OBSERVATION OF MULTIPLE MECHANISMS FOR STIMULATING ION WAVES IN IGNITION SCALE PLASMAS

The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been shown that there are at least three ways in which ion wav es can be stimulated in these plasmas and have a significant effect on the energy balance and distribution in the target. First ion waves ca n be stimulated by a single laser beam by the process of stimulated Br illouin scattering (SBS) in which an ion acoustic and a scattered elec tromagnetic wave grow from noise. Second, in a plasma where more than one beam intersects, ion waves can be excited at the ''beat'' frequenc y and wave number of the intersecting beams, causing the sidescatter i nstability to be seeded, and substantial energy to be transferred betw een the beams [R. K. Kirkwood et al., Phys. Rev. Lett. 76, 2065 (1996) ]. And third, ion waves may be stimulated by the decay of electron pla sma waves produced by stimulated Raman scattering (SRS), thereby inhib iting the SRS process. (C) 1997 American Institute of Physics.