bluuebunny/crossref_metadata_2025 huggingface dataset:
Theory of efficient shell implosions
Authors: Murakami Masakatsu , Nishihara Katsunobu , Takabe Hideaki
Published: March 2009

A theoretical model of spherical ablative implosion is presented. The implosion performances such as the target coupling efficiency are estimated from the aspect ratio and initial mass density of a target shell, provided the laser is fixed at moderate intensity for a given wavelength. The model is applied to the experimental results obtained for both plastic hollow shell targets and DT gas-filled GMB targets by use of the twelve-beam green GEKKO XII laser. In addition to the target coupling efficiency, it is shown for the gas-filled targets that the theoretical predictions of neutron yield, ion temperature, and fuel ρ and ρR are in good agreement with the experimental results. Reduction of neutron yields due to irradiation nonuniformity is also discussed, and 5% of absorption nonuniformity is found to be required for explaining the discrepancies in neutron yield between the experiments and the theory.
Numerical simulation for particle acceleration and trapping by an electromagnetic wave
Authors: Kawata Shigeo , Matsumoto Masami , Masubuchi Yukio
Published: March 2009

The interaction between particles and an electromagnetic (EM) wave is investigated numerically in the system of particle Vp × B acceleration by the EM wave. Numerical simulations show that the particle acceleration mechanism works well in the case of the appropriate number density of the imposed particles. When the interaction between particles and the wave is too strong, a part of the trapped and accelerated particles is detrapped. A condition is also presented for the efficient particle acceleration and trapping by the EM wave.
μ-Molecular formation under laser irradiation
Authors: Eliezer S. , Henis Z.
Published: March 2009

The possibility of enhancement of molecular formation by strong electromagnetic fields is discussed. The electron screening of the laser is considered. Rate production of ddμ and dtμ molecules in the presence of a laser field is estimated as a function of the resonance detuning.
Studies of light ion beam for inertial confinement fusion by induction adder
Authors: Miyamoto S. , Imasaki K. , Yasuda Y. , Yugami N. , Akiba T. , Tubakimoto K. , Zakou A. , Nakai S. , Yamanaka C.
Published: March 2009

Light ion beams for the energy drive for inertial confinement fusion (ICF) research have been studied on a super high voltage generation system (SHVS) using an inductive voltage adder system. A simple analysis implied the capability of the output voltage of several tens of MV. This system has a feasibility of acceleration of ions heavier than proton. The two-stage charge stripping ion diode is considered a SHVS diode. This diode reduces the size of the induction adder module and extends the possible power range in operation. We have constructed a prototype SHVS, which consists of eight stages of induction cavities (4MV, 40kA, 100ns) powered by a Reiden IV pulse power machine. The first ion diode experiments on the induction adder were performed with the beam extraction type ion diode (Br applied magnetic field). The injection plasma ion source was used to control the diode impedance and then the diode voltage. The time delay of ion current turn-on was reduced from 15–20 ns to less than 5 ns by this ion source.
LIBRA–A light ion beam inertial confinement fusion reactor conceptual design
Authors: Moses G. A. , Kulcinski G. L. , Bruggink D. , Engelstad R. , Lovell E. , Macfarlane J. , Musicki Z. , Peterson R. , Sawan M. , Sviatoslavsky I. , Wittenberg L. , Kessler G. , Möllendorff U. Von , Stein E. , Smith I. , Corcoran P. , Nishimoto H. , Fockler J. , Cook D. , Olson R.
Published: March 2009

The LIBRA light ion beam fusion commerical reactor study is a self-consistent conceptual design of a 330 MWe power plant with an accompanying economic analysis. Fusion targets are imploded by 4 MJ shaped pulses of 30 MeV Li ions at a rate of 3 Hz. The target gain is 80, leading to a yield of 320 MJ. The high intensity part of the ion pulse is delivered by 16 diodes through 16 separate z-pinch plasma channels formed in lOO torr of helium with trace amounts of lithium. The blanket is an array of porous flexible silicon carbide tubes with Li17Pb83 flowing downward through them. These tubes (INPORT units) shield the target chamber wall from both neutron damage and the shock overpressure of the target explosion. The target chamber is a right circular cylinder, 8·7 meters in diameter. The target chamber is ‘self-pumped’ by the target explosion generated overpressure into a surge tank partially filled with liquid that surrounds the target chamber. This scheme refreshes the chamber at the desired 3 Hz frequency without excessive pumping demands. The blanket multiplication is 1·2 and the tritium breeding ratio is 1·4. The direct capital cost of LIBRA is estimated to be $2200/kWe.
Industrial applications of pulse power and particle beams
Authors: Yatsui Kiyoshi
Published: March 2009

An overview is given of recent progress in the industrial applications of intense pulse power and associated particle beams, except for activities in inertial confinement fusion. In particular, several topics are discussed which relate to the applications in the R&D of materials, the excitation of short wavelength lasers, the generation of charged particle beams, and the development of plasma X-ray sources.

I. Applications in material processing. If intense pulsed charged particle beams are directed onto materials, only their surfaces where the beam energy is deposited are quickly heated up to very high temperatures. Using the pulsed beam in this way, we might expect to apply them in R&D of materials. Several novel attempts have been made, e.g., on the preparation of thin films by use of a high-density high-temperature plasma, surface modification by surface heating, and ion-beam mixing of multi-layers by use of the focused electron or ion beams, and so on. Furthermore, experimental studies have been done on the surface modification by ion implantation and the evaluation of the damage due to the irradiation by ion beams.

