bluuebunny/crossref_metadata_2025 huggingface dataset:
KrF laser produced plasmas
Authors: Offenberger A. A. , Fedosejevs R.
Published: March 2009

KrF and other short wavelength lasers are ideal candidates for producing hot dense plasmas since the laser energy can be absorbed with high efficiency by classical mechanisms, thereby virtually eliminating anomalous absorption and the production of non-thermal electrons. A high power KrF laser system employing optical beam multiplexing and stimulated Brillouin scattering to produce pulses as short as 1 ns and focused intensities on target of 1011−1014 W/cm2 has been developed for producing such plasmas and studying laser/plasma interaction phenomena. A variety of studies on absorption, transport, ablation, X-ray conversion and stimulated scattering instabilities have been pursued with this ¼ μm laser on single atomic number and multi-layer targets. This paper briefly describes some of the features of the KrF laser system and highlights some of the characteristics of the hot dense plasmas produced.
Synergism in inertial confinement fusion: a total direct energy conversion package
Authors: Prelas M. A. , Charlson E. J.
Published: March 2009

The products of fusion reactions have unique properties which can be used for direct energy conversion. These products are neutrons and ions. Neutrons can be transported very long distances through solid materials and can interact with certain elements which have a very high absorption cross section. Ions on the other hand have a very short transport length even in a gaseous medium. It is possible to utilize these products in an inertial confinement fusion reactor with two different direct energy conversion devices: a nuclear-pumped laser using neutrons from the fusion reaction; a photon generator material combined with a photovoltaic converter using the ionic fusion products.

It will be argued that a nuclear-pumped laser can be more efficient than a conventional laser. It will also be shown that an advanced energy conversion concept based on photon production and photovoltaics can produce ICF system efficiencies of 56%.
Theoretical studies on electron and radiation preheatings
Authors: Mima K. , Takabe H. , Nishiguchi A. , Kihara Y. , Nakai S.
Published: March 2009

In order to enhance the coupling efficiency, a low Z ablator is generally used for ICF targets. The ablator thickness is appropriately chosen so it is burned out by the end of a laser pulse. Then all of the implosion kinetic energy is contained in the DT fuel. However, a small amount of preheating degrades the compression in a hollow shell, DT fueled target implosion. In this paper, we investigate the preheating level of the fuel shell by Fokker–Planck simulations of the electron heat transport.

From the analysis, it is found that a thick surface layer of a laser irradiated low-Z target is preheated by Maxwellian tail electrons which have a long mean free path. Hence, we propose that the target be precompressed by a tailored pulse, in order to increase the shell ρΔR at the laser peak.
Physics of dense plasma research at MPQ
Authors: Witkowski S.
Published: March 2009

The main tool for the laser plasma work at MPQ (Max-Planck-Institut für Quantenoptik) is the ASTERIX iodine laser delivering 300 J/300 ps pulses at 1·3 m, operational also at 2ω and 3ω. A fifth 30-cm diameter am lifier is under construction to increase the pulse energy up to 2 kJ.

Soft X-ray radiation emitted by laser plasmas and its influence on energy transport and hydrodynamics is studied. Time and space resolved spectroscopic measurements of soft X-radiation from a variety of targets are compared with analytical models and computer results. Planck radiation is produced in gold cavities to study radiation hydrodynamics. Theoretical work comprises shock waves in solids, the electronic structure of very high density matter, radiation pumped X-ray laser and development of the appropriate computer codes.

