The emissivity of the rear of a shocked foil is spectrally and temporally resolved by coupling a transmission grating (1000 I/mm) and an X-UV streak camera (with a low density Csl photocathode), providing a high temporal resolution over a large spectral range. The shock is generated with two techniques: direct illumination of a single Al foil with a 0.26 μm wavelength laser (ablation pressure ≈ 50 Mbars) or by colliding an Al foil with a laser accelerated CH foil (generated pressures greater than 100–200 Mbars). Different thicknesses of Al are used in single foil experiments, and different initial spacing and impacted foil thicknesses are used in double foil experiments. Double foil experiments indicate that targets can be optimized for high pressure generation, and single foil experiments show that there is a radiative heat wave, around 200 eV, due to the heating of the foil by X rays emitted in the ablated region during the laser pulse. Double foil experiments have been compared with 2-D hydrodynamic Lagrangian simulations and single foil experiments have been compared with 1-D hydrodynamic Lagrangian simulations taking into account radiative heat transfer.

By using a linear analysis, a new type of thermal self-focusing instability without inverse bremsstrahlung absorption is analyzed. In the model it is assumed that part of the light is absorbed only at the critical surface and that the heat conduction is restricted to a layer on the target. Perturbations with wavelengths comparable to target radius are studied.

The Heavy Ion Fusion Accelerator Research (HIFAR) program of the U.S. Dept. of Energy has for several years concentrated on developing linear induction accelerators as Inertial Fusion (IF) drivers. This accelerator technology is suitable for the IF application because it is readily capable of accelerating short, intense pulses of charged particles with good electrical efficiency. The principal technical difficulty is in injecting and transporting the intense pulses while maintaining the necessary beam quality. The approach used has been to design a system of multiple beams so that not all of the charge has to be confined in a single beam line. The beams are finally brought together in a common focus at the target. This paper will briefly present the status and future plans of the program, and will also briefly review systems study results for HIF.

Plasmas of high reproducibility that are suitable for beam-plasma experiments are generated by a pulsed-power z-pinch discharge. The z-pinch device is designed as a plasma target for the investigation of ion beam-plasma interactions. The dynamic plasma state is characterized by the electron density, the electron temperature, and the magnetic field distribution, which are observed using time-resolved diagnostics. For z-pinch discharges in hydrogen, average electron densities of up to (2.6 ± 0.1) × 1018 electrons/cm3 were measured interferometrically. Electron temperatures in the range 2–7 eV are determined by time-resolved spectroscopy. The reproducibility of the electron density of the z-pinch discharge in terms of shot-to-shot fluctuations is estimated to be better than 3%. This is a favorable condition for performing beam-plasma experiments.

Recent direct-drive implosion experiments on the GEKKO XII laser with plastic hollow shell targets demonstrated compressed densities of ∼600 g/cm3 (∼600 times liquid density) at a temperature of ∼0.3 keV. The highly compressed core plasmas are indicated to be strongly coupled (average Coulomb energy/thermal energy ≈5) and partially degenerate (thermal energy/Fermi energy ≈0.3). The diagnostic method based on the secondary nuclear fusion reactions is presented to prove the electron degeneracy in the highly compressed core plasma. The yield ratio of the secondary DT neutrons to the primary DD neutrons in such highly compressed core plasmas was calculated with inclusion of the strong Coulomb-coupling effects, the varied degrees of the electron degeneracy, and the electronic shielding effects. It was found in our calculations that there is a significant dependence of the yield ratio on the compressed core density. For the plastic targets at the electron temperature of ∼0.3 keV, the yield ratio increases from 9 × 10−4 to 8 × 10−3 for densities from 10 to 1000 g/cm3. The preliminary experiments using deuterated plastic hollow shell targets suggested that the enhancement of the yield ratio provided evidence of the electron degeneracy.