II. Applications in the excitation of short wavelength lasers. Activities in the excitation of high-power, short wavelength lasers by using electron beams or ion beams have increased considerably.

III. Applications in the generation of charged particle beams, and the development of plasma X-ray source. With regard to new accelerator technologies, several attempts are underway on the application of the modified betatron or the development of a convergent electron beam accelerator with a plasma cathode.
Neutron localization measurements from a two-gun plasma focus device
Authors: Yeh T. R. , Wen M. , Tzeng C. C. , Shang D. J. , Yeh C. K. , Wu K. S. , Kuo Y. Y. , Hou W. S.
Published: March 2009

The simultaneous formation of the two deuterium plasma foci has been reported recently by Hou et al. in a Mather type two-gun plasma focus assembly with maximum bank energy of ∼700 kJ. In addition, these plasmas will evolve and then produce a disk-shaped plasma in the middle of the two plasma foci. Soft X-ray filter techniques which allow measurements of the electron temperature at both pinch points and the middle point yielded a few hundred eV for these three regions. Neutron localization measurements which were carried out with a collimator and a scintillator-fiber-photomultiplier assembly indicate that an enhancement of ∼80% in neutron yield is observed in the middle region as the separation between two electrodes is 9.1cm. Further experimental evidence shows that the neutron production in the middle region is the result of the beam-beam interaction in nature.
Dynamics of an argon gas-embedded Z-pinch micro-channel as a function of the initial preionization
Authors: Auguste T. , Chenais-Popovics C. , Etlicher B. , Gauthier J.-C. , Geindre J.-P. , Rouillé C.
Published: March 2009

We have studied experimentally the relation between the preionization of a plasma micro-channel in Argon at atmospheric pressure and the dynamics of the discharge initiated by preionization. Preionization is obtained in two different ways: (a) injecting the soft X rays produced by a 3 J, 3 ns YAG laser focused on a copper target through a pinhole (b) direct focusing of a 4ω laser (0·26 μm) along the Argon column. Both experiments and simple numerical models are presented in this paper.
Pulsed nuclear reactors in nuclear-pumped laser research
Authors: Voinov Alexei M.
Published: March 2009

An overview of nuclear-pumped laser programs conducted on various pulsed reactor types has been presented. The independent research undertaken in Russia and the United States have confirmed the concept of energy conversion from nuclear exothermal reactions to coherent optical radiation as feasible.
Nuclear-pumped gas lasers at temperatures up to 800˚C
Authors: Konak Alexei I. , Melnikov Sergei P. , Porkhaev Vladimir V. , Sinyanskii Anatolii A.
Published: March 2009

This article describes the design of a laser setup excited by 3He(n, p)3H reaction products and intended for investigations of the laser characteristics of 3He mixtures with metal vapors or other gases at temperatures up to 800˚C. This setup could also be used to study the effect of the medium heating on the characteristics of nuclear-pumped gas lasers.
Nonlinear electron beam guiding by a reduced-density channel
Authors: Dolique J.-M. , Khodja M.
Published: March 2009

Suggested by numerical simulations, recent experiments have shown that a significant guiding force is exerted by a reduced-density channel on electron beams propagating through initially un-ionized air. A theoretical analysis of this guiding force had been given that assumed uniform beam and channel and small beam-channel offset. From a 2-D model, relative to a beam slice, the guiding force is calculated in this article for arbitrary beamchannel offset and for various smooth beam and channel profiles. This calculation confirms the above-quoted experimental evidence of a guiding force significant with respect to the deflection force exerted by the earth's magnetic field. It also confirms the crucial role played by the secondary electron temperature distribution. Finally, it suggests optimal values for the ratio between channel and beam rms radii.
Simple spherical D-T targets for heavy-ion beam fusion
Authors: Basko M.M.
Published: March 2009

The results of 1-D numerical study are reported for a class of simple D-T targets driven by the beams of heavy ions. A simple target is defined as a uniform spherical metallic shell with the frozen D-T deposited on its inner surface and the D-T gas in the central cavity. Optimum target parameters have been found for several combinations of the three relevant driver parameters—the input energy Ein, the beam pulse duration tin, and the beam ion energy Eb. A simple box pulse profile was assumed. As a central set of driver parameters around which most of the calculations have been done, the values Ein = 6.12 MJ, tin = 17 ns, and Eb = 20 GeV have been adopted. It was found that all the targets from the class under consideration ignite uniformly over the entire fuel mass. Maximum energy gains amount to Gopt = 80–100. The physical picture of the target performance is analyzed in detail.
Hydrodynamic efficiency of energy transfer in experimental targets illuminated with heavy-ion beams
Authors: Basko M.M. , Molodtsov S.V. , Sokolovskii M.V. , Sharkov B.Yu.
Published: March 2009

The conditions for an experiment are being discussed in which the hydrodynamic efficiency could be measured and an optimum thermonuclear target design worked out that could be performed on a single-channel accelerator facility producing a 209Bi ion beam of ∼100 GeV per nucleus. As numerical simulations show, the expected values of the hydrodynamic efficiency are 5–10%, while the optimization of the target-beam system could be performed by compressing D-T gas in a conical cavity and registering some 109-1011 neutrons per shot.
Radiation effect on pellet implosion and Rayleigh-Taylor instability in light-ion beam inertial confinement fusion
Authors: Kawata S. , Sato T. , Teramoto T. , Bandoh E. , Masubichi Y. , Takahashi I.
Published: March 2009

