bluuebunny/crossref_metadata_2025 huggingface dataset:
Studies of hypervelocity impact problem by means of laser-target experiments—A new approach
Authors: Borodziuk S. R. , Kostecki J. L.
Published: March 2009

The paper presents experiments dealing with interaction of Nd-glass laser radiation with single and double planar Al foil targets. An ablatively accelerated thin foil may achieve high velocity which cannot be obtained in any other way (for the mass of the order of 10−7 g). It can be applied to investigate effects of collision between accelerated foil and planar metal target. The accelerated foil fragment may be regarded as a projectile. Craters arising in this way are similar to those obtained in hypervelocity impact (HVI) experiments. An additional comparison can be made with results of laser simulation method (LSM). The aim of our work was to find the scaling laws for the relative volumes of craters for the velocity range up to about 100 km/s. We should also like to compare results of both methods used by us: laser ablative acceleration method (LAAM) and laser simulation method with hypervelocity impact.
The spherical pinch: Generalized scaling laws and experimental verification of the stability of imploding shock waves in spherical geometry
Authors: Singh D. P. , Harith M. A. , Palleschi V. , Tropiano G. , Vaselli M. , Salingaros N. , Panarella E.
Published: March 2009

The Spherical Pinch (SP) is a particular variation of the inertial confinement scheme, in that the two criteria required for plasma fusion breakeven condition, namely the attainment of a sufficiently high plasma temperature and of a product nτ in excess of 1014 cm-3. sec, are satisfied through two separate mechanisms. The advantage of this approach is that the scaling laws for breakeven are easier to satisfy than in the classical inertial confinement scheme. The first derivation of the scaling laws for spherical pinch experiments (Panarella & Savic 1983; Panarella 1987) was obtained under the simplifying assumption of an infinitely small central plasma in a sphere reaching the required high temperature for fusion, and of an undefined time delay Δt between the creation of such central plasma and the launching of the peripheral shock waves used to contain the central plasma. The analysis reported in this paper removes these assumptions and derives scaling laws which are generalized in their parameters, in that they explicitly contain the radius Rp of the central plasma and the time delay Δt.
Spectral diagnostic of a resonantly laser created plasma
Authors: Bardet J. P. , Bobin J. L. , Dimarcq C. , Giry L. , Larour J. B. , Valognes J. C. , Zaibi M. A.
Published: March 2009

Plasma creation occurs when the frequency of a tunable dye laser is adjusted to the 589 nm D-doublet of the sodium atom. Occurrence and Stark broadening of emission lines in the fluorescence light are used as diagnostics. The time history of the electron density and temperature is inferred from these measurements. The peak electron density was found to be above 5 · 1016 cm−3 with a temperature lower than 1 eV.
Calculation of X-ray absorption structure above K-edge of laser shock-compressed aluminum
Authors: Djaoui A. , Hall T. A. , Albers R. C. , Rehr J. J. , Mustre J.
Published: March 2009

Aluminum sandwich foils can be compressed to more than twice the normal density by the use of shock waves generated by laser beams. We present calculations of the K-edge absorption structure of two fold compressed aluminum, and compare the results with experimental data. The atomic potential is calculated using a spherical band-structure model with Fermi-Dirac statistics for the electrons. The structure above the K-edge is calculated according to the Müller-Shaich formula for the propagating photo-electron. The mean free path of the electron is taken into account through a complex exchange correlation potential. An appropriate Debye-Waller factor is used to represent the effect of the relatively high temperature encountered in these experiments.
Research on the conversion effects of pulsed laser plasma electric signal
Authors: Lou Qihong
Published: March 2009

By focusing the TEA CO2 laser pulse onto a metal target in the vacuum cell, the backward jet of plasma produced by the laser pulse can create an electric pulse between the target and the cell wall. The effect of laser beam focusing parameter and vacuum condition on the conversion efficiency are investigated experimentally. The maximum output voltage is more than 300 V when the peak power density at the target surface is 1.4 × 109 W/cm2. The velocity of the plasma expansion is obtained by using separated collecting electrodes.
High-power laser beam shaping using apodized apertures
Authors: Lukishova S. G. , Pashinin P. P. , Batygov S. Kh. , Arkhangelskaya V. A. , Poletimov A. E. , Scheulin A. S. , Terentiev B. M.
Published: March 2009

This paper gives the results of the investigations of four types of apodized (soft) apertures for beam shaping of UV, visible and IR high-power lasers with near-Gaussian and flat-top transmittance. The apodized apertures (AA) are ≈3–45 mm in diameter, but the principles of fabrication of such apertures lends the possibility of apodizing beams with diameter <1 mm and >200 mm. The examples of studies of the AA in high-power lasers are presented. The possibility of avoiding the Fresnel diffraction ripples is proved experimentally.
Nonlocal electron transport in laser created plasmas
Authors: Mora P. , Luciani J.F.
Published: March 2009

