D. R. Harding
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Targets are an indispensable part of all inertial confinement fusion (ICF) and high-energy-density physics (HEDP) experiments: while a high-quality target does not guarantee the success of an experiment, a poor-quality one can definitely lead to failure. In ICF and HEDP experiments, the precision with which targets are fabricated is critical to obtaining successful results, and many crossdisciplinary scientific and technological challenges are involved in the fabrication process. These include the preparation of submillimeter-sized components with, in many instances, tolerances of tens to hundreds of nanometers, the assembly of these components with micrometer and sub-1000-arcsecond precision, and, finally, full characterization to confirm the dimensional tolerances. Worldwide, more and more researchers and groups are involved in the development of target fabrication techniques, and a great deal of progress has been made. This special issue of the journal Matter and Radiation at Extremes (MRE) on HEDP and ICF target fabrication consists of seven papers, covering the fabrication of target components, target assembly, and characterization.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.043001
R. B. Spielman
D. B. Reisman
This erratum1 is issued by the authors to note that part (b) of Fig. 1 was erroneously excluded in the published version of the manuscript. A correct version of Fig. 1 is provided here. The figure caption of Fig. 1 is repeated here, however the captions and text of the document remain unchanged.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.049901
S. N. Chen
Laser irradiation of solid targets can drive short and high-charge relativistic electron bunches over micron-scale acceleration gradients. However, for a long time, this technique was not considered a viable means of electron acceleration due to the large intrinsic divergence (~50° half-angle) of the electrons. Recently, a reduction in this divergence to 10°–20° half-angle has been obtained, using plasma-based magnetic fields or very high contrast laser pulses to extract the electrons into the vacuum. Here we show that we can further improve the electron beam collimation, down to ~1.5° half-angle, of a high-charge (6 nC) beam, and in a highly reproducible manner, while using standard stand-alone 100 TW-class laser pulses. This is obtained by embedding the laser-target interaction in an external, large-scale (cm), homogeneous, extremely stable, and high-strength (20 T) magnetic field that is independent of the laser. With upcoming multi-PW, high repetition-rate lasers, this technique opens the door to achieving even higher charges (>100 nC).
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.044401
We apply a hydrodynamic approach to analyze ejecta emanating from doubly shocked liquid metals. In particular, we are interested in characterizing ejecta velocities in such situations by treating the problem as a limiting case of the Richtmyer–Meshkov instability. We find existing models for ejecta velocities do not adequately capture all the relevant physics, including compressibility, nonlinearities, and nonstandard shapes. We propose an empirical model that is capable of describing ejecta behavior across the entire parameter range of interest. We then suggest a protocol to apply this model when the donor material is shocked twice in rapid succession. Finally, the model and the suggested approach are validated using detailed continuum hydrodynamic simulations. The results provide a baseline understanding of the hydrodynamic aspects of ejecta, which can then be used to interpret experimental data from target experiments.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.044402
A fourth harmonic generation (FHG) scheme in focusing beams is proposed and demonstrated for large aperture Nd:glass laser facilities. By placing the focusing lens before the FHG crystal, the problem of ultraviolet damage can be overcome, largely without affecting FHG conversion efficiency owing to the large angular acceptance of the non-critical phase matching technique. A numerical simulation of the FHG process indicates that angular acceptance can be appropriately increased by lowering the working temperature and jointing the two adjacent compensating angles, so that FHG in focusing beams with relatively small F numbers becomes feasible. With a 170mm3170mm37mmand 65% deuterated potassium dihydrogen phosphate crystal mounted in a high-precision, temperature-controlled system, high-efficiency FHG has been demonstrated in the focusing beam with a full beam convergence angle of 36 mrad. When driven with a 223 J, second harmonic radiation (2ω), 1 ns flat-top pulse with a beam area of 130 cm2, corresponding to 1.7 GW/cm2 2ω input intensity, 182 J of fourth harmonic radiation (4ω) were generated.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.045401
Y. J. Gu
Comprehensive understanding and possible control of parametric instabilities in the context of inertial confinement fusion (ICF) remains a challenging task. The details of the absorption processes and the detrimental effects of hot electrons on the implosion process require as much effort on the experimental side as on the theoretical and simulation side. This paper describes a proposal for experimental studies on nonlinear interaction of intense laser pulses with a high-temperature plasma under conditions corresponding to direct-drive ICF schemes. We propose to develop a platform for laser-plasma interaction studies based on foam targets. Parametric instabilities are sensitive to the bulk plasma temperature and the density scale length. Foam targets are sufficiently flexible to allow control of these parameters. However, investigations conducted on small laser facilities cannot be extrapolated in a reliable way to real fusion conditions. It is therefore necessary to perform experiments at a multi-kilojoule energy level on medium-scale facilities such asOMEGAor SG-III. An example of two-plasmon decay instability excited in the interaction of two laser beams is considered.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.045402
Beryllium carbide (Be2C) thin films have proven to be promising ablation materials, but the properties of Be2C coatings of the greater thickness required for inertial confinement fusion capsules are still unknown. In this work, Be2Ccoatings of various thicknesses (0.3–32.9 μm) are prepared byDC reactive magnetron sputtering. The influence of thickness on crystal properties, microstructure, and optical properties is investigated. The results indicate that the crystallinity of polycrystalline Be2C films improves with increasing thickness, while the grain size (~5 nm) and texture properties (without a preferred orientation) have only a weak dependence on thickness.Auniform featureless microstructure and smooth surface (root mean square roughness ~8 nm) are observed even in thick (32.9 μm) films, despite the presence of defects induced by contaminants. High densities (2.19–2.31 g/cm3) and high deposition rates (~270 nm/h) are realized, with the latter corresponding to the upper limit for the fabrication of Be2Ccoatings by magnetron sputtering. The transmittance of the films in the near-infrared region remains at a high level (>80%) and has only a weak dependence on thickness, while the transmittance in the visible region decreases with increasing thickness. In addition, the optical bandgap is estimated to be about 1.9 eV and decreases with increasing thickness owing to the presence of defects.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.045403
Z-pinch dynamic hohlraums (ZPDHs) could potentially be used to drive inertial confinement fusion targets. Double- or multishell capsules using the technique of volume ignition could exploit the advantages of ZPDHs while tolerating their radiation asymmetry, which would be unacceptable for a central ignition target. In this paper, we review research on Z-pinch implosions and ZPDHs for indirect drive targets at the Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics. The characteristics of double-shell targets and the associated technical requirements are analyzed through a one-dimensional computer code developed from MULTI-IFE. Some key issues regarding the establishment of suitable sources for dynamic hohlraums are introduced, such as soft X-ray power optimization, novel methods for plasma profile modulation, and the use of thin-shell liner implosions to inhibit the generation of prior-stagnated plasma. Finally, shock propagation and radiation characteristics in a ZPDH are presented and discussed, together with some plans for future work.
PDF全文 Matter and Radiation at Extremes, 2019年第4卷第4期 pp.046201