The spatial location of laser-driven, forward-propagating waves in a National-Ignition-Facility-relevant plasma

Ion acoustic and electron plasma waves, associated with backward-propagating stimulated Brillouin scattering and stimulated Raman scattering, have been diagnosed in a long-scale-length, nearly homogenous plasma with transverse flow. Thomson scattered light from a probe beam is employed to show that these waves are well localized in space and for a time much shorter than the laser pulse duration. These plasma conditions are relevant to hohlraum design for the National Ignition Facility inertial confinement fusion laser system. [R. Sawicki et al., Fusion Technol. 34, 1097 (1998)]. © 2000 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71338/2/PHPAEN-7-1-323-1.pd

Experimental evidence of the effect of heat flux on Thomson scattering off ion acoustic waves

International audienceThomson self-scattering measurements are performed in a preionized helium gas jet plasma at different locations along the laser propagation direction. A systematic and important variation of the intensity ratio between the blue and the red ion spectral components is observed, depending on whether the location of the probed region is in front of or behind the focal plane. A simple theoretical calculation of Thomson scattering shows that this behavior can be qualitatively understood in terms of a deformation of the electron distribution function due to the return current correlated with the classical thermal heat flu

Strong self-focusing in quasi-stationary laser plasmas

International audienceCollective Thomson scattering imaging has been used to study the propagation and self-focusing processes taking place during the interaction of a nanosecond laser beam with a preionized gas-jet plasma. The experiments have been carried out with a laser beam power PL exceeding greatly the critical power for ponderomotive self-focusingPc. It has been found that the position of the ion acoustic waves excited by stimulated Brillouin scattering depends only weakly on the initial focal position of the interactionlaser beam. These results, together with theoretical and numerical modeling, demonstrate that in such a regime (PL/Pc≫1)self-focusing is the dominant mechanism governing the localization of the interaction processes