bluuebunny/crossref_metadata_2025 huggingface dataset:
Results on light ion beam studies for inertial confinement fusion at the Institute of Laser Energetics
Authors: Imasaki K. , Miyamoto S. , Yugami N. , Akiba T. , Sawada S. , Emura K. , Mizuguchi Y. , Shimoura K. , Nishihara K. , Ozaki T. , Nakai S. , Yamanaka C.
Published: March 2009

Recent progress in research on Light Ion Beams-Inertial Confinement Fusion (LIB-ICF) at ILE, Osaka University is summarized. We report on pulsed power compression using PEOS, a super high voltage source, on diode physics, on beam trajectory control for focusing, on beam-target interactions and on a conceptual reactor design (Rokko I) in this article.
Chaotic behavior of resonant absorption in the microwave range
Authors: Cros B. , Chiron A. , Godiot J. , Matthieussent G. , Héron A.
Published: March 2009

The nonlinear evolution of electrostatic plasma waves excited by mode conversion is studied in an inhomogeneous, collisionless, unmagnetized plasma. Experiments in the microwave range (f = 3.5 GHz), performed in a plasma (ne ≃ 1011 cm−3) created in a multipolar discharge, show that the electrostatic plasma-wave evolution exhibits a transition from a nonlinear steady-state regime toward chaos, occurring when the pump field or the gradient length is increased. The Zakharov equations, which model the plasmawave evolution coupled with low-density perturbation, are solved numerically with parameters close to those of the experiment; this simulation allows a characterization of the two regimes.
A method for the automatic rezoning of 2-D Lagrangian codes for ICF implosions
Authors: Atzeni S. , Guerrieri A.
Published: March 2009

A method for the automatic, discrete rezoning of two-dimensional Lagrangian codes for inertial confinement fusion (ICF) implosions has been developed. The method, which applies to matrix-ordered, quadrilateral zone meshes, allows the preservation of the interface tracking property of the Lagrangian approach. Total mass and momentum are conserved exactly, total energy is approximately conserved, and numerical diffusion is kept to tolerable levels. The mesh generator, the mapping scheme, and the actual implementation in a two-temperature laser fusion code are described. The performance of the method is illustrated by several sample applications.
Absorption of ultrashort laser pulses in solid targets
Authors: Cornolti F. , Mulser P. , Hahn M.
Published: March 2009

Femtosecond laser pulses are capable of producing very high light intensities at moderate pulse energies. We study the laser light absorption at flux densities of 1017 W/cm2 and higher during the plasma formation and the plasma heating process. In the first stage multiphoton and collisional ionization dominate. Modification of the inverse bremsstrahlung absorption occur owing to ionization dephasing. In the second stage beam energy conversion is mainly by collisional absorption at normal incidence, and by resonance absorption at oblique illumination. Simultaneously strong electron heat conduction provides for plasma formation and heating in deeper layers of the solid not accessible to the laser light. The penetration depth of the laser beam is modified by the anomalous skin effect. The electron-ion collision frequency at the high laser intensities under consideration is determined by the oscillation energy of the electrons rather than by their thermal motion. Although it reaches high values (1014-1016 S-1), all kinds of solid targets become strongly reflecting (>60%) owing to the formation of electron densities largely exceeding those of solid-state plasmas. Effects modifying the degree of absorption are briefly discussed.
Investigations concerning plasma parameters and population inversion in laser-produced counterstreaming plasmas
Authors: Glas P. , Schnürer M.
Published: March 2009

We investigated the case where two laser-produced plasmas collide nearly head on. Special attention was devoted to the fundamentals necessary to realize a coherent X-ray source. A gas-dynamic computational analysis was performed to understand the evolution of the density, the temperature, and the velocity of merging plasmas. The spatial intensity distribution of selected spectral lines reveals that the interaction of plasmas of different nuclear charge and charge state is not strictly collision dominated. Using spectral line intensity ratios, we determined electron temperatures and electron number densities, as well as the intensity inversion on the 4–1 to 3–1 resonance transitions of [He]-like Al. Inversion occurs in the vicinity of the targets if identical materials are used (Al–Al) and is possibly indicated in the interaction zone for different ones (Al–Cu), too. The inversion factors (and the gain coefficient) for the 4–3 transition of [He]-like Al at about 130 Å were estimated.
Conversion of laser light into soft X rays with 3-ns and 30-ps laser pulses
Authors: Eidmann K. , Schwanda W.
Published: March 2009

The X-ray emission from planar targets made of aluminum, copper, or gold irradiated by a frequency-doubled Nd laser (530-nm wavelength and 1012–1014-W/cm2 laser intensity) was measured at two pulse durations: 3 ns and 30 ps. We absolutely measured the X-ray emission with spectral, temporal, and spatial resolution in the wavelength range 3 Å < λ < 250 Å by using filtered bolometers, a transmission grating spectrometer, X-ray diodes, and an X-ray streak camera as diagnostics. In addition, the absorption of laser light was measured. For the short, 30-ps laser pulse the conversion of incident laser energy into X rays was considerably less than that with the long, 3-ns pulse. This is caused by less absorption of laser light and, in addition, by less conversion of absorbed laser energy into X rays in the case of the short pulse. The results are compared with numerical simulations performed with the MULTI hydrocode.
Transient effects in laser-plasma X-ray spectrometers
Authors: Wark J. S.
Published: March 2009

