Hydrodynamics simulations of 2ω laser propagation in underdense gasbag plasmas

Abstract

Recent 2ω laser propagation and stimulated Raman backscatter (SRS) experiments performed on the Helen laser have been analyzed using the radiation-hydrodynamics code HYDRA [M. M. Marinak, G. D. Kerbel, N. A. Gentile, O. Jones, D. Munro, S. Pollaine, T. R. Dittrich, and S. W. Haan, Phys. Plasmas 8, 2275 (2001)]. These experiments utilized two diagnostics sensitive to the hydrodynamics of gasbag targets: a fast x-ray framing camera (FXI) and a SRS streak spectrometer. With a newly implemented nonlocal thermal transport model, HYDRA is able to reproduce many features seen in the FXI images and the SRS streak spectra. Experimental and simulated side-on FXI images suggest that propagation can be explained by classical laser absorption and the resulting hydrodynamics. Synthetic SRS spectra generated from the HYDRA results reproduce the details of the experimental SRS streak spectra. Most features in the synthetic spectra can be explained solely by axial density and temperature gradients. The total SRS backscatter increases with initial gasbag fill density up to ≈0.08 times the critical density, then decreases. Data from a near-backscatter imaging camera show that severe beam spray is not responsible for the trend in total backscatter. Filamentation does not appear to be a significant factor in gasbag hydrodynamics. The simulation and analysis techniques established here can be used in ongoing experimental campaigns on the Omega laser facility and the National Ignition Facility.

Quenching of the Nonlocal Electron Heat Transport by Large External Magnetic Fields in a Laser-Produced Plasma Measured with Imaging Thomson Scattering

“…The fluxlimiter was introduced primarily to reproduce experiments where simulations involve energy transport from the laser absorption region into a solid target [9]. However, the coronal plasmas have been difficult to model, though Spitzer-Harm diffusion has been successfully applied in a few experiments [10,11]. Currently there are outstanding questions regarding the relative importance of nonlocal heat transport and the effects of self generated magnetic fields in the complex hohlraum plasmas; furthermore, there are no measurements of electron heat transport in the presence of magnetic fields to compare with modeling calculations.…”

Laser light backscatter from intermediate and high Z plasmas

“…The non-local-thermodynamic -equilibrium (non-LTE) atomic physics model XSN [14] was used to generate opacities and calculate the ionization states of the materials. Previous hydra simulations of gasbag targets showed good agreement with experimental diagnostics [15].…”

The application of laser-driven proton beams to the radiography of intense laser–hohlraum interactions

“…We can assume here that self-generated magnetic fields arising during plasma ablation and expansion, e.g. via the ∇T e × ∇n e mechanism [20,21], will be negligibly small at the low densities at which the front is observed [10,22,23], and unable to contribute significantly to the proton deflection observed at the front [10], thus allowing use of equation (5).…”