bluuebunny/crossref_metadata_2025 huggingface dataset:
Ionic excimers and alkali dimer triplet-state excimer lasers
Authors: Xing Da , Ueda Ken-Ichi , Takuma Hiroshi
Published: March 2009

Vacuum UV fluorescences from ionic alkali-halide and rare-gas alkali excimers were observed by e-beam excitation. The two diffuse emissions centered at 185 and 154 nm from the CsF vapor were attributed to the bound-free B2Σ+ → X2Σ+ and D2Π → X2Σ+ bands of (CsF)+, respectively. And, the 164- and 133-nm diffuse bands from gas the mixture of Xe or Kr with hot vapor of Rb were assigned to the emissions of (XeRb)+ and (KrRb)+ ionic excimers. In addition, amplified spontaneous emissions of the Na2 violet, K2 yellow, and Rb2 orange diffuse bands were observed from e-beam-excited alkali vapor with argon buffer gas. The continuum spectra centered at 436, 574, and 604 nm were attributed to triplet-triplet Na2, K2, and Rb2 23Πg → 13Σu+ bound-free transitions, respectively. The dissociative recombination of Na3+, K3+, or Rb3+ is discussed as an efficient formation process of the upper states in e-beam pumping.
Advanced techniques of high-efficiency pulse compression for KrF lasers
Authors: Ueda Ken-Ichi , Nishioka Hajime , Kimura Kazuhiko , Takuma Hiroshi
Published: March 2009

A couple of advanced techniques of high-efficiency pulse compression for KrF lasers have been developed in our laboratory. As is well known, electron beam-excited KrF lasers have a capability of large output energy of 100- to 1,000-ns pulse duration. However, high-efficiency operation under a short-pulse input is difficult to achieve because of the reaction kinetics and short lifetime of KrF excimers. For developing ultrahigh peak-power lasers, the efficient pulse compression of ns to ps and ps to fs pulses is essential. We demonstrated advanced techniques, Raman pulse compression in a transient Raman regime, and pulse compression in saturated amplifiers with saturable absorbers.
Non-LTE atomic modeling for laser-produced plasmas
Authors: Takabe H. , Nishikawa T. , Nakamura S.
Published: March 2009

Atomic modeling of high-Z partially ionized plasma is essential for simulating radiation hydrodynamics of laser-produced plasma. A collisional-radiative model based upon an average atom model is used to calculate plasma opacity and emissivity. Because line radiations are most dominant in such plasma, the detail configuration accounting (DCA) for electronic state is required. We propose a statistical method to carry out the DCA with the use of the average population of bound electrons. Further modeling of line group made of the same transition from ions in different change states is discussed by considering the detail structure (hierarchy) of the line group.
Experimental testing of thin-shell stable acceleration for ICF schemes with direct and indirect drive
Authors: Bolotin V. A. , Burdonsky I. N. , Velikovich A. L. , Gavrilov V. V. , Golberg S. M. , Goltsov A. Yu. , Zhuzhukalo E. V. , Zavjalets S. V. , Kondrashov V. N. , Kovalsky N. G. , Pergament M. I. , Koshevoi M. O. , Rupasov A. A. , Shikanov A. S.
Published: March 2009

The present review is of the experimental investigations on laser-plasma interaction being carried out in past years at IAE. Experiments were conducted on the “Mishen” facility. The laser system of Mishen consists of two channels with output beam parameters as follows: the main beam—output energy 100–200 J (λ = 1.054 μm) in 3-ns pulse, divergence ∼2 × 10-4 rad, contrast ratio ∼106, power density at the target surface ∼1013–1014 W/cm2; the diagnostic beam–output energy 10–20 J (λ = 1.054 μm) and 5–10 J (λ = 0.53 μm) in 0.3-ns pulse, divergence ∼10-4 rad, power density 1013 - 1014 W/cm2. Our aim in this experiment is to study the different aspects of the ICF processes in flat geometry. The main issues of our studies are hydrodynamic aspects, including acceleration efficiency, high-velocity impact in cascade targets, hydrostability, and X-ray physicsconversion efficiency, heat transfer, and X-ray-driven targets.
Numerical simulation of implosion and burn of D–T ignitor/D3He fuel pellet for D3He inertial confinement fusion reactor
Authors: Nakashima H. , Shinohara M. , Wakuta Y. , Honda T. , Nakao Y. , Takabe H.
Published: March 2009

A parameter study of implosion, burn, and gain of D–T ignitor/D3He fuel pellets is presented for a D3He inertial confinement fusion reactor. It is found from burn simulation that attaining a quasi-isobaric state with a temperature of 4 keV and pR value of 2.5 g/cm2 for the D–T ignitor and 0.8 keV and 9.5 g/cm2 for the D3He main fuel would suffice to obtain a pellet gain of ∼40–50 required for the D3He reactor. With 30-MJ laser irradiation and the coupling efficiency of 10%, the density of the target is assumed to be imploded to 5,000 times the liquid density. However, in the implosion simulation to realize the above configuration it is found that after void closure the central hot D–T ignitor region is ignited, while the bulk of the D3He main fuel is still imploding with high velocities. This preignition of the D–T ignitor leads to a low compression of the main fuel and prevents the D–T/D3He pellet from obtaining the required pellet gain. The pellet gain obtained is only ∼3.
Effect of the surface finish on the stability of targets imploded by thermal radiation
Authors: Caruso A. , Pais V. A.
Published: March 2009

