We studied the smoothing of nonuniformities in the quasisteady expansion of a plasm ablated from a spherical target under a weakly nonuniform laser irradiation with overall heat conduction and magnetic generation effects. We also considered light refraction effects.

We investigated several examples of ion beam targets that utilize the energy efficiency of direct drive while optimizing on the symmetry requirements. Heavy-ion beams of charge state Z ≥ 3 at 5–10 GeV have ≲15–20 m bending radii with 3.5-T fields. Beams like these could be used with targets involving direct drive. Control of asymmetries in direct-drive ion beam targets depends on control of the effects of residual target asymmetries after an appropriate illumination scheme has been adopted. In this paper, we outline results of our investigations into ion beam target concepts in which the effects of residual asymmetries are ameliorated. The beams are placed according to our axially symmetric Gaussian-quadrature illumination scheme (Mark 1986). The targets survive the effects of residual asymmetries in our recent 2-D hydrodynamic simulations. We also briefly discuss the additional positive effects of polarized DT fuel on ion beam targets.

A computer model has been developed and benchmarked for the nuclear-pumped atomic carbon laser. Experiments have been performed with the atomic carbon laser and with the radiolysis of CO2 as a benchmark for the model. The results of the CO2 radiolysis are described.

A camera has been developed that directly measures the deuterium-tritium burn region of laser-driven inertial confinement fusion targets. Images are formed by 14-MeV thermonuclear neutrons emitted from the targets. Our demonstration instrument is based on a coded-aperture imaging technique known as penumbral imaging, and has produced images of high-yield (> 1012 neutrons) direct-drive targets with resolutions of 80 μm. The camera consists of four major components: the penumbral aperture, alignment hardware, detector system, and image analysis software.

Fuel areal density, 〈ρR〉, is a fundamental quantity for ICF implosions. For current and future targets, areal densities are large enough that a variety of neutron based diagnostic techniques can be used to determine fuel 〈ρR〉. These include measurements based on the secondary production of DT neutrons from initially pure deuterium fuel and, for higher 〈ρR〉 values, techniques utilizing high energy tertiary neutrons or lower energy scattered neutrons. This paper describes these techniques and gives an overview of the current experimental status.

Large (megagauss) “spontaneous” magnetic fields are produced by laser–plasma interactions when a short, powerful laser pulse is focused to a small diameter onto a solid target. The relevance of these magnetic fields to inertial confinement fusion applications depends on the numerous ways in which they can affect laser–plasma interactions and the resulting plasma. Theoretical studies have dealt with a variety (thermal, radiative, and dynamo) of generation mechanisms and with the associated transport and instability phenomena. The fields, originally observed with small induction probes placed near the target, have been studied in the focal region by optical methods. These optical diagnostics have used Faraday rotation of a probing laser beam and Zeeman profiles of emitted spectral lines.

The Rayleigh—Taylor instability is studied by means of a slab model and when slab thickness D is comparable to the ablation-to-critical surface distance. Under these conditions the perturbations originating at the ablation front reach the critical surface, and in order to determine the instability growth rate, we must impose boundary conditions at the corona. Stabilization occurs for perturbation wave numbers such that kD ˜ 10.

Results of novel experiments with laser-heated capillary targets are presented. In these experiments the interior of gold capillaries having a 200- or 700-μm inner diameter and a 2–12-mm length was axially irradiated by injection of the laser energy through one of the end openings. A frequency-doubled Nd:glass laser (λ = 0.53 μm) was employed, delivering 8-J energy in 3 ns. The experiments showed no significant backreflection of laser light. Depending on the capillary diameter and length, most of the laser energy is either transmitted or absorbed inside the capillary. The transmission of laser light was measured as a function of capillary length and found to be in good agreement with the predictions of a simple theoretical model. Two extreme cases could be identified. Capillaries with a 700-μm diameter show uninhibited laser light propagation due to multireflections off the inner wall. In contrast, at the entrance of capillaries with a 200-μm inner diameter a plasma plug forms that absorbs most of the laser energy. In both cases significant energy transport was observed to occur in the axial direction. A stable and strongly radiating plasma column is formed along the capillary axis by the collision of the radially imploding plasma. During the collision, part of the hydrodynamic energy of the plasma is converted into radiative energy. In a special case-a lower limit of ≊7% could be inferred for the conversion efficiency from laser light into X-ray radiation emitted from the rear opening of the capillary.

The increase in time-integrated divergence of a 1.7-MeV, 10-MA relativistic electron beam due to transport over 10 cm in a gas cell filled with 1 and 6 Torr of nitrogen was measured. The divergence was characterized by a multiple-pinhole beam sampling technique involving an aperture plate, an expansion region, and an attenuator plate followed by nylon radiochromic film. The divergence is determined by a fit of the measured deposition profile to response functions calculated using Monte Carlo coupled electronphoton transport codes. The initial value of 6.9° after the entrance foil is observed to increase to 12°. The errors in the measurement are quantified with Monte Carlo techniques. The response function fit gives a significantly better estimate of the divergence than a Gaussian fit.

