bluuebunny/crossref_metadata_2025 huggingface dataset:
Characteristics of a CW HF chemical laser calculated from a simplified two-dimensional model
Authors: Xuehua Zhou , Liyin Chen , Haitao Chen
Published: March 2009

A two-dimensional simplified model of an HF chemical laser is introduced. Using an implicit finite difference scheme, the solution of two adjacent parallel streams with diffusion mixing and chemical reaction is generated. A contour of the mixing and reaction boundary is obtained without presupposition. The distribution of the HF(u) concentrations, gas temperature and the optical small signal gain (αu, J) on the flowing plane (X, Y) are presented. Compared with the solution solved directly from a set of Navier–Stokes equations, the results of these two methods agree with each other qualitatively. The influences of the different velocity, temperature (T0) and composition of the two streams on the small signal gain after the nozzle exit are investigated. It is interesting that for larger J with a fixed u, the peaks of αu, J—T0 profiles move towards higher T0. The computing method is simple and only a short computing time is needed.
Bremsstrahlung collision contribution to entropy generation and attendant radial expansion in a self-pinched high-power relativistic electron beam propagating in a neutral gas
Authors: Dolique J.-M.
Published: March 2009

In the Bennett-Nordsieck self-pinched regime of high power REB propagation in a neutral atmosphere, radial expansion is generally associated with transverse entropy generation caused by elastic electron-neutral multiple scattering: LN ∝ 1/s′⊥ elast, where LN is the Nordsieck length, the distance for one e-folding of beam radius, and where s′⊥ elast is the elastic collision space rate of transverse mean entropy per particle.

For ultrarelativistic beams (γ ≳ 100), the bremsstrahlung, which is the dominant energy loss process, also plays an essential rôle in the radial expansion.

A general treatment could be based on the proper time evolution equation of the beam electron pressure 4-tensor pλμ (λ, μ = 0, 1, 2, 3) where source terms linked to elastic, inelastic and bremsstrahlung collisions are introduced, as is also a closure relation. This approach is currently being studied at LPPG.

When the various implied scale lengths have clearly different orders of magnitude, a much simpler approximate description may be given.

In the λmbrems < z < λstrbrems propagation distance range, where λmbrems is the depth threshold beyond which bremsstrahlung scattering becomes multiple, and λstrbrems a characteristic distance for bremsstrahlung straggling, the rôle of bremsstrahlung in radial expansion is similar to that of elastic multiple scattering. The calculated s′⊥ brems/s′⊥ elast increases rapidly with both propagation distance and beam electron energy. For γ ≫ 103, the bremsstrahlung transverse entropy source term s′⊥ brems is no more negligible before s′⊥ elast.

In the z > λstrbrems propagation distance range, where bremsstrahlung straggling is dominant, an evaluation of its effect is deduced by applying the Haftel–Lampe–Aviles criterion to a statistical study of this straggling. A completely different estimation, based on an oversimplified version of the above-cited general thermodynamic method, gives a result which is in rather good agreement.
Magnetic self-compression in laboratory plasmas, quasars and radio galaxies. Part I
Authors: Lerner Eric J.
Published: March 2009

A model of quasars and their associated jets as phenomena of magnetic selfcompression is presented. Magnetic field self-compression, as observed in laboratory plasma focus devices, results in increases in energy density of more than 108 and in even larger increases in transferred power density. Our model, based on the scaling of these phenomena to astrophysical dimensions, avoids the problems of gravitationallyconfined approaches. It presents a mechanism by which the energy of a quasar is immediately derived from a volume nearly 106 times larger than the observed quasar radiating volume and is ultimately derived from the volume of an entire protogalactic plasma cloud. The model's predictions of quasar energy, radiated power, lifetime, dimensions, density and rotational velocity are in good agreement with observations. Part II of this paper extends the model to radio galaxies and briefly discusses the role of similar self-compression processes in the origin of filamentary super-clusters of galaxies.
Resonance absorption initiated by self-focusing filamentation
Authors: Weihan Tan , Wenyan Yu , Zunqi Lin , Wuji Bi , Ximing Deng , Liming Ding
Published: March 2009

A theoretical model of resonance absorption initiated by self-focusing filamentation is proposed on the bases of experiments on the 2ω0 time resolved spectrum, slow ion emission and filamentation of 3ω0/2 emission. A number of aspects of the experimental results can be well explained by this model.
Magnetic fields generated by the Rayleigh-Taylor instability
Authors: Evans R. G.
Published: March 2009

In the absence of magnetic diffusion the self-generated magnetic field in a plasma is proportional to the fluid vorticity. The ratio of magnetic to fluid energy then shows that self-generated magnetic fields can only affect the Rayleigh Taylor growth rate for large k (wavelengths less then a few microns).
Analysis of directly driven ICF targets
Authors: Velarde G. , Aragones J. M. , Gago J. A. , Gamez L. , Gonzalez M. C. , Honrubia J. J. , Hortal J. L. , Martinez-Val J. M. , Minguez E. , Ocaña J. L. , Otero R. , Perlado J. M. , Santolaya J. M. , Serrano J. F. , Velarde P. M.
Published: March 2009