The effect of surface finish on the evolution of ICF targets has been studied. As driver for the implosion has been used a temporally profiled thermal radiation pulse (25 ns in duration) as that expected for the case of a high-gain (cm sized) capsule enclosed in a cavity. 2-D numerical simulations have been performed on a planar analog to investigate the stability to perturbations having wavelengths in the interval 2.5–40 μm and initial amplitudes of 0.03 and 1 μm. The simulations show perturbation growing due to hydrodynamic instabilities. The distortion of the ablation front reaches such a level to strongly enhance the ablation rate because of the increase in the exposed area and in the power absorbed per unit area. Two different phenomena have been identified: one, preferentially occurring for small wavelengths, in which the motion behind the first shock wave becomes turbulent and the symmetry is lost; the other, appearing for long wavelengths, in which a thermal radiation wave penetrates into the fuel. This preheating phenomenon is related to the formation of holes in the thermal shield due to the enhanced ablation and to matter transverse piling up. All these effects may render useless the 1-D-based design of a high-gain capsule exposed to a given thermal bath. However, it has been also observed that, for the longer wavelength (40 μm) and a smaller initial perturbation amplitude (e.g. 0.01 μm), during the temperature pulse the preheating does not occur and most of the fuel can be accelerated as a whole to speeds of the order of 2 × 107 cm/s or greater without a substantial onset of transverse velocities, even in the presence of the ablator piling up.
Hemispherical shock wave decay in laser-matter interaction
Authors: Gilath Irith , Eliezer Shalom , Eliezer Shalom , Bar Tuvia
Published: March 2009

A high-irradiance short pulsed laser was used to generate hemispherical shock waves in planar targets. A linear relationship was obtained between the laser energy for threshold spall conditions (EL) and the cubic target thickness (d): EL = 45.3d3 + 4.9, where EL is in J and d is in mm. It is found that the laser-induced ablation pressure decays with the distance to a power slightly greater than 2.
Two-stream instability for a light ion beam-plasma system with external magnetic field
Authors: Okada T. , Tazawa H.
Published: March 2009

For inertial confinement fusion (ICF), a focused light ion beam (LIB) is required to propagate stably through a chamber to a target. It is pointed out that the applied external magnetic field is important for LIB propagation. To investigate the influence of the external magnetic field on the LIB propagation, the electrostatic dispersion relation of the magnetized light ion beam-plasma system was analyzed. The particle in-cell (PIC) simulation results are presented for a light ion beam-plasma system with an external magnetic field.
Control of a high-current discharge radiation spectrum
Authors: Burtsev V.A. , Ermolaev Y.L. , Kalinin N.V. , Petrov I.B.
Published: March 2009

Results of the analysis and numerical calculations of continuous spectra of multicomponent multicharged plasma radiation are presented. Possibilities of control of the radiation spectrum by the mixture composition variation and programming in time the pulsed discharge current of the supply source are considered. Free and forced (by energy deposition or additional cooling) relaxation time estimations permit the definition of discharge parameters when plasma formation goes on under nonequilibrium conditions, leading to controlled energy redistribution over the spectrum.
A traveling wave approach to plasma pumping for X-ray sources
Authors: Jensen Reed J.
Published: March 2009

Progress in high-brightness excimer lasers and in optical angular multiplexing of excimer lasers presents an opportunity to provide very intense pumping of X-ray sources, both in favorable geometry and in traveling waves, all at low cost. The traveling-wave strategy can be tailored to the parameters of the system to be pumped. This design option can be of great importance for systems lasing at wavelengths in the kilovolt regime where upper level lifetimes are short, and where mirror technology is presently tenuous. Features of several design strategies are explored.
A Nuclear Pumped Laser for the Laboratory Microfusion Facility
Authors: Miley G. H.
Published: March 2009

The Laboratory Microfusion Facility (LMF) has been proposed to study Inertial Confinement Fusion (ICF) targets with reactor-grade gains. An advanced solid-state laser is the prime candidate as the driver for the LMF. However, here we present a conceptual design for an alternate approach using a Nuclear Pumped Laser (NPL).

A pulsed fission reactor is used to excite an oxygen-iodine laser in this design, based on preliminary data on nuclear pumping of O2(1δ). Although a working NPL of this specific type has not yet been assembled, we believe this concept holds great potential, both as a test facility driver and as a future power reactor.
Experimental study of free electron laser using cold relativistic electron beams
Authors: Toyoda K. , Kawamura Y.
Published: March 2009

Periodical short pulse trains were observed in the oscillation of the waveguide mode free electron laser, which could be explained as a self mode-lock oscillation of the free electron laser.

The spectra of the spontaneous emission and the induced absorption were observed, which were in good agreement with theoretical calculations.

