Kevin Glize

Shock-augmented ignition (SAI) [R. H. H. Scott ., ] is an alternative inertial confinement fusion concept that is designed to achieve high energy gain by combining improved resilience to instabilities with enhanced fuel compression. In SAI, lower implosion velocities can improve hydrodynamic stability and limited laser intensities reduce the excitation of detrimental laser-plasma instabilities, enabling greater areal density accumulation. Here we report an experimental investigation of SAI using a series of warm D 2 implosions. By timing the augmenting shock to arrive at the implosion center immediately prior to peak compression, the areal density and hot-spot pressure increase by 50% and 112%, respectively, relative to unoptimized designs. Ignition-scale simulations reproduce the observed timing dependence and demonstrate the potential of SAI for inertial fusion energy.

We present the first experimental validation at ignition scale of a linear kinetic ion-acoustic wave model for cross-beam energy transfer (CBET), using data from recent polar direct-drive experiments at the National Ignition Facility. In this configuration, CBET plays a critical role in both laser–target coupling efficiency and irradiation symmetry. While advanced CBET models have been successfully applied at OMEGA scale, their validation under ignition-relevant conditions—where CBET strongly impacts both energy deposition and shock geometry—has remained limited. Here, we use the fully coupled 3D radiation-hydrodynamics platform ASTER/IFRIIT to assess several CBET modeling approaches, including a linear kinetic ion-acoustic wave model, polarization effects, and inverse ray-tracing, without introducing tunable parameters. Through detailed sensitivity analyses, we quantify the impact of CBET, Langdon effects, thermal transport, and equation-of-state variations on laser energy deposition and shock dynamics. Good agreement is obtained between simulations and experimental measurements, both in terms of shock trajectories and angular distribution of scattered light. We show that CBET preferentially transfers energy away from the equatorial region—where beam overlap and gain are largest—leading to oblate shock shapes and spatially non-uniform absorption, with higher deposition at the poles and reduced absorption at the equator.

We present first experimental data obtained at the recently commissioned experimental platform to compare laser plasma instabilities (LPIs) driven by monochromatic and broad spectral bandwidth ( ≈ 0.5 % ) laser pulses with a wavelength of around 527 nm. The evaluation of LPIs at 10 ¹⁵ W cm ⁻² is shown by utilizing a full aperture backscatter diagnostic and side scatter diagnostics. For a broad bandwidth, our study indicates a suppression of stimulated Brillouin back- and side scattering as well as of the two plasmon decay instability, but an increase of stimulated Raman side scattering. An increase in both temperature and numbers of hot electrons is also identified by direct and indirect measurements.

Recent experiments at the National Ignition Facility and theoretical modeling suggest that side stimulated Raman scattering (SSRS) instability could reduce laser–plasma coupling and generate considerable fluxes of suprathermal hot electrons under interaction conditions envisaged for direct-drive schemes for inertial confinement fusion. Nonetheless, SSRS remains to date one of the least understood parametric instabilities. Here, we report the first angularly and spectrally resolved measurements of scattered light at laser intensities relevant for the shock ignition scheme (I ∼ 1016 W/cm2), showing significant SSRS growth in the direction perpendicular to the laser polarization. Modification of the focal spot shape and orientation, obtained by using two different random phase plates, and of the density gradient of the plasma, by utilizing exploding foil targets of different thicknesses, clearly reveals a different dependence of backward SRS (BSRS) and SSRS on experimental parameters. While convective BSRS scales with plasma density scale length, as expected by linear theory, the growth of SSRS depends on the spot extension in the direction perpendicular to laser polarization. Our analysis therefore demonstrates that under current experimental conditions, with density scale lengths Ln ≈ 60–120 μm and spot sizes FWHM ≈ 40–100 μm, SSRS is limited by laser beam size rather than by the density scale length of the plasma.

Using space-time-resolved Thomson scattering, we investigate experimentally the development of electrostatic waves in a preformed undercritical helium plasma driven by a 1.059 μm laser pulse of ∼1.5 ps duration and ∼10^{15-16} W cm^{-2} mean intensity. We observe the excitation of intense ion plasma waves (IAWs) over a broad wave number range, distinct from what is expected from stimulated Brillouin scattering or Langmuir decay instability. These IAWs are correlated with the occurrence of backward stimulated Raman scattering (B-SRS) at earlier times but persist much longer than the B-SRS-driven electron plasma waves. Particle-in-cell modeling reveals that they result from an ion acoustic instability triggered by the bulk electrons drifting against the ions to neutralize the current carried by the B-SRS-generated hot electrons. The properties of the simulated unstable IAWs match well with the measurements.

The ongoing improvement in laser technology and target fabrication is opening new possibilities for diagnostic development. An example is x-ray phase-contrast imaging (XPCI), which serves as an advanced x-ray imaging diagnostic in laser-driven experiments. In this work, we present the results of the XPCI platform that was developed at the OMEGA EP Laser-Facility to study multi-Mbar single and double shocks produced using a kilojoule laser driver. Two-dimensional radiation-hydrodynamic simulations agree well with the shock progression and the spherical curvature of the shock fronts. It is demonstrated that XPCI is an excellent method to determine with high accuracy the front position of a trailing shock wave propagating through an expanding CH plasma that was heated by a precursor Mbar shock wave. The interaction between the rarefaction wave and the shock wave results in a clear signature in the radiograph that is well reproduced by radiation-hydrodynamic simulations.

Improved laser illumination uniformity drives shocks and implosions to create more extreme high energy density environments. Predominantly, the geometry of experiments that can be performed is dictated by the layout of beams at laser facilities, limiting interfacility and multiscale investigations. This Letter presents the first automated, algorithmic approach for generating illumination configurations for high energy density experiments. The method is demonstrated in comparison to a polar direct-drive solid target experiment at the National Ignition Facility. The new illumination configuration is simulated to create greater than ×3 higher peak pressure and almost ×2 higher density by maintaining better shock uniformity. The optimization process is performed with reduced computational expense and isotropic plasma profiles while accounting for the impact of cross-beam energy transfer.

Experiments have been performed to investigate laser-plasma instabilities (LPIs) relevant to the direct-drive inertial confinement fusion (ICF) conditions at the Shenguang-II Upgrade (SG-II UP) laser facility during the double-cone ignition (DCI) experimental campaigns, with the overlapped laser intensity ranging from 6 × 10 14 W c m − 2 to 1.8 × 10 15 W c m − 2 . An overall LPI scenario has been built from the collection and investigation of angularly distributed scattered light. Across broad ranges of laser and plasma parameters, relevant to the direct-drive ICF conditions, the dominance of the stimulated Raman side scattering (SRSS) was confirmed, and its coexistence with the two-plasmon decay (TPD) was also observed. Significant SRSS scattered light was observed across an extremely wide range of emission angles, concentrated at large angles, and demonstrated to be robust throughout the parameter space. Time-resolved spectral measurements show distinctly different SRSS behaviors along different angles and a slightly higher threshold compared to the TPD. The overall SRSS energy loss was measured, indicating a scattered light energy fraction of up to 6%. These results are of crucial importance for the precise assessment of the LPIs in the DCI as well as other laser directly driven ICF schemes.