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Spherical implosions in inertial confinement fusion are inherently sensitive to perturbations that may arise from experimental constraints and errors. Control and mitigation of low-mode (long wavelength) perturbations is a key milestone to improving implosion performances. We present the first 3D radiation-hydrodynamic simulations of directly driven inertial confinement fusion implosions with an inline package for polarized crossed-beam energy transfer. Simulations match bang times, yields (separately accounting for laser-induced high modes and fuel age), hot spot flow velocities and direction, for which polarized crossed-beam energy transfer contributes to the systematic flow orientation evident in the OMEGA implosion database. Current levels of beam mispointing, imbalance, target offset, and asymmetry from polarized crossed-beam energy transfer degrade yields by more than 40%. The effectiveness of two mitigation strategies for low modes is explored.

International audience; Integrated hydrodynamics simulations of inertial confinement fusion rely on reduced physics models. To reproduce experimental trends, these models often feature tuning parameters, but this comes with a risk: over-tuning of one model can hide physics inadequacies in another. Ray-based models of cross-beam-energy transfer (CBET) represents one of these risks. Here we present an accurate and efficient model of CBET suitable for inline implementation in 3D hydrodynamics simulations. Inverse Ray Tracing (IRT) is used to compute the ray field in a 3D permittivity profile described on an unstructured tetrahedral mesh using the IFRIIT framework (Inline Field Reconstruction and Interaction using Inverse Tracing). CBET is accounted for through perturbations to the permittivity associated with ion acoustic waves driven by the overlapped fields. Large gradients in the permittivity are resolved by coupling the IRT to a recursive Adaptive Mesh Refinement (AMR) algorithm. The use of AMR also allows for the resolution of caustics, with accurate field reconstruction performed using the Etalon integral method. Comparisons of the model with wave-based solutions from the Laser Plasma Simulation Environment (LPSE) demonstrate its ability to control energy conservation and gain convergence through AMR depth only, without the use of ad hoc physical models or artificial tuning parameters.

A 3-D ray based model for computing laser fields in dissipative and amplifying media is presented. The eikonal equation is solved using inverse ray-tracing on a dedicated nonstructured 3-D mesh. Inverse ray-tracing opens the possibility of using Complex Geometrical Optics (CGO), for which we propose a propagation formalism in a finite element mesh. Divergent fields at caustics are corrected using an etalon integral method for fold-type caustics. This method is successfully applied in dissipative media by modifying the ray-ordering and root selection rules, thereby allowing one to reconstruct the field in the entire caustic region. In addition, we demonstrate how caustics in the CGO framework can disappear entirely for sufficiently dissipative media, making the complex ray approach valid in the entire medium. CGO is shown to offer a more precise modeling of laser refraction and absorption in a dissipative medium when compared to Geometrical Optics (GO). In the framework of Inertial Confinement Fusion (ICF), this occurs mostly at intermediate temperatures or at high temperatures close to the critical density. Additionally, GO is invalid at low temperatures if an approximated expression of the permittivity is used. The inverse ray-tracing algorithm for GO and CGO is implemented in the IFRIIT code, in the framework of a dielectric permittivity described in 3-D using a piecewise linear approximation in tetrahedrons. Fields computed using GO and CGO are compared to results from the electromagnetic wave solver Laser Plasma Simulation Environment. Excellent agreement is obtained in 1-D linear and nonlinear permittivity profiles. Good agreement is also obtained for ICF-like Gaussian density profiles in 2-D. Finally, we demonstrate how the model reproduces Gaussian beam diffraction using CGO. The IFRIIT code will be interfaced inline to 3-D radiative hydrodynamic codes to describe the nonlinear laser plasma interaction in ICF and high-energy-density plasmas.

Magnetic fields generated by the nonlinear Rayleigh-Taylor growth of laser-seeded three-dimensional broadband perturbations were measured in laser-accelerated planar targets using ultrafast proton radiography. The experimental data show self-similar behavior in the growing cellular magnetic field structures. These observations are consistent with a bubble competition and merger model that predicts the time evolution of the number and size of the bubbles, linking the cellular magnetic field structures with the Rayleigh-Taylor bubble and spike growth.

Magnetic fields generated by the Rayleigh-Taylor instability were measured in laser-accelerated planar foils using ultrafast proton radiography. Thin plastic foils were irradiated with $\ensuremath{\sim}4\mathrm{\text{\ensuremath{-}}}\mathrm{kJ}$, 2.5-ns laser pulses focused to an intensity of $\ensuremath{\sim}{10}^{14}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$ on the OMEGA EP Laser System. Target modulations were seeded by laser nonuniformities and amplified during target acceleration by the Rayleigh-Taylor instability. The experimental data show the hydrodynamic evolution of the target and MG-level magnetic fields generated in the broken foil. The experimental data are in good agreement with predictions from 2-D magnetohydrodynamic simulations.

Cryogenic-deuterium-tritium (DT) target compression experiments with low-adiabat (alpha), multiple-shock drive pulses have been performed on the Omega Laser Facility [T. R. Boehly, D. L. Brown, R. S. Craxton et al., Opt. Commun. 133, 495 (1997)] to demonstrate hydrodynamic-equivalent ignition performance. The multiple-shock drive pulse facilitates experimental shock tuning using an established cone-in-shell target platform [T. R. Boehly, R. Betti, T. R. Boehly et al., Phys. Plasmas 16, 056301 (2009)]. These shock-tuned drive pulses have been used to implode cryogenic-DT targets with peak implosion velocities of 3x10{sup 7} cm/s at peak drive intensities of 8x10{sup 14} W/cm{sup 2}. During a recent series of alphaapprox2 implosions, one of the two necessary conditions for initiating a thermonuclear burn wave in a DT plasma was achieved: an areal density of approximately 300 mg/cm{sup 2} was inferred using the magnetic recoil spectrometer [J. A. Frenje, C. K. Li, F. H. Seguin et al., Phys. Plasmas 16, 042704 (2009)]. The other condition--a burn-averaged ion temperature {sub n} of 8-10 keV--cannot be achieved on Omega because of the limited laser energy; the kinetic energy of the imploding shell is insufficient to heat the plasma to these temperatures. A {sub n} of approximately 3.4 keV wouldmore » be required to demonstrate ignition hydrodynamic equivalence [Betti et al., Phys. Plasmas17, 058102 (2010)]. The {sub n} reached during the recent series of alphaapprox2 implosions was approximately 2 keV, limited primarily by laser-drive and target nonuniformities. Work is underway to improve drive and target symmetry for future experiments.« less