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Interaction between stimulated raman scattering and ion acoustic waves in ignition relevant plasmas

Description: We have observed that the scattering of light by stimulated Langmuir waves (SRS) in ignition scale plasmas is dependent on the properties of the ion acoustic wave, indicating that a nonlinear coupling between the two waves limits the scattered energy.
Date: June 1, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas

Description: The laser and plasma conditions expected in ignition experiments using indirect drive inertial confinement have been studied experimentally. It has been found that there are at least three ways in which ion waves can be stimulated in these plasmas and have significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of Stimulated Brillouin Scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersect, ion waves can be excited at the `beat` frequency and wave number of the intersecting beams, causing the side scatter instability to be seeded, and substantial energy to be transferred between the beams [R. K. Kirkwood et. al. Phys. Re0319v. Lett. 76, 2065 (1996)]. And third, ion waves may be stimulated by the decay of electron plasma waves produced by Stimulated Raman Scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et. al. Phys. Rev. Lett. 77, 2706 (1996)].
Date: November 1, 1996
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Observation of multiple mechanisms for stimulating ion waves in ignition scale plasmas. Revision 1

Description: 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 waves can be stimulated in these plasmas and have significant effect on the energy balance and distribution in the target. First ion waves can be stimulated by a single laser beam by the process of Stimulated Brillouin Scattering (SBS) in which an ion acoustic and a scattered electromagnetic wave grow from noise. Second, in a plasma where more than one beam intersect, ion waves can Lie excited at the `beat` frequency and wave number of the intersecting beams,, causing the side scatter instability to be seeded, and substantial energy to be transferred between 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 plasma waves produced by Stimulated Raman Scattering (SRS), thereby inhibiting the SRS process [R. K. Kirkwood et. al. Phys. Rev. Lett. 77, 2706 (1996)].
Date: March 3, 1997
Creator: Kirkwood, R.K.; MacGowan, B.J. & Montgomery, D.S.
Partner: UNT Libraries Government Documents Department

Evidence of plasma fluctuations and their effect on the growth of stimulated Brillouin and stimulated Raman scattering in laser plasmas

Description: The reflectivity levels of stimulated Brillouin scattering (SBS) in recent large scale length laser plasma experiments is much lower than expected for conditions where the convective gain exponent is expected to be large. Long wavelength velocity fluctuations caused during the plasma formation process, or by parametric instabilities themselves, have been proposed as a mechanism to detune SBS in these experiments and reduce its gain. Evidence of large velocity fluctuation levels is found in the time-resolved SBS spectra from these experiments, and correlates with observed changes in the reflectivity of both SBS and stimulated Raman scattering (SRS). The authors present evidence of fluctuations which increase as the plasma density systematically increases, and discuss their effect on the growth of parametric instabilities.
Date: November 1, 1997
Creator: Montgomery, D.S.; Fernandez, J.C. & Cobble, J.A.
Partner: UNT Libraries Government Documents Department

Characterization of plasma and laser conditions for single hot spot interaction experiments

Description: The LANL TRIDENT laser system is being used for fundamental experiments which study the interaction of self-focusing, stimulated Raman scattering (SRS) and stimulated Brillouin scattering (SBS) in a single (diffraction limited) laser hot spot in order to better understand the coupling between these plasma instabilities. The diffraction limited beam mimics a single hot spot found in speckle distributions that are typical of random or kinoform phase plate (RPP or KPP) smoothing. A long scale length, hot plasma ({approximately} 1 mm, {approximately} 0.5 keV) is created by a separate heater beam, and the single hot spot beam is used to drive parametric instabilities. The focal plane distribution and wavefront of the single hot spot beam are characterized, and the intensity of the single hot spot can be varied between 10{sup 14}--10{sup 16} W/cm{sup 2}. The plasma density, temperature, and flow profiles are measured using gated imaging spectroscopy of collective Thomson scattering. Results of the laser and plasma characterization, and initial results of backscattered SRS, SBS, and beam steering in a flowing plasma are presented.
Date: November 1, 1998
Creator: Montgomery, D.S.; Johnson, R.P.; Cobble, J.A.; Fernandez, J.C.; Lindman, E.L.; Rose, H.A. et al.
Partner: UNT Libraries Government Documents Department

Experimental Program to Elucidate and Control Stimulated Brillouin and Raman Backscattering in Long-Scale Plasmas