The energy spread of the relativistic electron beam was measured using Thomson back scattering from a high power CO2, laser.
The pulsed laser damage sensitivity of optical thin films, thermal conductivity
Authors: Guenther Arthur H. , McIver John K.
Published: March 2009

Pulsed laser induced damage of optical thin films is, in general, initiated by the absorption of laser radiation by imperfections in the films or at interfaces between film layers and/or the substrate. A heat flow analysis of this process stresses the importance that the thermal conductivity of both the thin film host and that of the substrate play in establishing the laser-induced damage threshold. Unfortunately, recent work, which will be reviewed in this presentation, indicates that the thermal conductivity of thin films can be several orders of magnitude lower than that of the corresponding material in bulk form. This situation arises as a consequence of the film structure resulting principally from the deposition process. The importance of thermal conductivity will be compared to parameters such as absorption mechanisms, film materials, composition, and other variables. Its implication for the ultimate optical strength of materials and the direction in which thin film research and processing should proceed will be highlighted.
Laser fusion experiment
Authors: Nakai S.
Published: March 2009

The recent progress of laser fusion research has been remarkable in obtaining the high density of more than 100 times solid density (Nakai et al. 1988) and high temperature plasma producing thermonuclear neutrons of 1013 per shot (pellet gain of 0·2%) (Yamanaka et al. 1986a) and in the understanding of the implosion physics. The data bases of the laser fusion are rapidly being accumulated and the technologies for the advanced experiments have been developed, both of which enable us to proceed toward the fusion ignition experiment and the achievement of the breakeven conditions.
Implosion motion and fuel compression in direct or indirect driven target
Authors: Niu Keishiro
Published: March 2009

When a one-shell three-layer cryogenic target is irradiated by a driver beam of total energy 10 MJ and pulse width 30 ns, the pusher pressure increases to 1013 Pa, accelerating fuel toward target center, and the fuel implosion velocity reaches 3 × 105 m/s. A spherical hollow target plays the role of a supersonic converging nozzle, and the fuel is compressed to 269 times the solid density in the supersonic region and to 3·51 × 104 times in subsonic region. Nonuniform beam-energy-deposition in pusher layer causes nonuniform pusher pressure and hence nonuniform implosion, which reduces fuel compression significantly. The smoothing of pusher pressure by radiative energy transfer, or gas-filled target instead of cryogenic hollow target can be used to reduce the defect of nonuniform implosion. At last, the structure of an indirect driven target is proposed to smooth out pusher pressure in spite of nonuniform beam irradiation.
Internal structure of a partially ionized heavy ion. Isolated ion model
Authors: Furutani Y. , Totsuji H. , Mima K. , Takabe H.
Published: March 2009

An effective potential and an associated electron density in a partially ionized high-Z ion are evaluated within the framework of the Thomas–Fermi–Dirac–Weizsäcker statistical model of atoms. The results are then injected as an initial input into the one-electron Schrödinger equation, a procedure based on the density functional theory. The self-consistency between the two approaches is examined. For a partially ionized ion at zero and finite temperatures, a number of bound electrons is counted by a sum over the principal quantum number, which diverges due to the contribution from shallow bound (Rydberg) levels. A truncation of this sum is devised by application of the Planck–Larkin scheme to the Fermi distribution
High power laser development and experimental applications to X-ray lasers, and short pulse energy transport
Authors: Key M. H. , Baldis H. , Brown D. , Grande M. , Hooker C. , Kato Y. , Lewis C. , Norreys P. , O'Neill D. , Pert G. , Ramsden S. , Regan C. , Rose S. , Ross I. , Shaw M. , Tallents G. , Wooding E.
Published: March 2009

University research in the UK with high power lasers is carried out at the SERC's Central Laser Facility with a multi-terawatt neodymium glass laser, VULCAN, and a developmental KrF laser, SPRITE. These systems are briefly described together with the design of a new KrF laser to supersede VULCAN. The new laser design, SUPERSPRITE, is based on optical and Raman multiplexing which is being developed with the present SPRITE system. The specification of SUPERSPRITE is for 3.5 kJ in 1 ns and a peak power of 300 TW in short pulses. The new technology is seen as highly cost effective in relation to neodymium glass lasers. A resume of the development of XUV lasers in the UK in collaboration with laboratories overseas is given. The work is based on laser action through recombination in highly ionized ions and recent progress includes collaborative experiments on the GEKKO XII facility in Japan which have demonstrated laser action at the shortest wavelength to date at 45 A in Mg XII. The physics of energy transport in short pulses is fundamental to the extrapolation of recombination lasers to shorter wavelengths and is being studied from a more basic standpoint using both the VULCAN and SPRITE facilities. Some details of this work are given.
Atomic physics and hydrodynamics of laser driven Ar-filled plastic microballoon implosions
Authors: Mancini R. C. , Hooper C. F.
Published: March 2009

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.
A multigroup radiation analysis of the light ion beam energy conversion into X rays
Authors: Honrubia J. J.
Published: March 2009