X-ray spectroscopy is a widely used means of diagnosing densities and temperature within laser-produced plasmas. At X-ray energies above approximately 1 keV, Bragg crystal spectrometers are routinely used to record X-ray spectra. Quantitative measurements of plasma conditions can be obtained with a knowledge of crystal reflectivity and film or detector response. In such data analysis it is always assumed that the crystal response is constant in time. However, we show that under certain adverse experimental conditions the X-ray fluxes incident on the crystal are so high as to significantly transiently modify the reflection characteristics of the crystal. Such degradation need not necessarily be accompanied by a loss of observed spectral solution. The transient (nanosecond-time-scale) change in crystal reflectivity is due to a change from dynamical to more kinematic diffraction caused by an X-ray-induced thermal strain gradient in the surface layer of the crystal. The decay time of this strain is typically several nanoseconds. Calculations of some specific crystal reflectivities and rocking curves under such conditions are presented, and methods of minimizing the effect by appropriate filtering are discussed.
X-ray transmission grating spectrometer with CCD detector for laser plasma studies
Authors: Pína L. , Fiedorowicz H. , Koshevoi M. O. , Rupasov A. A. , Rus B. , Shikanov A. S. , Svoboda V.
Published: March 2009

A program is under way to develop methods and instrumentation based on charge-coupled device (CCD) sensors for hot plasma diagnostics. We have developed a new X-ray spectrometer in which a freestanding X-ray transmission grating is coupled to a CCD linear array detector with electronic digitized readout replacing film and its wet processing. This instrument measures time-integrated pulsed X-ray spectra with moderate spectral resolution (δλ ≤ 0.6 nm) over a broad spectral range (0.3–2 keV) with high sensitivity, linearity, and large dynamic range. The performance of the device was tested using laser plasma as the X-ray source.
Laser beat wave acceleration of particles
Authors: Dyson A. , Dangor A. E.
Published: March 2009

The laser beat wave programs at Rutherford Appleton Laboratory and Ecole Polytechnique are reviewed. The techniques used to generate by multiphoton ionization the highly uniform plasmas needed for the beat wave are described. Evidence of the generation of a 2% plasma wave using laser beams at 1.064 and 1.053 μm is presented. The plasma wave suffers damping, possibly by the modulational instability. The use of a high-power short laser pulse for plasma-wave generation by the wake-field process is discussed. This process has the advantage that there is no resonance as in the beat wave, and since the plasma wave is generated on the time scale of the plasma period, instabilities are unlikely to be important.
Acceleration and compression of matter due to laser heating and ablation
Authors: Afanasiev Yu. V. , Gamaly E. G. , Guskov S. Yu. , Demchenko N. N. , Rozanov V. B.
Published: March 2009

The model of evaporation, motion and compression of shell laser targets in low-entropy regime is considered. The evaporation rate and accelerating pressure in spherical targets are determined in the stationary corona model. The scaling relation are obtained which make it possible to correlate laser pulse and target parameters and optimize target compression and heating for various values of laser pulse wavelengths and energy. The results of this model are compared with numerical calculation of hydrodynamic and thermal conductivity equations.
The PHEBUS experimental facility operating at 250 ps and 0·53 μm
Authors: Thiell G. , Adolf A. , Andre M. , Fleurot N. , Friart D. , Juraszek D. , Schirmann D.
Published: March 2009

The experiments reported in this paper demonstrate that the PHEBUS laser facility is now currently being operated with high performances (4 TW with 250 ps pulses at 0·527 μm wavelength).

The output energy of the 2-beam PHEBUS laser system can be focused either in a small focal spot (80% of the incident energy is in a 220 μm diameter focal spot) for high intensity experiments (≥5 × 1015 W cm−2) or in very large spots (a few mm in diameter) at moderate intensities (1013 − 2·5 × 1014 W cm−2), for large scale experiments. It is shown that the spatial intensity distribution in the target plane is primarily due to intensity independent aberrations and to diffraction. Laser light absorption in plane aluminum and gold targets are interpreted in terms of inverse bremsstrahlung absorption that may account for 70 to 90% of absorbed energy. Finally, the plasma expansion is shown to be very planar and comparison with one-dimensional Lagrangian simulations gives flux limiter values of 0·03 and 0·02 respectively for Al and Au targets.
Reduction of Rayleigh–Taylor growth due to viscosity effects
Authors: Mulser P.
Published: March 2009

The effect of viscosity on the growth reduction of Rayleigh–Taylor modes is studied. It is shown that short wavelength perturbations are strongly damped; however the growth of the most relevant modes in fusion pellets is nearly unaffected.
Simultaneous x-ray and optical shadowgraphy of cavities heated by λ = 0.44 μm laser light
Authors: Földes I. B. , Sigel R. , Shi-Sheng Chen , Eidmann K. , Schmalz R. F. , Tsakiris G. D. , Witkowski S.
Published: March 2009

Gold cavity targets were irradiated with λ = 0.44 μm laser light at intensities ≤ 2.6 ×1013W/cm2. The outward motion of the cavity wall was investigated by simultaneous optical and x-ray shadowgraphy. The wall motion is attributed to the pressure generated by an ablative heat wave, driven by the soft x-rays in the cavity. The observed transparency of the cavities for the x-rays used for shadowgraphy allowed the determination of the density profile of the cavity wall which decays possibly due to fragmentation.
Volume ignition of laser driven fusion pellets and double layer effects
Authors: Cicchitelli L. , Eliezer S. , Goldsworthy M. P. , Green F. , Hora H. , Ray P. S. , Stening R. J. , Szichman H.
Published: March 2009