In this article the current capabilities at DENIM for the analysis of directly driven targets are presented. These include theoretical, computational and applied physical studies and developments of detailed simulation models for the most relevant processes in ICF. The simulation of directly driven ICF targets is carried out with the one-dimensional NORCLA code developed at DENIM. This code contains two main segments: NORMA and CLARA, able to work fully coupled and in an iterative manner. NORMA solves the hydrodynamic equations in a lagrangian mesh. It has modular programs coupled to it to treat the laser or particle beam interaction with matter. Equations of state, opacities and conductivities are taken from a DENIM atomic data library, generated externally with other codes that will also be explained in this work. CLARA solves the transport equation for neutrons, (Boltzmann), as well as for charged particles, and suprathermal electrons (Fokker-Planck), using discrete ordinates and finite element methods in the computational procedure. Parametric calculations of multilayered single-shell targets driven by heavy ion beams are also analyzed. Finally, conclusions are focused on the ongoing developments in the areas of interest such as: radiation transport, atomic physics, particle in cell method, charged particle transport, two-dimensional calculations and instabilities.
Radiative transport and preheat calculations of laser irradiated aluminum targets
Authors: Szichman H. , Salzmann D. , Krumbein A. D.
Published: March 2009

Calculations of the preheat of the cold region of an aluminum target by X-rays from the coronal region are presented. The computation was carried out by means of our 1-D hydrodynamics code, PLASMOR, which takes into consideration non-LTE steady state atomic physics. The radiation from the plasma is divided into 40 energy groups: 20 continuous groups (recombination + bremsstrahlung) from hv = 300 eV up to hv = 100 keV, and 20 lines, mainly (but not only) He-like and H-like lines. The hot coronal region is assumed to be optically thin to all radiation. The photoabsorption in the cold portion proceeds through the photo-ionization effect, and variations with density and temperature are taken into account by means of a simplified model. Black body radiative transport in the cold portion is also included. The effects of the radiation on the shock wave propagation as well as its influence on the density and temperature distribution in the shock compressed region were studied for trapezoidal and Gaussian laser pulse shapes.
X-ray spectroscopy of high-Z materials
Authors: Gauthier J. C. , Monier P. , Audebert P. , Chenais-Popovics C. , Geindre J. P.
Published: March 2009

The spectra of laser-produced plasmas of various materials of Z>70 have been interpreted as spin-orbit-split arrays of the 3d – 4f and 3d – 5f transitions for Ni-like to Ge-like ions. The excellent agreement between the model and the experiments indicated the possibility of their use for plasma diagnostics. First results from targets of Gold alloyed with Aluminium give an alternative diagnostic.
Electron acceleration by a localized electric field
Authors: Galmiche D. , Nicolle J. P. , Pesme D.
Published: March 2009

The acceleration of test electrons by a resonant, one—dimensional electric structure is studied in the convective regime with the Zakharov equations. Depending on the nonlinearity level the particle acceleration is due to diffusion or trapping by the plasma wave. Electron distributions are obtained and compared with 1-D particle code results. Influence of Landau damping formulation is discussed.
A high energy laser with controlled coherence
Authors: Schönnagel H. , Gunkel H. , Grzanna J.
Published: March 2009

The coherence of the laser radiation limits the average beam fluence in high power laser installations. The disadvantages of present optical schemes are analysed. A new optical scheme with controlled spatial coherence is described and its consequences are shown.
Rayleigh–Taylor instability: Modes and nonlinear evolution
Authors: Kull H. J.
Published: March 2009

Analytical models are presented for describing modifications of the classical Rayleigh–Taylor instability theory in the context of inertial confinement fusion. The effects of stratification, finite layers, compressibility, convection and heat conduction are analysed and their mutual importance is estimated. It is found, that convective stabilization dominates for usual flow parameters and can account for growth reductions by a factor of 2 to 3. It was further possible to calculate the nonlinear evolution with the help of representative flow models and to follow the dynamics of bubble, spike and vortex formation.
Soliton emission in the forced non-linear Schrödinger equation
Authors: Larroche O. , Casanova M. , Pesme D. , Bussac M. N.
Published: March 2009

The plasma waves generated by resonant absorption of light in the vicinity of the critical density of laser-produced plasmas, are modelled by a non-linear Schrödinger equation with additional terms accounting for the presence of a source and the inhomogeneity of the medium.

We use an average lagrangian method to describe the behaviour of the solutions of this equation in the range of parameters where periodic soliton generation occurs. An iterating scheme describing the successive emission of solitons yields values for this range of parameters which are in reasonable agreement with those found from direct numerical simulations of the non-linear Schrödinger equation.
Excimer laser development for fusion
Authors: Giovanielli D.
Published: March 2009

The future utility of inertial confinement fusion requires a new driver. Successful experiments coupling laser energy to targets, and our understanding of fuel capsule behavior strongly suggest that a Laboratory thermonuclear source is attainable and power production may be considered if a suitable driver with high efficiency, high repetition rate, and most importantly, low capital cost, can be identified. No adequate driver exists today; however, the krypton fluoride laser holds great promise (Rosocha et al. 1986). By the end of this decade, driver development can be brought to the point that a technically justifiable choice can be made for the future direction of ICF.
Recent experiments at the Rutherford Appleton Laboratory to study the laser driven compression of CH shell targets and the effects of increasing aspect ratio
Authors: Corbett J. , Lewis C. L. S. , Robertson E. , Saadat S. , Cunningham P. F. , Cole A. , Trucu E. , Key M. H. , Rose S. J.
Published: March 2009