Estimates indicate that dense plasmas with temperatures of several ten keV can be produced with the heavy ion accelerator now under construction at GSI-Darmstadt. Experiments are being prepared to be started in 1991. Measurements at the present UNILAC-accelerator confirm the theoretical prediction that the energy loss of heavy ions in a plasma is much higher than in cold matter.
Laser-produced dense plasma in extremely high pressure gas and its application to a plasma-bridged gap switch
Authors: Yamada J. , Okuda T.
Published: March 2009

When an extremely high pressure gas is irradiated by an intense laser light, a dense plasma produced at the focal spot moves towards the focusing lens with a high velocity. Making use of this phenomenon, a new plasma-bridged gap switch is proposed and its switching characteristics is experimentally examined. From the experiments, it is confirmed that the switching time is almost constant with the applied voltage only when the focal spot is just on the positive electrode, indicating that the bridging of gap is caused by the laser light.
Laser-induced plasmas in metal vapors
Authors: Bahns J. T. , Koch M. , Stwalley W. C.
Published: March 2009

Strong ionization in metal vapors is known to be very readily produced by a variety of pulsed and CW lasers. Particularly well known is ‘resonance’ ionization by pulsed or CW dye lasers operated at the atomic resonance lines (e.g. Na 3s → 3p). We also have experimental results for two other forms of ionization: ‘quasiresonant’ ionization using a CW dye laser (e.g. at the Na 3p → 4d transitions), and ‘two-photon resonance’ ionization using a pulsed dye laser (e.g. at the Na 3s → 4d two-photon resonances). Both new forms are visually characterized by bright ‘white sparks’ and correspond to reasonably high electron densities of ∼1014−1015 cm3 and low electron temperatures of ∼0·1−0·2 eV. The ‘quasiresonant’ ionization is remarkable in that it occurs even with a very low power 1 mW focused CW laser in 10 torr of Na. A variety of interesting atomic and molecular spectroscopic features have been observed and analyzed.
Non-uniform target illumination in deflagration regime. Refractive smoothing
Authors: Nicolás J. A. , Sanz J. , Sanmartín J. R. , Hilario J.
Published: March 2009

Refractive smoothing of weak non-uniformities in the illumination of laser targets is analyzed, assuming absorption at the critical density and restricting conduction to a thin layer, and using results from thermal smoothing, which is uncoupled from the refraction. Magnetic effects are included. Non-uniformity wavelengths comparable to the thickness of the conduction layer are considered; efficient smoothing exists at both short and long wavelengths in this range. Thermal focusing could make the ablated plasma unstable.
Radiation transport and atomic physics modeling in high-energy-density laser-produced plasmas
Authors: Eidmann K.
Published: March 2009

The radiation hydrodynamics in laser-produced high-energy-density plasmas has been successfully simulated by means of the MULTI hydrocode. It is used in combination with the SNOP atomic physics code, which uses a steady-state screened hydrogenic explicit ion model and which generates non-LTE opacity tables for MULTI. After a brief general review of the modeling of the radiation hydrodynamics in laser-produced plasmas, the underlying physical models of MULTI and SNOP are described in detail, with particular emphasis on atomic physics. Examples of simulations of the radiation transport in laser plasmas are presented. They include a laser-irradiated gold foil and a radiatively heated carbon foil.
Fokker–Planck modeling of electron transport in laser-produced plasmas
Authors: Epperlein E.M.
Published: March 2009

Fokker-Planck (FP) codes have become useful tools for modeling nonlocal heat-transport phenomena in laser-produced plasmas. Several possible simplifications to the FP equation as well as different numerical techniques available for its solution are investigated. The most robust and efficient approach is found to involve the diffusive approximation of the FP equation and the alternating-direction-implicit method of solution. The SPARK FP code, which has been developed along these principles, is described in detail. It incorporates fluid ions and solves for transport on either a two-dimensional Eulerian grid or a one-dimensional Lagrangian grid. Sample simulation results are presented, together with a discussion of possible improvements to the code.
Laser driven implosion
Authors: Yamanaka C.
Published: March 2009

