Modulational Instabilities and wave Collapse Driven by Broadband Turbulence

The interaction of broadband turbulence with plasmas has been studied in a number of regimes. Beam instabilities occur in this interaction when the phase velocity of the long- wavelength monochromatic wave is nearly equal to the group velocity of short-wavelength wavepackets, or quasi-particles, associated with the turbulent spectrum. It is shown that quasi-particle Landau-damping can take place, as well as quasi-particle modulational instabilities, thus establishing a direct link between short- and long-wavelength perturbations of the medium. Numerical simulations are reported for three cases (i) intense laser pulse driving a plasma wakefield, for use in plasma-based acceleration. (ii) a broadband distribution of drift modes coupling to zonal flows in a tokamak-like configuration, as well as the magnetopause, and (iii) wave collapse of strong Langmuir turbulence driven by electron beams.