bluuebunny/crossref_metadata_2025_split huggingface dataset:
Charged particle spectra from U-235 and B-10 micropellets and slab coatings
Authors: Chung A. K. , Prelas M. A. 
Published: March 2009

A novel method of utilizing fluorescence generated from the products of nuclear reactions offers the prospect of compact, high efficiency, multi-megajoule lasers. To overcome the problems associated with traditional laser (or energy converter)-fissile material interfaces, such as a uranium coating (low power density and low efficiency) or a gaseous uranium compound (low power density and deleterious effects on the laser kinetics and photon transport), a method suggested elsewhere of employing a reactor using a uranium aerosol fuel, interspersed with a fluorescer medium, is briefly reviewed. The charged particles produced by nuclear reactions in the fuel produce fluorescence in the core region of the reactor, through interactions with the fluorescer. This fluorescence can then be concentrated, to increase the effective power density in the laser medium, and used to drive a photolytic laser.One key issue in the above process is the charged particle spectrum from the fissile aerosol. These issues can be addressed theoretically based on the Dirac chord length distribution technique and an Arcen's function. The charged particle spectrum from a UO2 coating has been generated and benchmarked with the experimental data of Kahn et al., and Redmond et al. Agreement is generally good except near the end of the fission fragment tracks. The validity of this simple technique in approximating the rate of ion energy loss lends confidence to the generation of fission fragment spectra for other geometries (i.e. spherical in which transport efficiencies of over 60% appear achievable) using U, UO2 and U3O8. Work is also extended to the case of B-10 in a variety of configurations which are frequently used in modern energy conversion experimental devices.
Atomic physics for beam-target interactions
Authors: Deutsch C. 
Published: March 2009

This survey is devoted to a few basic atomic problems associated with the stopping of nonrelativistic pointlike ions in dense and hot matter, and also to the Stark broadening diagnostics of the resulting beam-produced plasmas.First, we consider the free electron contribution, taken in the RPA approximation with an exact dynamic dielectric function, valid at any temperature. Therefore, we obtain stopping power and straggling for any projectile velocity. The temperature dependence is of special relevance for a projectile energy smaller than 5 MeV/a.m.u.Next, we revise the Barkas effect (Z3 corrections) through a novel and compact formulation, which is based on an analogy with electron impact broadening theory. It facilitates inclusion of the non hydrogenic and electronic structure of the target ions, in a more selective way. The results may increase the usual Z2-stopping by 15 to 30 per cent corrections.Then, we show how the Stark broadening diagnostics of the compressed D + T fuel, seeded with high Z species, arising from the surrounding envelopes, may provide accurate determination of the electron number density ne. In this connection, it should be appreciated that the relatively long compression times (≃ 20 nsec) suggested by the HIBALL numerical simulation allow for a nearly Local Thermodynamic Equilibrium (LTE) state in the target, with Te ≃ Ti. As a consequence, spectroscopic measurements are expected to be easier to implement in HIF targets, than in laser ones.A tentative proposal for the use of Stark broadening diagnostics of inflight excited and highly stripped ion projectiles is displayed in § 5.Experiments involving an HIB produced by a standard accelerator, and interacting with an independently produced coronal plasma are finally outlined.
Model equation-of-state for any material in conditions relevant to ICF and to stellar interiors
Authors: Atzeni S. , Caruso A. , Pais V. A. 
Published: March 2009

A simple model Equation-of-State (EOS) for matter in conditions of interest to Inertial Confinement Fusion (ICF) and to Stellar Interiors is developed. It yields pressures and specific energies in good agreement with accurate EOS tabulations, for matter in the density range 10−6 < ρ < 104 g cm−3 and in the temperature range 0 ≤ T < 100 KeV, with the only exception being the liquid and gaseous phases of the undissociated molecular substances.This EOS can be used for any element or mixture, requiring, as input data, only the chemical composition (A, Z, and abundancy of each element of the mixture) and three macroscopic constants of the material.
Laser program development at CEL-V: overview of recent experimental results
Authors: Buresi E. , Coutant J. , Dautray R. , Decroisette M. , Duborgel B. , Guillaneux P. , Launspach J. , Nelson P. , Patou C. , Reisse J. M. , Watteau J. P. 
Published: March 2009

