Characteristic X-rays generated by high-intensity laser interaction with solids were investigated and used for determining the resulting hot electron populations. Spectrally as well as spatially resolved data are evaluated for this purpose. The experimental data were compared with Monte Carlo simulations to determine the electron energy distribution and geometric features of the electron beam. These results are in good agreement with PIC simulations. The self-generated low-resistivity channel of the electron beam results in a distinct difference in the generated rear-side X-ray spot when the electron beam propagates in an insulator rather than a metal. Self-generated electric fields prevent electron propagation into the vacuum. This fact is used for demonstrating photopumping of cobalt with copper Kα radiation, an experiment relevant to innershell X-ray laser schemes. The emission of cobalt is compared with that of nickel, which is not photopumped by copper Kα, and is found to be enhanced by a factor of 2.5.

In this paper, a new technical scheme of high-voltage, long-pulse generator, mostly based on solid-state power devices, including magnetic pulse compressor, Blumlein-type rolled strip pulse-forming line (RSPFL) and inductive voltage adder (IVA), is proposed and investigated numerically and experimentally. The generator has potential advantages of high average power level, high repetitive rate capability, long lifetime, and long pulse achievability, which meet the requirements of military and industrial application of the pulsed power technology. Specifically, a two-stage magnetic pulse compressor was set up with iron-based amorphous cores. Total compression ratio of the device is approximately 12 and the achieved voltage efficiency is up to 92%. Low impedance, long-duration Blumlein-type RSPFL was established with characteristic impendence and electrical length of 3 Ω and 100 ns, respectively. Mylar film was selected as the solid-state dielectric. Increased by a four-stage IVA, typical quasi-square pulse was obtained with peak current of 2.3 kA and duration over 200 ns. As the resistance of the dummy load was measured to be 60 Ω, the peak voltage was approximately 138 kV. Experiments show reasonable agreement with numerical analysis.

A general and powerful formalism has been developed for computation of energy-loss spectra of penetrating charged particles in the presence of charge exchange. Options on the input side are the cross sections for electron capture and loss, transition rates for radiative and nonradiative spontaneous processes and their associated energy losses or gains, and finally, cross sections for all processes that contribute to particle stopping but are not associated with charge exchange. The formalism generates an n × n transfer matrix, where n is the number of states needed for an adequate description of the projectile under consideration. This matrix delivers the joint distribution of energy loss and exit charge state for a given incident charge state and energy.

The formalism can be used in principle as an alternative for Monte Carlo simulation, but until now we have concentrated on direct evaluation of key experimental parameters related to the energy-loss spectrum integrated over all exit charge states, in particular, mean energy loss, straggling, and skewness. Generally, valid analytic expressions have been found for these quantities, each of which can be separated into a stationary term representing chargestate equilibrium and a transient depending on the incident charge state. A brief survey is given of current analytic and numerical efforts addressing other experimental parameters.

The mechanisms of level population in high pressure gas lasers pumped by ionizing radiation at the 3p-3s transitions of neon, the d-p transitions of argon, krypton, xenon, and triplet lines of mercury are analyzed. It is shown that dissociative recombination of molecular ions with electrons is not the basic process responsible for populating the p levels of inert gas atoms. It is assumed that the most likely channel for d-level population is direct excitation of atoms by secondary electrons and excitation transfer from buffer gas atoms, with p levels being populated by transitions from upper levels. Dissociative recombination of mercury molecular ions with electrons is the basic process responsible for populating the 73S1 level of mercury atoms.

This study investigates the interaction of picosecond laser pulses with sapphire and brass in air using scanning electron microscopy. A picosecond laser system operating at a wavelength of 785 nm, pulse width of 110 ps, and variable repetition rate (1–1000 Hz) was used in this study. The pulse width applied in this work was not widely investigated as it lies in the gap between ultrashort (femtosecond) and long (nanosecond) pulse width lasers. Different surface morphologies were identified using secondary electron and backscattered electron imaging of the ablated material. Thermal ablation effects were more dominant in brass than in sapphire. Exfoliation and fractures of sapphire were observed at high laser fluence. Compared with brass, multiple laser pulses were necessary to initiate ablation in sapphire due to its poor absorption to the incident laser wavelength. Ablation rate of sapphire was lower than that of brass due to the dissipation of a portion of the laser energy due to heating and fracturing of the surface.

We investigate the influence of the initial size of the proton layer on proton acceleration in the interaction of high intensity laser pulses with double-layer targets by using two-dimensional particle-in-cell code. We discuss the influence of proton layer initial sizes on the cut-off energy, energy spread, and divergence angle of proton beam. It is found that Coulomb explosion plays an important role on the proton cut-off energy. This causes the cut-off energy to increase for increasing proton layer thickness, at the expense of energy spread. The proton divergence angle reaches a peak value and then falls again with increasing the width. Proton divergence angle grows with target thickness. It is found that there is an optimal thickness to obtain the narrowest energy spread, which may provide an effective method (change the size of proton layer) to obtain high quality proton beams. This work may serve to improve the understanding of sheath field proton acceleration.