The realization of an ideal volume compression of laser-irradiated fusion pellets (by C. Yamanaka) opens the possibility for an alternative to spark ignition proposed for many years for inertial confinement fusion. A re-evaluation of the difficulties of the central spark ignition of laser driven pellets is given. The alternative volume compression theory, together with volume burn and volume ignition (discovered in 1977), have received less attention and are re-evaluated in view of the experimental verification by Yamanaka, generalized fusion gain formulas, and the variation of optimum temperatures derived at self-ignition. Reactor-level DT fusion with MJ-laser pulses and volume compression to 50 times the solid-state density are estimated. Dynamic electric fields and double layers at the surface and in the interior of plasmas result in new phenomena for the acceleration of thermal electrons to suprathermal electrons. Double layers also cause a surface tension which stabilizes against surface wave effects and Rayleigh–Taylor instabilities.
Total absorption of unpolarized radiation in a stratified plasma
Authors: Vukovic S. , Dragila R. , Smith A. M.
Published: March 2009

We demonstrate that 100% absorption of an unpolarized monochromatic light can be achieved in a plasma with a density profile characterized by a presence of a cavity and a steep density gradient across the critical region. These profiles can occur in a laser produced plasma due to the radiation pressure effects. The conditions were found when both s- and p -polarizations of the electromagnetic radiation which is obliquely incident upon a stratified plasma are totally absorbed at same angle of incidence. The effect is due to simultaneous excitation of surface and guided modes which are eigenmodes of the considered plasma structure. When these modes are excited some additional conditions must be satisfied which allow for full compensations of all dissipative processes by the radiation energy inflow.
Some Anomalies in the Raman spectrum from laser-produced plasmas
Authors: Boyd T. J. M. , Gardner G. A. , Coutts G. A.
Published: March 2009

Many experiments show features of the Raman spectrum at variance with the predictions of conventional theory. One persistent discrepancy, the cut-off in the spectrum of scattered light at about 1·5λ0, led Simon and Short to postulate that the scattered spectrum is not Raman light as such, but derives from enhanced Thomson scattering from plasmas in which a population of suprathermal electrons is present. We describe a set of simulations which model the propagation of a light wave through a plasma characterized by two electron temperatures with the hot electron fraction varying between 0 and 0·05. The results show that enhanced Thomson scattering will contribute to the spectra observed in some experiments at least and confirm the contention that the spectrum of the scattered light is not especially sensitive to the width of the suprathermal electron feature. We have also examined the effect of a finite quiver velocity on the enhanced Thomson spectrum as a function of the population of suprathermal electrons, in particular its effect on the wavelength bands.
Laser-driven implosion studies using the soft X-ray emission measurements
Authors: Denus S. , Fiedorowicz H. , Jeziak K. , Parys P. , Pawłowicz W. , Wołowski J.
Published: March 2009

The mass ablation rate and ablation pressure on laser-irradiated spherical microshells were measured using the space-resolved X-ray spectroscopy. A new method for the study of the ablation by means of the Doppler shifted X-ray images is proposed. The time-resolved measurements of X-ray emission from layered microtargets allow us to determine the heat front penetration through the microshell wall.
Radiation of stationary spherical ‘corona’ formed by heavy-ion beams
Authors: Afanasiev Yu. V. , Isakov V. A. , Khachiyan K. A.
Published: March 2009

The problem of heavy-ion beam energy conversion into the plasma self-radiation of the spherical target is considered by using the radiative conductivity approximation. It is shown that there is a single parameter γ which determines the spherical ‘corona’ structure and has the meaning of the ratio: the ion range/the effective heat range. The conversion coefficient increases with the increase in the parameter γ and becomes ∼ 1, when γ ≃ 102. Typical beam and target parameters of modern HIF designs correspond to γ ≃ 10 and conversion coefficients >50%. Thus, at quasistationary stage of the ‘corona’ expansion the target acceleration and implosion regime is basically the radiative one.
10-ps pulsation of laser plasma explained hydrodynamically by self-generated Bragg ripples and their decay and avoidance by smoothing
Authors: Aydin M. , Min Gu , Hora H.
Published: March 2009

The many years' of difficulty with laser fusion owing to the complexity of the interaction with the plasma has been clarified experimentally from the 10-ps pulsation of the interaction. The theoretical understanding of this pulsation is presented here from a hydrodynamic simulation of the interaction in which the generation of partial standing waves and the subsequent nonlinear-force-produced density ripple produces ideal Bragg reflection in the outermost part of the plasma. This all decays within about 10 ps hydrodynamically. The theory explains immediately why the 2-ps coherence at induced spatial incoherence avoids the pulsation and arrives at a smooth interaction similar to the random-phase plate or the use of broad-band laser spectrum irradiation.
ICF-related experiments at CEL-V
Authors: Andre M. , Bayer C. , Babonneau D. , Bernard M. , Bocher J. L. , Bruneau J. , Coudeville A. , Coutant J. , Dautray R. , Decoster A. , Decroisette M. , Desenne D. , Duborgel B. , Dufour J. M. , Jadaud J. P. , Juraszek D. , Garçonnet J. P. , Holstein P. A. , Lachkar J. , Louis-Jacquet M. , Mucchielli F. , Meyer B. , Lebreton J. P. , Ouvry J. , Schirmann D. , Schurtz G. , Véron D. , Watteau J. P.
Published: March 2009

