3
                ω
           transmitted beam diagnostic at the Omega Laser Facility

Froula, D. H.; Rekow, V.; Sorce, C.; Piston, K.; Knight, Russel; Alvarez, S. S.; Griffith, R. L.; Hargrove, D.; Ross, J. S.; Dixit, S.; Pollock, B.; Divol, L.; Glenzer, S. H.; Armstrong, William D.; Bahr, R.; Thorp, K.; Pien, G.

doi:10.1063/1.2221911

Cited by 14 publications

(6 citation statements)

References 8 publications

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“…Light scattered from the interaction beam is measured using a full-aperture backscatter station (FABS) [18], a near backscatter imager (NBI) [19], and a 3ω transmitted beam diagnostic (3ω TBD) [20]. Light scattered back into the original beam cone is collected by the FABS, where the SBS and the SRS spectra and energies are measured.…”

Section: Diagnosticsmentioning

confidence: 99%

Experimental basis for laser-plasma interactions in ignition hohlraums at the National Ignition Facility

et al. 2010

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A series of laser plasma interaction experiments at OMEGA (LLE, Rochester) using gas-filled hohlraums shed light on the behavior of stimulated Raman scattering and stimulated Brillouin scattering at various plasma conditions encountered in indirect drive ignition designs. We present detailed experimental results that quantify the density, temperature, and intensity thresholds for both of these instabilities. In addition to controlling plasma parameters, the National Ignition Campaign relies on optical beam smoothing techniques to mitigate backscatter. We show that polarization smoothing is effective at controlling backscatter. These results provide an experimental basis for forthcoming experiments on National Ignition Facility.

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Section: Diagnosticsmentioning

confidence: 99%

Experimental basis for laser-plasma interactions in ignition hohlraums at the National Ignition Facility

et al. 2010

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“…This new target platform together with recently commissioned suite of laser-plasma interaction diagnostics [16,17] allows the access to high temperature, long scale length conditions not previously available using gasbag [19,24], toroidal hohlraum [25,26], or gas-filled hohlraum targets. Laser-plasma interaction thresholds are sensitive to the electron temperature and the length of the density plateau in a plasma; electron temperatures in open geometry gasbag plasmas with roughly the same plasma scale-lengths are significantly lower than in the present hohlraum targets because of a factor of 10 larger energy density in hohlraums.…”

Section: Introductionmentioning

confidence: 99%

“…These measurements are complemented by the transmitted beam diagnostics [17] that measures the transmitted laser power, spectrum, and the near-field laser beam spot. This complete suite of diagnostics allows us to determine the beam energetics by completely accounting for the scattered and absorbed laser power [18].…”

Section: Introductionmentioning

confidence: 99%

“…2 for 8 kJ, 13.5 kJ, and 17 kJ heater beam energy into the hohlraum [11]. The Transmitted Beam Diagnostics [17] measures the laser light transmitted through the target chamber center (TCC) within twice the original f /6.7 beam cone of the Omega Beam 30 operated at 3ω. At 60 cm past TCC, a 25-cm-diameter uncoated fused silica focusing mirror, f = 44 cm, directs 4% of the transmitted light through a 10-cm diameter port on the target chamber.…”

Section: Introductionmentioning

confidence: 99%

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0.351 micron Laser Beam propagation in High-temperature Plasmas

Froula¹,

Divol²,

Meezan³

et al. 2007

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A study of the laser-plasma interaction processes have been performed in plasmas that are created to emulate the plasma conditions in indirect drive inertial confinement fusion targets. The plasma emulator is produced in a gas-filled hohlraum; a blue 351-nm laser beam propagates along the axis of the hohlraum interacting with a high-temperature (Te = 3.5 keV), dense (ne = 5 × 10 20 cm −3 ), long-scale length (L ∼ 2 mm) plasma. Experiments at these conditions have demonstrated that the interaction beam produces less than 1% total backscatter resulting in transmission greater than 90% for laser intensities less than I < 2 × 10 15 W-cm −2 . The bulk plasma conditions have been independently characterized using Thomson scattering where the peak electron temperatures are shown to scale with the hohlraum heater beam energy in the range from 2 keV to 3.5 keV. This feature has allowed us to determine the thresholds for both backscattering and filamentation instabilities; the former measured with absolutely calibrated full aperture backscatter and near backscatter diagnostics and the latter with a transmitted beam diagnostics. A plasma length scaling is also investigated extending our measurements to 4-mm long high-temperature plasmas. At intensities I < 5 × 10 14 W-cm −2 , greater than 80% of the energy in the laser is transmitted through a 5-mm long, high-temperature (Te > 2.5 keV) high-density (ne = 5 × 10 20 W-cm −3 ) plasma. Comparing the experimental results with detailed gain calculations for the onset of significant laser scattering processes shows a stimulated Brillouin scattering threshold (R=10%) for a linear gain of 15; these high temperature, low density experiments produce plasma conditions comparable to those along the outer beams in ignition hohlraum designs. By increasing the gas fill density (ne = 10 21 cm −3 ) in these targets, the inner beam ignition hohlraum conditions are accessed. In this case, stimulated Raman scattering dominates the backscattering processes and we show that scattering is small for gains less than 20 which can be achieved through proper choice of the laser beam intensity. The first three-dimensional (3D) simulations of a high power 0.351µm laser beam propagating through a high-temperature hohlraum plasma are also reported. We show that 3D linear kinetic modeling of Stimulated Brillouin scattering reproduces quantitatively the experimental measurements, provided it is coupled to detailed hydrodynamics simulation and a realistic description of the laser beam from its millimeter-size envelop down to the micron scale speckles. These simulations accurately predict the strong reduction of SBS measured when polarization smoothing is used.

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“…Light scattered from the interaction beam is measured using a full-aperture backscatter station (FABS), a near backscatter imager (NBI), and a 3ω transmitted beam diagnostic (3ωTBD) [26]. Light scattered back into the original beam cone is collected by the FABS; both stimulated Brillouin scattering (SBS) and stimulated Raman scattering (SRS) spectra and energies are independently measured.…”

mentioning

confidence: 99%