The radiation transport effect on pellet implosion and the Rayleigh-Taylor (R-T) instability are studied in a light-ion beam (LIB) inertial confinement fusion (ICF) by numerical simulation and analytic work. First, we present the nonuniformity-smoothing effect of the radiation transport on implosion symmetry in an LIB ICF fuel pellet. The 2-D implosion simulation shows that the initial nonuniformity can be smoothed out well in an LIB ICF pellet; for example, the initial nonuniformity of 6% is smoothed to 0.07% during the implosion phase. In addition, linear analyses for the R-T instability under nonuniform acceleration in space and under radiation are also performed: The nonuniform acceleration field in space does not change the growth rate (γ) of the R-T instability. However, this nonuniformity may suppress the growth itself of the R-T instability. Radiation may reduc the growth rate (γ).
Absolute study of spectra from laser-produced plasmas
Authors: Li Yao-Lin , Wang Xiao-Fang , Xu Zhi-Zhan , Chen Shi-Sheng , Qian Ai-Di
Published: March 2009

A method of absolutely unfolding the atomic spectrum by a pinhole transmission grating spectrometer (TGS) is discussed in detail. The numerical process considers both the factors of higher-dispersive-order overlapping of TGS and source-size widening effects. Real soft-X-ray spectra of aluminum, copper, and gold plasmas are presented of experiments performed on the Six-Beam Laser Facility at the Shanghai Institute of Optics and Fine Mechanics.
Review on spontaneous magnetic fields in laser-produced plasmas: Phenomena and measurements
Authors: Stamper J. A.
Published: March 2009

Large (megagauss) “spontaneous” magnetic fields are produced by laser–plasma interactions when a short, powerful laser pulse is focused to a small diameter onto a solid target. The relevance of these magnetic fields to inertial confinement fusion applications depends on the numerous ways in which they can affect laser–plasma interactions and the resulting plasma. Theoretical studies have dealt with a variety (thermal, radiative, and dynamo) of generation mechanisms and with the associated transport and instability phenomena. The fields, originally observed with small induction probes placed near the target, have been studied in the focal region by optical methods. These optical diagnostics have used Faraday rotation of a probing laser beam and Zeeman profiles of emitted spectral lines.
GW-level high-power CO2 laser system
Authors: Guoliang Zhuang , Shusheng Yu. , Wanqing Niu , Longlong Du , Mingfu Li , Hong Jiang
Published: March 2009

A Gw-level high-power CO2 laser system has been developed. A short laser pulse is cut out with a double Pockels cell electrooptical shutter from a hybrid CO2 laser oscillator and amplified with a three-stage dual-path TEA preamplifier, a two-stage TEA preamplifier, a large aperture TEA amplifier, and an electron beam-controlled final amplifier. All parts of the laser system are controlled with a control system. The laser output power is up to 3.2 × 109 W and laser pulse width is 4 ns full width at half maximum.
Equations of state for ions in non-LTE plasmas
Authors: Eliezer S. , Mínguez E.
Published: March 2009

For nonlocal thermodynamic equilibrium (LTE), the equations of state are not well defined and therefore the hydrodynamic equations are not applicable. In this case, the general transport equations (e.g., Boltzmann or Fokker–Planck) should be used. However, the coupling between atomic physics (rate equations) and the transport equations is extremely complicated. This article shows how the information given by the rate equations is translated into an effective potential. This “potential” theory is explicitly shown for two cases: lithium-like iron plasmas and aluminum plasmas. Moreover, it is suggested that the “collision terms,” and all other interactions that are not taken into account by the explicit rate equations, are described by a stochastic force given by a Langevin equation or equivalently by a Fokker-Planck equation in the ion density space.
Treatment of edge beams in a focusing self-magnetically Bθ-insulated ion diode
Authors: Westermann Thomas , Bauer Walter
Published: March 2009

When focusing light ions with intense light ion-beam diodes, problems occur with ions emitted at the edge of the anode plasma. Numerical studies investigating this well-known experimental observation are presented. Going beyond the computational simulations introduced by Westermann (1991 Appl. Phys. Lett. 58, 696), two suggestions for the case of the self-magnetically Bθ-insulated ion diode are presented to focus the beamlets emitted from outer parts of the anode. The first one is based upon the idea of changing nonemitting parts of the anode surface and the second one of shifting the emitting anode surface into the anode body.
Status and issues in the development of a γ-ray laser. II. Giant resonances for the pumping of nuclei
Authors: Collins C.B. , Carroll J.J. , Taylor K.N. , Sinor T.W. , Hong C. , Standifird J.D. , Richmond D.G.
Published: March 2009