Recent experiments to study the laser driven compression of CH shell targets and the effects of increasing aspect ratio using x-ray shadowgraph techniques are described. This work has been carried out at the Rutherford Appleton Laboratory's Central Laser Facility with 12 beam, 0·53 μm, 1·0 ns irradiation. X-ray shadowgraphy techniques have been used with a frame time of ∼100ps and spatial resolution of 5 to lOμm to obtain density profiles for the compressed targets. A systematic study of 150–200 μm targets with aspect ratios from ∼7 to ∼20 has been performed. The x-ray shadowgraphy techniques used are described, results in the form of x-radiographs presented and a discussion of preliminary results given.
A gamma ray laser based on induced annihilation of electron-positron pairs
Authors: Loeb A. , Eliezer S.
Published: March 2009

In this paper we propose the coherent amplification of gamma radiation of a system of parapositronium atoms. The nonlinear optics of positronium media is suggested. The induced annihilation transitions for the electron-positron plasma are compared with those of the positronium medium. It is suggested in this paper that the Bose–Einstein condensation could play a crucial role in the estimation of the induced annihilation of electron-positron pairs for dense (n ≳ 1016cm−3) and cold (T ≲ 104 °K) positronium systems. The calculated effects of the induced positron-electron decays might be observed in astrophysical objects such as pulsars, white dwarf stars etc. Furthermore, these transitions might play an important role in Klein–Alfven cosmology. Finally, with the further advancement of the positron technology, a gamma ray laser may be constructed.
X-ray optics for X-ray laser research applications
Authors: Ceglio N. M.
Published: March 2009

State of the art capabilities in soft X-ray lenses, multilayer mirrors, beamsplitters, and synthetically generated holograms are reviewed. Application of these capabilities in recent X-ray laser cavity experiments, and to the development of a soft X-ray interferometer and a high intensity (≥1013watt/cm2) soft X-ray laser are discussed.
Beam generations of three kinds of charged particles
Authors: Niu K. , Mulser P. , Drska L.
Published: March 2009

Analyses are given for beam generations of three kinds of charged particles: electrons, light ions, and heavy ions. The electron beam oscillates in a dense plasma irradiated by a strong laser light. When the frequency of laser light is high and its intensity is large, the acceleration of oscillating electrons becomes large and the electrons radiate electromagnetic waves. As the reaction, the electrons feel a damping force, whose effect on oscillating electron motion is investigated first. Second, the electron beam induces the strong electromagnetic field by its self-induced electric current density when the electron number density is high. The induced electric field reduces the oscillation motion and deforms the beam.

In the case of a light ion beam, the electrostatic field, induced by the beam charge, as well as the electromagnetic field, induced by the beam current, affects the beam motion. The total energy of the magnetic field surrounding the beam is rather small in comparison with its kinetic energy.

In the case of heavy ion beams the beam charge at the leading edge is much smaller in comparison with the case of light ion beams when the heavy ion beam propagates in the background plasma. Thus, the induced electrostatic and electromagnetic fields do not much affect the beam propagation.
Intense negative hydrogen ion production in high-power diodes
Authors: Papadichev V. A.
Published: March 2009

Some peculiarities of using negative ions for accelerators and CTR are examined. Highpower beams of fast atoms obtained by charge exchange of negative ions can have advantages over positive ion beams for inertial confinement fusion (ICF) since they do not experience any deviations, instabilities, and scattering. H− current up to 7 kA in a 100–200 ns pulse with densities up to 200 Å/cm2 and a voltage of 0.8 MV were obtained in experiments on magnetically insulated diodes at the Lebedev Physical Institute. Diagnostics of high-power H− beams are described. Experimental results on cathode plasma formation by surface discharge on a dielectric initiated by a bipolar prepulse or by laser illumination are presented. The dependence of H− yield on cathode current was determined and experiments on plasma stabilization are described. It is concluded that 1 kÅ/cm2 of H− can be obtained.
On relativistic self focusing
Authors: Lee P. H. Y.
Published: March 2009

Ponderomotive force initiated laser self focusing can be enhanced by relativistic electron motion in a laser plasma. We derive the nonlinear refractive index due to relativistic effects and find that relativistic self focusing becomes important for a 0·25 μm laser when the laser intensity exceeds 5 × 1018 W/cm2.
Thermodynamic properties and thermal conductivity of high density deuterium
Authors: Inoue Kazuko , Ariyasu Tomio
Published: March 2009

The phase diagram of high density (1023 ˜ 1027/cm3) deuterium is obtained by calculation. The values of specific heat, electrical resistivity and thermal conductivity in the metallic state are estimated over a wide range of temperature (10−2 ˜ 104 eV). The temperature dependences of these properties are shown in figures with the density. When T ≤ Tf (Tf: the Fermi temperature of electrons), the behavior is very similar to those of normal metals. At high temperatures where T ≥ Tf, the behavior is similar to that of completely ionized classical plasma.

