The first demonstration of a nuclear-pumped laser (NPL) dates back to the mid-1970s while theoretical studies started earlier. This history will be briefly reviewed, followed by a discussion of the present status of various NPL concepts. Both physics and engineering issues are noted. Most attention has been given to gaseous media due to problems associated with radiation damage in liquid- and solid-state media. Various pumping methods, ranging from direct pumping of the laser medium to the use of nuclear-pumped flashlamps, will be discussed. Recent experimental results on pumping of O2(1Δ), the first demonstration of a nuclear-pumped flashlamp-driven laser XeBr*-I, and the new 3He-Ne-H2 NPL will be presented. Potential applications and corresponding NPL requirements, e.g., the long delay time requirements for an inertial fusion driver based upon NPLs, will be reviewed.

Even though general conclusions cannot be derived for all the protection schemes in inertial confinement fusion (ICF) reactors, the feasibility of the ferritic alloy HT-9 as the main component of the first structural wall (FSW) in ICF facilities using thin-film Li17Pb83 liquid protection, flowing through porous tubes (INPORT), can be demonstrated as a solution in terms of radiation damage. Swelling and shift in the ductile-brittle transition temperature (DBTT) can be analyzed using the results of experimental fast-fission reactors, which are demonstrated to be good experimental tools in that ICF range. The good performance of HT-9 is remarkable. The generation of new solid transmutants and the depletion of initial constituents need also be considered. Further, a reduced-activation HT-9 (niobium-free) has been studied using recycling and shallow land burial (SLB) criteria. The recycling using that HT-9 is shown to be not feasible, as is SLB waste disposal. The unexpected critical role of some short-lived isotopes is remarkable, and more research on their nuclear data must be performed.

A spherical scheme is introduced for indirect drive, having as reference the application to inertial fusion energy. The concept uses the transmission of a radiation wave through a high-Z, low-density spherical radiator surrounding the capsule to be imploded. The low conversion efficiency to in-cavity radiation is somewhat compensated by using modest radiator-to-capsule gaps, the smoothing effects on the longest dominant nonuniformity wavelengths due to this separation being of the order of 10. Another factor of the order of 100–500 is related to the consequent use of a large number of beams. From the application of the loop condition relative to power plants, it is found that this approacrTbecomes practicable if drivers with efficiencies greater than 10% are assumed and if the fraction of circulating power is allowed to be 0.5, this implying a unitary cost of energy about a factor 1.5 greater than that associated to the more conventional fraction of 0.25.

Recent developments in research on drivers for inertial confinement fusion identified the need to develop laser amplifiers with efficiencies of 80% or more. This article discusses a novel free electron laser amplifier that is based on vacuum interaction of laser beams with electrons, clusters of condensed matter, or neutral atoms. The scheme is based on the inversion of the ponderomotive expulsion of plasma from a focussed laser beam. The problem of Liouville conservation of phase space is overcome by employing the laser pulse transient processes. The optical energy for amplification is provided by the transfer of the translative kinetic energy of electrons, clusters, or neutral atoms that are injected nearly laterally into the laser pulse. The gains predicted to be achievable with this process are of interest for clusters, although the cluster densities presently available are too low to achieve the desired level of amplification. Neutral beams are shown to have the greatest potential for achieving large amplifications.

The effect of surface finish on the evolution of ICF targets has been studied. As driver for the implosion has been used a temporally profiled thermal radiation pulse (25 ns in duration) as that expected for the case of a high-gain (cm sized) capsule enclosed in a cavity. 2-D numerical simulations have been performed on a planar analog to investigate the stability to perturbations having wavelengths in the interval 2.5–40 μm and initial amplitudes of 0.03 and 1 μm. The simulations show perturbation growing due to hydrodynamic instabilities. The distortion of the ablation front reaches such a level to strongly enhance the ablation rate because of the increase in the exposed area and in the power absorbed per unit area. Two different phenomena have been identified: one, preferentially occurring for small wavelengths, in which the motion behind the first shock wave becomes turbulent and the symmetry is lost; the other, appearing for long wavelengths, in which a thermal radiation wave penetrates into the fuel. This preheating phenomenon is related to the formation of holes in the thermal shield due to the enhanced ablation and to matter transverse piling up. All these effects may render useless the 1-D-based design of a high-gain capsule exposed to a given thermal bath. However, it has been also observed that, for the longer wavelength (40 μm) and a smaller initial perturbation amplitude (e.g. 0.01 μm), during the temperature pulse the preheating does not occur and most of the fuel can be accelerated as a whole to speeds of the order of 2 × 107 cm/s or greater without a substantial onset of transverse velocities, even in the presence of the ablator piling up.

A new scheme for a large-scale solid-state laser system for inertial confinement fusion application is proposed. Double-pass amplifiers composed of a large number of Nd:glass rods and flash lamps between them are used together with phase-conjugation cells and output stimulated Brillouin scattering pulse compressors. The results of the preliminary experimental tests are presented, and the advantages of the proposed scheme are discussed.

