With the advent of high-energy-density (HED) experimental facilities, such as high-energy lasers and fast Z-pinch, pulsed-power facilities, millimeter-scale quantities of matter can be placed in extreme states of density, temperature, and/or velocity. This has enabled the emergence of a new class of experimental science, HED laboratory astrophysics, wherein the properties of matter and the processes that occur under extreme astrophysical conditions can be examined in the laboratory. Areas particularly suitable to this class of experimental astrophysics include the study of opacities relevant to stellar interiors, equations of state relevant to planetary interiors, strong shock-driven nonlinear hydrodynamics and radiative dynamics relevant to supernova explosions and subsequent evolution, protostellar jets and high Mach number flows, radiatively driven molecular clouds and nonlinear photoevaporation front dynamics, and photoionized plasmas relevant to accretion disks around compact objects such as black holes and neutron stars.

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Experimental astrophysics with high power lasers and Z pinches

We describe RAGE, the 'radiation adaptive grid Eulerian' radiation-hydrodynamics code, including its data structures, its parallelization strategy and performance, its hydrodynamic algorithm(s), its (gray) radiation diffusion algorithm, and some of the considerable amount of verification and validation efforts. The hydrodynamics is a basic Godunov solver, to which we have made significant improvements to increase the advection algorithm's robustness and to converge stiffnesses in the equation of state. Similarly, the radiation transport is a basic gray diffusion, but our treatment of the radiation?material coupling, wherein we converge nonlinearities in a novel manner to allow larger timesteps and more robust behavior, can be applied to any multi-group transport algorithm.

https://iopscience.iop.org/article/10.1088/1749-4699/1/1/015005/pdf

The RAGE radiation-hydrodynamic code

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory, when completed in 2008, will contain a 192-beam, 1.8?MJ, 500?TW, ultraviolet laser system together with a 10?m diameter target chamber and room for 100 diagnostics. NIF is housed in a 26?000?m2 environmentally controlled building and is the world's largest and most energetic laser experimental system. NIF provides a scientific centre for the study of inertial confinement fusion and the physics of matter at extreme energy densities and pressures. NIF's energetic laser beams will compress fusion targets to conditions required for thermonuclear burn, liberating more energy than required to initiate the fusion reactions. Other NIF experiments will study physical processes at temperatures and pressures approaching 108?K and 1011?bar, respectively, conditions that exist naturally only in the interior of stars and planets. NIF is currently configured with four laser beams activated in late 2002. These beams are being regularly used for laser performance and physics experiments, and to date nearly 250 system shots have been conducted. NIF's laser beams have generated 106?kJ in 23?ns pulses of infrared light and over 16?kJ in 3.5?ns pulses at the third harmonic (351?nm). A number of target experimental systems are being commissioned in support of experimental campaigns. This paper provides a detailed look at the NIF laser systems, laser and optical performance, and results from laser commissioning shots. We also discuss NIF's high-energy density and inertial fusion experimental capabilities, the first experiments on NIF, and plans for future capabilities of this unique facility.

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The National Ignition Facility: enabling fusion ignition for the 21st century

The National Ignition Facility (NIF) at Lawrence Livermore National Laboratory is a stadium-sized facility that, when completed in 2008, will contain a 192-beam, 1.8-megajoule, 500-terawatt, ultraviolet laser system together with a 10-m-diam target chamber and room for 100 diagnostics. NIF is the world's largest and most energetic laser ex- perimental system and will provide a scientific center to study inertial confinement fusion and matter at extreme energy densities and pres- sures. NIF's energetic laser beams will compress fusion targets to con- ditions required for thermonuclear burn, liberating more energy than re- quired to initiate the fusion reactions. Other NIF experiments will study physical processes at temperatures approaching 10 8 K and 10 11 bar, conditions that exist naturally only in the interior of stars and planets. NIF has completed the first phases of its laser commissioning program. The first four beams of NIF have generated 106 kJ in 23-ns pulses of infrared light and over 16 kJ in 3.5-ns pulses at the third harmonic (351 nm). NIF's target experimental systems are being commissioned and experi- ments have begun. This work provides a detailed look at the NIF laser systems, laser and optical performance, and results from recent laser commissioning shots. We follow this with a discussion of NIF's high- energy-density and inertial fusion experimental capabilities, the first ex- periments on NIF, and plans for future capabilities of this unique facility. © 2004 Society of Photo-Optical Instrumentation Engineers. (DOI: 10.1117/1.1814767) Subject terms: high-energy-density physics; inertial confinement fusion; labora- tory astrophysics; solid-state lasers.

