding the modulational instability threshold for transverse perturbations and pointing to the likelihood of wave collapse, possibly directly from the beam-driven waves. Vyacheslavov et al (1995) noted that the dispersion of the beam-driven waves (at very low k) is magnetized, despite p ӷ⍀ e being satisfied. However, Newman's (1990a, 1990c) analyses imply that the characteristic nucleation wave number is substantially larger than the beam-driven one in this case and that the dispersion is essentially unmagnetized at that value of k [see Eqs.…”

Generation of powerful terahertz emission in a beam-driven strong plasma turbulence

“…Plasma emissions at ω p and 2ω p have been also observed in laboratory beam-plasma experiments [8,9,10,11]. In contrast to the problem of type III radio bursts, in which the density of wave energy W is saturated at weakly turbulent levels W/nT ∼ 10 −5 (n is the plasma density, T is the temperature of plasma electrons), we focus our attention on the regime of strong plasma turbulence W/nT ∼ 10 −2 − 10 −1 , which is more appropriate for laboratory experiments with powerful electron beams [12,13,14].…”

Ion heating, burnout of the high-frequency field, and ion sound generation under the development of a modulation instability of an intense Langmuir wave in a plasma

“…The analytical studies, laboratory-based experiments, and numerical simulations, performed at an early stage of studying these phenomena [18][19][20] , have confirmed the fact that in some cases, in the course of instability, a significant part of the pump-field energy is transformed into the energy of short-wave Langmuir oscillations 21,22 accompanied with bursts of fast particles [18][19][20][21][22][23][24][25][26][27][28][29][30][31] . The modulation instability of intense Langmuir waves in non-isothermal plasmas also leads to collective ion perturbations, in particular, to the generation of ion-sound waves [32][33][34][35] .…”