Inertial confinement fusion (ICF) has made great progress. In fact several significant scientific firsts have been achieved in the last year. These developments have presented the ICF community with an opportunity to embark on a new phase in ICF research. The key issues of laser fusion are to attain a high absorption of laser light in a plasma, to prevent preheating of fuel during the compression, and to achieve highly efficient implosion by uniform compression of fuel due to the homogeneous deposition of laser energy on the pellet surface. Direct drive and indirect drive have been investigated. The progress in both schemes is remarkable. The neutron yield by the stagnation free compression of the LHART target has attained 1013 which corresponds to a pellet gain of 1/500. The plastic shell target has reached a fuel density as large as 600 times the liquid density which is measured by the Si activation method as well as the D knockon method. A cryogenic foam target is now under investigation.
Double layer effects causing nearly uniform striated second harmonic emission from a laser irradiated plasma corona
Authors: Goldsworthy M. P. , Hora H. , Stening R. J.
Published: March 2009

The uniform side-on emission of second harmonic radiation has recently been measured from the corona of a laser irradiated plasma with large electron density gradients. A theoretical model has been developed to study the internal electric fields and double layers in such strongly inhomogeneous plasmas. The analytical model shows immediately a density-independent second harmonic term which reproduces very closely the measured intensity of the second harmonic. A detailed numerical evaluation of the term, for a plasma with a linear density profile (permitting Airy solutions), results in a net intensity with small spatial variation but also with both long and short wavelength periodicities exactly as measured. The observed vanishing of the periodicity, when broad band laser sources are used, can then immediately be explained from integration of the standing-wave like oscillations.
Radiation driven planar foil instability and mix experiments at the AWE HELEN laser
Authors: Hansom J. C. V. , Rosen P. A. , Goldack T. J. , Oades K. , Fieldhouse P. , Cowperthwaite N. , Youngs D. L. , Mawhinney N. , Baxter A. J.
Published: March 2009

This paper reviews recent developments and achievements in the program of planar foil instability experiments being performed at the AWE HELEN laser. Point projection Xray backlighting, with spectroscopy, is used to measure hydrodynamic mix in radiatively accelerated ablator/foil packages; the mix is identified in the experimental radiograph from the overlap of distinguishable spectral absorption features associated with each of the constituent materials.

The first part of the paper describes the backlighting technique, and briefly summarizes progress made in the past two years, leading to the first results being obtained on a “high mix” Parylene-C ablator/molybdenum payload package. The second part considers the full analysis of one such ‘high mix’ shot (Shot 7772), describing how the spatial distribution of mix has been quantified and considering the various sources of error. Comparisons are made with both one-dimensional and two-dimensional hydrocode simulations. Finally, various improvements and extensions to the experiment and codes are indicated.
Induction linac drivers for heavy ion fusion
Authors: Herrmannsfeldt W. B. , Keefe Denis
Published: March 2009

The Heavy Ion Fusion Accelerator Research (HIFAR) program of the U.S. Dept. of Energy has for several years concentrated on developing linear induction accelerators as Inertial Fusion (IF) drivers. This accelerator technology is suitable for the IF application because it is readily capable of accelerating short, intense pulses of charged particles with good electrical efficiency. The principal technical difficulty is in injecting and transporting the intense pulses while maintaining the necessary beam quality. The approach used has been to design a system of multiple beams so that not all of the charge has to be confined in a single beam line. The beams are finally brought together in a common focus at the target. This paper will briefly present the status and future plans of the program, and will also briefly review systems study results for HIF.
Laser beam filamentation in a plasma with a steep density profile
Authors: Limpouch J. , Lonĉar G. , Dragila R.
Published: March 2009

A numerical analysis is presented of the electrostrictive filamentation of an electromagnetic wave in the presence of a reflected wave. Maxwell's equations are solved in the steadystate simultaneously with one fluid hydrodynamics and a simplified equation of state to obtain a self-consistent solution. The threshold for filamentation is shown to be often below the laser intensity necessary to modify the plasma density profile, however, even weak profile modification substantially affects the filamentation.
Laser targets fabrication technologies
Authors: Suchańska R. , Muniak W.
Published: March 2009