This paper investigates prospects of utilizing a high-power laser-driven target-normal-sheath-acceleration proton beam for the experimental demonstration of the magnetic self-focusing phenomenon in charged particle beams. In the proposed concept, focusing is achieved by propagating a space-charge dominated ion beam through a stack of thin conducting and grounded foils separated by vacuum gaps. As the beam travels through the system, image charges build up at the foils and generate electric field that counteracts the beam's electrostatic self-field — a dominant force responsible for expansion of a high current beam. Once the electrostatic self-field is “neutralized” by the image charges, the beam currents magnetic self-field will do the focusing. The focal spot size and focal length depends on the choice of a number of foils and distance between foils. Considering the typical electrical current level of a target-normal-sheath-acceleration proton beam, we conclude that it is feasible to focus or collimate a beam within tens of millimeters distance, e.g., using 200–1000 Al foils, 0.5 µm thick each, with foil spacing ranging from 25 µm to 100 µm. These requirements are within technical capabilities of modern target fabrication, thus allowing the first possible demonstration of the pinch effect with heavy ion beams.

The guiding of a laser beam in a plasma channel formed by a short laser prepulse is investigated. Due to the self defocusing of an ionizing short laser prepulse, the plasma channel formed is axially nonuniform. When a delayed second laser beam is allowed to propagate through such a preformed plasma channel, convergence and divergence of the beam is observed due to the relative competition of the refraction and diffraction phenomenon. We have solved the wave equation governing the propagation characteristics of an ionizing prepulse and a delayed pulse by the moment theory approach. Results have been compared with the paraxial ray model of Liu and Tripathi (1994). The moment theory predicts the propagation of guided laser beam over several Rayleigh lengths.

A NIF-type hohlraum target (Lindl 1995; CEA 1995) is analyzed in an integrated calculation that uses last revision (4.2) of MULTI2D code (Ramis et al. 1992). The numerical simulation includes: Lagrangian mesh, tracking of laser beams, inverse bremsstrahlung absorption, 3D radiation transport, radiation-induced hydrodynamics of casing and window panes, and radiatively driven capsule implosion. Electron heat conduction (Spitzer with flux limiter), tabulated Equations of State (Sesame), and LTE opacities are also included. Detailed results on hydrodynamic evolution of the system, compression symmetry, and energy balance are also provided.

This issue of Laser and Particle Beams includes papers presented at the “Workshop on Simulations of Ultra Intense Laser Beams Interaction with Matter” held in Bordeaux, France, from 14 to 16 April, 2003. This workshop was organized jointly by the Polytechnic University (Madrid, Spain), University of Bordeaux 1 (Talence, France), University of Milano-Bicocca (Milan, Italy), and Commissariat à l'Energie Atomique (CEA, France), sponsored by the European Science Foundation (ESF), University of Bordeaux 1, and CEA.

We present a novel experiment for the generation of sculpted pulsed indium atomic beams of regular arrays in one and two-dimensions via rear side ablation of indium by two and four beams interference pattern using second harmonic of high power Nd: YAG laser under high vacuum (10−5 Torr).

The project ITEP-TWAC (Tera Watt Accumulator) being in progress at ITEP (Moscow) requires He-like ions for non-Liouvillean injection into the storage ring to accumulate ≈2·1013 particles with medium masses up to 59Co25+. Powerful lasers were found to be the best choice for those ions production. This work presents the experimental results of highly charge ion generation in plasmas produced by the second harmonic of Nd-glass laser facility with a total energy E ≤ 50 J and pulse duration of about 2.5 ns at GPI (Moscow). Ti and Ta targets were under investigation. An electrostatic ion energy analyzer and an ion charge collector were used to measure the ion charge state spectra at a 3-m distance from the targets. 5·107 He-like Ti ions per cm2 within 1 μs pulse as well as 107 Ta+41 per cm2 within 0.8 μs were observed.

We present experimental results on three dynamic properties of very strong double layers observed in a triple plasma device. First, it is observed that when an inductance of sufficient size is inserted in series with the external bias supply used to produce the double layer, disruptions in the plasma current occur accompanied by disruptions in the double layer potential. Second, it is observed that with all external reactances reduced as much as possible, a sort of jitter-motion occurs in the position of the double layer around its equilibrium position. Third, when the external bias supply is pulsed, the initial potential distribution is observed to have an essentially uniform slope, as in the case of a vacuum capacitor. The disruption phenomenon may be explained in terms of the behavior of the potential structure as a function of the bias voltage and this explanation is discussed along with the experimental evidence for its validity. A comparable understanding of the other two phenomena has not been achieved, but in both cases there are qualitative differences between the behavior reported here and what has been observed in Q-machines and these differences are discussed.