The parameters of self-generated electron beams have been measured and correlated to the dynamics of a 60 kV, 28 kJ plasma focus. The electron beam emission occurs in two periods: the first corresponds to the initial formation and disruption of the pinched plasma and terminates with the disruption of the plasma column, and the second period occurs after the breaking up of the focus plasma. The first period is characterized by high-energy electron beams, whereas in the second period the electron beams have lower average energies but higher currents. A relativistic electron beam is found to occur around the time of first compression, when the plasma is observed to be macroscopically stable, in contrast to measurements obtained from machines with similar energies but operating at lower voltages. The plasma X-ray emission is observed to be closely related to the electron beam characteristics. Possible mechanisms for the formation of the electron beams observed are discussed.

Focusing processes of rotating and propagating proton beams in a neutral hydrogen gas are studied numerically by using a two-dimensional hybrid code. Processes including beam impact ionization, plasma avalanche and field emission are taken into consideration. The plasma formation time depends on the initial gas density and the beam intensity. When 2-Torr neutral gas is filled initially, enough plasma density is created by the rising part of the beam pulse, so that the main pulse is focused and forms a rotating and propagatingbeam configuration.

We develop a renormalized technique to evaluate the stopping power for a test ion traversing a hot classical plasma. We show that the linear description of energy loss begins to break down at a distance much greater than the classical distance of closest approach. The close-collision contribution to the stopping power is on the same footing as that for distant collision. As a new result, we show the existence of nonanalytical terms in addition to the usual Z2 contribution to the stopping power.

A method for the compression of magnetic flux inside a cylindrical liner imploded by laser beams is analyzed using a thin shell model. Simple scaling relations are derived for a number of key parameters. The potential of this scheme, as a fast-rising magnetic pulse generator, is explored based on the scalings obtained.

In a series of experiments done at the Laboratory for Laser Energetics of the University of Rochester, Kr/Ar- and Ar-filled polymer shell targets were imploded using the 24 beam (351 nm) 2 KJ Omega laser system. We present results from the analysis of the X-ray line spectra recorded on these experiments. In particular, we discuss the Stark broadening of L-shell spectra, its application to plasma diagnostics, and the advantages of recording time-resolved spectra. We also show results from radiation-hydrodynamics modeling of these experiments.

The calculation of the multigroup opacities using several different atomic physics models is the main goal of this work. The atomic data, such as energy levels, bound-electron populations, oscillator strengths and effective charges are worked out by two atomic physics models using the average-atom concept. The result achieves multifrequency opacities. These are weighted with the Planck function or the real radiation field, making up finally the multigroup opacities in the selected number of groups.

The charge state and the level populations of ionic projectiles that are stopped in hydrogen plasma are calculated in the average ion model. It is shown that in available experimental systems the parameters can be chosen such that the end of the range will occur inside the plasma column. The predicted narrow region over which recombination occurs can be used as a check on plasma stopping-power theory and as a direct measurement of the range, using spectroscopic diagnostics.

A self-similar analysis of supersonic compression of a “screw-pinch” plasma is carried out that generalizes earlier analyses of pure θ-pinch and Z-pinch implosions. Solutions are found for various implosion modes. It is shown that the screw-pinch plasma implosion differs qualitatively from θ-pinch and Z-pinch implosions.

Until now a theoretical derivation of scaling laws for the effective charge Zeff of heavy ions penetrating matter has been lacking, although for cold gaseous targets there are well-established empirical relations of the form Zeff/Zp = f (up/ZpγZtδ), where vp and Zp are, respectively, the velocity and nuclear charge of the projectile ion, Zt, is the nuclear charge of the target atoms, and γ and δ are the scaling exponents. We show that the scaling exponents may be derived from an investigation of loss and capture rates. The treatment is based on the Bohr-Lamb criterion. This very crude criterion yields γ = 2/3. Our analysis allows the formulation of a modified criterion, yielding γ = 0.528 for cold gas, which deviates by only 2% from the often-used empirical Betz formula. The dependence on Zt, in cold gas is oscillatory and cannot be described by a simple exponent δ. The treatment is also applied to a fully ionized plasma, resulting in Zerf/Zp = f (upZt0.27/Zp1.39).

