Spatial, spectral, and statistical properties of the high-frequency electrostatic fluctuations in a beam-driven turbulent plasma

The spatial, spectral, and statistical properties of the high-frequency (om ega similar to omega (pe)) electrostatic fluctuations in an unmagnetized, s tatistically stable, beam-driven, strongly turbulent plasma are investigate d experimentally and the results are compared to the two-component model of Robinson and Newman. The fluctuations are found to consist of low-level wa ve activity [W]similar to 10(-2)-10(-3) punctuated by semiperiodic, intense , spiky field events [W]similar to1, where [W] is the normalized wave inten sity. The low-level wave activity has a spectral spread Deltak/k similar to Delta omega/omega similar to 30%, dispersion relation v(beam)similar to om ega /k, and correlation length l(c)approximate to3 lambda (ES) where lambda (ES) is the electrostatic wavelength, and shows evidence of low-intensity parametric decay products. The intense field events, on the other hand, sho w little correlation for l>lambda (ES), have a full width at half maximum o f l(f)<40<lambda>(D), where lambda (D) is the Debye length, and are nonprop agating. The results indicate that the two-component model, and the Zakharo v equations to which the model was originally verified, give an accurate de scription of strong Langmuir turbulence. (C) 2001 American Institute of Phy sics. [DOI: 10.1063/1.1328356].