This fundamental data for deuterium will help us understand the properties of fuel in inertial-confinement fusion and to solve the fluid equations for efficient compression of fuel pellets.
Particle beam fusion research at IAE in Beijing
Authors: Naiyan Wang , Runsheng Hong , Naigong Zeng , Yusheng Shan , Weiren Liu , Shigang Du , Chuangzhi Zhou , Xiaojun Wang , Ganchang Wan
Published: March 2009

The research of particle beam fusion and its related problems at The Institute of Atomic Energy in Beijing is evolving along the following five directions: 1. Pulsed power technology. An 80 GW intense electron beam accelerator has been built. Switch research is ongoing. 2. Diode research. The experimental research and theoretical simulation of electron pinch in the diode have been carried out. The pinch process has been investigated by measuring the area collapsing velocity of the pinching electron ring on the anode surface. Expanding velocities of the cathode and anode plasmas have been observed. The diode with large area cathode of 38 × 5 cm2 can produce a 46 kA electron beam current with a beam cross-section of 36 × 4 cm2 and good uniformity for pumping of a KrF laser. 3. Energy deposition of the electron beam on the targets has been studied by means of measurements of the intensity of soft X-rays, the energy spectrum of blow-off ions, the visible light spectra and the rear surface velocity of the target. These experiments show that the results are in agreement with the classical interaction mechanism for high Z targets, but it is several times higher than the classical result for low Z targets. 4. Electron beam propagation in neutral gases with various pressures space-and current-neutralization processes have been investigated. 5. The production of a KrF laser pumped by an electron beam. A laser beam with an energy of 13 J and pulse duration of 70 ns has been obtained.
Proton stopping in thin aluminum slabs
Authors: Goel B. P. , Moses G. A. , Peterson R. R.
Published: March 2009

Numerical simulations of proton stopping lengths in aluminum slab plasmas have been done using a modified version of the MEDUSA-KA code and compared to other published computations. Simulations have been performed for proton beam parameters consistent with future experiments on the KALIF light ion accelerator at KfK including carbon contamination of the beam. These simulations show that proton range shortening should be evident in KALIF experiments and that the carbon contamination must be removed to allow interpretation of the data.
Double layers and plasma-wave resistivity in extragalactic jets: cavity formation and radio-wave emission
Authors: Borovsky Joseph E.
Published: March 2009

Current driven electrostatic-wave- and electromagnetic-wave-produced resistivities do not occur in extragalactic jets for estimated values of the carried currents. Strong plasma double layers, however, may exist within self-maintained density cavities. The relativistic double-layer-emitted electron and ion beams drive plasma-wave resistivities in the low- and high-potential plasma adjacent to the double layers. The double-layeremitted electron beams may also emit polarized radio waves via a collectivebremsstrahlung process mediated by electrostatic two-stream instabilities.
Electric fields and double layers in plasmas
Authors: Singh Nagendra , Thiemann H. , Schunk R. W.
Published: March 2009

Various mechanisms for driving double layers in plasmas are briefly described, including applied potential drops, currents, contact potentials, and plasma expansions. Some dynamic features of the double layers are discussed. These features, as seen in simulations, laboratory experiments and theory, indicate that double layers and the currents through them undergo slow oscillations, which are determined by the ion transit time across an effective length of the system in which the double layers form. It is shown that a localized potential dip forms at the low potential end of a double layer, which interrupts the electron current through it according to the Langmuir criterion, whenever the ion flux into the double is disrupted. The generation of electric fields perpendicular to the ambient magnetic field by contact potentials is also discussed. Two different situations have been considered; in one, a low-density hot plasma is sandwiched between high-density cold plasmas, while in the other a high-density current sheet permeates a low-density background plasma. Perpendicular electric fields develop near the contact surfaces. In the case of the current sheet, the creation of parallel electric fields and the formation of double layers are also discussed when the current sheet thickness is varied. Finally, the generation of electric fields (parallel to an ambient magnetic field) and double layers in an expanding plasma are discussed.
A new hydrodynamic analysis of double layers
Authors: Goldsworthy M. P. , Green F. , Hora H.
Published: March 2009

A Genuine two-fluid model of plasmas with collisions permits the calculation of dynamic electric fields and double layers inside plasmas including oscillations and damping. For the first time a macroscopic model for coupling of electromagnetic and Langmuir waves was achieved with realistic damping. Starting points were laser produced plasmas showing very high dynamic electric fields in nonlinear force produced cavitons and inverted layers, in agreement with experiments. Applications for any inhomogeneous plasma as in laboratory or in astrophysical plasmas can then be followed up by a transparent hydrodynamic description. We find the rotation of plasmas in magnetic fields and a new second harmonic resonance. Explanation of inverted double layers, second harmonic emission from laser produced plasmas, and laser acceleration of charged particles by the very high fields of the double layers is given.
Linear Vlasov stability in one-dimensional double layers
Authors: Teichmann J.
Published: March 2009

Analytical study of the linear stability of one-dimensional double layers in nonmagnetized plasmas based on the solution of the Vlasov–Poisson system is presented. Electromagnetic effects are not included. A self-consistent equilibrium electrostatic potential Φ0(z) that monotonically increases from a low level at z = − ∞ to a high level at z = + ∞ is assumed. We model this potential as a piecewise continuous function of z and we assume that Φ0(z) has constant values for − ∞ z ≤ 0 and L ≤ z < ∞, L being the thickness of the double layer. The BGK states for the Vlasov–Poisson system provide an explicit expression for the velocity distribution of the reflected electrons required for the particular double layer configuration. The stability of the double layers is studied via the linearized Vlasov and Poisson equations using the WKB approximation.
Particle simulation of auroral double layers
Authors: Smith Bruce L. , Okuda Hideo
Published: March 2009