A significant effort has been made recently at CEL-V to improve laser facilities. OCTAL, the eight beam, 2 kJ laser, has been equipped with phosphate glass and KDP frequency tripling systems. PHEBUS, a two beam 20 kJ neodymium glass laser based on NOVA technology was denned and built and will be tested in early 1986 in close collaboration with Lawrence Livermore National Laboratory.In the field of diagnostics, the development of soft X-ray emission analysis has been emphasized.Most of the recent experimental results have been obtained at a short wave-length (0·35 μm). They deal with the effect of non-uniform illumination, 2D hydrodynamics with either plane or spherical targets, and the study of thermal transport inhibition.
Some aspects of double layer formation in a plasma constrained by a magnetic mirror
Authors: Lennartsson W. 
Published: March 2009

The discussion of parallel electric fields in the earth's magnetosphere has undergone a notable shift of emphasis in recent years, away from wave-generated anomalous resistivity towards the more large-scale effects of magnetic confinement of current carrying plasmas. This shift has been inspired in large part by the more extensive data on auroral particle distribution functions that have been made available, data that may often seem consistent with a dissipation-free acceleration of auroral electrons over an extended altitude range.Efforts to interpret these data have brought new vigor to the concept that a smooth and static electric field can be self-consistently generated by suitable pitch-angle anisotropies among the high-altitude particle populations, different for electrons and ions, and that such an electric field is both necessary and sufficient to maintain the plasma in a quasi-neutral steady state. This paper reviews and criticizes certain aspects of this concept, both from a general theoretical standpoint and from the standpoint of what we know about the magnetospheric environment. It is argued that this concept has flaws and that the actual physical problem is considerably more complicated, requiring a more complex electric field, possibly including double layer structures.
Directions for reactor target design based on the U.S. Heavy Ion Fusion Systems Assessment
Authors: Wilson D. C. , Dudziak D. , Magelssen G. , Zuckerman D. , Driemeyer D. 
Published: March 2009

The Heavy-Ion Fusion Systems Assessment project is nearing completion of a two-year effort. The resulting system modelwill be used to set directions for future target design work.Major uncertainties in target design were studied using thecost of electricity as a figure of merit. Net electric power was fixed at 1000 MW to eliminate large effects due to economies of scale. The system is relatively insensitive to target gain, factors of three changes in gain resulting in 8 to 12% changes in electricity cost. Possible increased peak power requirements pose only a small cost risk, but require many more beamlets for transport. A shortening ofthe required ion range causes both cost and beamlet difficulties. A factor of 4 decrease in the required range at a fixed driver energy increases electricity cost by 44% and raises the number of beamlets to 240. Finally, the heavy ion fusion system can accommodate large increases in target costs. Thus, to address the major uncertainties, target design should concentrate on requirements for ion range andpeak driver power.
Gas–puff Z pinches with strong axial magnetic fields
Authors: Felber F. S. , Wessel F. J. , Wild N. C. , Rahman H. U. , Fisher A. , Fowler C. M. , Liberman M. A. , Velikovich A. L. 
Published: March 2009

Ultrahigh axial magnetic fields have been compressed and measured in a gas-puff Z pinch. A 0·5-MA, 2–cm-radius annular gas-puff Z pinch with a 3-minute repetition rate was imploded radially onto an axial seed field, causing the field to compress. Axial magnetic field compressions up to 180 and peak magnetic fields up to 1·6 MG were measured. Faraday rotation of an argon laser (515·4 nm) in a quartz fiber on axis was the principal magnetic field diagnostic. Other diagnostics included a nitrogen laser interferometer, x-ray diodes, and magnetic field probes.The magnetic field compression results are consistent with simple snowplow and self-similar analytic models, which are presented. The axial magnetic fields strongly affect the Z pinch dynamics. Even small axial fields help stabilize the pinches, some of which exhibit several stable radial bounces during a current pulse.The method of compressing axial fields in a gas-puff Z pinch is extrapolable to the order of 100 MG. Scaling laws are presented. Potential applications of ultrahigh axial fields in Z pinches are discussed for x-ray lasers, inertial confinement fusion, and collimated sources of gamma radiation.
Quasi-static MHD processes in Earth's magnetosphere
Authors: Voigt Gerd-Hannes 
Published: March 2009