A γ-ray laser would stimulate the emission of radiation of wavelengths below 1 Å from excited states of nuclei. However, the anticipation of a need for high pump powers tended to discourage early research and the difficulties in demonstrating a device were first assumed to be insurmountable. Over the past decade, advances in pulsed-power technology have changed these perceptions and studies have built a strong momentum. A nuclear analog of the ruby laser has been proposed and many of the component steps for pumping the nuclei have been demonstrated experimentally. A quantitative model based upon the new data and concepts has shown the γ-ray laser to be feasible if some real isotope has its properties sufficiently close to the ideals modeled. The greatest positive impact upon feasibility has come from the discovery of giant resonances for pumping nuclei that greatly reduce the levels of pump power needed.
Measurement of multiphoton absorption and electron avalanche in optical thin films
Authors: Nishioka H. , Kawasumi T. , Ueda K. , Takuma H.
Published: March 2009

Measurements on nonlinear processes caused by multiphoton absorption and electron avalanche in optical thin films have been carried out using KrF lasers of 20-ns and 1.7-ps pulse duration. Multiphoton absorption of the order of 10-7 J was detected by a photoacoustic signal, and the nonlinear growth of photo-induced current due to the electron avalanche was analyzed dynamically. The correlation between damage threshold and carrier lifetime was investigated for oxide and fluoride coatings.
Line profile modeling for non-LTE partially ionized plasmas based on average atom model with l–splitting
Authors: Nishikawa T. , Takabe H. , Mima K.
Published: March 2009

We have developed a new opacity modeling of partially ionized high-Z plasma to solve radiation transport in fluid codes. The average atom model is used to describe the electronic state of the plasma. The electronic state of the plasma is determined by solving the collisional radiative equilibrium model. We have taken into account the electron energy level splitting owing to the difference in the azimuthal quantum number. To model the line groups made of the same electronic transitions from ions indifferent charge states, we used a statistical method and calculated the distribution of the charge states from the averaged electron population in each bound state. By using the new opacity model, we can well reproduce the X-ray spectra from the plasmas. It is found that the Δn = 0 transition can explain the peaked spectra near hv = 300 eV and l–splitted emission of the n = 5–4 transition can explain the flat spectra in the region of hv = 400–800 eV seen in the experiments.
Properties of an exploding foil neon-like germanium soft X-ray laser
Authors: Daido H. , Kato Y. , Murai K. , Yuan G. , Shiraga H. , Takabe H. , Nakai S. , Azuma H. , Miura E. , Lewis C. L. S. , O'Neill D. M. , Neely D. , Djaoui A.
Published: March 2009

We describe the properties of the exploding foil neon-like germanium soft X-ray lasers having wavelengths of 19–28 nm and gain length product of more than 10. The measured X-ray intensity of lasing lines from an exploding foil target has been explained with the results of the plasma hydrodynamic code from the viewpoint of suitable condition of electron density and temperature for creating population inversion.
Indirect drive for inertial fusion energy
Authors: Caruso A. , Strangio C.
Published: March 2009

A spherical scheme is introduced for indirect drive, having as reference the application to inertial fusion energy. The concept uses the transmission of a radiation wave through a high-Z, low-density spherical radiator surrounding the capsule to be imploded. The low conversion efficiency to in-cavity radiation is somewhat compensated by using modest radiator-to-capsule gaps, the smoothing effects on the longest dominant nonuniformity wavelengths due to this separation being of the order of 10. Another factor of the order of 100–500 is related to the consequent use of a large number of beams. From the application of the loop condition relative to power plants, it is found that this approacrTbecomes practicable if drivers with efficiencies greater than 10% are assumed and if the fraction of circulating power is allowed to be 0.5, this implying a unitary cost of energy about a factor 1.5 greater than that associated to the more conventional fraction of 0.25.
Laser–plasma research at MPQ
Authors: Sigel R. , Baumhacker H. , Brederlow G. , Eidmann K. , Fill E. , Massen J. , Meyer-Ter-Vehn J. , Schwanda W. , Stöckl Ch. , Tsakiris G. D. , Volk R. , Witkowski S. , Witte K. J.
Published: March 2009

The ASTERIX iodine laser delivers after frequency tripling to λ = 0.44-μm laser pulses with energies up to 500 J at a pulse duration of 300 ps for target experiments. Experimental investigations of radiative transfer in low- and high-Z materials are reported.
Suppression of stochastic pulsation in laser–plasma interaction by smoothing methods
Authors: Aydin M. , Hora H.
Published: March 2009

Smoothing of laser-plasma interaction by ISI, RPP, SSD, etc. was mainly directed to overcome lateral nonuniformity of irradiation. While these problems are in no way less important, we derived numerically the model of the Laue rippling and hydrorelaxation model for explanation of the measured temporal pulsation in the 10- to 40-ps range and how the smoothing schemes suppress these pulsations. The partial standing wave fields of the normally coherent laser-irradiated plasma corona is then suppressed by smoothing and conclusion for tests for this model, e.g., by the “question mark experiment” is given. The result provides a physics solution of the laser interaction problem for direct-drive inertial fusion energy
Atomic, molecular, and photonic processes in laser-induced plasmas in alkali metal vapors
Authors: Stwalley William C. , Bahns John T.
Published: March 2009