The classical linear Spitzer-Härm formula has been shown to lead to an overestimation of the electron heat flux in laser-plasma interaction experiments. We briefly review the classical theory of heat transport in a plasma, and give a simplified demonstration of the Spitzer-Härm formula. The electron heat conductivity is calculated for a large value of the ion charge Z. Correction due to a finite value of Z is evaluated with a simplified electron-electron collision operator. We then show that in a steep temperature gradient, the collisional mean free path of the electrons that transport the energy may be larger than the scale length of the temperature gradient. In this case the Spitzer-Härm formula overestimates the actual heat flux in the main part of the temperature gradient, and predicts a too small heat flux slightly away from the location of the large temperature gradient.A nonlocal macroscopic formula, which is a sort of convolution of the Spitzer-Härm heat flux by a delocalization function, is shown to accurately describe the electron heat flow in both smooth and steep temperature gradients. This nonlocal formula for the heat flow is analytically justified. A selection of slightly different delocalization functions proposed in the literature is compared to the original one and to the results of Fokker-Planck calculations of the heat flow.
Model for the Stark broadening of plasmas created by laser interaction with matter
Authors: Calisti A. , Godbert L. , Meftah T. , Mossé C. , Stamm R. , Talin B.
Published: March 2009

A model for the Stark broadening of ions in a high-density plasma created by laser has been developed by taking account of the full effect of a two-component plasma. One of the objectives of the work was to include the effect of ion dynamics in an efficient way. This has been achieved by using a stochastic process for mixing the different components that constitute a line profile. With the systematic use of fast algorithms, a code has been developed with the ability of treating complex atomic structures.
Application of the Model Microfield Method to the Stark broadening of ions
Authors: Gilles D. , Stehlé C.
Published: March 2009

We have proposed an extension of the Model Microfield Method to the case of ionic radiators. Special attention is given to the accurate treatment of plasma mixtures in terms of static and dynamic statistical properties of the plasma microfield. Line shapes of one electron Carbon and Argon illustrate the influence of ion dynamic effects.
Spectroscopic analysis of short-pulse laser-produced plasmas
Authors: Matte J.P. , Kieffer J.C. , Chaker M. , Côté C.Y. , Beaudoin Y. , Chien C.Y. , Coe S. , Mourou G. , Busquet M. , Gilles D. , Peyrusse O.
Published: March 2009

Experimental spectra of hot dense plasmas of aluminium produced by the interaction of a subpicosecond laser with solid targets at 1016 and 5 × 1017 W/cm2 are analyzed and discussed. A detailed analysis of the K-shell spectra is given through time-dependent calculations of atomic physics postprocessed to Fokker-Planck calculations of the laser-matter interaction. The non-Maxwellian character of the electron distribution function is shown. An evaluation of the electronic density and of the ion temperature 7i will be presented through Stark line broadening calculations. An X-ray spectrum from a Tantalum target also will be presented along with a preliminary interpretation.
A high-contrast all-glass ps-terawatt CPA laser system
Authors: Kalashnikov M.P. , Nickles P.V. , Will I. , Billhardt F. , Schnürer M.
Published: March 2009

We report on a compact, all-glass laser using a fiberless CPA technique as a potential system for the generation of extreme high-contrast picosecond pulses in the terawatt power range. New exciting experiments in the field of laser-matter interaction at extremely high intensities require both a high output energy and a very high peak to background intensity ratio (contrast). At present the system delivers 1.5 ps-pulses of 1.5-J energy with an intensity contrast of 4.109.
Radial inhomogeneity diagnostics deduced from space-resolved X-ray emission
Authors: Derfoul H. , Leboucher-Dalimier E. , Gharbi I. , Poquerusse A.
Published: March 2009

Radial inhomogeneity diagnostics in hot and dense laser plasmas are presented. By means of an analysis of the spatially resolved X-ray transverse emission of the plasma and of a theoretical modeling, we can access directly to the radial emission coefficient and to the transverse gradients. The intense aluminum Lyβ line has been chosen for this study, and different structured targets have been used to control the radiative transfer in the transverse direction. These targets (large or narrow emissive strips) give complementary results for the emission in the core (i.e., near the laser-target axis) or in the border of the plasma.
Detection of mercury in air by time-resolved laser-induced breakdown spectroscopy technique
Authors: Lazzari C. , Rosa M. De , Rastelli S. , Ciucci A. , Palleschi V. , Salvetti A.
Published: March 2009

For several years the laser-induced breakdown spectroscopy (LIBS) technique has been applied successfully to the problem of detecting small traces of pollutants in gases. The possible application of this method for the individuation of mercury in air is discussed. The laboratory prototype of the detection system is described in detail, and the sensitivity of the system for the diagnostics of small traces of mercury is determined. The reduced dimensions of the experimental apparatus and its relatively low cost make the LIBS method competitive with other laser-based methods for in situ analysis.
Intense ion beam from a magnetically insulated diode with magnetically controlled gas-breakdown ion source
Authors: Ueda M. , Greenly J.B. , Hammer D.A. , Rondeau G.D.
Published: March 2009

