In review, general results obtained by Institute of Physics and Power Engineering (IPPE) during 1981–1992 are presented in the field of physics of nuclear-induced plasmas in the following directions: processes of primary ionization of different media by nuclear reaction products; function of electron distribution in nuclear-induced plasmas; processes of excitation and relaxation; track structure of nuclear-induced plasmas. Prospects of study progress are discussed with a view to improve the current concepts of physics of elementary processes occurring in nuclear-induced plasmas and obtain experimental and theoretical data on process constants needed to calculate the nuclear-pumped lasers.

An overview of nuclear-pumped laser programs conducted on various pulsed reactor types has been presented. The independent research undertaken in Russia and the United States have confirmed the concept of energy conversion from nuclear exothermal reactions to coherent optical radiation as feasible.

The Lawrence Livermore National Laboratory (LLNL) Inertial Confinement Fusion (ICF) Program is addressing the critical physics and technology issues directed toward demonstrating and exploiting ignition and propagating burn to high gain with ICF targets for both defense and civilian applications. Nova is the primary U.S. facility employed in the study of the X-ray-driven (indirect drive) approach to ICF. Nova's principal objective is to demonstrate that laser-driven hohlraums can achieve the conditions of driver-target coupling efficiency, driver irradiation symmetry, driver pulseshaping, target preheat, and hydrodynamic stability required by hot-spot ignition and fuel compression to realize a fusion gain.

The LLNL ICF Program believes that the next major step in the national ICF Program is the demonstration of ignition and moderate gain (G ≤ 10). Recent theoretical and experimental results show that the ignition drive energy threshold can be reduced significantly by operating indirectly driven targets at radiation temperatures ∼ 1.3–1.6 times higher (thereby achieving higher implosion velocity) than originally proposed for the Laboratory Microfusion Facility (LMF). (Temperatures of ∼ 1.3 times higher have already been demonstrated on Nova.) Specifically, it should be possible to demonstrate ignition and propagating with burn about 1–2 MJ of laser energy as against the 5–10 MJ necessary for the high-yield LMF. LLNL proposes to upgrade the existing Nova facility to 1–2 MJ (2- to 4-ns pulses) and demonstrate ignition and propagating burn to moderate gain with appropriately scaled hydrodynamic equivalents of high-yield targets.

Once moderate gain has been demonstrated at 1–2.0 MJ on the Nova Upgrade, investigations into improving, by about 50%, the coupling efficiency between the driver and the capsule could provide gains >20 at about 1 MJ or less. A database for gain below 1-MJ driver energies could lead to a low-capital-cost Engineering Test Facility (ETF) for a first inertial fusion energy engineering reactor. Because the capital cost for both the target chamber and the driver scale with size, there is the opportunity to realize large savings by lowering the required driver energy necessary to demonstrate the technology for a first demonstration power plant. A target gain, G ∼ 25, at a driver energy, ED ∼ 0.75 MJ, would be self-sustaining for a driver efficiency of ∼10% and a thermal-to-electric conversion efficiency of ∼33% and at 12 Hz would generate ∼10 MW of gross electric power. Although the cost of electricity would be high, the combination of low capital cost and early demonstration of reactor technology would be an attractive step in the development of inertial fusion energy.

Vacuum UV fluorescences from ionic alkali-halide and rare-gas alkali excimers were observed by e-beam excitation. The two diffuse emissions centered at 185 and 154 nm from the CsF vapor were attributed to the bound-free B2Σ+ → X2Σ+ and D2Π → X2Σ+ bands of (CsF)+, respectively. And, the 164- and 133-nm diffuse bands from gas the mixture of Xe or Kr with hot vapor of Rb were assigned to the emissions of (XeRb)+ and (KrRb)+ ionic excimers. In addition, amplified spontaneous emissions of the Na2 violet, K2 yellow, and Rb2 orange diffuse bands were observed from e-beam-excited alkali vapor with argon buffer gas. The continuum spectra centered at 436, 574, and 604 nm were attributed to triplet-triplet Na2, K2, and Rb2 23Πg → 13Σu+ bound-free transitions, respectively. The dissociative recombination of Na3+, K3+, or Rb3+ is discussed as an efficient formation process of the upper states in e-beam pumping.

We suggest several cascade lasing schemes: (1) cascade of laser transitions between atom (ion) excited levels when the lower laser level of one laser transition is simultaneously the upper laser level of another transition located below; (2) successive lasing, first, on ion transitions, then after ion recombination on atom transitions; (3) while using multicomponent mixtures, successive lasing on atoms (ions) of separate components. These possibilities are discussed in terms of specific lasers, some of which have been studied experimentally.