The purpose of this paper is to demonstrate how the MHD equilibrium theory can be used to describe the global magnetic field configuration of Earth's magnetosphere and its time evolution under the influence of magnetospheric convection. The MHD equilibrium theory represents magneto-hydrodynamics in the slow-flow approximation. In this approximation time scales are long compared to typical Alfvén wave travel times, and plasma flow velocities are small compared to the Alfvén speed. Under those conditions, the inertial term ρ(dv/dt) in the MHD equation of motion is a small second order term which can be neglected. The MHD equilibrium theory is not a static theory, though, because time derivatives and flow velocities remain first order quantities in the continuity equation, in the thermodynamic equation of state, and in the induction equation. Therefore one can compute slowly time-dependent processes, such as magnetospheric convection, in terms of series of static equilibrium states. However, those series are not arbitrary; they are constrained by thermodynamic conditions according to which the magnetosphere evolves in time.It is an interesting question, whether or not the magnetosphere, driven by slow, lossless, adiabatic, earthward convection of magnetotail flux tubes, can reach a steady state. There exist magnetospheric equilibria in which magnetotail flux tubes satisfy the steady-state condition d/dt (Pρ−γ) = 0. Those configurations exhibit a deep magnetic field minimum in the equatorial plane, near the inner edge of the tail plasma sheet. The magnetosphere becomes tearing-mode unstable in the neighborhood of such a minimum, thus leading to periodic onsets of substorms in the inner plasma sheet. This explains why distinct magnetic field minima have not been observed in this region. Magnetic substorms seem to be an inevitable element of the global convection cycle which inhibit the establishment of an ultimate steady state.MHD equilibria discussed in this paper result from linear and non-linear solutions to the two-dimensional Grad-Shafranov equation for isotropic thermal plasma pressure.
Propagation of microsecond electron beams in gases and excimer laser-ionized channels in the ion-focused regime
Authors: Lucey R. F. , Gilgenbach R. M. , Tucker J. E. , Enloe C. L. 
Published: March 2009

Experiments have been performed to investigate the transport and stability of microsecond-pulselength intense relativistic electron beams in the ‘ion-focused regime’ (IFR) in low-pressure neutral gas and laser-preionized channels. Beams have been generated by the Michigan Electron Long Beam Accelerator (MELBA) which operates with parameters: voltage = −0·7 to −1 MV electrically compensated for collapsing diode impedance over the first 1·5 μs, pulselength = 0·1 to 4μs limited by diode closure, and current = 0·2 to 30 kA.Long pulse beam propagation experiments have demonstrated the following effects:1) At pressures of 1–230 m Torr in air and helium with no laser-preionized channel:a) the electron-beam transport efficiency peaks after times longer than the time calculated for beam-induced ionization to reach fe. = 1. Up to 100% efficient transport occurs during short spikes over a 1 m propagation distance.b) Within 100 ns of efficient transport the propagated beam exhibits rapid beam cutoff in air and helium. This initial pulse of propagated current is followed by a series of 10 ns to 60 ns duration spikes for the remainder of the injected beam pulse. At higher gas pressures usually less current is propagated in the later peaks. At the lowest pressure for which significant current is propagated (7·6 m Torr air, 14 m Torr helium) the maximum transported current occurs in one of the later peaks.2) In initial experiments with excimer-laser-ionized channels in diethylaniline at pressures of 3–8 × 10−4 Torr the electron-beam transport over 1·2 m is efficient (80% to 100%) for at least the first 0·5 μs and does not exhibit the erratic transport observed in the electron-beam induced channels. For fixed laser energy, a narrow pressure window exists for efficient and stable long pulse electron-beam transport. Pressures below optimal give inefficient transport while higher pressures cause ejection of the beam from the ionized channel at later times.
Simulation code for ICF including radiative energy transfer
Authors: Velarde G. , Aragonés J. M. , Honrubia J. J. , Martínez-Val J. M. , Mínguez E. , Ocaña J. L. , Perlado J. M. 
Published: March 2009