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.
Stimulated scattering from laser produced plasma
Authors: Offenberger A. A. , Santiago J. , Fujita M. , Fedosejevs R. , Rozmus W.
Published: March 2009

Stimulated Brillouin and Raman scattering are of considerable interest because of their importance to basic nonlinear plasma physics phenomena and to laser-driven inertial confinement fusion. Induced scattering can be substantial for high intensity (I), long wavelength (λ) lasers because the instability growth rates depend exponentially on Jλ2, and also for short wavelength, long scalelength (L) laser/plasma interaction because of nearly homogeneous or large convective gain conditions. Experimental results from both KrF and CO2 laser/plasma interaction studies are presented to illustrate important wavelength dependent features of induced scattering such as the nature of the instability (absolute, convective), threshold, spectra, reflectivity and saturation effects. Backscattering characteristics have been measured for solid target plasmas (aluminum, gold) produced by KrF laser pulses focused to intensities <1014 W/cm2 and gas targets (hydrogen, oxygen) by CO2 laser pulses at intensities <1013 W/cm2. Collisional absorption dominates the KrF laser experiments, whereas particle heating and increased Landau damping dominate the CO2 laser experiments. Current theoretical work concerned with nonlinear effects in Langmuir wave localization, wave collapse and particle heating (generating characteristic high temperature electrons) is also presented.
Nonlinear stage in the development of hydrodynamic instability in laser targets
Authors: Gamaly E. G. , Lebo I. G. , Rozanov V. B. , Favorsky A. P. , Fedyanin A. O. , Myshetskaya E. E. , Tishkin V. F.
Published: March 2009

The development of a hydrodynamic instability in laser targets is studied by means of a 2-D numerical code “ATLANT”. During the linear stage, the perturbations grow as:

In the nonlinear stage the growth rate of the Rayleigh-Taylor instability is reduced, and new harmonics are generated. The effect of the nonuniformity of the laser irradiation has been investigated for long-wave and short-wave perturbations. The growth rate of short-wave perturbations may be effectively decreased by means of symmetrical pre-pulses.
Magnetic control of the plasma flows in laser targets
Authors: Gus'kov S.Yu. , Rozanov V.B. , Pisarczyk T.
Published: March 2009

The idea of controlling the plasma flows in laser targets by action of a strong external magnetic field (H ≥ 1 MG) is presented. The magnetic control of plasma flows for the keeping of a transparency of entrance holes of indirect-compression targets and other type targets operating at an introduction of the laser beams into the interior of the target is suggested. It is shown that the magnetic field, transverse versus the direction of the propagation of the plasma flow with an intensity of 2–4 MG, causes a decrease (1.5–3 times) of the closing speed of holes for the laser beam introduction into the hohlraum target.
Second harmonic emission from laser-preformed plasmas as a diagnostic for filamentation in various interaction conditions
Authors: Schifano E. , Baton S.D. , Labaune C. , Renard N. , Biancalana V. , Giulietti A. , Giulietti D.
Published: March 2009

Second harmonic emission from underdense laser-preformed plasmas has been investigated in forward direction with respect to the interaction beam axis. Two series of measurements have been performed using two focusing conditions and changing the intensity of the interaction beam. Effects of beam smoothing by random phase plates on second harmonic emission were also tested. Novel information on density and intensity gradients driven by filamentation instability was obtained.
Passage of laser light through a hole-plasma shutter
Authors: Mašek K. , Králiková B. , Krása J. , Láska L. , Rohlena K. , Skála J. , Štirand O. , Trenda P. , Rus B. , Bessarab A.V. , Garanin S.G. , Kirillov G.A. , Kiryanov Yu.F. , Kochemasov G.G. , Ryadov A.B. , Sukharev S.A. , Suslov N.A. , Zaretskii A.I.
Published: March 2009

The interaction of a plasma produced by irradiation of perforated foils with laser pulses was studied. The laser beam of the first harmonics of the iodine laser (λ = 1.315 μm) system PERUN was focused by anf/2 optics (f = 20 cm) on a hole in the foil target of high-Z material. The laser energy and the temporal shape of the pulses were monitored both before and behind the hole. Foils of two different materials (Pb, Cu) were used, and a series of hole diameters 2rH ranging from 100 μm to 500 μm were tested. The diameter of the laser focal spot 2r0 was about 150 μm. For hole diameters smaller than 300 μm, a shortening of the laser pulse was observed, demonstrating the effect of plasma shutter. The pulse shortening, which depends on the hole diameter, corresponds to the reduction in the pulse energy passing through the hole. An analysis of the experimental data is based on hydrodynamic computations, and the physics of the process is illustrated by a simple analytical model.
Numerical study of microcylinder target for recombination X-ray laser
Authors: Aoki T. , Yabe T. , Ozaki T. , Kuroda H.
Published: March 2009