The production of laser-induced plasmas, which ordinarily occurs only at high laser powers, occurs at far lower laser powers using resonant and collisional phenomena in alkali metal vapors. For example, 10 torr of Na vapor can be significantly ionized to produce a bright white ball with as little as 1 mW of focused cw dye laser power (e.g., at the 3p → 4d transitions at 568.3 and 568.8 nm). We first discuss the alkali metal vapors in general (1) and their important ionization processes (2), especially those occurring at photon energies below the atomic ionization energy. We then discuss the striking wavelength dependences of ionization. For example, cw laser irradiation of these vapors gives completely different behavior at slightly different wavelengths (Stwalley 1990): 10 torr of sodium vapor at 568.2 nm, where the vapor shows only molecular fluorescence and is sufficiently quiescent that highly stable, narrow-band, optically pumped lasers based upon the fluorescent transitions can easily be constructed (Bahns 1983; Bahns et al. 1983; Verma et al. 1983); and, at 568.3 nm, where a “quasiresonant” laser-induced plasma forms and strong emission (including violet excimer bands, a potential laser) is produced (Koch & Collins 1979; Bahns et al. 1989a; Bahns et al. 1989b). We will analyze and reinterpret the classic subthreshold ionization studies (3) and survey recent laser-induced plasma studies (4). We also discuss dissociative recombination and its selectivity for producing strong excimer emission (5) the predicted electronic spectra of the alkali metal molecular ions (6).
A technique to study Rayleigh–Taylor instability by α-particle backlighting
Authors: Fews A. P. , Savage M. , Lamb M. J.
Published: March 2009

A novel α-particle backlighting technique has been developed to diagnose laser plasmas, enabling small changes in the thickness modulation to be measured, down to ~0.1 μm. In this technique, a laser-driven implosion of a D–T target produces a bright pulse of α-particles that is used to shadow a separately driven foil. Each α-particle loses range in the foil, and each such measurement forms an individual local determination of the foil thickness at the time of passage of the particles. A shadow image of the driven foil can also be produced, of spatial resolution limited by source size and multiple Coulomb scattering in the driven plasma. The technique is illustrated here with a preliminary study of fluid instabilities in laser-accelerated planar foils. Foils were accelerated using both unsmoothed and smoothed laser drive beams. Foils driven by beams smoothed by random-phase plates showed a much reduced modulation.
Three-dimensional α-particle imaging of laser-driven implosions
Authors: Fews A.P. , Lamb M.J. , Savage M.
Published: March 2009

A technique is demonstrated for optimally generating three-dimensional reconstructions of images formed using a minimal quantity of data. The results are illustrated using thermonuclear α-particles from laser-driven implosions. The images are generated with a maximum entropy deconvolution algorithm from sets of three or four penumbral imaging cameras. It is demonstrated that this approach provides superior resolution and reveals structures not visible from the corresponding two-dimensional reconstructions of the constituent data. This technique can be successfully applied even when the total number of particles recorded in the image is less than 1000.
Self-similar expansion of laser plasmas with nonlocal heat flux
Authors: Ramírez J. , Sanmartín J.R.
Published: March 2009

A previous hydrodynamic model of the expansion of a laser-produced plasma, using classical (Spitzer) heat flux, is reconsidered with a nonlocal heat flux model. The nonlocal law is shown to be valid beyond the range of validity of the classical law, breaking down ultimately, however, in agreement with recent predictions.
Tandem acceleration of dust plasma and impact fusion
Authors: Pozwolski A.E.
Published: March 2009

The achievement of hypervelocities (40 km/s or more) is considered by the electrostatic simultaneous acceleration of dust particles positively and negatively charged. This ensures current neutralization. Beams carrying several grams of matter look feasible. The mutual impact of these macroparticles results in temperatures in the fusion range.
Application of pulse power technology to inertial confinement fusion: Focusing and propagation of proton beam
Authors: Niu K.
Published: March 2009

It is the aim of this article to design a fusion power plant whose electric output power is 1 GW and find a way for breaking through fusion technically and energy economically. Proton beams whose total energy is 12 MJ, pulse width 30 ns, and beam number 6 are chosen here as the energy driver. Because of the low quality of these proton beams, the target should be indirect driven and its radius should be large. The target with the radius of 8.7 mm is the spherical cryogenic hollow one, which has double shells and five layers. The reactor has double solid walls. The inner wall rotates around the axis to induce a centrifugal acceleration. Flibe as the coolant protects the solid walls from damage and breeds tritium. The key technology of this power plant is for beam focusing and propagation. To suppress beam divergence by the electrostatic force due to unneutralized proton charge, simultaneous electron beam launching is proposed. When the excess electron beam current is –50 kA, the induced magnetic field in the azimuthal direction confines the beam in a radius of 5 mm, provided that the beam path is covered by the metal guide whose radius is 6 mm.
Random-phase plate effects on burn-through measurements of laser-irradiated plane-layered targets
Authors: Evans R. , Ahmad Z. , Hall T.A. , Zakharenkov Y.A.
Published: March 2009

The application of random-phase plates in laser beams to improve the uniformity of target ablation is investigated by combining the simultaneous X-ray and particle emission measurements of ablation characteristics. It is shown that if some hot spots with dimensions of a few µm exist on target they persist at least during the initial stages of the laser interaction process, producing a local maximum in the ablation pressure. Lateral energy transport, inferred from the neutral particle measurements, has little influence on absorbed energy redistribution (only 1% of the energy is transported from the laser focal spot to an outer region of 2 mm size).
Present status and prospect of KrF laser physics and technology–large volume excitation and UV optics
Authors: Ueda Ken-Ichi
Published: March 2009