A magnetically insulated diode with an active anode source has been developed which produces a high-quality intense ion beam. The anode plasma of annular shape is produced independently of the main diode power pulse by the inductive breakdown of a radially expanding gas cloud supplied by a fast puff valve and nozzle configuration. The diode was developed on a 1010-W pulsed power generator that typically produces 150-kV, l-μs pulses. Prompt ion beam turn-on was attained in this diode when an adequate delay between pulsing the plasma source and delivering the diode power pulse was chosen. The neutral atom density in the diode accelerating gap was sufficiently low that the presence of the neutrals did not limit the beam pulse duration. When the puff valve was filled with H2 gas, a pure proton beam was produced, within the 20% uncertainty of the measurement technique. Proton beam pulses longer than 1 μs and current densities higher than 100 A/cm2 at 70–150 keV were generated.
Numerical simulation of mixing by Rayleigh–Taylor and Richtmyer–Meshkov instabilities
Authors: Youngs D.L.
Published: March 2009

Rayleigh-Taylor (RT) and Richtmyer–Meshkov (RM) instabilities at the pusher–fuel interface in inertial confinement fusion (ICF) targets may significantly degrade thermonuclear burn. Present-day supercomputers may be used to understand the fundamental instability mechanisms and to model the effect of the ensuing mixing on the performance of the ICF target. Direct three-dimensional numerical simulation is used to investigate turbulent mixing due to RT and RM instability in simple situations. A two-dimensional turbulence model is used to assess the effect of small-scale turbulent mixing in the axisymmetric implosion of an idealized ICF target.
Spectral structure in synchrotron radiation
Authors: Whitney Cynthia Kolb
Published: March 2009

Although synchrotron radiation is thought to be well understood in a theoretical sense, the practicalities of controlling a synchrotron source sometimes seem difficult. Often the output spectrum contains sharp peaks, especially at the high-frequency end of the spectrum. These spikes are unwanted because they rob power from desired frequency intervals, and unexpected because idealized theory predicts a quite smooth spectrum. In the face of such difficulties, it has been natural to suspect some sort of engineering shortfall. But the present paper argues that the spectral structure may point instead to an imperfection of theory.
TEM analysis of multimodule effects on coax-parallel-plate transitions for PBFA II
Authors: Johnson W. A. , Warne L. K.
Published: March 2009

Single-module analysis and experimental scale model testing indicate that a new design of the pulse-forming and transformer sections of the Particle Beam Fusion Accelerator II (PBFA II) will improve the energy transport efficiency of this machine by greater than 50%. However, these results have not considered multimodule, cross-coupling effects. This paper presents an approximate analysis of these cross-coupling effects, predicts problems that will occur, and indicates how to overcome them. Although this analysis is directed specifically at PBFA II, the techniques presented apply to the design of pulsed power machines with open-transmission lines whenever abrupt junctions occur.
Nonlinear stage in the development of hydrodynamic instability in laser targets
Authors: Gamaly E. G. , Favorsky A. P. , Fedyanin A. O. , Lebo I. G. , Myshetskaya E. E. , Rozanov V. B. , Tishkin V. F.
Published: March 2009

The development of hydrodynamic instability in laser targets is studied by means of the 2D numerical code “ATLANT.” At the linear stage, perturbations grow as At the nonlinear stage, the growth rate of Rayleigh-Taylor instability is reduced and new harmonics are generated. The effect of the nonuniformity of laser irradiation has been investigated for long- and shortwave perturbations. The growth rate of short-wave perturbations may be effectively decreased by means of symmetrical prepulses.
Hydrodynamic efficiency of illumination by ion beams
Authors: Basko M. M.
Published: March 2009

The hydrodynamic efficiency of conversion of the energy of fast charged particles into the kinetic energy of the bulk motion of plane-parallel shells is investigated in the framework of two simple models–one based on the stepwise density profile and the other employing a self-similar solution. The analytical estimates obtained are substantiated with ID hydrodynamic calculations. In case of spherical shells, the three key dimensionless parameters determining the values of the hydrodynamic efficiency are pointed out; the dependence of the hydrodynamic efficiency on these parameters has been explored numerically. The effects of a nonuniform energy deposition (increasing by the end of the fast particle ranges) and of a nonuniform absorber composition are also discussed.
Argon ion excitation by relativistic electrons: I. Collision cross sections and deposition efficiencies
Authors: McGarrah D. B. , Brake M. L.
Published: March 2009

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)3s23p44sand (Ne)3s23p43dconfigurations and for 40 transitions between excited energy levels from 4sand 3dto 4porbitals. 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.
Lisk-Broom: A laser concept for clearing space debris
Authors: Phipps Claude
Published: March 2009

So-called “space junk” forced a change of plan for a recent Shuttle mission. However, ground-based lasers with atmospheric-turbulence-compensating beam directors represent a singularly effective method of de-orbiting space junk, because they use cheap Earth-based power, and because they lend themselves to rapid retargeting. Plasma physics and lasertarget interaction theory dictate the laser parameters for a particular mission. We will discuss a practical laser system and beam director with 20-kW average power at 0.5-µm wavelength that is capable of clearing most low-Earth-orbit objects with mass less than 100 kg in about 4 years. This is a special application of the Laser Impulse Space Propulsion (LISP) concept, by which objects are propelled in space by the ablation jet produced on their surface by a remote laser.
Energy spectra of electrons emitted from laser irradiated low-density gas and the correspondence principle of electromagnetic interaction
Authors: Boreham B.W. , Hora H. , Hora H.
Published: March 2009