A microcylinder target is proposed for a recombination X-ray laser generation and is investigated by a numerical simulation. The size of the target is of the order of 1 cm in the axial direction and 100 μm in the inner radius. The target has an axial slit of 20 μm wide through which a line-focused laser illuminates the inner wall. The hot plasma produced inside is confined, and a part of this is blown out through the slit. This plasma cools due to the free expansion, so that a gain of a recombination X-ray laser appears outside the microcylinder. When a large enough amount of hot plasma is produced inside, it plays the role of a reserver. Numerical results show that the quasi-cw (continuous wave) gain of Hα line is obtained outside the aluminum microcylinder when the plasma, which has not recombined yet, is supplied continuously.
Polari interferometer with automatic images processing for laser plasma diagnostic
Authors: Pisarczyk T. , Arendzikowski R. , Patron Z. , Parys P.
Published: March 2009

Automated three-channel polari-interferometer measurements of electron density distributions and magnetic fields in a laser plasma are presented. Each of the polari-interferometer channels, interferometric, Faraday, and “tenebral” (shadow), has been equipped with a CCD camera with the matrix (512 × 512). With special software for each of the channels, not only the distribution of the electron density on the basis of interferograms is obtained, but also the distributions of magnetic fields in plasma using the information from the Faraday and shadow images. The results of testing investigations obtained in the plasma experiment are the main part of this work.
The method of an intense electron beam modulation
Authors: Astrelin V.T. , Lebedev S.V.
Published: March 2009

A new method of intense relativistic electron beam modulation at frequencies up to ∼1 GHz is suggested. Current modulation is provided by using the azimuthal magnetic field of the beam to control the beam reflection from the magnetic mirror. The results of computer simulations for a 2-MeV, 20–50-kA beam are presented.
Thermal effects of hot electron halo in a laser-imploded Z-layered plasma pellet
Authors: Palleschi V. , Singh D. P. , Harith M. A. , Vaselli M.
Published: March 2009

Coupling of the core with the surrounding corona of hot electrons produced around the plasma critical surface in a spherically symmetric laser-imploded Z-layered plasma target has been analyzed. Considering that the energy equipartition exists between the cold electrons of the core and the hot coronal electrons in the core–corona overlapping region, the analytic expression for core–corona coupling has been derived. The efficiency of heat transfer from the hot corona to the cold core depends on the laser wavelength, mean electron temperature in the ablation region, and the width of the Z-layer in the plasma pellet. Numerical results indicate that short wavelength lasers are favorable for efficient heating of the core by the surrounding hot corona. The core-corona coupling increases primarily with the mean electron temperature up to a certain extent and beyond that further laser flux transfer to the hot corona results in decoupling of the core from the corona. The presence of Z-layer is likely to reduce the electron mean free path in the ablation region and affects the laser wavelength scaling of the core-corona coupling. It is also found to have positive influence on the maximum coupling efficiency of the core with the hot corona.
Argon ion excitation by relativistic electrons: II. Chemical kinetics
Authors: McGarrah D. B. , Brake M. L.
Published: March 2009

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.
Ultrashort pulse laser-produced Al/Si plasma
Authors: Davis J. , Clark R. , Giuliani J.
Published: March 2009

The X-ray emission from an ultrashort-pulse laser incident on a solid aluminum and a layered aluminum /silicon slab is investigated with a non-LTE radiation-hydrodynamics model coupled to a Helmholtz wave equation for P-wave polarization. A fraction of the absorbed energy is expended in the production of fast electrons, which are transported and deposited in the cold material. These electrons create K-shell vacancies that produce characteristic Kα line radiation. A time history of the emission spectra, including the Kα lines and continuum radiation, is presented for a laser intensity of 1017 W/cm2.
Time-resolved hard X-ray emission from a small plasma focus
Authors: Moo S.P. , Wong C.S.
Published: March 2009

Some results of an experimental study of the hard X rays emitted from a 15-kV, 3-kJ plasma focus operated in argon are reported. The temporal evolution of the hard X rays detected by a plastic scintillator-photomultiplier detector and the voltage across the focus tube measured by a resistive voltage divider are simultaneously recorded on a two-channel digitizing oscilloscope. Metal absorbers of various thicknesses are used to provide some indications of the energies of the X rays. When the time delay of the detector system with respect to the anode voltage is taken into account, the hard X rays are observed to be emitted about 15 ns before the peak of the anode voltage and last for about 100 ns. There are two periods of emission, the X rays emitted in the first period being more intense, more energetic, and more directional than the X rays emitted in the second period. The X rays are attributed to the bombardment of the anode by energetic electrons generated in the pinch and the disruption phases of the focus.
German heavy-ion ICF activities: Status and prospects
Authors: Bock R.
Published: March 2009

The main goals of the German program are the study of key issues of inertial fusion with intense beams of heavy ions. The completion of the new heavy-ion synchrotron and storage ring facility SIS/ESR at GSI opens new directions for experimental investigations on beam dynamics at high intensity and on beam/target interaction. In addition, new accelerator scenarios will be investigated based on non-Liouvillean beam-handling techniques.
New results obtained with sulphur and bromine ions interacting with a Z-pinch hydrogen discharge
Authors: Gardes D. , Bimbot R. , Rivet M. F. , Servajean A. , Fleurier A. , Hong D. , Deutsch C. , Maynard G.
Published: March 2009