Implosion experiments performed at Centre d'Etudes de Limeil-Valenton in the indirect drive scheme using the two-beams Nd:glass laser facility Phebus at the energy level = 6 kJ (blue light) are presented. A final density of compressed DT close to 100 ρ0 has been obtained; it has been deduced from radiochemistry of the activated silicon atoms in the pusher. The best irradiance uniformity on the microballoon was evaluated to = 15% rms. Phebus has also been equipped with an optical fiber oscillator to study the effect of a smoothing technique on coupling processes: It appeared that at 0·53 μm absorption efficiency is increased by =15–20%. With the eight-beams Octal laser, hydrodynamic instabilities development in accelerated planar targets has been investigated both for direct and indirect drives; the mixing zone detected at the light-heavy interface does not present visible bubble-and-spike like structures and is less developed in the indirect configuration. Atomic physics in laser plasmas is also deeply studied; a particular effort has been made on absorption spectroscopy, a powerful diagnostic of ionization dynamics in cold and dense plasmas. Experiments have been realized either in multilayered targets or using rear-side X-ray emission of thin Au foils to heat the samples. To reach fuel ignition conditions, more powerful lasers, in the range of megajoule, will be needed. Their design needs further technological developments to reduce the capital cost in $/W. At Limeil, we work mainly on high-damage threshold optical coatings, using the sol-gel process, high-quality, low-cost mirror fabrication, using the replica technics, and incoherent laser pulse generation for beam smoothing.
Laser-plasma interaction properties through second harmonic generation
Authors: Abdelli S. , Khalfaoui A. , Kerdja T. , Ghobrini D.
Published: March 2009

An experimental analysis is conducted to visualize sidescattered second harmonic spectra originating from the critical surface of a plasma produced from a 1, 064-nm laser beam. It is shown that longitudinal and transverse wave-scattering mechanisms producing the second harmonic may also alter the local plasma parameters. These irregular plasma parameter variations and the perturbed spatial uniformity of the incident laser beam can, in turn, be visualized through the second harmonic behavior. This work confirms the origin of the second harmonic production in an inhomogeneous plasma. Time evolution of the optical density of this harmonic showed spectral shifts due to the Doppler effect related to the critical surface dynamics. On the time-integrated spectra, shifted secondary peaks have been observed, indicating that the second harmonic takes its origin also from parametric decay as well as electron decay instability. Other properties of the interaction physics are deduced from the present second harmonic study.
X-ray pulsation caused by collapse processes in laser interaction with plasma
Authors: Arnas C. , Briand J. , Moor J. F. , Armengaud M. , Gomes A.
Published: March 2009

The time-resolved X-ray emission recorded from a plasma produced by a Nd laser at high intensity (>1014 W/cm2) shows successive bursts. They are correlated with the pulsation of the back-scattered second harmonic spectrum obtained during the same shot. Both results show that the plasmons resonantly excited at the critical surface by the laser waves can undergo quasiperiodically the collapse process.
Targets for investigation of X-ray laser–plasma emission
Authors: Suchańska R.
Published: March 2009

Two methods of target technology for investigation of X-ray laser–plasma emission are presented. The first deals with steel and gold microcapillary targets. They are about 200 μm in inner diameter and about 500 μm in length. The second method deals with metal plus plastic targets of reduced and controlled density in the range of 1.6–8.1 g/cm3 for Cu + polyethylene (PE) and 1.6–7.6 g/cm3 for Fe + PE.
Short-wavelength-laser requirements for direct-drive ignition and gain
Authors: McCrory R.L. , Soures J.M. , Knauer J.P. , Letzring S.A. , Marshall F.J. , Skupsky S. , Seka W. , Verdon C.P. , Bradley D.K. , Craxton R.S. , Delettrez J.A. , Epstein R. , Jaanimagi P. , Keck R. , Kessler T. , Kim H. , Kremens R.L. , McKenty P.W. , Short R.W. , Yaakobi B.
Published: March 2009

Inertial confinement fusion (ICF) requires high compression of fusion fuel to densities approaching 1000 times liquid density of deuterium-tritium (D–T) at central temperatures in excess of 5 keV. The goal of ICF is to achieve high gain (of the order of 100 or greater) in the laboratory. To meet this objective with minimum driver energy, a number of central issues must be addressed. Research in ICF with laser drivers has shown the importance of using short wavelength (λ < 0.5 µm). To achieve conditions for high gain at driver energies of a few megajoules or less, high intensities (>1014W/cm2) are required. The directdrive approach to ICF is more energy efficient than indirect drive if the stringent drive symmetry and hydrodynamic stability requirements can be met by a suitable laser irradiation scheme and target design. Experiments carried out at 351 nm on the 2-kJ, 24-beam OMEGA laser system at the Laboratory for Laser Energetics (LLE) at the University of Rochester, and future experiments to be performed on a 30-kJ upgrade of this laser, can resolve the remaining physics issues for direct drive: (1) energy coupling and transport scaling; (2) irradiation-uniformity requirements for high gain; (3) hydrodynamic stability constraints; and (4) hot-spot and main-fuel-layer physics. We review progress made on achieving uniform drive conditions with the OMEGA system and present results for direct-drive cryogenic-fuel-capsule and CD-shell, “surrogate” cryogenic-capsule implosion experiments that illustrate the constraints imposed by hydrodynamic instabilities and drive uniformity on the design of high-performance direct-drive targets. Target designs have been identified that will explore the ignition-scaling regime using the OMEGA Upgrade. Experiments on the OMEGA Upgrade will signal whether or not there is a high probability of achieving modest to high gain using direct drive on an upgrade of the NOVA facility.
Performance of the ASHURA KrF laser and its upgrading plan
Authors: Owadano Y. , Okuda I. , Matsumoto Y. , Matsushima I. , Koyama K. , Tomie T. , Yano M.
Published: March 2009