New improvements in the atomic physics models for numerically treating high density plasmas, typical of ICF, together with new algorithms for multigroup radiation transport are presented.The performance of Large High Aspect Ratio Targets has been numerically determined by using those models implemented in a one-dimensional hydro code. Some differences from experiments are identified, and a comparative analysis with other numerical codes is given.
Pellet and implosion scaling
Authors: Nakai S. 
Published: March 2009

Recent progress of pellet implosion research is remarkable in the obtainment of a high density (100 times solid density) and a high temperature plasma (which produces thermonuclear neutrons of 1013 per shot or a pellet gain of 0·2%) and in the corresponding understanding of the implosion physics. The data bases for laser fusion have been accumulated in preparation for a fusion ignition experiment and the achievement of break-even condition, which is estimated to be possible with 100 kJ blue laser.The recent progress of driver technology, such as new types of solid state lasers, excimer laser, light ion beam (LIB), heavy ion beam (HIB) and free electron laser, now enabled us to design a high pellet gain experiment with a MJ driver.
Sound waves and shock waves in high-density deuterium
Authors: Inoue Kazuko , Ariyasu Tomio 
Published: March 2009

The possibility of compressing the cryogenic hollow pellet of inertial confinement nuclear fusion with multiple adiabatic shock waves is discussed, on the basis of the estimation of the properties of a high-density deuterium plasma (1024−1027 cm−3, 10−1−104 eV), such as the velocity and the attenuation constant of the adiabatic sound wave, the width of the shock wave, and the surface tension.It is found that in the course of compression the wavelength of the adiabatic sound wave and the width of the weak shock wave sometimes become comparable to or exceed the fuel shell width of the pellet, and that the surface tension is negative. These results show that it is rather difficult to compress stably the hollow pellet with successive weak shock waves.
Synergism in inertial confinement fusion: a total direct energy conversion package
Authors: Prelas M. A. , Charlson E. J. 
Published: March 2009

The products of fusion reactions have unique properties which can be used for direct energy conversion. These products are neutrons and ions. Neutrons can be transported very long distances through solid materials and can interact with certain elements which have a very high absorption cross section. Ions on the other hand have a very short transport length even in a gaseous medium. It is possible to utilize these products in an inertial confinement fusion reactor with two different direct energy conversion devices: a nuclear-pumped laser using neutrons from the fusion reaction; a photon generator material combined with a photovoltaic converter using the ionic fusion products.It will be argued that a nuclear-pumped laser can be more efficient than a conventional laser. It will also be shown that an advanced energy conversion concept based on photon production and photovoltaics can produce ICF system efficiencies of 56%.
Theoretical studies on electron and radiation preheatings
Authors: Mima K. , Takabe H. , Nishiguchi A. , Kihara Y. , Nakai S. 
Published: March 2009

In order to enhance the coupling efficiency, a low Z ablator is generally used for ICF targets. The ablator thickness is appropriately chosen so it is burned out by the end of a laser pulse. Then all of the implosion kinetic energy is contained in the DT fuel. However, a small amount of preheating degrades the compression in a hollow shell, DT fueled target implosion. In this paper, we investigate the preheating level of the fuel shell by Fokker–Planck simulations of the electron heat transport.From the analysis, it is found that a thick surface layer of a laser irradiated low-Z target is preheated by Maxwellian tail electrons which have a long mean free path. Hence, we propose that the target be precompressed by a tailored pulse, in order to increase the shell ρΔR at the laser peak.
Physics of dense plasma research at MPQ
Authors: Witkowski S. 
Published: March 2009

The main tool for the laser plasma work at MPQ (Max-Planck-Institut für Quantenoptik) is the ASTERIX iodine laser delivering 300 J/300 ps pulses at 1·3 m, operational also at 2ω and 3ω. A fifth 30-cm diameter am lifier is under construction to increase the pulse energy up to 2 kJ.Soft X-ray radiation emitted by laser plasmas and its influence on energy transport and hydrodynamics is studied. Time and space resolved spectroscopic measurements of soft X-radiation from a variety of targets are compared with analytical models and computer results. Planck radiation is produced in gold cavities to study radiation hydrodynamics. Theoretical work comprises shock waves in solids, the electronic structure of very high density matter, radiation pumped X-ray laser and development of the appropriate computer codes.Estimates indicate that dense plasmas with temperatures of several ten keV can be produced with the heavy ion accelerator now under construction at GSI-Darmstadt. Experiments are being prepared to be started in 1991. Measurements at the present UNILAC-accelerator confirm the theoretical prediction that the energy loss of heavy ions in a plasma is much higher than in cold matter.
Radiation driven planar foil instability and mix experiments at the AWE HELEN laser
Authors: Hansom J. C. V. , Rosen P. A. , Goldack T. J. , Oades K. , Fieldhouse P. , Cowperthwaite N. , Youngs D. L. , Mawhinney N. , Baxter A. J. 
Published: March 2009

