In this Letter, we introduce a new inline model for stimulated Raman scattering (SRS), which runs on our radiation hydrodynamics code TROLL. The modeling follows from a simplified version of a rigorous theory for SRS, which we describe, and accounts for nonlinear kinetic effects. It also accounts for the SRS feedback on the plasma hydrodynamics. We dubbed it PIEM because it is a fully PredIctivE Model, no free parameter is to be adjusted \textit{a posteriori}~in order to match experimental results. PIEM predictions are compared against experimental measurements performed at the Ligne d'Int\'egration Laser. From these comparisons, we discuss PIEM ability to correctly catch the impact of nonlinear kinetic effects on SRS.

The advection by a flow of ponderomotively driven density fluctuations may lead to the deflection of a laser pulse. This effect, known as beam bending, may modify the irradiation geometry and energy deposition in high energy laser plasma experiments. A kinetic modeling of beam-bending of a Gaussian laser pulse is proposed and validated by means of “particle-in-cell” simulations over a vast parametric domain, demonstrating the importance of accounting for kinetic damping of driven ion-acoustic waves. The transient regime is also addressed and compared to kinetic simulations.

for neutron-radiography applications. A number of different targets were fielded in experiments on the OMEGA laser. The 1.8-mm diameter plastic (CH) capsules featured either one or two laser-entrance holes (LEH's), and were either lined with deuterated plastic (CD), or filled with 1.5-atm deuterium gas. Contrary to predictions by the hydrodynamics code HYDRA, the experiments exhibit a strong correlation between total neutron yield and CD liner thickness, indicating substantial mix of CH wall material into the ablated CD coronal plasma. The thickest liner targets with approximately 10 kJ of incident laser energy performed consistent with previously published data, while the data at 18 kJ laser energy may also be subject to mix from wall material. The yield from the gas-filled capsules was less than from 10-μm CD lined targets at the same laser energy, which may als be explained by wall material mixing into the fusion fuel. Finally, the experiments demonstrated similar performance between a 1-LEH and a 2-LEH target irradiated with comparable laser-energies, a key finding for demonstrating the utility of the inverted-corona neutron source for radiography applications. Future work will focus on developing the platform for NIF experiments.

The NIF Rugby High Foot campaign results, with 8 shots to date, are compared with the 2D FCI2 design simulations. A special emphasis is placed on the predictive features and on those areas where some work is still required to achieve the best possible modelling of these MJ-class experiments.

The indirect-drive scheme to inertial confinement fusion uses a large number of laser beams arranged in a symmetric angular distribution. Collective laser plasma instabilities can therefore develop that couple all the incident laser waves located in a cone to the daughter wave growing along the cone symmetry axis [D. F. DuBois et al., Phys. Fluids B 4, 241 (1992)]. With complementary diagnostics of Thomson scattering and of the scattered light, we demonstrate the occurrence of collective stimulated Brillouin sidescattering driving collective acoustic waves in indirect-drive experiments.

The CEA/DAM ICF experimental program is currently conducted on LIL and Omega with the goal of improving our simulation tool, the FCI2 code. In this effort, we focus on typical ICF observables: hohlraum radiation drive history, capsule core shape and neutron emission history, hydrodynamic instability growth. In addition to integrated experiment, specific designs are also helpful to pinpoint a particular phenomenon. In this article, we review our current efforts and status, and our future projects on Omega and LMJ.

P. E. Masson-Laborde, S. Hüller, D. Pesme, H. Bandulet, S. Depierreux, P. Loiseau, and Ch. Labaune CEA, DAM, DIF, F-91297 Arpajon Cedex, France Centre de Physique Théorique (CPHT), CNRS, École Polytechnique, Palaiseau, France Institut National de la Recherche Scientifique (INRS), Varennes, Québec J3X1S2, Canada and LULI, CNRS, Université Pierre et Marie Curie, École Polytechnique, Palaiseau, France

A direct experimental comparison of rugby-shaped and cylindrical shaped gas-filled hohlraums on the Omega laser facility demonstrates that higher coupling and minimal backscatter can be achieved in the rugby geometry, leading to significantly enhanced implosion performance. A nearly 50% increase of x-ray drive is associated with earlier bangtime and increase of neutron production. The observed drive enhancement from rugby geometry in this study is almost twice stronger than in previously published results.

