High-sensitivity interferometry measurements of initial density distributions are reviewed for a wide range of gas-puff nozzles used in plasma radiation source (PRS) z-pinch experiments. Accurate gas distributions are required for determining experimental load parameters, modeling implosion dynamics, understanding the radiation properties of the stagnated pinch, and for predicting PRS performance in future experiments. For a number of these nozzles, a simple ballistic-gas-flow model (BFM) has been used to provide good physics-based analytic fits to the measured r, z density distributions. These BFM fits provide a convenient means to smoothly interpolate radial density distributions between discrete axial measurement locations for finer-zoned two-dimensional MHD calculations, and can be used to determine how changes in nozzle parameters and load geometry might alter implosion dynamics and radiation performance. These measurement and analysis techniques are demonstrated for a nested-shell nozzle used in Double Eagle and Saturn experiments. For this nozzle, the analysis suggests load modifications that may increase the K-shell yield.

We report the results of measurements aimed to check the phase lock of time-delayed, collinear, harmonic pulses and to verify the possibility of performing Ramsey-like spectroscopy in the XUV. We demonstrate that for harmonics of medium order and for the peak intensities available with our laser system, the generation of collinear phase-locked harmonic pulses is indeed possible and that such pulses can be used to achieve high-resolution spectroscopy in the short-wavelength region.

The goal of the experiments on “Module A-5” and S-300 machines for some 15 years was to study the “liner-converter” inertial confinement fusion (ICF) scheme. A new class of fast instabilities of z pinches was studied both in experiments and in analytical theory. Stabilization of the light liner has been achieved by means of an extrinsic magnetic field. Formation of thin overheated current-carrying shells has been predicted analytically and seems to be really observed. Both theory and simulations predict growing Te and heat flux onto the converter by using heterogeneous z pinches with spatially separated regions of efficient energy exchange and of efficient heat conductivity. In our first experiments of this kind, impurities were inserted by means of placing thin glass fibers into a He jet. Growing intensity of the spectral lines of He-like chlorine from the cathode surface confirms the growth of heat flux. Theoretical investigations and 2.5-D simulations were devoted to some basic points of this program.

Analytical interest in nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) is related to their high mutagenicity and potential presence in a variety of environmental media such as diesel exhaust and urban air particulate matter. Furthermore, fundamental interest in these molecular systems stems from the photophysics of the labile NO2 functional group, which has been investigated using mass spectrometry. The nitro-PAHs, 1-nitronaphthalene, 9-nitroanthracene, and 1-nitropyrene, have been studied using both femtosecond (λ = 395 and 790 nm) and nanosecond (λ = 266 nm) lasers coupled to a reflectron time of flight mass spectrometer. Analysis of mass spectra taken over a range of intensities (1014–1015 W/cm2) has demonstrated that structurally specific ions can be observed for each molecule, with little or no fragmentation at lower intensities. It has also been found that an intact parent ion can be detected using femtosecond ionization at 395 nm in each case. This work demonstrates the potential use of laser desorption/femtosecond laser mass spectrometry (LD/FLMS) as an analytical technique for the detection of nitro-PAHs and other environmental pollutants and as a means of studying the photodynamics of labile molecular systems.

We report on the observation of neutrons resulting from a thermonuclear reaction D + D = 3He(0.82 MeV) + n(2.45 MeV), taking place in plasma created on the surface of a modified solid-state target. The plasma was produced by a 200-fs laser pulse with intensity in excess of 1016 W/cm2 and energy of only 0.3 mJ.

High-amplitude plasma wake waves are excited by high-density relativistic electron bunches (REB) moving in a plasma. The wake-fields can be used to accelerate charged particles, to serve as electrostatic wigglers in plasma free-electron lasers (FEL), and also can find many other applications. The electromagnetic fields in the region occupied by the bunch control the dynamics of the bunch itself. This paper presents the results of 2.5-dimensional numerical simulation of the modulation of a long REB in a plasma, the excitation of wake-fields by bunches in a plasma, in particular, in magnetoactive plasma. The previous one-dimensional study has shown that the density-profile modulation of a long bunch moving in plasma results in the growth of the coherent wake-wave amplitude. The bunch modulation occurs at the plasma frequency. The present study is concerned with the REB motion, taking into account the plasma and REB nonlinearities. It is demonstrated that the nonlinear REB/plasma dynamics exerts primary effect on both the REB self-modulation and the wake-field excitation by the bunches formed. We have demonstrated that a multiple excess of the accelerated bunch energy εmax over the energy of the exciting REB is possible in a magnetoactive plasma for a certain relationship between the parameters of the “plasma–bunch–magnetic field” system (owing to a hybrid volume–surface character of REB-excited wake-fields).