We report on our work to simulate auroral double layers (DL's) with ‘realistic’ particle-in-cell models. An early model simulated weak DL's formed in a self-consistent circuit but under conditions subject to the ion-acoustic instability. More recent work has focused on strong DL's formed when currentless jets are injected into a dipole magnetic field.
Anomalous transport in discrete arcs and simulation of double layers in a model auroral circuit
Authors: Smith Robert A.
Published: March 2009

The evolution and long-time stability of a double layer in a discrete auroral arc requires that the parallel current in the arc, which may be considered uniform at the source, be diverted within the arc to charge the flanks of the U-shaped double-layer potential structure. A simple model is presented in which this current re-distribution is effected by anomalous transport based on electrosatic lower hybrid waves driven by the flank structure itself. This process provides the limiting constraint on the double-layer potential. The flank charging may be represented as that of a nonlinear transmission line. A simplified model circuit, in which the transmission line is represented by a nonlinear impedance in parallel with a variable resistor, is incorporated in a 1-d simulation model to give the current density at the DL boundaries. Results are presented for the scaling of the DL potential as a function of the width of the arc and the saturation efficiency of the lower hybrid instability mechanism.
The feasibility of measuring the nuclear reaction cross sections at energies of several KeV in a target under laser compression
Authors: Kukulin V. I. , Krasnopol'sky V. M. , Voronchev V. T.
Published: March 2009

The work proposes a straightforward method for determining the nuclear reaction cross sections at extremely low energies (E ≃ 1–100 keV) on the basis of the measurements of the relative yield of fast particles which are products of the nuclear reactions in a target under laser compression. On the other hand, the proposed method makes it possible to find the averaged form of the ion velocity distribution function if the low-energy behaviour of the respective cross sections is known.
Recent progress of studies on intense particle beam at Nagaoka—ETIGO Project
Authors: Yatsui Kiyoshi , Shimotori Yutaka , Ikeda Mitsugu , Takahashi Akira , Tanabe Tsutomu , Aga Keigo , Kanai Akifumi , Araki Yuhzo , Masugata Katsumi , Kawata Shigeo , Murayama Minoru
Published: March 2009

Recent experimental and theoretical research on intense pulsed particle beams involving the ETIGO Project at the Technological University of Nagaoka is reviewed. Experimentally, we review the following: (1) studies on local divergence angle in parameter space, (2) development of self-magnetically insulated “Plasma-Focus Diode,” (3) beam focusing by z-discharged plasma channel, (3) measurement of ablation process of beam-target interaction, (4) time-resolvable measurement of energy and species, (5) inductive postacceleration of highly neutralized ion beam, (6) construction of new pulse-power machine, and pulse-compression experiment by plasma erosion opening switch. A brief summary is also given on the development of 2.5-dimensional particle-in-cell computer simulation code.
Basic plasma physics research in pulsed-power technology at Ecole Polytechnique
Authors: Doucet H. J. , Buzzi J. M. , Gazaix M. , Jones W. D. , Lamain H. , Moustaisis S. , Rouille C.
Published: March 2009

Various aspects of the pulsed power research program at Ecole Polytechnique are reviewed. Topics include a surface and a flashboard switch, the development of plasma guns for both switching and z-pinch diodes, and studies of beam control and synchronization.
Current neutralization of ion beam rotating and propagating in plasma
Authors: Aoki Takayuki , Niu Keishiro
Published: March 2009

The current-neutralization fraction of a rotating and propagating light ion beam (LIB) injected into a low density plasma is investigated numerically. The beam space charge is essentially neutralized by a redistribution of the background plasma electrons in a time duration equal to the inverse of electron plasma frequency. When the density of the background plasma is comparable with that of the beam, incomplete current neutralization occurs because the strong magnetic field induced by the intense ion beam restricts the return plasma current.

In the simulation, the ion beam and the background plasma are treated as the fluids coupled with Maxwell's equations and Ohm's law, including the effect of the magnetic field on electrical conductivity. The calculations assume that the ion beam is injected in an unsteady fashion into the uniform plasma. It is found that the return current strongly depends on the density of the background plasma. The beam deceleration and the acceleration of the beam head and tail are also considered.
Cooling and focusing of a relativistic charged particle beam in crossed laser field
Authors: Fuli Li , Bertolotti M. , Sibilia C. , Ronsivalle C. , D'Auria G.
Published: March 2009

A new method to focus a relativistic charged particle beam is suggested and studied. This idea is based on the use of the ponderomotive force which arises when a periodic electromagnetic field is created, as in the case of two crossed laser beams.
Investigation of a self-magnetically insulated Bθ-diode
Authors: Citron A. , Kühn W. , Rogner A. , Schimassek W. , Stoltz O.
Published: March 2009

An ion diode, where the insulating magnetic Bθ-field is produced by the diode current itself, has been investigated. Using a novel Thomson-parabola spectrometer that is capable of detecting up to 41 beam traces at a single shot and a carbon activation diagnostic the ion beam has been analyzed. The diode, operating at “KALIF”, delivers ion beams of 750 kA at energies of about 0·7 MeV. The focusing version of the diode shows a focus size of 1 cm2, the beam is neutralized to 98–99%, the proton content is about 60%.
Progress on the relativistic magnetron
Authors: Benford J. , Sze H. , Bromley D. , Harteneck B.
Published: March 2009