Kα satellite spectroscopy can be a valuable technique for diagnosing conditions in high energy density plasmas. Kα emission lines are produced in intense light ion beam plasma interaction experiments as 2p electrons fill partially open Is shells created by the ion beam. In this paper, we present results from collisional-radiative equilibrium (CRE) calculations which show how Kα emission spectroscopy can be used to determine target plasma conditions in intense lithium beam experiments on Particle Beam Fusion Accelerator-II (PBFAII) at Sandia National Laboratories. In these experiments, 8–10 MeV lithium beams with intensities of 1–2 TW/cm2 irradiate planar multilayer targets containing a thin Al tracer. Kα emission spectra are measured using an X-ray crystal spectrometer with a resolution of λ/∆λ = 1200. The spectra are analyzed using a CRE model in which multilevel (NL ∼ 103) statistical equilibrium equations are solved self-consistently with the radiation field and beam properties to determine atomic level populations. Atomic level-dependent fluorescence yields and ion-impact ionization cross sections are used in computing the emission spectra. We present results showing the sensitivity of the Kα emission spectrum to temperature and density of the Al tracer. We also discuss the dependence of measured spectra on the X-ray crystal spectral resolution, and how additional diagnostic information could be obtained using multiple tracers of similar atomic number.

In conventional inertial confinement fusion (ICF), a high power laser system is used to compress a cryogenic target and create energy. One of the challenges for ICF cryogenics is producing the homogeneous and uniform fuel on the inside surface of a spherical polymer shell. In this report, we will discuss a conceptual approach based on freestanding targets and the results of our recent and current developments.

The temporal correlation between neutron and hard X-ray (HXR) emissions from a hundred joules plasma focus device (PF-400J) was studied. A method, time history analysis, to estimate the time of origin of neutrons with respect to HXRs is applied. In most of the discharges, it was found that neutrons are originated before HXRs in the axial direction and after HXRs in the radial direction. In some discharges, the time difference between HXRs and neutrons origin was found large enough, so that it can be interpreted that those neutrons would have been originated before the pinch. A qualitative discussion is conjectured to explain the experimental observations.

Conversion of CH4 molecule into higher hydrocarbons using two different wavelengths of 248 nm KrF laser and 355 nm of third harmonic of Nd:YAG laser is studied experimentally and theoretically. The stable products are analyzed and the effect of pressure on conversion of methane is measured. The detected reaction products are C2H2, C2H4, and C2H6. The conversion efficiency of 33.5% for 355 nm in comparison to 2.2% conversion for 248 nm for C2H2 is achieved. The potential of laser parameters as an important variable in controlling of final products is investigated.

Laser-produced copper plasma in the presence of variable transverse external magnetic field in air is investigated using optical emission spectroscopy. As the magnetic field increases from 0 to 0.5 T, the intensity of Cu I lines initially increases and then decreases slightly at a 0.5 T. The maximum intensity enhancement of all five Cu I lines occurs at a magnetic field of 0.3 T. The increase in intensity is attributed to an increase in the electron impact excitation of Cu. With increase in magnetic field, the electron density and temperature were found to increase due to increase in the confinement of plasma. The difference in intensity enhancement factor is due to the difference in excitation rate coefficients. The surface morphology of irradiated copper target is also analyzed at 0.3 T magnetic field at which the density is maximum and reveals the formation of Cu/Cu2O/CuO nanoparticles (NPs). More NPs are formed at the peripheral region than at the central region of the ablated crater and is due to the oxidation of Cu atom in the plasma–ambient interface. The larger grain size of nanostructures in the presence of magnetic field is due to an increase in the inverse pulsed laser deposition. The intensity of Raman peak of Cu2O decreases in the presence of magnetic field and that of CuO increases which is more likely due to conversion of Cu2O to CuO. The photoluminescence intensity of CuO increases in the presence of magnetic field due to the phase transformation of Cu2O to CuO in agreement with the result of Raman spectroscopy.

Interaction between energetic electrons and a circularly polarized laser pulse in a relativistic plasma channel is studied. Laser radiation can be resonantly absorbed by electrons executing betatron oscillations in the channel and absorbing angular momentum from the laser. The absorbed angular momentum manifests itself as a strong axial magnetic field (inverse Faraday effect). The magnitude of this magnetic field is calculated and related to the amount of the absorbed energy.

Various gas lenses are briefly reviewed, together with their imperfections. We discuss the applicability of these lenses as objectives for telescopes and as the final focusing element of high-power laser systems: cw lasers in industry and pulsed lasers for plasma research. A novel phase conjugate experiment employing a gas lens is described. Pulsed gas lenses are proposed as a solution to the problems of high laser fluence and radiation damage in post-break-even fusion experiments.