In this paper, we present and compare the two different XUV interferometric techniques using high-order harmonics that have been developed so far. The first scheme is based on the interference between two spatially separated phase-locked harmonic sources while the second uses two temporally separated harmonic sources. These techniques have been applied to plasma diagnostics in feasibility experiments where electron densities up to a few 1020 e−/cm3 have been measured with a temporal resolution of 200 fs. We present the main characteristics of each technique and discuss their respective potentials and limitations.

A computational study of tungsten wire array z pinches on the Z facility at Sandia National Laboratories shows that individual wires form a core–corona structure early in the current pulse. Further analysis indicates that at 1 mm or smaller interwire gap, the expanding and later merging wire plasmas prevent the growth of m = 0 sausage modes. Although a completely uniform shell is not observed in the simulations, the Hussey–Roderick profile—a characteristic of uniform shell implosions—is seen. Differences in shell characteristics between small- and large-diameter wires are observed, possibly explaining performance differences between these two arrangements.

The energy-momentum conservation law is used to investigate the interaction of pulses in the framework of nonlinear electrodynamics with Lorentz-invariant constitutive relations. It is shown that for the pulses of the arbitrary shape, the interaction results in phase shift only.

A method of creating all-optical devices for logic information processing is presented. The mechanism is based on virtual photon interaction in quantum field description, or dipole moment interaction in classical description. The device consists of two optical information bits channels and one optical bits channel of logic commands like AND, NOT, OR. A variety of logic operations can be achieved on one optical setup by polarization change of the logic bits which determines the logic commands. I present another application for the method as an information channels selector.

The high-order harmonic generation process was studied using laser pump pulses of different duration, down to 7 fs. The time profile of this kind of pulse corresponds to a few optical cycles at the fundamental frequency, and therefore a cycle-to-cycle variation of the maximum amplitude occurs. These facts violate the adiabatic approximation of the generation process, giving rise to new aspects of the physical process. The comparison of results with pulses in the two regimes are reported and discussed. The modeling of the complete generation and propagation process in three dimensions is also presented.

During the last few years, we have concentrated on developing plasma radiation sources (PRS) for the longer current rise time (up to 300 ns) of the direct-drive Decade Quad (DQ; Price et al., 1999). In particular, we have developed an argon gas-puff PRS that produces a high quality pinch with an ∼200-ns implosion time, twice the implosion time of typical z pinches. We have shown that large-diameter, solid-fill (i.e., the gas density is a smooth function of the radial distance rather than a discrete shell) gas puffs can achieve adequate heating and stability for long-implosion z pinches with good K-shell yield.

The wakefield acceleration driven by a single laser pulse in a narrow plasma-filled solid waveguide is considered. Parameters of the waveguide which provide the maximum energy gain of accelerated particles at a given length and peak power of the driver are found in the approximation of a relativistically weak driver. The obtained formulas are illustrated by calculating the electron energy gain achievable with the terawatt laser of Utsunomiya University.

Two of the key issues of a krypton fluoride (KrF) laser driver for inertial fusion energy are the development of long life, high transparency pressure foils (to isolate vacuum in the electron beam diode from a working gas in the laser chamber), and the development of durable, stable, optical windows. Both of these problems have been studied on the single-pulse e-beam-pumped KrF laser installation GARPUN. We have measured the transport of electron beams (300 keV, 50 kA, 100 ns, 10 × 100 cm) through aluminum-beryllium and titanium foils and compared them with Monte Carlo numerical calculations. It was shown that 50-μm thickness Al-Be and 20-μm Ti foils had equal transmittance. However, in contrast to Ti foil, whose surface was strongly etched by fluorine, no surface modification nor fatal damages were observed for Al-Be foils after ∼1000 laser shots and protracted fluorine exposure. We also measured the 8% reduction in the transmission of CaF2 windows under irradiation by scattered electrons when they were set at 8.5 cm apart from the e-beam-pumped region. However an applied magnetic field of ∼0.1 T significantly reduced electron scattering both across and along the laser cell at typical pumping conditions with 1.5 atm pressure working gas. Thus the e-beam-induced absorption of laser radiation in optical windows might be fully eliminated in an e-beam-pumping scheme with magnetic field guiding.