It is expected (Hora & Handel 1987) that the energy spectra of electrons emitted from laserirradiated atoms in low-density gases would be fundamentally different for laser intensities above and below the threshold of a correspondence principle. Below such a threshold, the emission is a quantum mechanical interaction while, in contrast, above the threshold it is a classical process. Both of our earlier experiments (Boreham & Hora 1979; Boreham & Luther-Davies 1979) and those of several others, including some very recent results (Monot et al. 1993) confirm—after some controversy—the existence of such a correspondence principle. Details are discussed.
Miniature magnetic bottle confined by circularly polarized laser light
Authors: Kolka E. , Eliezer S. , Paiss Y.
Published: March 2009

A new concept of hot plasma confinement in a miniature magnetic bottle induced by circularly polarized laser light is suggested. Magnetic fields generated by circularly polarized laser light may be of the order of megagauss. In this configuration the circularly polarized laser light is used to obtain confinement of a plasma contained in a good conductor vessel. The poloidal magnetic field induced by the circularly polarized laser and the efficiency of laser absorption by the plasma are calculated. The confinement in this scheme is supported by the magnetic forces. The Lawson criterion for a DT plasma might be achieved for number density n = 5.1021 cm-3 and confinement time τ = 20 ns. The laser and plasma parameters required to obtain an energetic gain are calculated.
High-pressure He-Cd and He-Zn lasers pumped by a hard ionizer
Authors: Karelin A.V. , Yakovlenko S.I. , Tarasenko V. F. , Fedenev A. F.
Published: March 2009

This paper presents the results of theoretical and experimental studies on high-pressure He-Cd and He-Zn lasers. It is shown that using the hard ionizer approximation makes it possible to readily and efficiently simulate the plasma chemical processes that occur in the active media of high-pressure lasers pumped by electron and ion beams as well as by nuclear reaction products in electron-beam experiments. Laser oscillation was achieved at λ = 325, 441.6, 533.7, and 537.8 nm for the cadmium ion and at λ = 610.3 nm for the zinc ion.
Acceleration of particles by relativistic electron plasma waves driven by the optical mixing of laser light in a plasma
Authors: Ebrahim N.A. , Douglas S.R.
Published: March 2009

Electron acceleration by relativistic electron plasma waves is studied by theory and particle simulations. The maximum acceleration that can be obtained from this process depends on many different factors. This paper presents a study of how these various factors impact on the acceleration mechanism. Although particular reference is made to the laser plasma beatwave concept, the study is equally relevant to the acceleration of particles in the plasma wakefield accelerator and the laser wakefield accelerator.
Principles of non-Liouvillean pulse compression by photoionization for heavy-ion fusion drivers
Authors: Hofmann Ingo
Published: March 2009

Photoionization of single-charged heavy ions has been proposed recently by Rubbia (1989) as a non-Liouvillean injection scheme from the linac into the storage rings of a driver accelerator for inertial confinement fusion. The main idea of this scheme is the accumulation of high currents of heavy ions without the usually inevitable increase of phase space. Here we suggest the use of the photoionization idea in an alternative scheme: if it is applied at the final stage of pulse compression (replacing the conventional bunch compression by an rf voltage, which always increases the momentum spread), there is a significant advantage in the performance of the accelerator. We show, in particular, that this new compression scheme can potentially relax the tough stability limitations, which were identified in the heavy-ion fusion reactor study HIBALL (Badger et al. 1984). Moreover, it is promising for achieving higher beam power, which is suitable for indirectly driven fusion targets (1016 W/g, in contrast with 1014 W/g for the directly driven targets in HIBALL).

The idea of non-Liouvillean bunch compression is to stack a large number of bunches (typically 50–100) in the same phase-space volume during a change of charge state of the ion. A particular feature of this scheme with regard to beam dynamics is its transient nature, since the time required is one revolution per bunch. After the stacking the intense bunch is ejected and directly guided to the target. The present study is a first step in exploring the possibly limiting effect of space charge under the parameter conditions of a full-size driver accelerator. Preliminary results indicate that there is a limit to the effective stacking number (non-Liouvillean “compression factor”), which is, however, not prohibitive. Requirements on the power of the photon beam from a free-electron laser are also discussed. It is seen that resonant cross sections of the order of 10−15 cm2 lead to photon beam powers of a few megawatts.
Nonlinear Z correction to the stopping power in a hot electron gas
Authors: Tu Khiet
Published: March 2009

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.
Time-dependent collisional radiative model of ionizing and recombining plasmas
Authors: Minoo H. , Cukier M. , Haidar J.
Published: March 2009

A time-dependent collisional radiative model, based on a five-charge state at any spacetime point in the plasma, is elaborated in order to follow the basic atomic physics processes in a plasma undergoing ionization and recombination. This model can either be used independently or be included in a magnetohydrodynamics code of a transient plasma. In the latter case, the efficiency of the model makes it particularly useful in saving computing time of hydrodynamic codes developed in connection with ion-driven fusion.
Analytical approximation for oscillator strengths of H-like ions
Authors: Minguez E.
Published: March 2009