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The National Ignition Facility

We have developed an accelerator architecture that can serve as the basis of the design of petawatt-class $z$-pinch drivers. The architecture has been applied to the design of two $z$-pinch accelerators, each of which can be contained within a 104-m-diameter cylindrical tank. One accelerator is driven by slow ($\ensuremath{\sim}1\text{ }\ensuremath{\mu}\mathrm{s}$) Marx generators, which are a mature technology but which necessitate significant pulse compression to achieve the short pulses ($\ensuremath{\ll}1\text{ }\ensuremath{\mu}\mathrm{s}$) required to drive $z$ pinches. The other is powered by linear transformer drivers (LTDs), which are less mature but produce much shorter pulses than conventional Marxes. Consequently, an LTD-driven accelerator promises to be (at a given pinch current and implosion time) more efficient and reliable. The Marx-driven accelerator produces a peak electrical power of 500 TW and includes the following components: (i) 300 Marx generators that comprise a total of $1.8\ifmmode\times\else\texttimes\fi{}{10}^{4}$ capacitors, store 98 MJ, and erect to 5 MV; (ii) 600 water-dielectric triplate intermediate-store transmission lines, which also serve as pulse-forming lines; (iii) 600 5-MV laser-triggered gas switches; (iv) three monolithic radial-transmission-line impedance transformers, with triplate geometries and exponential impedance profiles; (v) a 6-level 5.5-m-diameter 15-MV vacuum insulator stack; (vi) six magnetically insulated vacuum transmission lines (MITLs); and (vii) a triple-post-hole vacuum convolute that adds the output currents of the six MITLs, and delivers the combined current to a $z$-pinch load. The accelerator delivers an effective peak current of 52 MA to a 10-mm-length $z$ pinch that implodes in 95 ns, and 57 MA to a pinch that implodes in 120 ns. The LTD-driven accelerator includes monolithic radial transformers and a MITL system similar to those described above, but does not include intermediate-store transmission lines, multimegavolt gas switches, or a laser trigger system. Instead, this accelerator is driven by 210 LTD modules that include a total of $1\ifmmode\times\else\texttimes\fi{}{10}^{6}$ capacitors and $5\ifmmode\times\else\texttimes\fi{}{10}^{5}$ 200-kV electrically triggered gas switches. The LTD accelerator stores 182 MJ and produces a peak electrical power of 1000 TW. The accelerator delivers an effective peak current of 68 MA to a pinch that implodes in 95 ns, and 75 MA to a pinch that implodes in 120 ns. Conceptually straightforward upgrades to these designs would deliver even higher pinch currents and faster implosions.

/pdf/architecture-of-petawatt-class-z-pinch-accelerators-eqi07hh1a7.pdf

Architecture of petawatt-class z-pinch accelerators.

Supersonic fluid flow and the interaction of strong shock waves to produce jets of material are ubiquitous features of inertial confinement fusion (ICF), astrophysics, and other fields of high energy-density science. The availability of large laser systems provides an opportunity to investigate such hydrodynamic systems in the laboratory, and to test their modeling by radiation hydrocodes. We describe experiments to investigate the propagation of a structured shock front within a radiation-driven target assembly, the formation of a supersonic jet of material, and the subsequent interaction of this jet with an ambient medium in which a second, ablatively driven shock wave is propagating. The density distribution within the jet, the Kelvin–Helmholz roll-up at the tip of the jet, and the jet’s interaction with the counterpropagating shock are investigated by x-ray backlighting. The experiments were designed and modeled using radiation hydrocodes developed by Los Alamos National Laboratory, AWE, and Lawrence Livermore National Laboratory. The same hydrocodes are being used to model a large number of other ICF and high energy-density physics experiments. Excellent agreement between the different simulations and the experimental data is obtained, but only when the full geometry of the experiment, including both laser-heated hohlraum targets (driving the jet and counter-propagating shock), is included. The experiments were carried out at the University of Rochester’s Omega laser [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)].

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M. L. Gittings

Papers

Supersonic jet and shock interactions