The physics and technology for e-beam generation, large volume excitation and the ultra-violet optics for high power KrF lasers is presented. The potential, due to the charge deposition, induces a return current in the plasma which balances the e-beam current. The local equilibrium mechanism stabilizes the large volume excitation using intense electron beams. The spatial and temporal characteristics of large aperture diodes are analyzed. Substantial progress in ultra violet optics in Japan has been achieved. The damage threshold of HR dielectric coating increases up to 11 J/cm2 by using low absorption materials.
Development of a high-power KrF laser system, ASHURA
Authors: Owadano Y. , Okuda I. , Matsumoto Y. , Tanimoto M. , Tomie T. , Koyama K. , Yano M.
Published: March 2009

The present status of the development of a high-power KrF laser system, Ashura, is described. The main amplifier has generated 710 J (95 ns) at the pumping density of 1·lMW/cm3 with the wall plug efficiency of 2·0%. Maximum power of 9·0 GW (200 J/22 ns) per beam has been obtained from the beam lines of six-time pulse multiplexing. Power density of 1 × 1014 W/cm2 has been achieved on target with a 10−6 pre-pulse.
Present and future of laser fusion
Authors: Yamanaka C.
Published: March 2009

The key issues of laser fusion are to achieve highly efficient implosion by the ablation and to reach the high gain of a fuel pellet. Measures of the success are the neutron yield and the areal density of the fuel. Recent results show the neutron yield per laser shot to be 1013, and the ρR is 0·2g/cm2. These data seem to be approaching the breakeven condition.
X-ray diagnostics for fusion plasmas
Authors: Fujita J. , Morita S. , Sakurai M.
Published: March 2009

We have developed medium and high resolution X-ray crystal spectrometers for measurements of charge state distributions of impurity ions, density of suprathermal electrons and ion temperature in magnetically confined plasmas. The techniques utilizing these spectrometers are, in principle, applicable to laser produced plasmas, especially in their expanding phase. The role of X-ray spectroscopy to produce useful data for atomic physics as well as for plasma diagnostics is emphasized. A beam-line has been designed and installed to the Ultraviolet Synchrotron Radiation Facility (UVSOR) at IMS, Okazaki, for the purpose of establishing calibration techniques for optical components, detectors and spectrometers in the range from ultraviolet to soft X ray for plasma diagnostics. Characteristics of the beam and its application to the study of interaction between synchrotron radiation and hot dense plasmas are described. Synchrotron radiation can replace the dye laser which has so far been used as a light source in the laser-induced fluorescence method to obtain population density of specified levels in a plasma.
Energy transport experiments at Institute of Laser Engineering, Osaka University
Authors: Tanaka K. A. , Kato Y. , Nakai S. , Shiraga H. , Yabe T. , Yamanaka T. , Endo T. , Kodama R. , Yamanaka C.
Published: March 2009

Emissions from the rear side of the targets were temporally resolved by irradiating an ultraviolet (UV) laser on Al and Au thin targets. A difference was clearly observed between the above two targets. Given the fact that absorbed laser energy is converted with a very high efficiency to soft x-rays in a high Z plasma, a characteristic emission peak only observed for Au targets was attributed to the effect of soft x-ray energy transport. The ablation pressures estimated from the emissions indicate that the pressure scaling for Au is close to the one by x-ray radiation rather than by a UV laser. With soft x-ray irradiation, energy transport in A1 foils was also studied. An ablation pressure was estimated by the shock speed.
Volume compression and volume ignition of laser driven fusion pellets
Authors: Kasotakis G. , Cicchitelli L. , Hora H. , Stening R. J.
Published: March 2009

Volume compression and volume ignition of laser compressed pellets has an enormous advantage against spark ignition since the alpha self-heat substantially contributes as an additional stimulation of nuclear fusion reactions. We present here improved computations of volume ignition in agreement with the classical fact that the generated fusion energy is larger than the bremsstrahlung energy in DT only at temperatures above 4·5 keV. This result is in very close agreement with Kidder's (1974) values, and in agreement with recent computations of Mimaet al.(1987). The extension of these calculations to higher densities and input energies results in the self-absorption of bremsstrahlung at an initial temperature of about 1 keV only, much below the classical 4·5 keV. A fuel burnup fraction above 80% is shown to be possible.
Nanolithography for VLSI and ULSI
Authors: Namba Susumu
Published: March 2009

Lithography techniques hold the key to achieving ultra large-scale integration (ULSI) and they have been a major research subject. For fabrication of ULSI devices, a quarter micron or smaller pattern delineation with nanometer scale accuracy is required. Various techniques using electron, ion and photon beams have been investigated to fulfill these requirements. The present paper discusses the characteristics of several key lithography techniques and their limitations.
RF production of high density plasmas for accelerators
Authors: Chen Francis F.
Published: March 2009

Preliminary experimental results are shown on the production of plasmas by low frequency helicon waves. At constant rf frequency and power, the results show a maximum in density as the dc magnetic field is varied. The measurements confirm the theoretical expectation that the plasma is ionized by Landau damping of the radiofrequency waves.
Electron linear accelerator based on cross field acceleration principle
Authors: Nishida Yasushi
Published: March 2009