The understanding and the control of high-power laser propagation into underdense plasma is important to achieve inertial confinement fusion. During this process, the interaction of the laser with the plasma filling the hohlraum can lead to significant loss of laser energy which prevent ignition. Self-focusing or filamentation of the laser light is one of these phenomena which are desired to be mitigated since it also affects the uniformity of the laser illumination on the hohlraum wall. It has been recently shown [1] that (1) a proper treatment of heat transport in hydrodynamic codes is crucial to model filamentation, especially in the case of high temperature gradients where heat transport exhibits non-local behavior, and (2) filamentation can occur even if the plasma conditions are below the commonly envisioned instability threshold.

The origin of the low level of stimulated Brillouin scattering (SBS) observed in laser-plasma experiments carried out with a single laser speckle is investigated by means of three-dimensional simulations and modeling in the limit when the laser beam power P is well above the critical power for ponderomotive self-focusing We find that the order of magnitude of the time averaged reflectivities, together with the temporal and spatial SBS localization observed in our simulations, are correctly reproduced by our modeling. It is observed that, after a short transient stage, SBS reaches a significant level only (i) as long as the incident laser pulse is increasing in amplitude and (ii) in a single self-focused speckle located in the low-density front part of the plasma. In order to describe self-focusing in an inhomogeneous expanding plasma, we have derived a new Lagrangian density describing this process. Using then a variational approach, our model reproduces the position and the peak intensity of the self-focusing hot spot in the front part of the plasma density profile as well as the local density depletion in this hot spot. The knowledge of these parameters then makes it possible to estimate the spatial amplification of SBS as a function of the laser beam power and consequently to explain the experimentally observed SBS reflectivity, considerably reduced with respect to standard theory in the regime of large laser beam power.

Spatial autoresonance is investigated as a mechanism for the enhancement of stimulated Raman scattering (SRS) in the kinetic regime (kLλD > 0.29). Autoresonance in 3-wave simulations was demonstrated in a previous study [Chapman et al., Phys. Plasmas 17, 122317 (2010)]. These results are applied to particle-in-cell (PIC) simulations. Good agreement is found between PIC simulations and a 3-wave model using a nonlinear frequency shift beyond the regime usually referred to as “weakly kinetic”. Autoresonance is studied for a range of values of kLλD.

New solutions to the coupled three-wave equations describing parametric scattering instabilities are presented. This analytical and numerical study investigates the impact of autoresonance on stimulated Raman scattering in an inhomogenous plasma, where the dominant plasma wave nonlinearity is due to wave-particle interactions (a kinetic-type nonlinearity). Under conditions in the plasma relevant to laser fusion, it is shown that the electron plasma wave may become phase-locked to the beating between a laser pump wave and a backscattered light wave. This phase-locked solution may grow to a significant amplitude. It is shown that the growth of the electron plasma wave will lead to a break-down of the phase-locking and hence its maximum attainable amplitude is inherently limited.

The energy spectrum of hot electrons emitted from the interaction of a relativistically intense laser with an Al plasma is measured at a repetition rate of 0.5 kHz by accumulating ∼103 highly reproducible laser shots. In the 1017–2×1018 W/cm2 range, the temperature of electrons escaping the plasma along the specular direction scales as (Iλ2)0.64±0.05 for p-polarized pulses incident at 45°. This scaling is in good agreement with three-dimensional particle-in-cell simulations and a simple model that estimates the hot-electron temperature by considering the balance between the deposited laser intensity and the energy carried away by those electrons.