Achieved performance of and the future plan for the ASHURA, a 700-J KrF laser, are described. Nanosecond pulses (3–20 ns) with a bandwidth of 50 cm-1 have been produced by gain switching of a preamplifier. The pulses have been six-time angularly multiplexed and double-pass amplified by two electron-beam-pumped amplifiers. The output from the main amplifier is strongly saturated, and maximum energy of 660 J has been extracted in 90 ns with a stage gain of 40. Focused by an f = 1m spherical lens, maximum power density of 6 × 1014 W/cm2 can be obtained on target. The energy density ratio of prepulse on target has been suppressed below 1/107. The ASHURA is being upgraded by adding a next-stage amplifier that aims at 10-kJ output energy in 270 ns.
Application of dense plasma beams to the development of a high-efficiency lateral injection laser amplifier
Authors: Boreham B.W. , Waller J.W. , Cicchitelli L. , Khoda-Baksh R. , Rowlands T. , Hora H.
Published: March 2009

Recent developments in research on drivers for inertial confinement fusion identified the need to develop laser amplifiers with efficiencies of 80% or more. This article discusses a novel free electron laser amplifier that is based on vacuum interaction of laser beams with electrons, clusters of condensed matter, or neutral atoms. The scheme is based on the inversion of the ponderomotive expulsion of plasma from a focussed laser beam. The problem of Liouville conservation of phase space is overcome by employing the laser pulse transient processes. The optical energy for amplification is provided by the transfer of the translative kinetic energy of electrons, clusters, or neutral atoms that are injected nearly laterally into the laser pulse. The gains predicted to be achievable with this process are of interest for clusters, although the cluster densities presently available are too low to achieve the desired level of amplification. Neutral beams are shown to have the greatest potential for achieving large amplifications.
Inorganic liquid laser doped with neodymium and uranyl
Authors: Dyachenko P.P. , Kalinin V.V. , Seregina E.A. , Shevchuk O.D. , Tichonov G.V. , Gilyarov O.N. , Krasilov Yu.I. , Kulikovskiy B.N. , Novoderyozhkina T.L.
Published: March 2009

Spectral-luminescent properties of the Nd3+-activated laser liquid based upon POCl3-SnCI4 upon excitation by-products of nuclear reactions have been researched. It was concluded that the main luminescence characteristics such as T, Δλ, and λmax depend slightly upon the way of the medium excitation. It was obtained that the pumping efficiency δ of the upper working level is directly proportional to the activator ions' concentration and almost independent of the uranyl presence in the liquid. The measured values t, Δλ, λmax, and δ were used for the estimates of some parameters of nuclear-pumped lasers based upon phosphorus oxychloride. The effect of the Nd3+ ions laser action from the 4F3/2 level to the 4I11/2 level (λ = 1,050 nm) in aprotic liquids POCI3-SnCl4 in the presence of uranium by flashlamp pumping has been obtained.
Heavy-ion beam-pumped lasers: Optical gain on the 476.5-nm Ar II transition
Authors: Wieser J. , Ulrich A. , Busch B. , Gernhäuser R. , Krötz W. , Ribitzki G. , Salvermoser M. , Murnick D.E.
Published: March 2009

The possibility of heavy-ion beam-pumped ion lasers is demonstrated by observation of optical gain on the 476.5-nm Ar II 4p–4s ion laser transition in argon gas excited by 2.5–ns pulses of 110–MeV 32S ions with repetition rates up to 156 kHz. The particle energy per pulse was about 20 μJ. The projectiles were stopped in the target at pressures between 5 and 35 kPa. The beam from an argon ion probe laser operated at 476.5 nm was used to determine gain amplitude and time structure from a measured transient increase of the probe laser intensity when target excitation by the ion beam was present. The maximum gain observed was (0.5 ± 0.1) x 10-3 at a target gas pressure of 5 kPa. The optical gain observed in argon is consistent with calculations based upon an analysis of spectroscopic studies of rare gas targets excited by heavy-ion beams.
Practical, visible wavelength nuclear-pumped laser
Authors: Shaban Y.R. , Miley G.H.
Published: March 2009

A practical, visible nuclear-pumped laser (NPL) has been sought at the University of Illinois and other laboratories for a number of years. Yet, the results from successful visible NPLs to date have not been fully satisfactory, e.g., the threshold pumping power is too high for conventional applications. Progress in recent studies of 3He-Ne-H2 as a candidate NPL operating in the visible region at 585.3 nm on the 2P1,-1S2 Ne transition is described. We obtained lasing on the above transition for 3He-Ne-H2 concentrations of 1,140, 588, and 412 torr, respectively, with the laser cavity placed in the beamport of the University of Illinois TRIGA reactor. The threshold thermal neutron flux is 1014 n/cm2-s, corresponding to a threshold pumping power of 5 W/cm3.
Observations of two-stream collisional instability due to interaction of monoenergetic relativistic electron beams with gas
Authors: Batenin V.M. , Danilov A.V. , Ikonnikov A.O. , Ilchenko S.A. , Kunavin A.T. , Markov A.V. , Sapozhnikov D.V. , Tokar P.M. , Vovk I.V. , Yakovlev V.Y. , Zhivopistsev V.S.
Published: March 2009