Inertial confinement fusion (ICF) requires high compression of fusion fuel to densities approaching 1000 times liquid density of deuterium-tritium (D–T) at central temperatures in excess of 5 keV. The goal of ICF is to achieve high gain (of the order of 100 or greater) in the laboratory. To meet this objective with minimum driver energy, a number of central issues must be addressed. Research in ICF with laser drivers has shown the importance of using short wavelength (λ < 0.5 µm). To achieve conditions for high gain at driver energies of a few megajoules or less, high intensities (>1014W/cm2) are required. The directdrive approach to ICF is more energy efficient than indirect drive if the stringent drive symmetry and hydrodynamic stability requirements can be met by a suitable laser irradiation scheme and target design. Experiments carried out at 351 nm on the 2-kJ, 24-beam OMEGA laser system at the Laboratory for Laser Energetics (LLE) at the University of Rochester, and future experiments to be performed on a 30-kJ upgrade of this laser, can resolve the remaining physics issues for direct drive: (1) energy coupling and transport scaling; (2) irradiation-uniformity requirements for high gain; (3) hydrodynamic stability constraints; and (4) hot-spot and main-fuel-layer physics. We review progress made on achieving uniform drive conditions with the OMEGA system and present results for direct-drive cryogenic-fuel-capsule and CD-shell, “surrogate” cryogenic-capsule implosion experiments that illustrate the constraints imposed by hydrodynamic instabilities and drive uniformity on the design of high-performance direct-drive targets. Target designs have been identified that will explore the ignition-scaling regime using the OMEGA Upgrade. Experiments on the OMEGA Upgrade will signal whether or not there is a high probability of achieving modest to high gain using direct drive on an upgrade of the NOVA facility.

Bandwidth effects on laser-plasma interaction were investigated with a ¼-μm laser. Planar targets were irradiated with a 1- to 40-cm–1 bandwidth laser at I = 1 × 1013–4 × 1015 W/cm2. Above 3 × 1013 W/cm2, stimulated Brillouin scattering (SBS) was observed with 1 cm–1 light. This process was strongly reduced with a 40-cm–1 light. Evolution of the convective SBS was studied with 1-D fluid simulation code. Bandwidth effect on the SBS growth was discussed to compare the theoretical prediction and experimental results. The scalelength dependence exists for the SBS reduction with a broadband laser.

The nuclear-pumped laser program at the Institute for Technical Physics at Chelyabinsk- 70 is described. Work has primarily concentrated on rare gas and metal vapor lasers.

The time and wavelength dependencies of luminescence resulted from 11 low-lying Cd II levels in He-Cd medium excited by 252Cf fission fragments have been measured in the temperature range from 553 to 669 K and various buffer gas pressures (1.5–5 atm). The method used is based upon applying multichannel coincidence technique and single-photon spectrometry. The lifetime, pumping rate, and luminescence spectral line width data obtained for 325- and 441.6-nm transitions have been used to estimate lasing characteristics of He-Cd medium under optimal conditions.

The Nova Upgrade Facility is being designed to achieve inertial confinement fusion (ICF) ignition and gain. A baseline design of the laser and experimental facilities has been completed, and a development plan, which includes a fully integrated laser demonstration, has been formulated. With adequate funding, the activities in this plan could be completed by late 1993. Construction of the Nova Upgrade beginning at that time would make possible the achievement of ICF ignition before the end of the decade.

An atomic model of the laser-produced Al plasma has been developed and used to analyze excitation processes of recombination pumping soft X-ray lasers. A soft X-ray gain for H-like Balmer-α line and He-like 3d-2p transition in short-pulse intense KrF laser (IL = 1014–1015 W/cm2, T = 10–100 ps)-produced Al plasmas are calculated for various laser temporal pulse shapes to find the condition for efficient production of population inversion. Results from different models are compared and requirements for the atomic model for X-ray laser design are discussed.

Numerical simulation of active media nuclear-pumped lasers on noble gases and their mixtures with metal vapors are presented. Prospects of creation of high-power short-wavelength nuclear-pumped excimer lasers are discussed.

We present the cross section for the ejection of electrons from helium and argon by 252Cf fission fragments, differential in the ejected electron energy. The electron energy ranges from 10 to 1,500 eV. The experimentally obtained cross sections are compared with calculations in the framework of Gryzinski&s theory and Gerjuoy&s theory. The results of the energy loss partitioning are presented. It is demonstrated that there is reasonable agreement between Gerjuoy&s theory and experiment.

Validation of the direct-drive approach to inertial confinement fusion requires the development of a 351-nm wavelength, 30-kJ, 50-TW laser system with flexible pulse shaping and irradiation uniformity approaching 1%. An upgrade of the existing OMEGA direct-drive facility at Rochester is planned to meet these objectives. In this article, we review the design rationale and specifications of the OMEGA Upgrade laser with particular emphasis on techniques planned to achieve the required degree of beam smoothing, temporal pulse shape, and beam-to-beam power balance.

A couple of advanced techniques of high-efficiency pulse compression for KrF lasers have been developed in our laboratory. As is well known, electron beam-excited KrF lasers have a capability of large output energy of 100- to 1,000-ns pulse duration. However, high-efficiency operation under a short-pulse input is difficult to achieve because of the reaction kinetics and short lifetime of KrF excimers. For developing ultrahigh peak-power lasers, the efficient pulse compression of ns to ps and ps to fs pulses is essential. We demonstrated advanced techniques, Raman pulse compression in a transient Raman regime, and pulse compression in saturated amplifiers with saturable absorbers.

This article describes the design of a laser setup excited by 3He(n, p)3H reaction products and intended for investigations of the laser characteristics of 3He mixtures with metal vapors or other gases at temperatures up to 800˚C. This setup could also be used to study the effect of the medium heating on the characteristics of nuclear-pumped gas lasers.