Targets designed to produce ignition on the Laser Megajoule (LMJ) are being simulated in order to set specifications for target fabrication. The LMJ experimental plans include the attempt of ignition and burn of an ICF capsule with 160 laser beams, delivering up to 1.4 MJ and 380 TW. New targets needing reduced laser energy with only a small decrease in robustness have then been designed for this purpose. Working specifically on the coupling efficiency parameter, i.e. the ratio of the energy absorbed by the capsule to the laser energy, has led to the design of a rugby-ball shaped cocktail hohlraum; with these improvements, a target based on the 240-beam A1040 capsule can be included in the 160-beam laser energy-power space. Robustness evaluations of these different targets shed light on critical points for ignition, which can trade off by tightening some specifications or by preliminary experimental and numerical tuning experiments.

We investigate the production of electron beams from the interaction of relativistically-intense laser pulses with a solid-density SiO(2) target in a regime where the laser pulse energy is approximately mJ and the repetition rate approximately kHz. The electron beam spatial distribution and spectrum were investigated as a function of the plasma scale length, which was varied by deliberately introducing a moderate-intensity prepulse. At the optimum scale length of lambda/2, the electrons are emitted in a collimated beam having a quasimonoenergetic distribution that peaked at approximately 0.8 MeV. A highly reproducible structure in the spatial distribution exhibits an evacuation of electrons along the laser specular direction and suggests that the electron beam duration is comparable to that of the laser pulse. Particle-in-cell simulations which are in good agreement with the experimental results offer insights on the acceleration mechanism by the laser field.

Many nonlinear processes may affect the laser beam propagation and the laser energy deposition in the underdense plasma surrounding the pellet. These processes, associated with anomalous and nonlinear absorption mechanisms, are fundamental issues in the context of Inertial Confinement Fusion. The work presented in this article refers to laser-plasma interaction experiments which were conducted under well-controlled conditions, and to their theoretical and numerical modeling. Thanks to important diagnostics improvements, the plasma and laser parameters were sufficiently characterized in these experiments to make it possible to carry out numerical simulations modeling the laser plasma interaction in which the hydrodynamics conditions were very close to the experimental ones. Two sets of experiments were carried out with the LULI 2000 and the six beam LULI laser facilities. In the first series of experiments, the interaction between two single hot spots was studied as a function of their distance, intensity and light polarization. In the second series, the intensity distribution of stimulated Brillouin scattering (SBS) inside the plasma was studied by means of a new temporally resolved imaging system. Two-dimensional (2D) simulations were carried out with our code Harmony2D in order to model these experiments. For both series of experiments, the numerical results show a, very good agreement with the experimental ones for what concerns the main SBS features, namely the spatial and temporal behavior of the SBS-driven acoustic waves, as well as the average SBS reflectivities. Thus, these well diagnosed experiments, carried out with well defined conditions, make it possible to benchmark our theoretical and numerical modelings and, hence, to improve our predictive capabilities for future experiments.

A parameter study of stimulated Brillouin scattering is presented, that covers a large parameter space of laser intensity and plasma density (I = 1 −10 1014W/cm2, n/nc = 0.03 −0.69). The relative importance of kinetic effects in SBS driven ion-acoustic waves is examined in a hybrid PIC model in which electrons are approximated by an isothermal Boltzmann distribution and which allows the detailed study of ion kinetic effects. A regime of weak kinetic effects, where phenomenological terms within a fluid model are likely to work is identified. The hydrodynamic model HarmoNHY (1), using a reduced decompo- sition model complements the investigation and allows to define the phenomenological parameters of the nonlinear frequency shift within the regime of weak kinetic effects. A recent analysis (2) of the parametric instability of ion acoustic waves has emphasised the importance of the parametric decay of the driven ion acoustic wave into subharmonics. Indeed the inclusion of subharmonics into HarmoNHY is found to be one of the necessary ingredients to reproduce the kinetic results.