Ultrahigh intensity lasers can potentially be used in conjunction with conventional fusion lasers to ignite inertial confinement fusion (ICF) capsules with a total energy of a few tens of kilojoules of laser light, and can possibly lead to high gain with as little as 100 kJ. A scheme is proposed with three phases. First, a capsule is imploded as in the conventional approach to inertial fusion to assemble a high‐density fuel configuration. Second, a hole is bored through the capsule corona composed of ablated material, as the critical density is pushed close to the high‐density core of the capsule by the ponderomotive force associated with high‐intensity laser light. Finally, the fuel is ignited by suprathermal electrons, produced in the high‐intensity laser–plasma interactions, which then propagate from critical density to this high‐density core. This new scheme also drastically reduces the difficulty of the implosion, and thereby allows lower quality fabrication and less stringent beam quality and symmet...

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Ignition and high gain with ultrapowerful lasers

This self-contained, comprehensive book describes the fundamental properties of soft x-rays and extreme ultraviolet (EUV) radiation and discusses their applications in a wide variety of fields, including EUV lithography for semiconductor chip manufacture and soft x-ray biomicroscopy. The author begins by presenting the relevant basic principles such as radiation and scattering, wave propagation, diffraction, and coherence. He then goes on to examine a broad range of phenomena and applications. The topics covered include EUV lithography, biomicroscopy, spectromicroscopy, EUV astronomy, synchrotron radiation, and soft x-ray lasers. He also provides a great deal of useful reference material such as electron binding energies, characteristic emission lines and photo-absorption cross-sections. The book will be of great interest to graduate students and researchers in engineering, physics, chemistry, and the life sciences. It will also appeal to practicing engineers involved in semiconductor fabrication and materials science.

X-Rays and Extreme Ultraviolet Radiation: Principles and Applications

The interaction of a 1053 nm picosecond laser pulse with a solid target has been studied for focused intensities of up to 1019 W cm−2. The maximum ion energy cutoff Emax (which is related to the hot electron temperature) is in the range 1.0–12.0 MeV and is shown to scale as Emax≈I1/3. The hot electron temperatures were in the range 70–400 keV for intensities up to 5×1018 W cm−2 with an indication of a high absorption of laser energy. Measurements of x-ray/γ-ray bremsstrahlung emission suggest the existence of at least two electron temperatures. Collimation of the plasma flow has been observed by optical probing techniques.

http://www.qitech.biz/papers_refereed/phys_plasmas_fast_electrons_97.pdf

A study of picosecond laser–solid interactions up to 1019 W cm−2

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

Relativistic nonlinear effects in plasmas

Interferometric data resolved to 1 ..mu..m and 15 psec confirm the significant role of radiation pressure during high-intensity laser-plasma interactions. Specifically observed manifestations include electron density shelves, and small- and large-scale deformations of transverse isodensity of surfaces.

Interferometric Confirmation of Radiation-Pressure Effects in Laser-Plasma Interactions

An enclosing "box" calorimeter has been used to measure the polarization and angular dependence of 1.06-\ensuremath{\mu}m laser-light absorption under experimental conditions approximating those assumed by Estabrook, Valeo, and Kruer in their simulations; i.e., \ensuremath{\sim}${10}^{16}$ W/${\mathrm{cm}}^{2}$ plane waves incident on a planar plasma. A clear resonance absorption maximum was observed for $p$-but not for $s$-polarized incident radiation as predicted.

Polarization and Angular Dependence of 1.06-μm Laser-Light Absorption by Planar Plasmas

Laser induced fusion is the forerunner of a class of inertial confinement schemes in which hydrogen isotopes are heated to thermonuclear conditions in a very short period. The process is characterized by such short time scales that fuel confinement is achieved through its’ own finite mass and expansion velocity, approaching 1 μm/psec for ignition temperatures of order 10 keV (108 °K). With current laser powers limited to several terrawatts one readily estimates, on the basis of energy conservation, target mass, and expansion velocity, that target size and laser pulse duration are on the order of 100 μm and 100 psec, respectively. Within these constraints, targets have been heated and confined to the point where thermonuclear conditions have been achieved [1]. An important aspect affecting implosion dynamics is the process through which light is absorbed and apportioned between thermal and non-thermal particle distributions. In this paper we briefly review candidate absorption mechanisms, pointing out that the dominance of one or the other is strongly dependent on electron density gradient lengths in the surrounding plasma atmosphere. Since the gradient lengths are roughly proportional to sound speed times laser pulse heating time, we expect different mechanisms to dominate in short ∿ 100 psec) and long (≳ 1 nsec) irradiation experiments.

J. M. Auerbach

Papers

Interferometric Confirmation of Radiation-Pressure Effects in Laser-Plasma Interactions

Polarization and Angular Dependence of 1.06-μm Laser-Light Absorption by Planar Plasmas

Picosecond Interferometry of Laser Fusion Targets