The main objective of this work is to find analytical formulas for the oscillator strength f of hydrogen-like ions. It is well known that f is proportional to the energy of the transitions between eigenstates (ΔE), and to the square of the R matrix. Therefore, the problem of calculating f can be reduced to finding analytical expressions for both parameters, ΔE and R. Hence these expressions would be in accordance with quantum results based on more sophisticated calculations.
Collision times in plasmas
Authors: Reimann U. , Toepffer C.
Published: March 2009

Collision times in plasmas are usually defined in connection with the time evolution of the ensemble-averaged scattering angle . Extrapolating the short-time behaviour ϑshort(t), one obtains the collision time tc by setting ϑshort(tc) = π/2. We have shown with the help of computer simulations that this procedure is ambiguous, as we can clearly distinguish three regimes for ϑ(t). There is always an initial ballistic regime with ϑ(t) ∝ t with dominant pairwise interactions. This lasts up to times α/υth where α is the mean distance between the particles and υth their mean velocity. This is followed by a diffusive regime with ϑ(t) ∝ t½, which is characterized by many small-angle scattering events. Eventually, this diffusion will lead to a uniform distribution of the directions of the velocity. So ϑ(t) will saturate towards π/2 in a third asymptotic regime. For large plasma parameters Γ ≫ 1, this asymptotic behaviour will be modulated by a damped oscillation of ϑ(t) with the plasma frequency. For such strongly coupled plasmas the diffusive regime is suppressed and one observes a direct transition from the initial ballistic to the asymptotic collective regime characterized by the plasma oscillation. Parameters such as the diffusion constant and the transition times are estimated with the help of analytical models.
Hydrodynamic flow simulations with relevance to heavy ion induced fusion
Authors: Schneider V. , Lutz K. J. , Maruhn J. A.
Published: March 2009

The irradiation of cylindrical targets by intense heavy ion beams was studied using a two-dimensional numerical simulation code including radiation effects on the hydrodynamical flow. Solid and hollow Aluminum targets as well as gas tubes are studied for various beam configurations with a view to identifying the characteristic features of the flow and possible observables, especially the emitted radiation from Xenon gas tubes.
An efficient shock capturing scheme for ion beam target simulation
Authors: Gupta N. K. , Munz C. D. , Goel B.
Published: March 2009

A high resolution shock capturing numerical scheme in Lagrangian geometry is presented for ion beam target simulations. The scheme can accommodate any given analytical or tabular equation of state. Numerical results for a number of test problems show that the scheme is free from spurious numerical oscillations near strong gradients. Results are also presented for the simulation of a typical proton beam from the pinch reflex diode of Karlsruhe light ion beam facility KALIF incident on slab aluminum target.
Heating matter by intense heavy ion beams at SIS energies
Authors: Schneider V. , Maruhn J.
Published: March 2009

The hydrodynamic flow in cylindrical aluminum targets irradiated by intense Xenon beams is discussed for three different beam-target combinations. Solid targets, targets with enclosed cavities, and hollow beams are considered to study the effects of energy deposition and compression waves in matter. Emphasis is put on the occurrence of converging shock waves. The assumed beam intensity of 40TW/cm2 is in the scope of the GSI-SIS/ESR facility that will start operating in 1990/91.

A two-dimensional hydrodynamic code, including the energy deposition of heavy ions, a realistic equation of state, and realistic transport coefficients, is used in numerical simulations to obtain information on the temperature and density distributions and the relevant time scales that have to be expected in these experiments.
X-ray diagnostics of dense plasmas produced by high-energy heavy ions
Authors: Laux W. , Jacoby J. , Hoffmann D.H.H.
Published: March 2009

Plasmas with solid-state density at temperatures of a few eV will be produced in the near future at GSI by high-energy heavy ions. To diagnose these plasmas, novel methods–based on hard X-ray diagnostics–have to be applied. An investigation of the hydrodynamic expansion of the target requires a space- and time-resolved measurement of the plasma density. The determination of the target density independently of its temperature is obtained by a special X-ray pinhole camera enabling a selective registration of the target K-shell emission in combination with space- and time-resolved beam intensity measurements.
Evaluation of ablation plasma characteristics of intense, pulsed, ion-beam evaporation
Authors: Kang Xiangdong , Masugata Katsumi , Yatsui Kiyoshi
Published: March 2009

Basic characteristics of an ablation plasma produced by an intense, pulsed, ion beam have been evaluated from the measurement of ion-flux density by a biased ion collector. The target mass loss is detected by the measurement of the weight of the target in the comparison before and after the shot. A one-dimensional hydrodynamic model is introduced with the assumption of a high-power, light-ion beam-driven expansion and the following adiabatic expansion into vacuum. With this model, it is possible for us to deduce the temperature and the pressure from the data of the ion flux and the mass loss of the target, respectively. This method is also applicable to other intense pulsed energy sources such as lasers or electron beams.
Fragmentation and stopping of heavy cluster ions in a lithium target
Authors: Deutsch Claude , Tahir Naem A.
Published: March 2009

Correlated stopping of N ion debris flowing at same velocity in a lithium target is worked out from the Basbas-Ritchie model of 2-cluster stopping in degenerate electron jellium. A very large energy loss enhancement is demonstrated. It is strongly modulated by the ions' topological arrangement. Relevance to inertial fusion driven by intense cluster ion beam is stressed.
Application of Hartree-Fock theory of fluctuations to opacity calculation
Authors: Blenski T. , Morel S.
Published: March 2009