The experimental setup developed at Orsay for studying ion beam-plasma interactions of relevance to inertial confinement fusion has been significantly improved. In this connection, the fast valves displayed on both sides of the plasma discharge play an essential role. The amount of residual gas is then reduced by a factor of 3. New and accurate results for the stopping and the effective charges of S7+ and Br6+ in the MeV/u energy range are presented.
Secondary nuclear fusion reactions as evidence of electron degeneracy in highly compressed fusion fuel
Authors: Setsuhara Y. , Azechi H. , Miyanaga N. , Furukawa H. , Ishizaki R. , Nishihara K. , Katayama M. , Nishiguchi A. , Mima K. , Nakai S.
Published: March 2009

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.
Ion-beam-driven plasma described by rate equations
Authors: Kärcher B. , Meyer-Ter-Vehn J.
Published: March 2009

Ionization distributions and radiation spectra of a dense plasma driven by intense ion beams are studied by solving stationary rate equations. Expressions for the rate coefficients are derived. Optically thin plasmas of hydrogen and carbon are considered neglecting hydrodynamic motion. Results on level populations versus temperature, on power balance and equilibrium states, and also on emission spectra are given. In particular, the transition from beam-determined plasma states to thermal equilibrium states is discussed. Beam parameters are chosen close to those in experiments now being planned.
Thermodynamic properties of nonideal plasmas with multiple ionization and Coulomb and hard-core interactions
Authors: Kahlbaum Torsten , Förster Andreas
Published: March 2009

We present a theoretical approach to the thermodynamic properties of nonideal plasmas consisting of neutral atoms, multiply charged ions, and free electrons. Starting with the free energy, we describe the ionization equilibrium of this system by a coupled set of mass action laws (Saha equations). Our model of interaction takes into account Coulomb forces between all charged particles and hard-core forces between all heavy particles and the electrons. The influence of multiple ionization and different interaction parts on plasma composition, mean charge, and equation of state is discussed for xenon. Finally, we show the potential occurrence of the plasma phase transition.
Charge-state distributions of chlorine ions interacting with cold gas and with fully ionized plasma
Authors: Chabot M. , Gardès D. , Kiener J. , Damache S. , Kubica B. , Deutsch C. , Maynard G. , Pouey M. , André W. , Fleurier C. , Hong D. , Wohrer K. , Hoffmann D.H.H.
Published: March 2009

Charge transfer of 4.3 MeV/u chlorine ions passing through a discharge plasma target is used as a probe to determine the plasma density and the ratio of impurities inside the plasma column. Charge-state distributions of 2 MeV/u chlorine ions passing through the plasma are then measured and compared to corresponding measurements in the cold gas. Stopping power measurements are also performed in both cases.
Three-dimensional, tight focusing of intense pulsed light-ion beam by spherical plasma focus diode
Authors: Jiang Weihua , Sakagami Toshiya , Masugata Katsumi , Yatsui Kiyoshi
Published: March 2009

A new type of ion-beam diode, self-magnetically insulated, spherical plasma focus diode (SPFD), was developed. With the SPFD, three-dimensional focusing of an intense pulsed light-ion beam was obtained. Experiments and simulations were carried out to study the behavior of the SPFD. In the experiments, diagnostic results of the Rutherford scattering pinhole camera and the shadow-box showed that the ion beam was focused into a small cylindrical area with ∽0.5 mm in diameter and ∽2.5 mm in length. The average ion-beam current density at the anode surface was found to be ∽2 kA/cm2. In the simulations, it was observed that most of the diode gap is well insulated by the self-magnetic field induced by the diode current. The electron sheath in the diode gap significantly enhances the ion flow from the anode. As a result, the ion current density is several times higher than the single-species space-charge limited value.
Inhomogeneous mixing of D and T fuels in inertial confinement fusion
Authors: Kawata Shigeo
Published: March 2009

Numerical analyses show that a 40% mixing inhomogeneity of the deuterium (D) and tritium (T) concentrations in a DT pellet still gives a sufficient fusion energy output in DT inertial confinement fusion (ICF), as long as the D and T total amounts are equal. This new result means that fusion energy output is rather insensitive to the inhomogeneous fuel mixing in the DT ICF pellet.
Angular dependence of M and N band radiation and the effect of angular anisotropy on the total conversion efficiency of X rays emitted from a laser irradiated gold foil
Authors: Gupta N.K. , Kumar V.
Published: March 2009

In this paper, we present the results of our theoretical studies on the angular dependence of M and N band peaks emitted from a laser irradiated gold foil. The M band peak is seen to be nearly isotropic, while the magnitude of the N band peak decreases as we move away from normal to the foil. The trend is similar to that reported in the experiments of Chase et al.: (1977) for aluminium foil. It is also observed that the N band peak shifts towards longer wavelength as the angle φ relative to the normal to the target increases. We also present the effect of angular anisotropy on time and frequency integrated total conversion efficiency of laser light into X rays using a high Z target. As compared with the diffusion approximation, a significant reduction in conversion efficiency is observed for a wide range of laser powers, and wavelengths.
Measurements of thermal transport in plasmas produced by picosecond laser pulses
Authors: Gizzi L.A. , Mackinnon A.J. , Riley D. , Viana S.M. , Willi O.
Published: March 2009