High-power relativistic magnetrons operating in both S-Band and X-Band (4 GHz) and 8·5 GHz) have been developed with a variety of extraction methods. Using a six window radial extraction scheme, the S-Band magnetron produces ∼3·6 GW. The X-Band magnetron produces 0·05 GW with one radial extraction window. Axial extraction from all six vanes produced power in excess of 0·3 GW. Enhanced erosion and gap closure occur in the smaller X-Band resonator.
Anomalous transport in discrete arcs, double layers in experiments, simulations, and space
Authors: Smith Robert A.
Published: March 2009

This paper presents a survey of selected results of laboratory experiments and numerical simulations of plasma double layers. Emphasis is given to discrimination between features peculiar to the experimental or numerical investigation and results which may have general implications for double layers in space similar to that of laser or particle beam produced plasma. The discussion concentrates on certain aspects pertaining to dynamics, structure, and stability of double layers considering the effects of boundary conditions (trapped particles, Bohm conditions, and applied potentials), waves and turbulence, collisions, and volume ionization.
The use of flows with uniform velocity gradient in modelling free expansion of a polytropic gas
Authors: Pert G. J.
Published: March 2009

The free expansion of a heated mass of uniform gas (e.g. a laser produced plasma) can be modelled by self-similar motion with a linear velocity gradient. Using a series of numerical solutions we have shown that a reasonable representation is obtained by the use of a matching parameter relating the scale lengths in the prototype and its model, and that the representation improves as the ratio of the heating and disassembly times increases. In this paper we re-examine these two inferred results, and re-derive them on an analytic basis. The extension of the theory to multi-structured bodies shows that such systems of symmetric form allow self-similar motion, as does the particular case of an asymmetric one-dimensional foil. The case of isothermal foils is examined in detail to illustrate the derivation of the matching conditions.
The free-electron-laser synchronous harmonic generator—A high power source of submillimeter waves
Authors: Cassedy E. S.
Published: March 2009

A harmonic generator of submillimeter wavelength radiation, operating on a relativistic electron beam, is proposed. The device is shown to operate on principles of parametric interactions, under the particular conditions of an electric-quadrupole pump field which is propagating synchronously with the electron beam. Using a fluid model, it is shown that a cascade of parametric sum and difference frequencies in the transverse beam modes should occur, with each harmonic component growing convectively along the beam. The physical effect, termed the “sonic condition”, has been observed previously on a non-relativistic device emitting output radiation in the UHF range. A realization for relativistic beams is proposed, using an FEL structure as the parametric pump, a closed waveguide synchronous pump region and an output coupling of the gyrotron type. Possible advantages over the present state-of-the-art for high-power submillimeter electron-beam devices are discussed.
Recent results from the Nova program at LLNL
Authors: Campbell E. M.
Published: March 2009

Recent improvements to the Nova laser and target experiments addressing laser–plasma interaction physics, hydrodynamic stability, implosion physics, and X-ray laser physics are summarized. Highlights include demonstrated laser performance exceeding Nova's original design goals, the observation of improved target compressions with temporally shaped laser pulses, and demonstrated lasing at wavelengths shorter than 45 Å.
Athena — an advanced Nd: glass laser driver for ICF
Authors: Lowdermilk W. H.
Published: March 2009

The design for an advanced, flash-lamp-pumped Nd: glass laser for inertial confinement fusion (ICF) research and applications is summarized. The laser consists of multiple beam lines, each of which delivers 145-kJ, O.35-μm, 8-ns laser pulses, with pulse shape and bandwidth capabilities consistent with requirements for driving ICF capsules to high gain.
Prospects for high-power KrF lasers
Authors: Shaw M. J.
Published: March 2009

This paper reviews the current status of high-power KrF lasers and considers their prospects for future development. The main laser requirements imposed by target physics considerations are identified and KrF lasers are shown to be uniquely capable of satisfying them. Some design considerations are given for (a) ultrashort-pulse high-power systems, (b) high-power coherent beam generation using Raman amplifiers, and (c) incoherent beam amplification.
Nonlinear optics concept for high-peak-power lasers
Authors: Pasmanik G. A. , Makarov A. I. , Shilov A. A.
Published: March 2009

Possibilities are discussed of using Brillouin cells to produce high-peak-power radiation with the diffraction-limited divergence. The major emphasis is on the problems of coherent beam coupling at the output of several optical channels and of laser-pulse compression.
Self-similar Langmuir collapse at critical dimension
Authors: Bergé L. , Dousseau PH. , Pelletier G. , Pesme D.
Published: March 2009

Two spherically symmetric versions of a self-similar collapse are investigated within the framework of the Zakharov equations, namely, one relative to a vectorial electric field and the other corresponding to a scalar modeling of the Langmuir field. Singular solutions of both of them depend on a linear time contraction rate Ξ(t) = V(t* – t), where t* and V = – Ξ denote, respectively, the collapse time and the constant collapse velocity. We show that under certain conditions, only the scalar model admits self-similar solutions, varying regularly as a function of the control parameter V from the subsonic (V ≪ 1) to the supersonic (V ≫ 1) regime.
Low-fluence laser–target coupling
Authors: Combis P. , Cazalis B. , David J. , Froger A. , Louis-Jacquet M. , Meyer B. , Nierat G. , Saleres A. , Sibille G. , Thiell G. , Wagon F.
Published: March 2009