To understand in detail what happens with an imploding wire array would require one to account for many different processes beginning with the wire explosion and ending with the Rayleigh–Taylor instabilities. Haines (1998) has performed a heuristic analysis of the multiwire array implosion and suggested that the dynamics and behavior of the wire array pinch be divided into four distinct phases. These phases are as follows: the electrical explosion of an individual wire (Phase 1), merging of the wire plasmas and the current shell formation (Phase 2), running-in of the wire array (Phase 3), and the stagnation of the pinch at the axis (Phase 4).

A laser–plasma interaction experiment was performed in order to match effective conditions for wake-field electron acceleration. A 30-fs pulse was made to interact with a preformed plasma generated via the exploding foil technique from a 1-μm-thick plastic film. The irradiance of the femtosecond pulse in the plasma was 1020 Wcm−2. The interaction conditions were investigated via imaging and spectroscopy at the fundamental and the second harmonic of the laser frequency, both forward and backward. Our data clearly show that conditions suitable for electron acceleration are achieved close to the propagation axis and can be easily reproduced from shot to shot. In contrast, significant growth of instabilities occurs at the boundaries of the interaction region. These observations are consistent with a preliminary evidence of forward acceleration of high-energy electrons. Optical, X-ray, and γ-ray data obtained for different positions of the foil target with respect to the laser focal plane further support this promising scenario.

A multiwire screw pinch, a variant of a z-pinch load, is proposed as a means for further improvement of load performance for high-current 100-ns pulsed-power generators used for terawatt X-ray radiation. Wires twisted along a curved load surface are suggested to be an effective way to create an axial magnetic field and to generate and to maintain rotation of the subsequently formed plasma shell due to conservation of angular momentum. A multiwire screw pinch is predicted to mitigate the growth of the magneto-Rayleigh–Taylor instabilities, to provide a higher pinch compression ratio and more effective X-ray generation compared to classical z-pinch loads. A model based on the self-consistent simulation of the dynamics of a twisted plasma shell and the development of Rayleigh–Taylor (R-T) perturbations on a plasma surface is proposed to quantitatively study the effect of various physical factors on the generation of X rays. The model provides us with a tool for the analysis of processes that occur during the implosion of the plasma-shell–wire-core system. We plan for the R-T perturbations to break through the plasma shell at the moment when the internal radius of a shell becomes zero, where the greatest possible values of kinetic energy and X-ray radiation power ought to be obtained. The results of numerical simulations for the Sandia National Laboratories' Z generator are presented and discussed.

Brillouin backscattering instability is investigated in inhomogeneous collisional plasma. The slow-coupling equations for the instability in a medium with linear density ramp are obtained. For large inhomogeneity scale length, the homogeneous growth rate is found to be modified by a factor of

[1/square root(2) times square root(ω02/ (ω02 + νe2) + ω0/square root(ω02 + νe2))]

For the convective instability, the amplification factor is found to be

[Λ = (|γB0|2/2β)(ω02/ω02 + νe2)]

The presence of collisions leads to a reduction in both the growth rate and the amplification factor, where the threshold intensity for the instability to occur increases.

Flyer acceleration experiments are carried out using a KrF laser system with a pulse duration of 10–15 ns and an intensity of ∼1.0 × 1013 W/cm2. Three-layered targets (aluminum–polyimide–tantalum) are used. First, an average velocity of laser-driven tantalum flyers with a thickness of 4 and 8 μm is estimated. Then, in a collision of a flyer with a copper layer attached to a diamond plate, we measure a transit time of a shock wave in the diamond. The impact velocity is estimated based on the transit time and a numerical simulation. This numerical simulation also shows that the initial peak pressure caused by the impact of a 4-μm-thick flyer is kept at 11 Mbar for 12–13 μm in thickness. Finally, whether this thickness is enough for EOS measurements is discussed.

New fields of X-ray source applications (X-ray laser and high order harmonic generation) could appear if an intensity higher than 1012 Wcm−2 is reached. Following this goal, we have started a complete investigation of the X-ray beam wavefront both numerically and experimentally. The first XUV wavefront sensor has been developed and tested on different XUV sources. For a better comprehension of the experimental results, a numerical work (ray-trace code) has been performed. We present and discuss the first results obtained on the X-ray laser at 21.2 nm.