The direct-drive, laser-based approach to inertial confinement fusion (ICF) is reviewed from its inception following the demonstration of the first laser to its implementation on the present generation of high-power lasers. The review focuses on the evolution of scientific understanding gained from target-physics experiments in many areas, identifying problems that were demonstrated and the solutions implemented. The review starts with the basic understanding of laser–plasma interactions that was obtained before the declassification of laser-induced compression in the early 1970s and continues with the compression experiments using infrared lasers in the late 1970s that produced thermonuclear neutrons. The problem of suprathermal electrons and the target preheat that they caused, associated with the infrared laser wavelength, led to lasers being built after 1980 to operate at shorter wavelengths, especially 0.35 μm—the third harmonic of the Nd:glass laser—and 0.248 μm (the KrF gas laser). The main physics areas relevant to direct drive are reviewed. The primary absorption mechanism at short wavelengths is classical inverse bremsstrahlung. Nonuniformities imprinted on the target by laser irradiation have been addressed by the development of a number of beam-smoothing techniques and imprint-mitigation strategies. The effects of hydrodynamic instabilities are mitigated by a combination of imprint reduction and target designs that minimize the instability growth rates. Several coronal plasma physics processes are reviewed. The two-plasmon–decay instability, stimulated Brillouin scattering (together with cross-beam energy transfer), and (possibly) stimulated Raman scattering are identified as potential concerns, placing constraints on the laser intensities used in target designs, while other processes (self-focusing and filamentation, the parametric decay instability, and magnetic fields), once considered important, are now of lesser concern for mainline direct-drive target concepts. Filamentation is largely suppressed by beam smoothing. Thermal transport modeling, important to the interpretation of experiments and to target design, has been found to be nonlocal in nature. Advances in shock timing and equation-of-state measurements relevant to direct-drive ICF are reported. Room-temperature implosions have provided an increased understanding of the importance of stability and uniformity. The evolution of cryogenic implosion capabilities, leading to an extensive series carried out on the 60-beam OMEGA laser [Boehly et al., Opt. Commun. 133, 495 (1997)], is reviewed together with major advances in cryogenic target formation. A polar-drive concept has been developed that will enable direct-drive–ignition experiments to be performed on the National Ignition Facility [Haynam et al., Appl. Opt. 46(16), 3276 (2007)]. The advantages offered by the alternative approaches of fast ignition and shock ignition and the issues associated with these concepts are described. The lessons learned from target-physics and implosion experiments are taken into account in ignition and high-gain target designs for laser wavelengths of 1/3 μm and 1/4 μm. Substantial advances in direct-drive inertial fusion reactor concepts are reviewed. Overall, the progress in scientific understanding over the past five decades has been enormous, to the point that inertial fusion energy using direct drive shows significant promise as a future environmentally attractive energy source.

Direct-drive inertial confinement fusion: A review

Fusion,四个来自上海的大男孩。2008年第一周,他们发行属于自己的第一张创作专辑《如果未来》。一点一点向梦想靠近的他们坦言:"一开始组乐队只是为了爱好,只是在玩,但是玩着玩着,发现已经不能不玩,可是如果要继续玩,我们需要更大的力气与努力。"这种勇气,我们坚信:音乐、如果,爱,就要,继续!

Fusion 如果,爱

We investigate the spreading at variable rate of a water drop on a smooth hydrophobic substrate in an ambient oil bath driven by electrowetting. We find that a thin film of oil is entrapped under the drop. Its thickness is described by an extension of the Landau-Levich law of dip coating that includes the electrostatic pressure contribution. Once trapped, the thin film becomes unstable under the competing effects of the electrostatic pressure and surface tension and dewets into microscopic droplets, in agreement with a linear stability analysis. Our results recommend electrowetting as an efficient experimental approach to the fundamental problem of dynamic wetting in the presence of a tunable substrate-liquid interaction.