Low-fluence laser interaction with metallic target is investigated in a wide range of irradiance, from 5 × 106 to 1011 W/cm2, with 4- and 30-ns laser-pulse durations and 1.06-μm wavelength. Edge effects are avoided by means of large surfaces of irradiation (5 cm2). Specific diagnostics such as a ballistic pendulum and a piezoelectric quartz gauge are developed to measure the total momentum imparted to the target, as well as the temporal evolution of the stress at the rear side of the target. Specular reflection and sidescattering of the laser light from the target are also measured. The behavior of 2024 aluminum alloy is particularly studied. The results are interpreted in terms of liquid-vapor transition and change in laser absorption.

In light of experimental data, the theoretical analysis of surface absorption is reviewed, showing the dependence on metal temperature and laser wavelength. The thermal and mechanical coupling is also calculated.

Numerical simulations are performed with a 1–D Lagrangian hydrodynamic code including modifications for low-pressure regimes. The multiphase equation of state is extended to take into account negative pressures. An elastoplastic module is introduced into the code. A quite good agreement is obtained with the measurements of the stress and of the mechanical coupling coefficient.
Scaling laws for spherical pinch experiments
Authors: Singh D. P. , Palleschi V. , Vaselli M. , Panarella E.
Published: March 2009

In spherical pinch (SP) experiments, the plasma heated at the center of a cell to reach ignition temperature is confined by imploding shock waves for a time long enough to satisfy the Lawson criterion for plasma fusion. In earlier theoretical studies, the expansion of the central plasma either is neglected or is assumed to be radially uniform. In the present paper, the energy is considered to be deposited instantaneously at the center of the cell and the nonlinear heat conduction equation is solved to study the temporal evolution of the central plasma. Incorporating the ignition condition for the average temperature of the expanding fireball, and its confinement by imploding convergent shock waves, which may be fired from the periphery of the cell with some time delay, the scaling laws for satisfying the Lawson criterion are investigated in detail. The relevant calculations indicate that the cumulative effects of the convergent shock waves in the vicinity of the center of the cell play an important role in these scaling laws.
On the process of Mach wave generation in air
Authors: De Rosa M. , Famá F. , Palleschi V. , Salvetti A. , Singh D. P. , Vaselli M.
Published: March 2009

The process of Mach wave generation in air is studied in both plane and spherical geometries. The experimental results reported here are theoretically interpreted using the predictions of a self-similar model of strong explosion along with the hydrodynamic equations of a perfect gas, and a good agreement is found.
Frequency spectra of the Raman-backscattered light in an inhomogeneous plasma
Authors: Bonnaud Guy , Pesme Denis , Pellat René
Published: March 2009

The behavior of the stimulated Raman scattering is investigated in a laser-irradiated plasma with an inhomogeneous density profile, by means of wave-coupling simulations. In the case of a regular hydrodynamic-like profile, a spectral broadening is observed when the laser irradiance is increased and is found to result from a coupling between the convective and the absolute Raman scattering, via pump depletion. In the case where a short-scale modulation of the density is superimposed on the profile, the spectrum is strongly influenced by the propagation velocity of the modulation and by the sinusoidal/chaotic nature of the modulation.
Effect of radiation on the time-resolved rear-side emission of laser-illuminated foils at 0.25 μm: Comparison with simulations
Authors: Benattar R. , Malka V. , Meyer-Ter-Vehn J. , Murakami M.
Published: March 2009

Experiments were performed at Ecole Polytechnique in order to study the effect of preheating of targets by X rays during interaction with a powerful 4ω laser. Thin aluminum foils (typically of 5–15-μm thickness) are used as targets. The emission at 40 and 80 eV is recorded by Schwarzchild microscopes and is time resolved. By assuming a blackbody emission of the rear side of the foil just at the beginning of the emission, we deduce the temperature, by measuring the ratio of the emissivity at the two wavelengths. Experimental results are presented for an energy varying between 10 and 30 J delivered at the fourth harmonic of the neodymium laser in a pulse of 0.5-ns time duration focused in a 100-μm-diameter focal spot. Simulations performed with the code MULTI including radiative transfer are presented in order to show the effect of radiation on the process of heating of the target material. Radiation spectra emitted from the laser side and the rear side, as well as the temperature and density evolution as a function of time and mass coordinate, are shown.
Spectral diagnosis of a laser-produced XUV source using a digital camera system with pinhole transmission grating
Authors: Böwering N. , Döhring T. , Gärner U. , Heinzmann U.
Published: March 2009

For spectral diagnosis, a repetitive laser-produced soft-X-ray source was examined in the range 2–40 nm using a spectrometer containing a pinhole transmission grating, an image converter, and a CCD camera. Via digital recording the detection system provides fast on-line data accumulation with spectral and spatial resolution. With this detector the performance of the light source was studied with respect to spectral emission characteristics, long-term stability, and reproducibility by recording spectra for different solid targets and liquid lead.
Energy and angular distribution of ions emitted from a plasma after relativistic self-focusing of laser beams
Authors: Häuser Thomas , Scheid Werner
Published: March 2009