In this paper we present measurements of energy transport in hot, high-density plasmas produced by picosecond laser interaction with solid targets. The propagation of the ablative heat wave was studied by using X-ray-ultraviolet (XUV) spectroscopy with picosecond temporal resolution. Measurements show that for laser intensities on target above 1016 W/cm2, strong inhibition of heat flux toward the cold target occurs. A detailed modelling of the experimental data is presented in which heat transport and absorption processes are taken into account self-consistently. Finally the role played by lateral transport and self-induced magnetic fields in our experiment is also discussed.
Magnetic field generation by short ultraintense laser pulse in underdense plasmas
Authors: Bychenkov V. Yu. , Tikhonchuk V.T.
Published: March 2009

The theory of magnetic field generation due to the interaction of short relativistic laser pulses with underdense plasmas has been developed. The magnetic field is generated due to the inverse Faraday effect occurring witha circularly polarized laser pulse. The spatial distribution of the magnetic field is investigated. It is shown that the magnetic field magnitude depends on the relationship between the laser beam radius and the plasma skin-depth.
Shock waves in gas and plasma
Authors: Niu K.
Published: March 2009

A shock wave is a discontinuous surface that connects supersonic flow with subsonic flow. After a shock wave, flow velocity is reduced, and pressure and temperature increase; entropy especially increases across a shock wave. Therefore, flow is in nonequilibrium, and irreversible processes occur inside the shock layer. The thickness of a shock wave in neutral gas is of the order of the mean free path of the fluid particle. A shock wave also appears in magnetized plasma. Provided that when the plasma flow is parallel to the magnetic field, a shock wave appears if the governing equation for velocity potential is in hyperbolic type in relation with the Mach number and the Alfvén number. When the flow is perpendicular to the magnetic field, the Maxwell stress, in addition to the pressure, plays a role in the
shock wave in plasma. When the plasma temperature is so high, as the plasma becomes collision-free, another type of shock wave appears. In a collision-free shock wave, gyromotions of electrons around the magnetic field lines cause the shock formation instead of collisions in a collision-dominant plasma or neutral gas. Regardless of a collision-dominant or collision-free shock wave, the fluid that passes through the shock wave is heated in addition to being compressed. In inertial confinement fusion, the fuel must be compressed. Really, implosion motion performs fuel compression. A shock wave, appearing in the process of implosion, compresses the fuel. The shock wave, however, heats the fuel more intensively, and it makes it difficult to compress the fuel further because high temperatures invite high pressure. Adiabatic compression of the fuel is the desired result during the implosion, without the formation of a shock wave.
Multimode modelling of the Rayleigh-Taylor instability
Authors: Town R.P.J. , Findlay J.D. , Bell A.R.
Published: March 2009

This paper presents a comparison of Haan's mode coupling model with two-dimensional hydrocode simulations. In the light of these results, a new saturation criterion is developed that is used in a new, extended mode coupling model. The new extended model accurately follows the mode development to amplitudes 2 to 3 times larger than Haan's model.
The CERN laser–ion source
Authors: Collier J. , Hall G. , Haseroth H. , Kugler H. , Kuttenberger A. , Langbein K. , Scrivens R. , Sherwood T. , Tambini J. , Sharkov B. , Shumshurov A. , Masek K.
Published: March 2009

This paper describes the first results of a feasibility study undertaken at CERN to determine whether a laser-produced plasma can be used as a source of intense highly charged heavy ion beams. A variety of important measurements have been made, and the results are encouraging. Furthermore, a beam of highly charged light ions produced by the laser ion source has been accelerated successfully in a radio frequency quadrupole (RFQ) structure.
Space-charge compensation of highly charged ion beam from laser ion source
Authors: Kondrashev S.A. , Collier† J. , Sherwood† T. R.
Published: March 2009

The problem of matching an ion beam delivered by a high-intensity ion source with an accelerator is considered. The experimental results of highly charged ion beam transport with space-charge compensation by electrons are presented. A tungsten thermionic cathode is used as a source of electrons for beam compensation. An increase of ion beam current density by a factor of 25 is obtained as a result of space-charge compensation at a distance of 3 m from the extraction system. The process of ion beam space-charge compensation, requirements for a source of electrons, and the influence of recombination losses in a spacecharge-compensated ion beam are discussed.
Study of multicharged heavy ion generation from CO2 laser-produced plasma
Authors: Baranov V.Yu. , Makarov K.N. , Roerich V.C. , Satov Yu.A. , Starostin A.N. , Stepanov A.E. , Sharkov B.Yu. , Baranov V.Yu. , Makarov K.N. , Roerich V.C. , Satov Yu.A. , Starostin A.N. , Stepanov A.E. , Langbein K. , Sherwood T.R.
Published: March 2009

