Theoretical opacities are required for calculating energy transport in plasmas. In particular, understanding stellar interiors, inertial fusion, and Z pinches depends on the opacities of mid-atomic-number elements over a wide range of temperatures. The 150–300 eV temperature range is particularly interesting. The opacity models are complex and experimental validation is crucial. For example, solar models presently disagree with helioseismology and one possible explanation is inadequate theoretical opacities. Testing these opacities requires well-characterized plasmas at temperatures high enough to produce the ion charge states that exist in the sun. Typical opacity experiments heat a sample using x rays and measure the spectrally resolved transmission with a backlight. The difficulty grows as the temperature increases because the heating x-ray source must supply more energy and the backlight must be bright enough to overwhelm the plasma self-emission. These problems can be overcome with the new generation...

http://absimage.aps.org/image/DPP08/MWS_DPP08-2008-000780.pdf

Experimental investigation of opacity models for stellar interiors, inertial fusion, and high energy density plasmas

https://aip.scitation.org/doi/pdf/10.1016/j.mre.2016.01.003

Progress in octahedral spherical hohlraum study

A recent publication [K. Lan et al., Phys. Plasmas 21, 010704 (2014)] proposed a spherical hohlraum with six laser entrance holes of octahedral symmetry at a specific hohlraum-to-capsule radius ratio of 5.14 for inertial fusion study, which has robust high symmetry during the capsule implosion and superiority on low backscatter without supplementary technology. This paper extends the previous one by studying the laser arrangement and constraints of octahedral hohlraum in detail. As a result, it has serious beam crossing at θL≤45°, and θL=50° to 60° is proposed as the optimum candidate range for the golden octahedral hohlraum, here θL is the opening angle that the laser quad beam makes with the Laser Entrance Hole (LEH) normal direction. In addition, the design of the LEH azimuthal angle should avoid laser spot overlapping on hohlraum wall and laser beam transferring outside hohlraum from a neighbor LEH. The octahedral hohlraums are flexible and can be applicable to diverse inertial fusion drive approaches...

Octahedral spherical hohlraum and its laser arrangement for inertial fusion

High-convergence ignition-like double-shell implosion experiments have been performed on the Omega laser facility [T.R. Boehly et al., Opt. Commun. 133, 495 (1997)] using cylindrical gold hohlraums with 40 drive beams. Repeatable, dominant primary (2.45 MeV) neutron production from the mix-susceptible compressional phase of a double-shell implosion, using fall-line design optimization and exacting fabrication standards, is experimentally inferred from time-resolved core x-ray imaging. Effective control of fuel-pusher mix during final compression is essential for achieving noncryogenic ignition with double-shell targets on the National Ignition Facility [Paisner et al., Laser Focus World 30, 75 (1994)].

/pdf/hohlraum-driven-ignition-like-double-shell-implosions-on-the-2qw4m1rfwr.pdf

Hohlraum-driven ignition-like double-shell implosions on the Omega laser facility

https://aip.scitation.org/doi/pdf/10.1016/j.mre.2016.02.001

First demonstration of improving laser propagation inside the spherical hohlraums by using the cylindrical laser entrance hole

The Hohlraum physics experiments performed on the SGIII-prototype laser facility are simulated by using our two-dimensional radiation hydrodynamic code LARED-H, and the influence of laser intensity on the two-dimensional Hohlraum simulations is studied. Both the temporal radiation temperature and the x-ray spectrum from the simulations agree well with the observations, except that the simulated M-band fraction (greater than 2 keV) is obviously smaller than the observation. According to our study, the coupling efficiency from laser to x-ray is around 70% for SGIII-prototype laser facility Hohlraums.

Simulation study of Hohlraum experiments on SGIII-prototype laser facility

In ignition targets designs, U or U based cocktail hohlraum are usually used because the Rosseland mean opacity of U is higher than for Au at the radiation temperature for ignition. However, it should be noted that the opacity of U is obviously lower than for Au when the radiation temperature falls into a low temperature region. Because the depth penetrated by radiation is only several micrometers under a 300eV drive, and also because there is a prepulse longer than 10 ns prepulse at temperatures lower than 170 eV in the radiation drive of ignition target designs. Therefore we propose an Au + U + Au sandwich hohlraum for ignition targets in this work. Compared to the cocktail, the sandwich not only remarkably simplifies the fabrication and uses less depleted U material, but also increases the albedo during the prepulse.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/S0263034609990590

Study on Au + U + Au sandwich Hohlraum wall for ignition targets

Measurements of iron-plasma absorption spectrum over 150–1200 eV photon energy range were reported at temperature T = (72 ± 4) eV. The electron temperature was diagnosed with the absorption spectrum of aluminum mixed with iron. The density was not diagnosed directly but obtained from a radiative hydrodynamic simulation with the Multi-1D code. The broad photon energy range enables simultaneous observation of the L-shell and M-shell transitions that dominate the radiation transport at this temperature. The spectrally resolved transmission data were compared to the detailed-configuration-accounting model calculations and reasonable agreement was found.

L- and M-shell absorption measurements of radiatively heated Fe plasma

A two-dimensional (2D) multigroup radiation transfer hydrodynamics code LARED-R-1 is used to simulate a supersonic wave experiment performed earlier by the Livermore group. The main result is that, contrary to the conclusion of Back et al. (2000a), the average-atom opacity model is sufficient to explain the obtained experimental results, provided that an adequate description of the radiation transport was used. The simulation results from LARED-R-1 show the spectrum of radiation in foam with radius and length of several optical depths is not in Planckian distribution and the angular intensity distribution is anisotropic.

Study on two-dimensional transfer of radiative heating wave

http://iopscience.iop.org/article/10.3847/0004-637X/816/1/36/pdf

Xujun Meng

Papers

Simulation study of Hohlraum experiments on SGIII-prototype laser facility

Study on Au + U + Au sandwich Hohlraum wall for ignition targets

L- and M-shell absorption measurements of radiatively heated Fe plasma

Study on two-dimensional transfer of radiative heating wave

Opacity Measurement and Theoretical Investigation of Hot Silicon Plasma