This paper reviews recent developments and achievements in the program of planar foil instability experiments being performed at the AWE HELEN laser. Point projection Xray backlighting, with spectroscopy, is used to measure hydrodynamic mix in radiatively accelerated ablator/foil packages; the mix is identified in the experimental radiograph from the overlap of distinguishable spectral absorption features associated with each of the constituent materials.The first part of the paper describes the backlighting technique, and briefly summarizes progress made in the past two years, leading to the first results being obtained on a “high mix” Parylene-C ablator/molybdenum payload package. The second part considers the full analysis of one such ‘high mix’ shot (Shot 7772), describing how the spatial distribution of mix has been quantified and considering the various sources of error. Comparisons are made with both one-dimensional and two-dimensional hydrocode simulations. Finally, various improvements and extensions to the experiment and codes are indicated.
Time dependence of the inversion condition and optimized X-ray emission in recombining laser-produced plasmas
Authors: Brunner W. , John R.W. 
Published: March 2009

The recombination X-ray laser scheme is considered in the case of recombining plasmas produced by laser pulses which are short to such a degree that the condition for inversion in X-ray transitions of the ions is essentially time-dependent. Using an analytic four-level model, applicable for H-like and Li-like ions, we calculate the inversion conditions for the 4→3, 3→2, and 2→l transitions in H-like ions as functions of time. As we have already shown, a drastic change occurs, especially for the 3→2 transition. To achieve inversion, for short times the free-electron density as a function of the temperature Te, Neinv(Te), must be greater than a critical density Nesh (Te), Neinv(Te) > Nesh(Te), whereas for longer times in the quasi-steady state, Neinv(Te) must be smaller than a critical density Neqv(Te), Neinv(Te) < Nequ(Te). We also consider the evolution of the inversion condition in the intermediate time domain. The time duration of the existence of the short-time 3→2 inversion condition–in the time interval from the initial state with unoccupied lower levels to the quasi-steady state—is in the main determined by t α 1/A21; for example, one has t ≈ 730 fs for Na.In a plasma produced in particular by optical-field ionization, during the initial cascade populating the excited levels, an inversion may be possible in the 2→1 resonance line transition in the transient regime. The inversion in this transition is of interest especially because of the arising possibility to achieve X-ray gain at shorter wavelengths. In the transient case, an inversion occurs for a small time depending on the temperature Te and the density N.In addition, we discuss generally the time behavior of the population densities (especially of N3) and show that an optimal population density occurs, on the one hand, for very short times (fs region, depending on Z). On the other hand, however, the optimal (ion-)density-temperature relation is determined via a time of the optimal population density required with regard to the experimental conditions.
Effective results for points on certain subvarieties of tori
Authors: BÉRCZES ATTILA , GYŐRY KÁLMÁN , EVERTSE JAN-HENDRIK , PONTREAU CORENTIN 
Published: March 2009

AbstractThe combined conjecture of Lang-Bogomolov for tori gives an accurate description of the set of those pointsxof a given subvarietyof$\mathbb{G}_{\bf m}^N(\oQ )=(\oQ^*)^N$, that with respect to the height are “very close” to a given subgroup Γ of finite rank of$\mathbb{G}_{\bf m}^N(\oQ)$. Thanks to work of Laurent, Poonen and Bogomolov, this conjecture has been proved in a more precise form.In this paper we prove, for certain special classes of varieties, effective versions of the Lang-Bogomolov conjecture, giving explicit upper bounds for the heights and degrees of the pointsxunder consideration. The main feature of our results is that the points we consider do not have to lie in a prescribed number field. Our main tools are Baker-type logarithmic forms estimates and Bogomolov-type estimates for the number of points on the varietywith very small height.