High-intensity laser beams propagating in a plasma become focused because the index of refraction depends on the relativistic mass of the electron and therefore is a function of the electric field strength through the electron velocity. Around the focus the laser field has such a high density of energy that electrons and ions are emitted owing to the nonlinear force arising from this field. The equations of motion for the electrons and the ions and the Maxwellian equations for the laser and plasma fields are solved under certain approximations. We calculate the maximal energy and the angular distribution of the emitted ions and compare the results with experimental data.
Experiments on high-power ion beam generationin self-insulated diodes
Authors: Bystritskii V. M. , Glyshko Yu. A. , Sinebrjukhov A. A. , Kharlov A. V.
Published: March 2009

Experimental results are given on high-power ion beams (HPIB) generation in a vacuumspherical focusing diode with self-magnetic insulation, obtained from the nanosecond accelerator PARUS with 0.2-TW power and 60-ns pulse duration for a matched load. When the passive plasma source of the ions was used, the efficiency of the HPIB generationwas measured to be as high as 20% for 700-kV diode voltage and 10-kA/cm2 beam density in the focal plane.

The application of a coaxial plasma opening switch (POS) prior to the diode resultedin a factor-of-1.8 increase in the diode power in comparison with a match operation inthe absence of a POS.
Recent Livermore research on ion beam fusion targets: Utilization of direct-drive efficiency during optimization of symmetry and utilization of polarized DT fuel
Authors: Mark James W.-K.
Published: March 2009

We investigated several examples of ion beam targets that utilize the energy efficiency of direct drive while optimizing on the symmetry requirements. Heavy-ion beams of charge state Z ≥ 3 at 5–10 GeV have ≲15–20 m bending radii with 3.5-T fields. Beams like these could be used with targets involving direct drive. Control of asymmetries in direct-drive ion beam targets depends on control of the effects of residual target asymmetries after an appropriate illumination scheme has been adopted. In this paper, we outline results of our investigations into ion beam target concepts in which the effects of residual asymmetries are ameliorated. The beams are placed according to our axially symmetric Gaussian-quadrature illumination scheme (Mark 1986). The targets survive the effects of residual asymmetries in our recent 2-D hydrodynamic simulations. We also briefly discuss the additional positive effects of polarized DT fuel on ion beam targets.
Measurements of the divergence of a 10-MA relativistic electron beam transported in a gas cell
Authors: Harper-Slaboszewicz V. J. , Fowler W. E.
Published: March 2009

The increase in time-integrated divergence of a 1.7-MeV, 10-MA relativistic electron beam due to transport over 10 cm in a gas cell filled with 1 and 6 Torr of nitrogen was measured. The divergence was characterized by a multiple-pinhole beam sampling technique involving an aperture plate, an expansion region, and an attenuator plate followed by nylon radiochromic film. The divergence is determined by a fit of the measured deposition profile to response functions calculated using Monte Carlo coupled electronphoton transport codes. The initial value of 6.9° after the entrance foil is observed to increase to 12°. The errors in the measurement are quantified with Monte Carlo techniques. The response function fit gives a significantly better estimate of the divergence than a Gaussian fit.
Measurements and laser-wavelength dependence of mass-ablation rate and ablation pressure in planar layered targets
Authors: Dahmani F. , Kerdja T.
Published: March 2009

Layered-targets experiments at 1.06-μm laser light have been performed in order to measure mass-ablation rate ṁ and ablation pressure Pa as a function of absorbed laser flux Ia and laser wavelength λL at irradiances of 1011-4.5 × 1012 W/cm2. The results can be put in the forms ṁ(g/cm2-s) ≈ 4.25 × 105[Ia(W/cm2)/1014]5/9(1 μm/λL)4/9 and Pa(Mbar) ≈ 20[Ia(W/cm2)/1014]7/9(1 μm/λL)2/9, which are consistent with the estimates obtained from a steady-state self-regulated model for plasma heating and with hydrodynamical simulations. Results show also a small lateral energy transport.
Solid antimatter
Authors: Michaelis M. M. , Bingham R.
Published: March 2009

The problems of creating solid antimatter are listed and examined. Laser driven accelerators may reduce the technological and financial magnitude of the task.
Nanosecond air breakdown parameters for electron and microwave beam propagation
Authors: Ali A. W.
Published: March 2009

Air breakdown by avalanche ionization plays an important role in the electron beam and microwave propagations. For high electric fields and short pulse applications one needs avalanche ionization parameters for modeling and scaling of experimental devices. However, the breakdown parameters, i.e., the ionization frequency vs E/p (volt. cm−1. Torr−1) in air is uncertain for very high values of E/P. We review the experimental data for the electron drift velocity, the Townsend ionization coefficient in N2 and O2 and develop the ionization frequency and the collision frequency for momentum transfer in air. We construct the E/p vs Pτ diagram and show that our results are in better agreement with the most recent short pulse air breakdown experiments, compared to those predicted by the expression of Felsenthal & Proud (1965). This is because they extrapolate an expression for the drift velocity, linear in E/p, to high values of E/p. Experimentally the drift velocity varies as (E/p)½ in the region of E/p > 100.