We have studied experimentally the beam-plasma two-stream dissipative collisional instability of relativistic electron beams (REB) injected into plasma produced by interaction of REB with neutral nitrogen. The gas pressure ranged from 0.02 to 8 Torr. REB (T = 100 μs, E = 300 keV, 7 = 3–15 A) were injected into gas through a pulsed foilless valve. An external magnetic field was not used. A description of the experimental setup and that of applied diagnostics are presented. In some of the experiments the inner walls of a metallic interaction chamber were covered with microwave-absorbent material. We present the experimental dependence of the critical current of two-stream instability on gas pressure and beam penetration length. We have also measured the distribution of microwave emission along the beam axis. The influence of plasma self-radiation on the instability was observed and is attributed to a feedback. A possible mechanism of the feedback is discussed.
Thermalization of synchrotron radiation from field-aligned currents
Authors: Peter William , Peratt Anthony L.
Published: March 2009

Three-dimensional plasma simulations of interacting galactic-dimensioned current filaments show bursts of synchroton radiation of energy density 1·2 ×10−13 erg/cm3 which can be compared with the measured cosmic microwave background energy density of 1·5 × 10−13 erg/cm3. However, the synchrotron emission observed in the simulations is not blackbody. In this paper, we analyze the absorption of the synchrotron emission by the current filaments themselves (i.e., self-absorption) in order to investigate the thermalization of the emitted radiation. It is found that a large number of current filaments (>1031) are needed to make the radiation spectrum blackbody up to the observed measured frequency of 100 GHz. The radiation spectrum and the required number of current filaments is a strong function of the axial magnetic field in the filaments.
High-current electron beam nonlinear relaxation in plasma and electron acceleration
Authors: Karfidov D. M. , Nikolov N. A. , Malinov P. N. , Trifonov I. P.
Published: March 2009

A nonlinear relaxation is observed when an electron beam interacts with plasma in an external magnetic field. An acceleration of electrons to energies which are more than twice that of the initial beam energy is observed. The acceleration mechanism is connected with the modulation instability of the plasma waves which is excited when the beam relaxes.
Electron acceleration in plasma under the action of strong electromagnetic radiation
Authors: Gavrilov E. M. , Rubenchik A. M. , Shvets V. F.
Published: March 2009

The acceleration of electrons in a laser plasma at the densities below the critical one is investigated by a particle simulation. It is shown that the stabilization of parametric instability and limitation of the energies of the accelerated electrons take place. The structure of the plasma electron distribution function is examined.
Soft X-ray laser pointing and focusing experiments
Authors: Nilson D. G. , Brown S. B. , Keane C. J. , Macgowan B. J. , Matthews D. L. , Trebes J. E. , Wood O. R. , Silfvast W. T.
Published: March 2009

Recent advances in X-ray laser research have significantly increased the possibilities for X-ray laser applications. In this paper, we report the first demonstration of pointing and focusing of a soft X-ray laser beam. A LLNL selenium soft X-ray laser at 206 and 209 Å was used in these experiments. Two state of the art 76 mm diameter multilayer mirrors were used to collimate and refocus the laser onto a set of cross hairs which were constructed from 100 μm diameter wires. The cross hairs were located 4.6 m from the X-ray laser source. Results show that the laser can be pointed to within 75 μrad and focused to a 235 μm diameter spot. It is expected that eventually spot sizes near 100 μm and flux levels of 100J/cm2 at X-ray irradiances up to 1012W/cm2 can be provided to a remote application, using a similar beam relaying system.
Requirement of uniformity for fuel ignition and uniformity in high neutron yield implosion
Authors: Takabe H. , Mima K. , Nakai S.
Published: March 2009

An ignition condition for a compressed DT sphere is studied by the use of balance relation between a heating term (alpha-particle heating) and cooling terms (expansion, radiation, and electron heat conduction). The resultant condition was compared with the model simulation carried out by Fraley et al. (1974). Effect of implosion uniformity is one of the most important elements in evaluating the laser energy required for fuel ignition. Increase of the laser energy as a function of implosion nonuniformity is shown. For a self-consistent study of implosion dynamics, a two-dimensional fluid code is developed and used for analyzing the recent high neutron yield experiment (Takabe et al. 1988). Two-dimensional fluid dynamics driven by laser irradiation nonuniformity is studied to explain the difference between the experimental result and the result of 1-D fluid simulation.
Some aspects of the unified model of non-ideal high-parameter plasmas: electron EOS and conduction coefficients
Authors: Drska L. , Vondrasek J.
Published: March 2009

We present two partial models applied in the atomic physics subpackage used in numerical simulations of pulsed-source-driven, non-ideal high-parameter plasmas. These are an electron EOS model and a model for electron conductivity coefficient calculations. The EOS model uses Dharma-Wardana exchange and a correlation correction that depends on both electron density and temperature. The electron thermal and electrical conductivity calculations are based on the Balescu-Lenard equation.
Analysis, design and construction of copper vapor laser system
Authors: Cavalieri Stefano , Pini Roberto , Salimbeni Renzo , Vanni Umberto , Vannini Matteo , Burlamacchi Pio , Fini Lorenzo
Published: March 2009