Calculations of the electron impact excitation cross sections and deposition efficiencies for singly ionized argon with electrons of energies up to and including relativistic values have been made using the first Born approximation and the generalized oscillator formalism. Deposition efficiencies for fast electrons were generated from the Peterson and Green integral equation. Cross sections and efficiencies were produced for 29 transitions from the ground state configuration of Arii to excited energy levels with (Ne)3s23p44s and (Ne)3s23p43d configurations and for 40 transitions between excited energy levels from 4s and 3d to 4p orbitals. Efficiencies are constant for electron energies above 1 keV to 10 MeV. Electrons ejected from inner shells contribute up to 12% of the efficiency of the transition for electrons above 10 keV.

Recently, we have developed a one-dimensional radiation-hydrodynamics code called SARA that implicitly solves the multigroup radiation transport equations. A high-order differencing algorithm as well as multifrequency-grey synthetic acceleration techniques are used to obtain a robust algorithm that can be extensively used for radiation energy transport problems and radiative regimes.

The major goal of writing this code has been to explore the performance of the indirectdrive light ion beam capsules. Numerical results show that the efficiency of the energy conversion into soft X rays and the power flux amplification factor are high enough to efficiently compress the fuel capsule for a wide range of ion beam parameters.

A model of an electron beam interacting with neutral argon was developed by solving the chemical kinetic rate equations for the time-dependent populations of ground and excited levels of Arl and Aril as well as the populations of electron energy groups. Intensities of spectral lines were calculated, from predicted population densities and Einstein coefficients, and compared to experimental results.

The thermal plasma is generated during the beam pulse and persists for some time after the pulse is terminated. Low energy levels of Arii with a 4s or 4p valence electron have similar time profiles to the plasma density. However, high energy levels of Aril with a 4p′ or 4p′ valence electron have similar temporal profiles as the beam current. They are populated predominantly by direct ionization and exceed levels populated by thermal electrons. The 4p′ levels decay rapidly to 4s′ levels, which have very high beam deposition efficiencies for being pumped back to the 4p′ levels. In this way, certain transitions such as 4s′–4p′ in ArII are pumped directly by the electron beam. Without direct ionization, these transitions would be negligible compared to those transitions which have lower energy levels.

The results of the interaction of laser beams integrated by an optical system composed of two arrays of 256 elements each are presented. Optical dark-field shadowgraphy as well as interferograms show significant smoothing effects when compared with experiments performed in the same conditions but without beam integrators.

General aspects of the excitation of matter with heavy-ion beams are discussed. Lasers in the wavelength region between 1 and 3 μm in rare-gas mixtures pumped with 1.9-GeV xenon, 100-MeV sulphur, 3.6-MeV argon, and 3.3-MeV helium ions are described as examples for lasers pumped by heavy-ion beams. The beam power ranges from a few watts (dc) to about 1 MW during short pulses of about 1-ns length. Optical gain can be measured with an intracavity method. Data on the shape of the volume excited by a 100- MeV 32S beam are shown. An experimental setup for time-resolved optical spectroscopy in a wide wavelength region between a few nanometers and about 700 nm is described. Emission spectra of rare gases excited by heavy-ion beams are discussed and optical gain on ion lines and excimer bands is estimated for different target and beam parameters. Collisional processes in the target gas were studied by time-resolved optical spectroscopy. Population densities of selected 3p levels in Ne I, II, and IV and rate constants for collisional depopulation of excited levels were determined. Experiments planned at the heavy-ion synchrotron SIS at Gesellschaft für Schwerionenforschung in Darmstadt are discussed.

A numerical analysis is presented of the electrostrictive filamentation of an electromagnetic wave in the presence of a reflected wave. Maxwell's equations are solved in the steadystate simultaneously with one fluid hydrodynamics and a simplified equation of state to obtain a self-consistent solution. The threshold for filamentation is shown to be often below the laser intensity necessary to modify the plasma density profile, however, even weak profile modification substantially affects the filamentation.