Bremsstrahlung emission from laser - produced plasmas

Kephart, J. F.; Godwin, R. P.; McCall, Gene H.

doi:10.1063/1.1655398

Cited by 84 publications

(20 citation statements)

References 4 publications

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“…A third explanation was offered for similar results ( Fig. 11-2 below) obtained in earlier work by Kephart et al 108 in terms of thermal flux inhibition (Sec. XI).…”

Section: B Suprathermal Electronssupporting

confidence: 58%

“…These observations included electrons with energies greater than 50 keV, a large fraction of the laser energy appearing as fast ions, and less laser energy than expected being transmitted through thin foils. In related experiments, Kephart et al 108 reported x-ray spectra up to 50 keV, indicating a clear suprathermal electron component. A number of these observations were then modeled by Malone et al 591 They used a 1-D hydrodynamics code with a single electron temperature in which the heat flux was given by , except that f B was replaced by a much smaller number, f, now known as the "flux limiter."…”

Section: Thermal Transportmentioning

confidence: 99%

“…Gitomer and Henderson 592 found that hard x-ray spectra such as those of Kephart et al 108 could be fit with appropriate assumptions for the absorption fraction into hot electrons and their temperature. However, suprathermal electron models that could provide quantitative predictions of data such as the observations considered by Malone et al 591 were never developed before the move to short-wavelength lasers in the 1980s, when interest in such models declined as a result of the dramatic decrease in the energy observed in hot electrons.…”

Section: Thermal Transportmentioning

confidence: 99%

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Direct-drive inertial confinement fusion: A review

et al. 2015

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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.

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“…A third explanation was offered for similar results ( Fig. 11-2 below) obtained in earlier work by Kephart et al 108 in terms of thermal flux inhibition (Sec. XI).…”

Section: B Suprathermal Electronssupporting

confidence: 58%

Section: Thermal Transportmentioning

confidence: 99%

Section: Thermal Transportmentioning

confidence: 99%

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Direct-drive inertial confinement fusion: A review

et al. 2015

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“…Une fraction de ces électrons très énergétiques (> 10 keV) pénètre dans la cible solide, induisant l'émission d'un rayonnement X. La partie énergétique du spectre de cette émission (X durs de 10 à 100 MeV) se présente sous la forme de raies caractéristiques dépendant du Z de la cible (Ka, Ko,...) et d'un fond continu (bremsstrahlung ou rayonnement de freinage) [2]. L'étude du rayonnement X dur obtenu lors d'une interaction laser-plasma a fait l'objet de nombreuses études dans plusieurs laboratoires.…”

Section: Introductionunclassified

“…L'étude du rayonnement X dur obtenu lors d'une interaction laser-plasma a fait l'objet de nombreuses études dans plusieurs laboratoires. Les premières expériences ont été réalisées avec de très grosses installations laser de puissance délivrant des impulsions laser relativement longues (nanoseconde) dans le domaine de l'infra-rouge [2][3][4][5][6][7][8][9]. Le développement de ces sources X pour l'imagerie médicale a été proposé très tôt [10].…”

Section: Introductionunclassified