The Hartree-Fock theory of fluctuations leading to simple formulae for configuration probabilities is used in a Detailed Configuration Accounting calculation of opacity in the case of an iron plasma. A direct Detailed Term Accounting method is also applied. The correlations of subshell occupation numbers, which are accounted for in the HF theory, show small effect on the theoretical spectrum corresponding to conditions of a recent measurement.
Polarization of atomic radiative transitions in crossed electric and magnetic fields
Authors: Jacobs V.L. , Filuk A.B.
Published: March 2009

A density-matrix approach is under development for the investigation of the angular distribution and polarization of atomic radiative emissions in crossed quasi-static electric and magnetic fields. Particular interest has centered on applications to spectroscopic observations in the intense fields of the high-power light-ion inertial fusion device PBFA II at Sandia National Laboratories, and to magnetic field measurements in tokamak plasmas. Noteworthy features of our general density-matrix analysis include allowances for the mixing of both the bound and continuum field-free atomic eigenstates in an arbitrary arrangement of electric and magnetic fields, and for the possible coherent excitation of the nearly degenerate field-dependent atomic substates that produce the overlapping Stark-Zeeman components. The influence of directed collisional excitation may also be taken into account. From the angular-momentum selection rules, specific results have been obtained for observation of polarized radiative emissions in the direction of the magnetic field.
Stopping power of heavy ions in strongly coupled plasmas
Authors: Zwicknagel G. , Toepffer C. , Reinhard P.-G.
Published: March 2009

We investigate the stopping power of heavy ions in strongly coupled electron plasmas by performing molecular dynamics (MD) computer simulations. A comparison with conventional weak coupling theories shows that these fail in describing the stopping power at low ion velocities and strong coupling. Then nonlinear screening effects become important and this causes a change in the dependence of the stopping power on the ion charge Zp at low ion velocities. From the MD simulation, we find the stopping power to behave like ZP1.43 instead of the weak coupling behavior Zp2 ln(const/Zp). Similar results were recently obtained by experiments in connection with electron cooling at heavy ion storage rings.
Systematic ion-atom interaction cross sections and stopping powers in the plane wave Born approximation
Authors: McGuire Eugene J.
Published: March 2009

In Chapter 14 of Atomic and Molecular Processes, Bates (1962) outlines a procedure for calculating ion-atom cross sections in the plane-wave Born approximation (pwBa). The procedure involves integration over the product of elastic scattering factors or generalized oscillator strengths for excitation or ionization from both projectile and target. We have programmed this procedure to use our large database of excitation and ionization generalized oscillator strengths (GOS). The program calculates both cross sections (CS) and stopping power (SP) on a subshell basis. The calculations are done in the center of mass system where the distinction between projectile and target is lost. Thus, the SP in the laboratory frames of both target and projectile are symmetrical in nuclear and net charges. The traditional simple modeling of SP, using scaled proton SP and an effective projectile charge, is unsymmetrical, and therefore dubious as a guide for extrapolating to ion-ion SP. At high projectile energy, the SP curves, as a function of increasing projectile charge, approach the scaled protonic result from above, indicating that lowering the average charge raises the SP, in contradiction to the traditional picture that the projectile SP increases with increasing effective charge (assuming there is an underlying physical reality relating the effective and average charge). Comparison with experimental SP data (mostly from 30 years ago) shows generally poor agreement for Li ion projectiles in the 1–10 MeV range.
The inversion condition for the X-ray Balmer-α transition in consideration of the modeled time-dependent Lyman-α reabsorption in a rapidly recombining laser-produced plasma
Authors: John R.W.
Published: March 2009

The time-dependent condition for population inversion in the X-ray 3 → 2 transition in hydrogen-like ions of a recombining plasma produced by a short laser pulse is studied. The population densities of the energy levels are theoretically obtained in a collisional-radiative plasma model; the reabsorption of the 2 → 1 resonance line is taken into account via the escape probability. A new feature is first that the escape probability is treated as an explicitly time-dependent function,E21(r,t). On the basis of a four-level model of the H-like ions, the rate differential equations governing the time development of the population densities are considered, including time-dependent pumping terms and coefficients. Furthermore, specially modeling the time dependence ofE21(r,t), and assuming the other rate coefficients to be approximately constant with respect to time, via the explicit closed-form solution of the corresponding rate equations, the Balmer-α inversion condition ΔN32(r,t) > 0 is given in terms containing confluent hypergeometric functions and depends on rate coefficients, pumping terms, and explicitly on the time. For the free-electron densityNeof the recombining plasma, this relation means a condition depending on atomic and plasma state parameters and qualitatively changing in the course of time.
Laser wakefield and beat-wave generation by multiple and chirped laser pulses
Authors: Cairns R.A. , Johnson D. , Bingham R.
Published: March 2009