In this work construction characteristics and performance of a small scale self-heating copper vapor laser are presented. Analytical design of the thermal isolator is reported in some detail. Particular attention has been given to the knowledge of power deposition in the discharge to evaluate the component losses. In the optimized conditions the laser mean power is over 5 W, confirming the expected values. Details of the measurements on the system are also reported.
New diagnostic developments for intense ion beam experiments
Authors: Leeper R. J.
Published: March 2009

A review of recent developments in intense ion beam diagnostics used in the international light ion inertial confinement fusion (ICF) programs will be presented. These developments have occurred in each of the several generic classes of diagnostics, namely, imaging diagnostics, particle spectrograph diagnostics, nuclear activation, and visible spectroscopy. Critical beam parameters measured by the new diagnostics include spatial profile, absolute number, species, anode plasma temperature and density, voltage, current density, and power density. A unique feature of most of these diagnostics is that they are capable of operating in hard (multi-MeV) X-ray (bremsstrahlung) backgrounds of some 109–1011 rad/s. The operating principles of each diagnostic will be summarized in the paper with examples of how the diagnostics may be integrated together to form a complete diagnostic system. The paper will close with a discussion of two new data acquisition systems that have been developed for intense beam diagnostics.
Experimental and numerical investigation of a self-magnetically Bθ-insulated ion diode
Authors: Westermann Th. , Schimassek W.
Published: March 2009

This is a short summary of research on the self-magnetically Bθ-insulated ion diode originally proposed by K. Zieher (1981, 1983, 1984, 1984a). We report the most recent progress. For detailed discussions see the forthcoming publications (Schimassek 1989; Westermann 1989). After the exploratory work of Zieher the efforts of recent years have concentrated on the numerical simulation (Westermann 1988; 1988a; 1988b), the development of detailed diagnostic tools (Rogner & Schultheiss 1986; Kühn & Rogner 1985; Klumpp & Bluhm 1986) and the focusing properties of the Bθ-diode (Citron et al. 1986; Bauer et al. 1987; Schimassek et al. 1988; Westermann 1988c). Experiments and numerical simulations on three modifications of the diode will be reported (version I, II, III).
Studies of the spatial and temporal evolution of a dense plasma focus in the X-ray region
Authors: Choi P. , Wong C. S. , Herold H.
Published: March 2009

The dynamics of the plasma evolution in a dense plasma focus has been studied using a streak camera system in the soft X-ray region. The experiments were performed on a medium energy plasma focus operating with a hydrogen-argon admixture. The streak camera system employed provides nanosecond resolution and allows the plasma to be viewed simultaneously through two different filters to achieve energy resolution. Observations are made in the radial direction and along the pinch axis. Collimated X-ray PIN diodes suitably filtered were used to provide additional information on the structure of the X-ray emitting regions of the plasma. The plasma focus is observed to be totally dynamical and continuously evolving in nanosecond time scale. Hot spots are observed to form among the moving plasma at various times. Such continuous nanosecond time scale evolution of the focus pinch in the X-ray region have not been reported previously.
Simulations of hydrodynamic flow in gas targets irradiated by intense ion beams
Authors: Schneider V. , Maruhn J.
Published: March 2009

A two-dimensional hydrodynamic code is discussed. It includes the treatment of energy deposition by heavy ions and the calculation of transport coefficients. Loss terms due to volume radiation in the emission limit and a realistic equation of state (SESAME tables or the equation of state of an ionized gas including the solution of the Saha equations to determine the degree of ionization) are considered.

Numerical simulations are performed to study the hydrodynamic flow in cylindrical tubes filled with the noble gases Argon and Xenon respectively. Target and beam parameters are chosen in close analogy to the GSI-RFQ beam-target experiments.

The conditions for the formation of a shock wave at the interface between matter heated by the ion beam and cold matter are investigated. It turns out that, in addition to ionization effects, shock heating has a strong influence on the maximum target temperature. Depending on the temperatures to be reached with a given deposition power, either expansion or radiation cooling could be the dominant cooling mechanism. As a result we can conclude that hydrodynamic motion produces a lot of structure that should be observable in the GSI experiments.
Conceptual design of a 170-MJ hydrogen fluoride laser for fusion
Authors: Phipps C. R.
Published: March 2009

We have completed the conceptual design of a 170-MJ laser system consisting of two identical, opposing, 0·4 M-litre, 84-MJ HF subsystems, which together deliver 105 ‘useful’ MJ in 50 ns (FWHM duration) to a laser-fusion target during its hydrodynamic drive interval. We achieved extreme design simplicity by eliminating most optics, using an inexpensive, very-high-energy-density gain medium, propagating the laser beam at the maximum fluence permitted by optical breakdown in the laser medium, and by using replicated simple subsystems for pulsed power. The infrared spectrum of the HF laser lies outside the ultraviolet range favored by the U.S. laser fusion program for optimum target coupling efficiency. However, the laser architecture we describe is an alternative for laser fusion systems which offers dramatic improvements in simplicity, compactness, and efficiency, which advantages will be even more pronounced when equally efficient, visible-wavelength chemical lasers become available.
Mathematical modeling of the thermonuclear burning in DHe3 targets with D-T ignition
Authors: Burtsev V.A. , Gus'kov S.Y. , Rozanov V.B. , Il'In D.V. , Levkovsky A.A. , Sherman V.E. , Starbunov Y.N. , Zmitrenko N.V.
Published: March 2009

