Laser-supported ionization wave in under-dense gases and foams

Gus'kov, Sergei Yu; Limpouch, J.; Nicolaï, Ph.; Tikhonchuk, V. T.

doi:10.1063/1.3642615

Cited by 59 publications

(41 citation statements)

References 20 publications

(30 reference statements)

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“…2, we compare 1D time-resolved images of (a) the incident laser light (referred as RPP-beam) and (b) the modified laser light after propagation into the foam (referred as PII-beam). The foam begins transmitting at t ¼ (0.7 6 0.1) ns when the ionization front breaks through, giving a mean ionization velocity of (4.0 6 0.6) 10 2 lm/ns, in agreement with previous theoretical modelling 23 and experiments. 12,24 The instantaneous transmission rate is higher than 60% at t ¼ 1 ns and increases to almost 100% at the end of the pulse, corresponding to a mean intensity of 2 Â 10 14 W/cm 2 .…”

Section: A Experimental Resultssupporting

confidence: 88%

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Reduction of stimulated Brillouin backscattering with plasma beam smoothing

et al. 2015

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Plasma induced incoherence (PII) can strongly modify the growth rates of stimulated scattering instabilities. A special double-target design was used to quantify the effect of PII on stimulated Brillouin scattering (SBS). Successive shots using all or part of these targets led to the characterization of temporal and spatial incoherence of a laser pulse after propagation through a foam plasma and to the quantification of the reduction of SBS from the second target. Numerical simulations were used to identify the main physical mechanisms in play. V C 2015 AIP Publishing LLC.

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Section: A Experimental Resultssupporting

confidence: 88%

“…This difference comes from the additional laser energy absorption which is needed to explode and homogenize the foam structures, and can be taken into account by adding a temporal delay of the laser energy deposition in the code, as explained in Ref. 23. We used our past experimental results with foams to adjust the delay.…”

Section: B Numerical Simulationsmentioning

confidence: 99%

Reduction of stimulated Brillouin backscattering with plasma beam smoothing

et al. 2015

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“…The last column in Table II shows that 4 mg/cm enough so that their density has become lower than the critical density, the laser can pass through and interact with the following ones. This was studied theoretically by Gus'kov et al 37 , who estimated the ionization front velocity as a function of the foam parameters and provided some comparison to experiments. This was followed by additional experimental investigations 38 .…”

Section: A Heat Front Velocity Comparisonsmentioning

confidence: 99%

“…Using formula (27) of Ref. 37, and multiplying by the number of pores in one laser skin depth as suggested in the same reference, we match the experimental velocities for targets A and B by choosing α = 0.65 and 0.62, respectively. However, the velocity depends very strongly on α, so that these predictions typically vary by a factor of 2.…”

Section: A Heat Front Velocity Comparisonsmentioning

confidence: 99%

Bright x-ray sources from laser irradiation of foams with high concentration of Ti

et al. 2014

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Low-density foams irradiated by a 20 kilojoule laser at the Omega laser facility (NY, USA) are shown to convert more than 5% of the laser energy into 4.6 to 6.0 keV x rays. This record efficiency with foam targets is due to novel fabrication techniques based on atomic-layer-deposition of Ti atoms on an aerogel scaffold. A Ti concentration of 33 atomic % was obtained in a foam with a total density of 5 mg/cm 3 . The dynamics of the ionization front through these foams were investigated at the 1 kilojoule laser of the Gekko XII facility (Japan). Hydrodynamic simulations can reproduce the average electron temperature but fail to predict accurately the heat front velocity in the foam. This discrepancy is shown to be unrelated to the possible water adsorbed in the foam but could be attributed to effects of the foam micro-structure.

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“…Indeed, during its propagation through the foam plasma, the laser drives parametric instabilities, such as forward Stimulated Brillouin Scattering 69 leading to an effective smoothing of the hot spot pattern. Due to the low density of the foam, the ionization wave is supersonic and no shock is created, [70][71][72] in contrary to the case of overdense foams.…”

Section: A Experimental Configurationmentioning

confidence: 99%

Progress in indirect and direct-drive planar experiments on hydrodynamic instabilities at the ablation front

et al. 2014

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Understanding and mitigating hydrodynamic instabilities and the fuel mix are the key elements for achieving ignition in Inertial Confinement Fusion. Cryogenic indirect-drive implosions on the National Ignition Facility have evidenced that the ablative Rayleigh-Taylor Instability (RTI) is a driver of the hot spot mix. This motivates the switch to a more flexible higher adiabat implosion design [O. A. Hurricane et al., Phys. Plasmas 21, 056313 (2014)]. The shell instability is also the main candidate for performance degradation in low-adiabat direct drive cryogenic implosions [Goncharov et al., Phys. Plasmas 21, 056315 (2014)]. This paper reviews recent results acquired in planar experiments performed on the OMEGA laser facility and devoted to the modeling and mitigation of hydrodynamic instabilities at the ablation front. In application to the indirect-drive scheme, we describe results obtained with a specific ablator composition such as the laminated ablator or a graded-dopant emulator. In application to the direct drive scheme, we discuss experiments devoted to the study of laser imprinted perturbations with special phase plates. The simulations of the Richtmyer-Meshkov phase reversal during the shock transit phase are challenging, and of crucial interest because this phase sets the seed of the RTI growth. Recent works were dedicated to increasing the accuracy of measurements of the phase inversion. We conclude by presenting a novel imprint mitigation mechanism based on the use of underdense foams. The foams induce laser smoothing by parametric instabilities thus reducing the laser imprint on the CH foil. V C 2014 AIP Publishing LLC. [http://dx.

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Laser-supported ionization wave in under-dense gases and foams

Cited by 59 publications

References 20 publications

Reduction of stimulated Brillouin backscattering with plasma beam smoothing

Reduction of stimulated Brillouin backscattering with plasma beam smoothing

Bright x-ray sources from laser irradiation of foams with high concentration of Ti

Progress in indirect and direct-drive planar experiments on hydrodynamic instabilities at the ablation front

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