Generation of large amplitude plasma waves using high-power lasers in either the wakefield or beat-wave scheme is considered. We show how the nonlinear behavior of the plasma wave may make it advantageous to split the total energy into more than one pulse in the wavefield scheme. When a beat wave is generated by a pulse of finite length, we show how the final wave amplitude may be enhanced if the frequency of one or both pulses is chirped in such a way that the wavelength of the beat increases from the front to the back of the pulse.
Optical emission spectroscopy of laser-produced carbon plasma at moderate and low irradiance in an ambient atmosphere
Authors: Thareja R.K. , Abhilasha  , Dwivedi R.K.
Published: March 2009

The plasma produced during pulsed-laser deposition of thin carbon films is studied in the presence of ambient gases (Air, He, Ar) at low and moderate irradiances of Nd:YAG laser. The presence of ambient gas shows a pronounced effect on the dynamics of the plasma plume. At moderate intensity, we report an appearance of a peculiar double-peak structure in the temporal profile of the C II transition in laser-produced carbon plasma as it expands into a background gas. We believe that the structure originates mainly due to stratification of the plasma into fast and slow ion components at the interface where Rayleigh-Taylor instability occurs. Thin carbon films deposited on silicon in the presence of argon gas have shown the characteristic features of diamond-like carbon in X-ray diffraction and Raman Spectroscopy. The X-ray diffraction pattern of carbon film deposited at 1 torr of argon gas pressure shows the dominance of (111), (220), (311), and (400) crystalline plane of cubic diamond.
A study of laser plasmas as X-ray sources in the 1–10 keV spectral region
Authors: Bastiani S. , Bastiani S. , Giulietti A. , Gizzi L.A. , Ceccotti T. , Macchi A. , Giulietti D.
Published: March 2009

An experimental investigation on X-ray emission from laser-produced plasmas is presented and the properties of such an emission of interest for application purposes are examined. Plasmas were generated by focusing 1 μm, 3 ns Nd laser pulses onto Al and Cu targets at an intensity of 1013 W/cm2. The temporal evolution of the emission and its spectral features were investigated by using an X-ray streak-camera and an X-ray photodiode. In the case of Cu targets, the analysis of the emission showed two spectral components. The main component was centered at ≈ 1.2 keV and a minor component, whose intensity was measured to be 10-3 of the previous component, was observed at ≈7 keV. The X-ray conversion efficiency, in the investigated spectral region, was measured to be 1% for Cu targets and 0.3% for Al targets.
High-precision measurement of velocity profiles in laser-created chlorine plasma
Authors: Renner O. , Krouský E. , Mißalla T. , Förster E. , Hölzer G.
Published: March 2009

A vertical dispersion variant of the Johann spectrometer has been used to record the highresolution X-ray spectra of the chlorine He-like resonance line group emitted from lowradiance plasma. The emission profiles were measured at two observation angles and decomposed into single spectral lines by using a fit based on the Levenberg-Marquardt algorithm. The results of computerized analysis of the one-dimensional (1-D) spatially resolved spectra were used to evaluate the distribution of the main plasma parameters. The electron temperature gradient 7.5·104 eV cm-1 was computed by modeling the measured spectra with the collisional-radiative package RATION. The blowoff maximum velocities 4.2–6.1·107 cm s-1 and the velocity gradients 0.9–1.6·109 s-1 were determined from the Doppler shifts of individual spectral lines within their different spatial extent.
Stimulated Raman scattering in plasmas produced by short intense laser pulses
Authors: Barr H.C. , Boyd T.J.M. , Gordon F.I. , Berwick S.J.
Published: March 2009

Stimulated Raman scattering driven by intense subpicosecond laser drivers is analyzed, in particular, the effects of the pulse shape and relativity on the instability and its characteristic spectra. The analysis is carried out in the pulse group velocity frame (Lorentz transformed) where growth rates for backscattering are decreased relative to their values when analyzed in the laboratory frame, while forward-scattered growth rates have greatly enhanced values. A range of intensities and densities is considered, appropriate to recent experiments, which ranges from strongly coupled scattering at high densities (even for forwardscattering) to stimulated Compton scattering regimes for backscattering and relativistically trapped forwardscattering at low densities. The inhomogeneities in intensity and density cause mode conversion between waves inside and outside the pulse. This can be at a modest level, as for backscattering, or extreme as in the case of forwardscattering when the Raman scattered light can be trapped within the laser pulse. The consequent feedback between modes within the pulse allows solutions, absolutely growing in the pulse frame, to be found.
Ablation effects in weakly nonlinear stage of the ablative Rayleigh–Taylor instability
Authors: Hasegawa Susumu , Nishihara Katsunobu
Published: March 2009

Weakly nonlinear stage of the ablative Rayleigh-Taylor instability has been studied by the perturbation theory. Mode coupling of linear growing waves with wave numbers kA and kB drives new excited waves with wave numbers k0 (= kA ± kB, 2kA, 2kB). We have investigated time evolution of the excited waves and found that the ablation effect plays an important role even in the nonlinear stage to reduce amplitude of the excited waves. Differences between an ablation surface and a classical contact surface have been discussed. Dependence of the excited wave amplitude on the wavenumber k0, the ablation velocity va, and the effective gravity g is also investigated.
Self-compression of laser-produced plasma into thin monovelocity shell
Authors: Orishich A.M. , Shaikhislamov I.F. , Posukh V.G.
Published: March 2009

