Rayleigh–Taylor and Richtmyer-Meshkov instability induced flow, turbulence, and mixing. II

A novel method by C. Zhou and R. Betti [Bull. Am. Phys. Soc. 50, 140 (2005)] to assemble and ignite thermonuclear fuel is presented. Massive cryogenic shells are first imploded by direct laser light with a low implosion velocity and on a low adiabat leading to fuel assemblies with large areal densities. The assembled fuel is ignited from a central hot spot heated by the collision of a spherically convergent ignitor shock and the return shock. The resulting fuel assembly features a hot-spot pressure greater than the surrounding dense fuel pressure. Such a nonisobaric assembly requires a lower energy threshold for ignition than the conventional isobaric one. The ignitor shock can be launched by a spike in the laser power or by particle beams. The thermonuclear gain can be significantly larger than in conventional isobaric ignition for equal driver energy.

http://absimage.aps.org/image/DPP06/MWS_DPP06-2006-000513.pdf

Shock Ignition of Thermonuclear Fuel with High Areal Density

Inertial fusion energy (IFE) has been considered a promising, nearly inexhaustible source of sustainable carbon-free power for the world’s energy future. It has long been recognized that the control of hydrodynamic instabilities is of critical importance for ignition and high-gain in the inertial-confinement fusion (ICF) hot-spot ignition scheme. In this mini-review, we summarize the progress of theoretical and simulation research of hydrodynamic instabilities in the ICF central hot-spot implosion in our group over the past decade. In order to obtain sufficient understanding of the growth of hydrodynamic instabilities in ICF, we first decompose the problem into different stages according to the implosion physics processes. The decomposed essential physics pro- cesses that are associated with ICF implosions, such as Rayleigh-Taylor instability (RTI), Richtmyer-Meshkov instability (RMI), Kelvin-Helmholtz instability (KHI), convergent geometry effects, as well as perturbation feed-through are reviewed. Analyti- cal models in planar, cylindrical, and spherical geometries have been established to study different physical aspects, including density-gradient, interface-coupling, geometry, and convergent effects. The influence of ablation in the presence of preheating on the RTI has been extensively studied by numerical simulations. The KHI considering the ablation effect has been discussed in detail for the first time. A series of single-mode ablative RTI experiments has been performed on the Shenguang-II laser facility. The theoretical and simulation research provides us the physical insights of linear and weakly nonlinear growths, and nonlinear evolutions of the hydrodynamic instabilities in ICF implosions, which has directly supported the research of ICF ignition target design. The ICF hot-spot ignition implosion design that uses several controlling features, based on our current understanding of hydrodynamic instabilities, to address shell implosion stability, has been briefly described, several of which are novel.

Theoretical and simulation research of hydrodynamic instabilities in inertial-confinement fusion implosions

A discrete Boltzmann model (DBM) is proposed to probe the Rayleigh-Taylor instability (RTI) in two-component compressible flows Each species has a flexible specific-heat ratio and is described by one discrete Boltzmann equation (DBE) Independent discrete velocities are adopted for the two DBEs The collision and force terms in the DBE account for the molecular collision and external force, respectively Two types of force terms are exploited In addition to recovering the modified Navier-Stokes equations in the hydrodynamic limit, the DBM has the capability of capturing detailed nonequilibrium effects Furthermore, we use the DBM to investigate the dynamic process of the RTI The invariants of tensors for nonequilibrium effects are presented and studied For low Reynolds numbers, both global nonequilibrium manifestations and the growth rate of the entropy of mixing show three stages (ie, the reducing, increasing, and then decreasing trends) in the evolution of the RTI On the other hand, the early reducing tendency is suppressed and even eliminated for high Reynolds numbers Relevant physical mechanisms are analyzed and discussed

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Discrete Boltzmann modeling of Rayleigh-Taylor instability in two-component compressible flows.

The two-dimensional Richtmyer-Meshkov Instability(RMI) system and the coexisting system combined with Rayleigh-Taylor Instability(RTI) are simulated with a multiple-relaxation time discrete Boltzmann model. It is found that, for the RMI system, the correlation between globally averaged non-organized energy flux and nonuniformity of temperature is nearly 1; the correlation between globally averaged non-organized momentum flux and nonuniformity of velocity and that between globally averaged thermodynamic non-equilibrium strength and nonuniformity of density are also high. In the coexisting system combined with RTI, the collaboration and competition mechanisms of the two instabilities are investigated. In the case where RMI dominates, an interesting interface inversion process is observed. The parameter regions for RMI dominates and RTI dominates are given. The effects of gravity acceleration and Mach number on nonequilibrium are carefully studied, via which the effects of RTI and RMI strengths on the extent of material mixing are better probed.

Collaboration and competition between Richtmyer-Meshkov instability and Rayleigh-Taylor instability

It is demonstrated that the growth of acceleration-phase instabilities in inertial confinement fusion implosions can be controlled, especially in the high-foot implosions [O. A. Hurricane et al., Phys. Plasmas 21, 056314 (2014)] on the National Ignition Facility. However, the excessive growth of the deceleration-phase instabilities can still destroy the hot spot ignition. A scheme is proposed to retard the deceleration-phase Rayleigh–Taylor instability growth by shock collision near the waist of the inner shell surface. Two-dimensional radiation hydrodynamic simulations confirm the improved deceleration-phase hot spot stability properties without sacrificing the fuel compression.

W. H. Ye

Papers

A scheme for reducing deceleration-phase Rayleigh–Taylor growth in inertial confinement fusion implosions