In inertial confinement fusion experiments, the symmetrical implosion calls for a new scheme: a nonsupported pellet. In this article, the first experiment is conducted using a plastic pellet covered with thin ferromagnetic material. In the system, the digital-phase-lead-compensator takes the position-related signal and processes it to provide a driving signal for the magnetic suspender. The suspended pellet is irradiated by the Gekko XII laser, having its total energy 2700 J with pulse width 800 ps at the wavelength 0.53 μm. The X-ray pinhole photograph confirms the spherically symmetrical implosion at the pellet core. At irradiation, the neutron yield is also observed.

We report experiments that were carried out at the inductive storage machine GIT-4 with wire arrays. The tungsten wire array parameters were the following: the mass per centimeter was equal to 370 μg/cm, the length was 4 cm, and the initial radius was 0.2 cm. When the wire array current was 1.5 MA, the rise time was 100 ns and the total radiation energy was 50 kJ at the 80–100–kJ energy transferred to the wire array.

The ASTERIX iodine laser delivers after frequency tripling to λ = 0.44-μm laser pulses with energies up to 500 J at a pulse duration of 300 ps for target experiments. Experimental investigations of radiative transfer in low- and high-Z materials are reported.

Smoothing of laser-plasma interaction by ISI, RPP, SSD, etc. was mainly directed to overcome lateral nonuniformity of irradiation. While these problems are in no way less important, we derived numerically the model of the Laue rippling and hydrorelaxation model for explanation of the measured temporal pulsation in the 10- to 40-ps range and how the smoothing schemes suppress these pulsations. The partial standing wave fields of the normally coherent laser-irradiated plasma corona is then suppressed by smoothing and conclusion for tests for this model, e.g., by the “question mark experiment” is given. The result provides a physics solution of the laser interaction problem for direct-drive inertial fusion energy

We have studied experimentally the beam-plasma two-stream dissipative collisional instability of relativistic electron beams (REB) injected into plasma produced by interaction of REB with neutral nitrogen. The gas pressure ranged from 0.02 to 8 Torr. REB (T = 100 μs, E = 300 keV, 7 = 3–15 A) were injected into gas through a pulsed foilless valve. An external magnetic field was not used. A description of the experimental setup and that of applied diagnostics are presented. In some of the experiments the inner walls of a metallic interaction chamber were covered with microwave-absorbent material. We present the experimental dependence of the critical current of two-stream instability on gas pressure and beam penetration length. We have also measured the distribution of microwave emission along the beam axis. The influence of plasma self-radiation on the instability was observed and is attributed to a feedback. A possible mechanism of the feedback is discussed.

The production of laser-induced plasmas, which ordinarily occurs only at high laser powers, occurs at far lower laser powers using resonant and collisional phenomena in alkali metal vapors. For example, 10 torr of Na vapor can be significantly ionized to produce a bright white ball with as little as 1 mW of focused cw dye laser power (e.g., at the 3p → 4d transitions at 568.3 and 568.8 nm). We first discuss the alkali metal vapors in general (1) and their important ionization processes (2), especially those occurring at photon energies below the atomic ionization energy. We then discuss the striking wavelength dependences of ionization. For example, cw laser irradiation of these vapors gives completely different behavior at slightly different wavelengths (Stwalley 1990): 10 torr of sodium vapor at 568.2 nm, where the vapor shows only molecular fluorescence and is sufficiently quiescent that highly stable, narrow-band, optically pumped lasers based upon the fluorescent transitions can easily be constructed (Bahns 1983; Bahns et al. 1983; Verma et al. 1983); and, at 568.3 nm, where a “quasiresonant” laser-induced plasma forms and strong emission (including violet excimer bands, a potential laser) is produced (Koch & Collins 1979; Bahns et al. 1989a; Bahns et al. 1989b). We will analyze and reinterpret the classic subthreshold ionization studies (3) and survey recent laser-induced plasma studies (4). We also discuss dissociative recombination and its selectivity for producing strong excimer emission (5) the predicted electronic spectra of the alkali metal molecular ions (6).

An experiment on Al-Cu impedance-match targets, carried out at the Shenguang highpower laser facility, is described. The shock adiabat of Cu in the pressure region 0.4- 0.8 TPa, measured experimentally, is close to the extrapolated results of the data at lower pressure obtained with a high-explosive loading facility and also is in agreement with the data at high pressure measured in the underground nuclear test environment.

We calculated Stark-broadened absorption line profiles for n = 1 to n = 2 inner-shell transitions in the L-shell ions of Ar for electron number densities between 5 × 1023 cm-3 and 5 × 1024 cm-3 and for temperatures in the range 100–600 eV. These line profiles are used to calculate the frequency-dependent optical depth of hot, dense Ar plasmas. We also investigated the possibility of using Stark-broadened absorption line profiles for diagnostic applications.