Powerful lasers have the potential to be used for power sources of the high energy particle accelerators. However, we have to convert the transverse wave into a longitudinal one which can trap the charged particles in the wave trough to accelerate them. In order to obtain a high field-gradient in an accelerator, several new concepts have been proposed. One of them is a beat wave accelerator (BWA) which uses a nonlinear optical mixing of two laser beams. Another concept is a Cross Field Acceleration (or a Vp × B acceleration) scheme, in which the trapped particles in the wave trough are accelerated along the wavefront and across the static magnetic field applied externally. An overview is presented including some new results.
Hydrodynamics of supercritical region in laser ablated plasmas
Authors: Vaselli M. , Palleschi V. , Singh D. P.
Published: March 2009

The laser ablated plasma flow and subsequent plasma density profile in steep plasma temperature gradient in spherical geometry are studied. Using local flux-limited model of heat flow the effect of flux-inhibition on the hydrodynamics of plasma ablation zone is investigated. The radial variation of thermal flux through local flux-limited model with recently accepted numerical range of flux-limit ≈ 10% of the free streaming is in close agreement with Spitzer's classical thermal conduction reduced by about an order of magnitude which may be attributed to the presence of megagauss level self-generated magnetic fields as predicted earlier to interpret experimental observations on X-rays emission spectra.
Repetitive semiconductor opening switch and application to short pulse generation
Authors: Chauchard E. A. , Kung C. C. , Lee Chi H. , Rhee M. J.
Published: March 2009

We describe the operation of a repetitive semiconductor opening switch in conjunction with inductive energy storage systems. Different materials and switch configurations are examined. A new method of generating square pulses of nanosecond duration is implemented. It utilizes the opening switch and a current charged transmission line.
Ionospheric accelerator
Authors: Tajima T. , Horton W. , Nishikawa S. , Nishikawa T.
Published: March 2009

Ionospheric acceleration of high energy particles by a short wavelength microwave pulse is discussed. The intense electromagnetic waves in an ionospheric (F2) or magnetospheric plasma can be self-trapped above a threshold power. The self-binding property and the consequent self-induced transparency of the triple soliton structure of two electromagnetic waves and a plasma wave allow the propagation of an intense electromagnetic pulse without the severe and wasteful distortion that accompanies low power pulse propagation. The effects of magnetospheric fluctuations on the particle beam transport are considered. The fluctuation-induced transport seems to be within the margin of tolerance for useful beam transport. Orbits of negatively charged particles are stable. While synchrotron radiation loss for electrons is prohibitive, that of muons and antiprotons is negligible. A corresponding terrestrial application is also suggested.
Computer modeling of ICF target chamber phenomena
Authors: Moses Gregory A. , Peterson Robert R.
Published: March 2009

The target chamber of an inertial confinement fusion (ICF) power plant or high-yield test facility must be designed to absorb the target produced Xrays and ions and survive the resulting effects. The target chamber conditions must be restored in fractions of a second for high repetition rate power applications. Computer modeling of these phenomena is essential because equivalent conditions cannot be produced in laboratory experiments prior to the first ignition of high-yield ICF targets. Choices of models are dictated by specific reactor design strategies. The two major strategies, gas protection and sacrificial first surfaces, are used as a guide to our discussion. Physical models for ion, electron, and X-ray deposition are discussed, along with physical and numerical modeling of the resulting phase changes intarget chamber structures. The hydrodynamics and radiative transfer in the target chamber vapors and plasmas are central topics.
Three-dimensional simulations of the Rayleigh–Taylor instability during the deceleration phase
Authors: Town R.P.J. , Jones B.J. , Findlay J.D. , Bell A.R.
Published: March 2009

The growth of the Rayleigh-Taylor instability in three dimensions is ex amined during the deceleration phase of an inertial confinement fusion implosion. A detailed discussion of the three-dimensional hydrocode, PLATO, is presented. A review of previous calculations is given, concentrating on theshape of the R-T instability in three dimensions. Results of the growth rate during the linear phase, the saturation amplitude, and the nonlinear evolution are presented.
Ultrashort powerful laser matter interaction: Physical problems, models, and computations
Authors: Gamaly E.G.
Published: March 2009

The different physical models, computational methods, and results describing the properties of a plasma produced by an ultrashort laser pulse interacting with a solid target at different laser intensities are presented. The basic issues affecting the laser-plasma interaction are considered, including: the different absorption mechanisms; the formation of a transient, nonequilibrium, asymmetric electron distribution function; the energy losses; the role of instabilities and the ponderomotive force; ion expansion and acceleration; and surface wave propagation along the boundary of the plasma. The article concludes with a discussion of the range of applicability of the different approximations and future perspectives for the field.
Computational modeling for X-ray lasers
Authors: Pert G.J.
Published: March 2009

Various problems involved in the simulation of current X-ray laser experiments are discussed. The methods are based on laser-plasma simulation techniques with simultaneous calculation of the ionization dynamics, and are particularly appropriate for collisional and recombination pumped systems.
Semi-classical calculation of atomic processes and numerical simulation of dense plasmas
Authors: More R.M.
Published: March 2009

Modern numerical simulations of hot dense plasma require atomic data including equations of state, opacities, and coupling coefficients for energy exchange between photons, electrons, and fast and thermal ions. While these coefficients may be calculated by complicated quantum-statistical theories, in many cases the simpler semi-classical theory gives a reasonably accurate first approximation.
Simulation codes for light-ion diode modeling
Authors: Quintenz J.P. , Seidel D.B. , Kiefer M.L. , Pointon T.D. , Coats R.S. , Rosenthal S.E. , Mehlhorn T.A. , Desjarlais M.P. , Krall N.A.
Published: March 2009