Description: Laser-plasma instability is a serious concern for indirect-drive inertial confinement fusion (ICF), where laser beams illuminate the interior of a cavity (called a hohlraum) to produce X-rays to drive the implosion of a fusion capsule. Stimulated Raman and Brillouin backscattering (SRS and SBS) could result in unacceptably high laser reflectivities. Unfortunately, it is impossible at present to fully simulate these processes realistically. The authors experimental program aims to understand these instabilities by pursuing a dual strategy. (1) They use a gas-filled hohlraum design, which best approaches ignition-hohlraum conditions, on the Nova laser to identify important non linear trends. (2) They are shifting towards more fundamental experiments with a nearly diffraction-limited interaction laser beam illuminating extremely well characterized plasmas on the Trident laser facility at Los Alamos to probe the relevant fundamental processes.
Date: October 19, 1998
Creator: Fernandez, J.C.; Cobble, J.A.; Montgomery, D.S. & Wilke, M.D.
Partner: UNT Libraries Government Documents Department

Experimental Investigation of Short Scalelength Density Fluctuations in Laser-Produced Plasmas

Description: The technique of near forward laser. scattering is used to infer characteristics of intrinsic and controlled density fluctuations in laser-produced plasmas. Intrinsic fluctuations are studied in long scalelength plasmas where the fluctuations exhibit scale sizes related to the size of the intensity variations in the plasma forming and interaction beams. Stimulated Brillouin forward scattering and filamentation appear to be the primary mechanism through which these fluctuations originate. The beam spray which results from these fluctuations is important to understand since it can affect symmetry in an inertial confinement fusion (ICF) experiment. Controlled fluctuations are studied in foam and exploding foil targets. Forward scattered light from foam targets shows evidence that the initial target inhomogeneities remain after the target is laser heated. Forward scattered light from an exploding foil plasma shows that a regular intensity pattern can be used to produce a spatially correlated density fluctuation pattern. These results provide data which can be used to benchmark numerical models of beam spray.
Date: November 1, 1999
Creator: Moody, J.D.; MacGowan, B.J.; Glenzer, S.H.; Kirkwood, R.K.; Kruer, W.L.; Williams, E.A. et al.
Partner: UNT Libraries Government Documents Department

Experimental Investigation of Short Scalelength Density Fluctuations in Laser-Produced Plasmas

Description: The technique of near forward laser scattering is used to infer characteristics of intrinsic and controlled density fluctuations in laser-produced plasmas. Intrinsic fluctuations are studied in long-scale length plasmas where we find that the fluctuations exhibit scale sizes related to the intensity variation scales in the plasma-forming and interaction beams. Stimulated Brillouin forward scattering and filamentation appear to be the primary mechanism through which these fluctuations originate. The beam spray resulting from these fluctuations is important to understand since it can affect symmetry in an inertial confinement fusion (ICF) experiment. Controlled fluctuations are studied in foam and exploding foil targets. Forward scattered light from foam targets shows evidence that the initial target inhomogeneities remain after the target is laser heated. Forward scattered light from an exploding foil plasma shows that a regular intensity pattern can be used to produce a spatially correlated density fluctuation pattern. These results provide data which are being used to benchmark numerical models of beam spray.
Date: January 5, 2000
Creator: Moody, J.D.; MacGowan, B.J.; Glenzer, S.H.; Kirkwood, R.K.; Kruer, W.L.; Montgomery, D.S. et al.
Partner: UNT Libraries Government Documents Department

Laser/matter interactions by laser-launched plates and direct laser shocks

Description: Explosives, gas guns, laser-launched flyer plates, and direct laser-irradiation can be used to generate shocks and high-stress in materials. Each method has a unique diameter and thickness of shock that can be generated. In past years, small laboratory lasers have been used to launch flyer plates 2 - 200-pm thick to terminal velocities 0.1 to 5 k d s . Over the past few years we have been using our TRIDENT laser facility (1kJ in 0.2 to 2ps) to accelerate larger diameter (8 mm) and thicker (0.1 - 1.5 mm) flyer plates. These larger diameters and thicker one-dimensional plates more closely compliment traditional experimental methods such as gas guns. The 8-mm diameter and 1-mm thick flyer plates can impart shocks in metals for constitutive dynamic property measurements. The versatility of laser-driven plates permits spatial and temporal profiles of the flyer plate impact on sample targets. LASNEX models and parameters of the laser drive can be used to optimize optical coupling efficiency. The flyer plate launch, acceleration, terminal velocity, and, depending on the experiment, flyer plate impact on to target materials are recorded using point-interferometry (VISAR), and line-imaging interferometry. These high speed optical and laser experimental methods will be described along with ancillary methods, and material data. Constitutive properties of bulk materials, rate effects, and grain size and/or orientation have been studied for several metals including copper, beryllium, gold, and some alloys.
Date: January 1, 2003
Creator: Paisley, Dennis L.; Swift, D. C. (Damian C.); Kopp, R. A. (Roger A.); Montgomery, D. S. (David S.); Johnson, R. P. (Randall P.); Munson, C. P. (Carter P.) et al.
Partner: UNT Libraries Government Documents Department