Beam scattering and low-frequency fluctuations in a beam-driven strongly turbulent plasma

The scattering of an electron beam in angle and energy in an unmagnetized, statistically stable, strongly turbulent plasma is investigated experimentally and the results are compared to a theoretical model derived using the Born approximation and the two-component model of strong Langmuir turbulence. It is found that for a typical wave intensity level [W]similar to0.04 the scattering in angle is theta similar to3 degrees, and in energy is DeltaU similar to 25 eV for a 400 eV beam. The scattering of the beam in both angle and energy is found to agree well with the theory. The low-frequency (omega similar to omega (pi)) fluctuations are also measured in this investigation and their magnitude Deltan/n is compared to the two-component model of strong Langmuir turbulence. It is found that [Delta (2)]/n(2)proportional to [W](beta) where beta similar to1.3 for the experiment and is predicted to be beta similar to1.98 by the model. The results indicate that the two-component model, and the Zakharov equations to which the theory was originally verified, give an accurate description of strong Langmuir turbulence. In addition, the validity of transit time scattering theory, based on the Born approximation, is confirmed. (C) 2001 American Institute of Physics. [DOI: 10.1063/1.1328357].