Electrowetting-induced oil film entrapment and instability

This letter reports two novel electrode design considerations to satisfy two very important aspects of EWOD operation—(1) Highly consistent volume of generated droplets and (2) Highly improved accuracy in the generated droplet volume. Considering the design principles investigated two novel designs were proposed; L-junction electrode design to offer high throughput droplet generation and Y-junction electrode design to split a droplet very fast while maintaining equal volume of each part. Devices of novel designs were fabricated and tested, and the results are compared with those of conventional approach. It is demonstrated that inaccuracy and inconsistency of droplet volume dispensed in the device with novel electrode designs are as low as 0.17 and 0.10%, respectively, while those of conventional approach are 25 and 0.76%, respectively. The dispensing frequency is enhanced from 4 to 9 Hz by using the novel design.

/pdf/accurate-consistent-and-fast-droplet-splitting-and-2b4c2uhv0i.pdf

Accurate, consistent, and fast droplet splitting and dispensing in electrowetting on dielectric digital microfluidics

In electric-field-mediated droplet microfluidics, there are two distinct architectures – closed systems using parallel-plate electrodes and open systems using coplanar electrodes fabricated on an open substrate. An architecture combining both closed and open systems on a chip would facilitate many of the chemical and biological processes now envisioned for the laboratory on a chip. To accomplish such an integration requires a means to move droplets back and forth between the two. This paper presents an investigation of the requirements for such manipulation of both water and oil droplets. The required wetting conditions for a droplet to cross the open/closed boundary is revealed by a force balance analysis and predictions of this model are compared to experimental results. Water droplets can be moved between closed and open systems by electrowetting actuation; droplet detachment from the upper plate is facilitated by the use of beveled edge. The force model predicts that driving an oil droplet from a closed to an open structure requires an oleophobic surface. This prediction has been tested and confirmed using silicon wafers made oleophobic by re-entrant microstructures etched into the surface.

Moving droplets between closed and open microfluidic systems.

The double emulsion (DE) droplets used for fabrication of cryogenic foam targets for inertial confinement fusion experiments require precisely controlled volumes. On-chip electric field actuated mi...

/pdf/on-chip-double-emulsion-droplet-assembly-using-3ijvgnwgda.pdf

On-chip double emulsion droplet assembly using electrowetting-on-dielectric and dielectrophoresis

The electric-field–assembly technique proposed for making fusion targets uses the electrical force from dielectrophoresis and electrowetting-on-dielectric phenomena to form droplets of oil and wate...

Effect of a Surfactant on the Electric-Field Assembly of Oil-Water Emulsions for Making Foam Targets

Surfactant-containing water droplets were produced using a 75-Vrms pondermotive force operating at 10 kHz. Heat from a 30-V direct-current source, applied to a 2 × 0.1-mm region of the fluid, was instrumental in rupturing a low-surface-energy liquid membrane and forming the droplet. The low voltage allows quick and accurate dispensing of droplets without dielectric breakdown. Nanoliter-sized (~7.6-nL) butanol-styrene droplets were formed using 133 Vrms at 900 Hz. Microliter-sized oil droplets (~0.6 to 10.5 μL) were formed using high voltage (460 to 672 Vrms at 100 Hz). Oil-water emulsions were formed and moved horizontally, overcoming frictional and surface tension forces. Large oil droplets were also moved to a wider electrode spacing, where the emulsion can take the spherical shape of a target. This was only achieved by transporting the emulsion down an inclined slope (45 deg) using gravity to augment the electric force. All the steps are in place to form targets from oil-water-oil and water-oil...

Using Digital Microfluidics to Dispense, Combine, and Transport Low-Surface-Energy Fluids

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On-chip double emulsion droplet assembly using electrowetting-on-dielectric and dielectrophoresis

Effect of a Surfactant on the Electric-Field Assembly of Oil-Water Emulsions for Making Foam Targets

Using Digital Microfluidics to Dispense, Combine, and Transport Low-Surface-Energy Fluids