The spatial profile, as well as ion-velocity distribution of laser-produced plasmas can be controlled experimentally by varying the time-form of laser pulse. A compression of nearly all produced plasma into a thin monovelocity spherical shell has been observed for the first time. A hydrodynamic numerical simulation shows that the shell generates due to special dynamics of ion ablation and geometry of experiment.
Characteristics of rapidly recombining plasmas suitable for high-gain X-ray laser action
Authors: Zhang J. , Key M.H. , Norreys P.A. , Danson C. , Neely D. , Rose S.J. , Walsh F. , Tallents G.J. , Dwivedi L. , Holden M. , Holden P.B. , Pert G.J. , Ramsden S.A. , Lewis C.L.S. , Macphee A.G. , You Y.L.
Published: March 2009

Recombining plasmas produced by picosecond laser pulses are characterized by measuring ratio of intensities of resonance lines of H- and He-like ions in the plasmas. It is found that the rapidly recombining plasmas produced by picosecond laser pulses are suitable for highgain operation.
Free nuclei gamma-ray lasing
Authors: Rivlin Lev A.
Published: March 2009

We discuss two different approaches for observing induced gamma-ray emission of nuclei, departing from known attempts to use the Moessbauer transitions that have so far proven unsuccessful. Both approaches (presented at the 11th and 12th International Conferences on Laser Interaction and Related Plasma Phenomena) are based on the elimination of pernicious influence of Doppler line-broadening in ensembles of free nuclei, particularly in atom and ion beams.
Two-dimensional beam smoothing technique for KrF laser systems
Authors: Matsushima Isao , Yashiro Hidehiko , Tomie Toshihisa , Okuda Isao , Matsumoto Yuji , Miura Eisuke , Takahashi Eiichi , Owadano Yoshiro
Published: March 2009

Broad-band random-phase (BRP) irradiation is one of the beam smoothing techniques for KrF laser drivers. We have introduced this technique into the KrF laser system ASHURA. By one-dimensional (ID) BRP smoothing, the speckle pattern in conventional random-phase irradiation has been removed. Two BRP beams were overlap-focused on the target incoherently. Although the obtained profile is rather smooth, some low-frequency nonuniformity remains. To improve the uniformity, a new technique for two-dimensional (2D) smoothing has been proposed. In this technique, a wedged etalon is used to get angular dispersion to the orthogonal direction to the ID BRP effect. The preliminary experiment has been carried out.
Guest editor's preface: Laser and particle induced shock waves — A perspective
Authors: Eliezer S.
Published: March 2009

The science of high pressure (Eliezer et al. 1986; Eliezer & Ricci 1991) is studied experimentally in the laboratory by using static and dynamic techniques. In static experiments the sample is squeezed between pistons or anvils. The conditions in these static experiments are limited by the strength of the construction materials. In the dynamic experiments shock waves are created. Since the passage time of the shock is short in comparison with the disassembly time of shocked sample, one can do shock-wave research for any pressure that can be supplied by a driver, assuming that a proper diagnostic is available. In the scientific literature, the following shock-wave generators are discussed: chemical explosives, nuclear explosions, rail guns, two stage light-gas gun, exploding foils, magnetic compression, and high-power lasers.
Hugoniot EOS measurements at Mbar pressures
Authors: Evans A.M. , Freeman N.J. , Graham P. , Horsfield C.J. , Rothman S.D. , Thomas B.R. , Tyrrell A.J.
Published: March 2009

The AWE HELEN laser is being used to measure high-pressure Hugoniot data by the impedance match method. Indirect drive is used to generate pressures of up to 10 Mbar in the aluminum reference material. We are aiming to measure shock velocities in our targets to ± 1 %, leading to errors in pressure and particle velocity of the order of ±2%. This requires improvements in target fabrication and characterization, streak camera calibration and data analysis, coupled with investigations into shock planarity and attenuation. Our latest results have accuracies of 2–4% in shock velocity but have identified work that should allow us to achieve our intended level of accuracy. Experiments have been done with copper and chlorinated plastic; our results are compared with theory, and, for copper, with U.S. and Russian gas-gun, explosively or nuclear-driven experiments.
Optical emissivity from a laser-driven shock-heated dense plasma
Authors: Mahdieh M.H. , Hall T.A.
Published: March 2009

The aluminium side of two-layer Al-Plastic targets were irradiated with a long pulse (∼ 2.4 ns FWHM) 1.06-μm laser light at intensities up to 7 × 1013 W/cm2. The time history of the thermal emission of the confined rear surface of the aluminum was measured. Visible emission only occurs for a short time after the arrival of the laser-generated shock waves. Over the range of the measurements, the duration and the intensity of the emission reduce with increasing laser intensity. The experimental results are in good agreement with the results of a simple phenomenological model that assumes a linear temperature and density profile on the shock front. The values of shock velocity and maximum temperature and density that were used in the model were found using the hydrodynamic simulation code MEDUSA. From the model the shock width was measured for different conditions by matching the emission of the experiment and model. It is found that the time history of the emission is strongly sensitive to the ionization potential of the plastic that is assumed to change with density from ∼ 4 eV at zero pressure to zero at high densities. The technique provides a way to measure the pressure metallization of large band gap insulators.