3D simulations of inertial confinement fusion implosions part 1: inline modeling of polarized cross beam energy transfer and subsequent drive anomalies on OMEGA and NIF

Abstract

Inertial confinement fusion experiments are sensitive to Cross-Beam Energy Transfer (CBET), a nonlinear laser-plasma instability that redistributes laser energy in the coronal plasma through self-generated Ion Acoustic Wave (IAW) gratings. The detailed CBET coupling depends on the polarization state of the crossing wavefields. CBET itself can also scramble the beam polarizations by inducing ellipticity through the IAW grating, and rotating the seed polarization toward that of the pump. We develop a ray-based model that describes the polarized CBET coupling and that is compatible with the framework of 3D inline radiative hydrodynamics simulations. The model is implemented in the ASTER/IFRIIT code and validated against an academic test case and an offline polarized CBET post-processor. It is then applied to the detailed configuration of the Distributed Polarization Rotator system on OMEGA, where results highlight how polarized CBET induces significant low modes in the collisional absorption source term. Finally, the modeling is applied to a simple indirect-drive configuration, comparing CBET calculations with 96 unpolarized or polarized beams with 24 unpolarized quads. It is shown that these cases produce similar power amplification per cone of beams grouped with similar polar angles. However, the 96 beam geometry itself is found to reduce azimuthal variations in quad power after the interaction and favors beams with larger polar angles within the cones, an effect that is amplified by the polarized CBET. Application of the model to inline calculations of OMEGA implosions are presented in a companion paper.

3D simulations of inertial confinement fusion implosions part 2: systematic flow anomalies and impact of low modes on performances in OMEGA experiments

“…Finally, simulations with experimentally measured balance and pointing, plus the effect of offset, are referred to as χ B,P,O . For each simulation set, we consider different configurations of the CBET modeling: no CBET, unpolarized CBET [12] and polarized CBET [5].…”

“…Naturally, these latter simulations cannot make use of the polarized CBET model. More information on the DPR configuration on OMEGA and the detailed spot profiles formulations is given in the companion paper in [5].…”

“…Including the effect of CBET amplifies the mode 10 by about a factor of 2 for 94 712 and 3 for 94 343. For reference, offline estimations with BeamletCrosser [8] and IFRIIT were of 4 (see [5]). This large amplitude mode 10 is significant enough to lead to target perforation, as illustrated in figure 8.…”

“…In addition, while the l = 1 mode may be somewhat reduced, higher modes cannot all be mitigated simultaneously, as illustrated in figure 9(a) from modes l = 4 and up. Since the polarized CBET anomaly itself induces a variety of low modes, not only l = 1 (see [5]), this suggests that any serious attempt at reducing all sources of low modes on OMEGA must consider the redesign of the DPR system itself.…”

“…The aim of this paper is to assess the contributions from various sources of low modes to DT flow velocity and direction in order to (a) quantify the sensitivity of current target designs to the best setup performances of the OMEGA laser system, and (b) assess whether the source of the systematic flow can be identified. For that purpose, we make use of state-of-the-art 3D radiation hydrodynamics simulations, and notably, the first inline polarized cross-beam energy transfer (CBET) model detailed in the companion paper [5] and summarized in [6].…”