X-ray spectroscopical and microscopical methods are used for the determination of the spectral and spatial distribution of X-ray intensity of laser-produced plasmas. The use of Bragg reflections of two-dimensionally bent crystals enables the X-ray microscopical imaging in narrow spectral ranges (Δλ/λ = 10−4 to 10−2) with wavelengths 0.1 nm < λ > 2.6 nm. It is possible to adapt, in the X-ray microscope, the distances, magnification, position, and width of the spectral window to the special conditions of the laser facility. Manufacturing and testing of the two-dimensionally bent crystals requires a great deal of effort. It was demonstrated that a spatial resolution of about 5 μm was achieved, and that the experimentally determined reflectivity was found to be in close agreement with the dynamical theory of X-ray interferences. Due to high luminosity of the X-ray microscope, in experiments with laser-produced plasmas it was necessary to attenuate the radiation with aperture-limiting diaphragms or filters down to 0.01–1% of the original intensity in the case of a magnification of about one. Emission of the resonance line W 1–2, the intercombination line of helium-like ions, and Lyman alpha line were imaged simultaneously with a three-channel microscope. Such images form the foundation for establishing the Ne(r), Tz(r) maps.

For first investigations of hot dense matter produced by intense heavy-ion beams we built an electrostatic quadrupole doublet that focused Ar+and Kr+ ions of 45 keV/amu after acceleration through the radio frequency quadrupole (RFQ) accelerator at the GSI onto a small spot of approximate area 1 mm2. This beam then deposited a specific beam power of about 1.5 GW/g to targets.

The radiation hydrodynamics of a 125-μm thin carbon layer illuminated by thermal radiation of Trad = 200 eV temperature is studied within a multigroup radiation model. Whereas a major part of the incident photons deposit their energy by K-shell absorption close to the surface, soft photons below the K edge and hard photons (hv > 800 eV) penetrate deeper into the material and drive a heat wave with a sharp front. A nonablated mass fraction of 20% is accelerated with a hydrodynamic efficiency of 11%. About half of the incident radiation flux is reemitted by the heated carbon plasma. The heat front trajectory can be reproduced by the analytical heating wave model when effective opacity parameters corresponding to the most penetrating components are used.

Analyses are given for beam generations of three kinds of charged particles: electrons, light ions, and heavy ions. The electron beam oscillates in a dense plasma irradiated by a strong laser light. When the frequency of laser light is high and its intensity is large, the acceleration of oscillating electrons becomes large and the electrons radiate electromagnetic waves. As the reaction, the electrons feel a damping force, whose effect on oscillating electron motion is investigated first. Second, the electron beam induces the strong electromagnetic field by its self-induced electric current density when the electron number density is high. The induced electric field reduces the oscillation motion and deforms the beam.

In the case of a light ion beam, the electrostatic field, induced by the beam charge, as well as the electromagnetic field, induced by the beam current, affects the beam motion. The total energy of the magnetic field surrounding the beam is rather small in comparison with its kinetic energy.

In the case of heavy ion beams the beam charge at the leading edge is much smaller in comparison with the case of light ion beams when the heavy ion beam propagates in the background plasma. Thus, the induced electrostatic and electromagnetic fields do not much affect the beam propagation.

The design for an advanced, flash-lamp-pumped Nd: glass laser for inertial confinement fusion (ICF) research and applications is summarized. The laser consists of multiple beam lines, each of which delivers 145-kJ, O.35-μm, 8-ns laser pulses, with pulse shape and bandwidth capabilities consistent with requirements for driving ICF capsules to high gain.

The temperatures and the densities of plasmas produced by high-power lasers vary widely but in certain cases are similar to those found in astrophysical plasmas. In recent years our understanding of intense laser–matter interaction and the evolution of the resulting

plasma has increased to the point where experiments can be designed to produce plasmas that allow astrophysical models to be tested. In this paper I review experimental work on laser-produced plasmas that is relevant to astrophysics. In the fields of highlyionized ion line identification and radiative opacity, relevant measurements have already been performed. Other experiments that could be performed with current laser facilities, including studies of X-ray nebula plasmas and complex radiation line transport, are described. In addition, experiments to investigate plasmas under more extreme conditions, which may be achievable with more powerful lasers, are mentioned.

Layered-targets experiments at 1.06-μm laser light have been performed in order to measure mass-ablation rate ṁ and ablation pressure Pa as a function of absorbed laser flux Ia and laser wavelength λL at irradiances of 1011-4.5 × 1012 W/cm2. The results can be put in the forms ṁ(g/cm2-s) ≈ 4.25 × 105[Ia(W/cm2)/1014]5/9(1 μm/λL)4/9 and Pa(Mbar) ≈ 20[Ia(W/cm2)/1014]7/9(1 μm/λL)2/9, which are consistent with the estimates obtained from a steady-state self-regulated model for plasma heating and with hydrodynamical simulations. Results show also a small lateral energy transport.

This paper reviews the current status of high-power KrF lasers and considers their prospects for future development. The main laser requirements imposed by target physics considerations are identified and KrF lasers are shown to be uniquely capable of satisfying them. Some design considerations are given for (a) ultrashort-pulse high-power systems, (b) high-power coherent beam generation using Raman amplifiers, and (c) incoherent beam amplification.

Some peculiarities of using negative ions for accelerators and CTR are examined. Highpower beams of fast atoms obtained by charge exchange of negative ions can have advantages over positive ion beams for inertial confinement fusion (ICF) since they do not experience any deviations, instabilities, and scattering. H− current up to 7 kA in a 100–200 ns pulse with densities up to 200 Å/cm2 and a voltage of 0.8 MV were obtained in experiments on magnetically insulated diodes at the Lebedev Physical Institute. Diagnostics of high-power H− beams are described. Experimental results on cathode plasma formation by surface discharge on a dielectric initiated by a bipolar prepulse or by laser illumination are presented. The dependence of H− yield on cathode current was determined and experiments on plasma stabilization are described. It is concluded that 1 kÅ/cm2 of H− can be obtained.