It is shown that there is a principal possibility of effective burning with gain G > 200 of ecologically clean DHe3 fuel in reactor-type targets without increase of driver energy. The proper target consists of DHe3 fuel and a D-T ignitor with a central hot spark. Under proper conditions, the D-T burning wave reaches the DHe3 range with the temperature sufficient for ignition of DHe3 plasma. The simulation was carried out by means of TERA code based upon self-consistent solution of a kinetic equations system for products of primary and secondary thermonuclear reactions by the Monte Carlo method and a hydrodynamic equations system.
Laser action on the (B–X) band of HgI at 445 nm
Authors: Mahmood Mohammad F.
Published: March 2009

Dissociative excitation of the HgI (B–X) band system and atomic mercury lines was observed during collisions of CO+ ions with CH3HgI molecules in the laboratory kinetic energy range 100–1000 eV. By the use of the integrated intensity of the most intense band of the (B–X) transition of the HgI radical at 445 nm, emission cross sections were measured at different kinetic energies of these ions.
Doppler-shift decoupling of radiation reabsorption in expanding laser-produced plasmas
Authors: Brunner W. , John R. W.
Published: March 2009

To investigate the influence of radiation reabsorption on the level populations of ions in an expanding laser-produced plasma of intermediate density, we start with the system of rate equations for the population densities coupled with the line-radiation transport equation, the dynamical Doppler effect due to the differential macroscopic velocity field included. In a physically motivated approximation, for spatially varying absorption and emission, and general three-dimensional plasma geometry, an integral equation describing the effect of Lyman-a radiation reabsorption on the spatial behavior of the population density of the upper resonance level is derived. Assuming a sufficiently large velocity gradient so that the Doppler-induced frequency shift dominates the linewidth, after asymptotically evaluating the frequency integral involved in the kernel we are led to a simplified integral equation exhibiting the reduction of radiation reabsorption by Doppler decoupling. In particular, in the case of a cylindrical, radially expanding laser plasma we discuss this Fredholm equation for the reabsorption-influenced population density.
High-power laser-produced plasmas and astrophysics
Authors: Rose S. J.
Published: March 2009

The temperatures and the densities of plasmas produced by high-power lasers vary widely but in certain cases are similar to those found in astrophysical plasmas. In recent years our understanding of intense laser–matter interaction and the evolution of the resulting

plasma has increased to the point where experiments can be designed to produce plasmas that allow astrophysical models to be tested. In this paper I review experimental work on laser-produced plasmas that is relevant to astrophysics. In the fields of highlyionized ion line identification and radiative opacity, relevant measurements have already been performed. Other experiments that could be performed with current laser facilities, including studies of X-ray nebula plasmas and complex radiation line transport, are described. In addition, experiments to investigate plasmas under more extreme conditions, which may be achievable with more powerful lasers, are mentioned.
Rayleigh-Taylor instability study for heavy-ion beam driven, high-gain ICF implosions
Authors: Caruso A. , Pais V. A. , Parodi A.
Published: March 2009

We carried out a numerical analysis on the stability of targets designed to produce fusion energy gains close to 100 when irradiated with an appropriate heavy ion beam. To reach such performances, we found that a high-Z radiation shield was necessary to screen the DT fuel from the radiation coming from the surrounding hot material. As opacity of high-Z materials is only weakly density dependent, we considered targets with lead shields both at solid density and with a density equivalent to that of the contiguous external material. The behaviour of both kinds of targets has been studied by introducing a small spatial nonuniformity on the external surface of the lead shield. Targets with low-density shields have been tested with a beam intensity perturbation, too. Because density gradients are very sharp and ablation is practically absent, we have found these implosions to be Rayleigh-Taylor unstable. The evolution has been followed in the nonlinear regime because the full hydrodynamical-radiative model with a nonlinear heavy ion energy deposition and mesh correction was used.
Tritium content of a DT pellet in inertial confinement fusion
Authors: Kawata Shigeo , Nakashima Hideki
Published: March 2009

A numerical and analytical estimation and a one-dimensionalhydrodynamic simulation show that a 30%reduction of the tritium content in a D-T pellet still gives sufficient energy output in aD-T inertial confinement fusion reactor.In other words, the tritiumb content can be reduced significantly without a significant reduction in the D-T fusion energy output.This new result also meansthat the tritium inventory can be reduced significantly before and during the reactor operation in the D-T inertial confinement fusion.This result comes from the contribution of a D-D reaction to the D-T reaction.
Polystyrene shells from pellets containing a chemical blowing agent
Authors: Marchisio C.
Published: March 2009

A new method for fabricating polystyrene ICF targets has been investigated. A solid solution of polystyrene (PS) containing a chemical blowing agent (CBA) is divided into small granules. These granules are blown into spherical shells in a vertical furnace. By varying the type and amount of CBA as well as furnace parameters, we have been able to produce PS shells 200–600 μm in diameter with wall thicknesses from 4–20 μm.
Influence of collector ions on operation of magnetically insulated diode
Authors: Komarov O. L. , Saveljev Yu. M. , Engelko V. I. , Vrba P.
Published: March 2009

We studied the formation of the collector ion flow in magnetically insulated diodes (MID) with plate-, sphere-, and cone-shaped cathodes. The ions are formed as a result of the ionization of residual gas by electron bombardment and are focused into the cathode plasma region. This effect can negatively influence diode operation in the microsecond range of pulse duration.