The results of lead ion generation with charge state from Pb10+ to Pb35+ from laser-heated plasma are presented. CO2 lasers producing 10.6-μm wavelength radiation at power densities in the range 4.1011-6.1014 W/cm2 in TBKI and CERN were used. Results of detailed numerical simulations presented in the paper are in good agreement with the experimental data. Work done in collaboration with CERN, ITEP, and TBKI was aimed at the specification of requirements for a laser system that will be able to drive an ion source for the hadron collider (LHC) at CERN.
Quadrupole field geometries for intense electron beam acceleration
Authors: Humphries Stanley
Published: March 2009

High-intensity electron beams could be focused in low-frequency RF accelerators and induction linear accelerators by adding transverse components to the accelerating electric field. Calculations with a 3D code show that quasielectrostatic focusing is sufficient to transport kiloampere electron beams in RF accelerators and the high-energy sections of induction accelerators. The elimination of conventional magnetic focusing systems could lead to reductions in the volume and weight of high-current electron accelerators. Two novel quadrupole geometries are investigated: a periodic array of spherical electrodes with alternating displacements and a set of plate electrodes with elliptical apertures.
Low-temperature preparation of BaTiO3 thin films by intense, pulsed, ion beam evaporation
Authors: Sonegawa T. , Grigoriu C. , Masugata K. , Yatsui K. , Shimotori Y. , Furuuchi S. , Yamamoto H.
Published: March 2009

Cubic barium titanate (BaTiO3) thin films have been prepared in situ, on a low-temperature substrate, Al/SiO2/Si(100), by intense, pulsed ion beam evaporation. We have first proposed a new deposition configuration, backside deposition, which, in comparison with standard frontside deposition, produces very smooth thin films, Rα (mean roughness) ≈ 3 ∼ 9 nm, without any droplets. There is no significant change of the dielectric constant in the frequency range of 10 ∼ 105 Hz. The dielectric constant for the film deposited at the substrate temperature of 200˚C is typically ∼90 at 1 kHz.
Basic and applied atomic spectroscopy in high-field ion diode acceleration gaps
Authors: Bailey J.E. , Filuk A.B. , Carlson A.L. , Johnson D.J. , Lake P. , McGuire E.J. , Mehlhorn T.A. , Pointon T.D. , Renk T.J. , Stygar W.A. , Maron Y. , Stambulchik E.
Published: March 2009

Achieving inertial confinement fusion using a light-ion-beam driver requires continued improvement in understanding ion diode physics. The power delivered to a light-ion beam target is strongly influenced by the evolution of the charge-particle distributions across the ion beam acceleration gap. Our strategy is to determine this evolution from time- and space-resolved measurements of the electric field using Stark-shifted line emission. In addition to diode physics, the unique high-field (∼10 MV/cm, ∼6T) conditions in present experiments offer the possibility to advance basic atomic physics, for example by measuring field ionization rates for tightly bound low-principal-quantum-number levels. In fact, extension of atomic physics into the high-field regime is required for accurate interpretation of diode physics measurements. This paper describes progress in ion diode physics and basic atomic physics, obtained with visible-light atomic spectroscopy measurements in the ∼20 TW Particle Beam Fusion Accelerator II ion diode.
Photons emission and charge-exchange contributions to the energy loss of swift heavy ions in dense matter
Authors: Maynard G. , Mabong S. , Katsonis K.
Published: March 2009

In this paper we determine the inelastic contribution to the energy losses by swift heavy ions in dense matter. At equilibrium, the charge transfer stopping is determined by a simple energy balance and the excitation stopping is determined by the photons emission. Using an average atom model, we determine the density influence on these inelastic stoppings.
Enhanced energy loss of heavy ions passing a fully ionized hydrogen plasma
Authors: Kowalewicz R. , Boggasch E. , Hoffmann D.H.H. , Jacoby J. , Laux W. , Stöckl C. , Weyrich K. , Miyamoto S.
Published: March 2009

Experiments are presented that demonstrate the high stopping power of fully ionized hydrogen plasma for low-energy heavy ions. A plasma with electron densities up to 7.1016 cm–3 at temperatures above 1 eV was created by an electrical discharge. In the described experiment, a stopping power of 1.08 GeV/(mg/cm2) was measured using singly charged krypton ions at 45–keV/u energy. The measured stopping power exceeds the corresponding value in cold hydrogen gas by a factor of 35. These measurements confirm the theoretical stopping power predictions close to the expected maximum in a fully ionized plasma.
Light ion beam driven inertial confinement fusion: Requirements and achievements
Authors: Bluhm H.J. , Keßler G. , Petersen R.R.
Published: March 2009

In this paper we compare the requirements for a light ion beam driven inertial confinement fusion (ICF) reactor with the present achievements in pulsed power technology, ion diode performance, beam transport, and target physics. The largest gap exists in beam quality and repetition rate capability of high-power ion diodes. Beam quality can very likely be improved to a level sufficient for driving a single-shot ignition facility, if the potential of two-stage acceleration is used. Present schemes for repetition rate ion diodes allow either too low power densities or create too large beam divergence. On the other hand, repetitively operating pulsed-power generators meeting the requirements for an ICF reactor driver can be built with present technology. Also, a rather mature target concept has been developed for indirect drive with light ion beams.