The computational tools used in the investigation of light-ion diode physics at Sandia National Laboratories are described. Applied-B ion diodes are used to generate intense beams of ions and focus these beams onto targets as part of Sandia's inertial confinement fusion program. Computer codes are used to simulate the energy storage and pulse forming sections of the accelerator and the power flow and coupling into the diode where the ion beam is generated. Other codes are used to calculate the applied magnetic field diffusion in the diode region, the electromagnetic fluctuations in the anode-cathode gap, the subsequent beam divergence, the beam propagation, and response of various beam diagnostics. These codes are described and some typical results are shown.
High-density, direct-drive implosion experiments
Authors: McCrory R. L. , Soures J. M. , Verdon C. P. , Marshall F. J. , Letzring S. A. , Kessler T. J. , Knauer J. P. , Kim H. , Kremens R. L. , Skupsky S. , Keck R. L. , Bradley D. K. , Seka W. D. , Jaanimagi P. A. , Delettrez J. A. , McKenty P. W.
Published: March 2009

A critical test of direct-drive laser-fusion has been conducted with the demonstration of DT compression to densities in the range of 100–200 times liquid density in experiments on the University of Rochester's OMEGA laser facility. The high-density cyrogenic experiments used 351-nm laser pulses with energies of 1500–1800 J and pulse widths in the range of 600–700 ps.
2-D Simulation for focus of rotating and propagating ion beam in neutral gas
Authors: Aoki Takayuki , Niu Keishiro
Published: March 2009

Focusing processes of rotating and propagating proton beams in a neutral hydrogen gas are studied numerically by using a two-dimensional hybrid code. Processes including beam impact ionization, plasma avalanche and field emission are taken into consideration. The plasma formation time depends on the initial gas density and the beam intensity. When 2-Torr neutral gas is filled initially, enough plasma density is created by the rising part of the beam pulse, so that the main pulse is focused and forms a rotating and propagatingbeam configuration.
Analysis of the atomic physics models for the multigroup opacities calculation
Authors: Mínguez E. , Gámez M. L.
Published: March 2009

The calculation of the multigroup opacities using several different atomic physics models is the main goal of this work. The atomic data, such as energy levels, bound-electron populations, oscillator strengths and effective charges are worked out by two atomic physics models using the average-atom concept. The result achieves multifrequency opacities. These are weighted with the Planck function or the real radiation field, making up finally the multigroup opacities in the selected number of groups.
Laboratory laser-produced astrophysical-like plasmas
Authors: Ripin B. H. , Manka C. K. , Peyser T. A. , McLean E. A. , Stamper J. A. , Mostovych A. N. , Grun J. , Kearney K. , Crawford J. R. , Huba J. D.
Published: March 2009

Laser-produced plasmas have many properties similar to, or which can be scaled to, those encountered in space, magnetospheric, ionospheric, and astrophysical situations. We describe several such experiments performed with the PHAROS III Nd-laser facility at NRL.
Effect of the hydrodynamic instability on the burn-through time measurements
Authors: Fiedorowicz H. , Kolanowski M.
Published: March 2009

Thermal energy transport in laser-irradiated glass microshells coated with polystyrene/metal layers seems to be dominated by hot spots. These are connected with filaments which are enhanced by hydrodynamic instability of the Rayleigh-Taylor type.
Fabrication of ICF reactor targets based on symmetrization of solid fuel
Authors: Foreman Larry R. , Hoffer James K.
Published: March 2009

Tritium self-heats at a rate of 97 W/mole because of its β activity. This energy drives preferential sublimation of solid T2 or DT from regions where a layer is thicker and warmer to regions where the layer is thinner and colder. A frozen tritium layer inside an isothermal container approaches isotropy exponentially with a time constant as short as 14.4 minutes. Targets Isotropized by Radioactively Induced Sublimation (IRIS) and sized for an ICF reactor demonstrate high gain and offer real fabrication advantages.
Dynamics of double stimulated Brillouin scattering
Authors: Pättikangas T. J. H. , Salomaa R. R. E.
Published: March 2009

The pump wave reflected from the overdense plasma may play an important role in the dynamics of stimulated Brillouin scattering. The particular case of Double Stimulated Brillouin Scattering (DSBS) suggested by Zozulya, Silin, & Tikhonchuk [Sov. Phys. JETP 59, 756 (1984)] is studied here in detail. In DSBS the incident pump wave and the reflected pump wave scatter from a common ion acoustic wave. Some steady state properties of DSBS are reviewed. The analysis of DSBS dynamics is based on a series of ‘numerical experiments’.At small pump intensities the system asymptotically approaches a true steady state. When the intensity is increased the solution turns into a regular pulse train with intensity dependent period. Connections between the pulses and soliton-like solutions of a damped sine-Gordon equation are discussed.
2-D studies of non-uniformly irradiated spherical shells
Authors: Atzeni Stefano
Published: March 2009

The effect of long scale-length irradiation non-uniformities on the implosion of two different directly driven, gas filled shells (representative of large families of laser fusion targets) is studied by means of 2-D numerical fluid simulations. Quantitative results are given for parameters measuring the shell deformation and the azimuthal variation of the (density × radius) product (<ρR) as functions of the wavelength and of the amplitude of the irradiation non-uniformity. The reflection of the imploding shock wave is also qualitatively illustrated.