The paper describes different types of plane targets, the method for obtaining metal microballoons from Au, Ag, and Cu with diameters of 600–1200 μm and wall thickness of 5–20 μm, and spherical cascade and cannonball type targets.
Picosecond high power KrF laser system for X-ray laser research
Authors: Tomie T. , Okuda I. , Owadano Y. , Tanimoto M. , Matsumoto Y. , Komeiji S. , Koyama K. , Matsushima I. , Yaoita A. , Yano M.
Published: March 2009

Fundamental parameters are studied for the detailed design of a picosecond high power KrF laser system. The saturation energy density of 2.3 mJ/cm2and gain recovery time of 1.9 ns in ane-beam pumped KrF laser are observed. A 6 ps pulse is amplified to 1.9 J. The system at the Electrotechnical Laboratory is expected to deliver 10 ps pulses with total energy of several tens of joules in several beams.
Plasma evolution in laser-irradiated hollow microcylinders
Authors: Balmer J. E. , Weber R. , Cunningham P. F. , Lädrach P.
Published: March 2009

Hollow microcylinder targets, 200–300 μm in diameter, have been internally irradiated at up to 5 · 1014 W/cm2 with Nd:glass laser pulses directed through an axial entrance slit. The plasma evolution in the interior of the cavities was diagnosed with a pinhole imaging X-ray streak camera and a Nomarski-type interferometer. Plasma collision near the center of the cylinder is observed about 300 ps after the irradiating laser pulse. The experimental results are confirmed by a one-dimensional Eulerian fluid code.
Laser produced plasma refractometry
Authors: Zakharenkov Yu. A. , Kosterin A. V. , Shikanov A. S. , Pikalov V. V. , Preobrazhensky N. G.
Published: March 2009

A method of probing beam refraction is suggested for the investigation of laserproduced plasma with high density gradients. The refraction angle α of a probing ray as a function of ray impact parameter p is used as input data. Different experimental realizations of α(p) measurements are considered. Results from laser produced plasma interferograms processed with phase shift and refractometry methods are compared.
Progress in inertial confinement fusion physics at Centre d'Etudes de Limeil-Valenton
Authors: André M. , Babonneau D. , Bayer C. , Bernard M. , Bocher J-L. , Bruneau J. , Coudeville A. , Coutant J. , Dautray R. , Decoster A. , Decroisette M. , Desenne D. , Dufour J-M. , Garçonnet J-P. , Holstein P-A. , Jadaud J-P. , Jolas A. , Juraszek D. , Lachkar J. , Lascaux P. , Breton J-P. Le , Louis-Jacquet M. , Meyer B. , Mucchielli F. , Rousseaux C. , Schirmann D. , Schurtz G. , Véron D. , Watteau J-P.
Published: March 2009

The laser program developed at the Centre d'Etudes de Limeil-Valenton, Saint-Georges, France (CEL-V) is concentrated on a systematic investigation of indirect drive fusion; by comparison with direct drive, this process is expected to provide the required irradiation uniformity with relaxed constraints on laser beam quality. The main concerns are radiative transfer and preheat, hydrodynamic instabilities, and high-density X-ray driven implosions. Ablative implosion experiments have been conducted with the two beams at the Phebus facility (5 kJ, 1.3 ns, 0.35 μm). Symmetry was proved to be controlled by the casing structure, following scaling laws describing hohlraum physics. A compressed DT density ∼100 ρ0 (ρ0 liquid DT density) has been deduced from activation measurements. Different aspects of the soft X-ray transfer processes, and particularly of the ablation of a low-Z material, which drives the capsule implosion, are dealt with in detailed investigations. Reported here are results on X-ray reemission and penetration in several materials, and on induced hydrodynamics of accelerated foils. The laser energy required to reach fuel ignition conditions has been evaluated from numerical simulations as well as from analytical models, taking into account hohlraum physics, capsule implosion, hot spot formation, and burn propagation. Several crucial parameters have been drawn, the most important being the radiation temperature. A target gain in the order of 10 appears achievable with a 2-MJ laser.
Investigation of energy transfer in plane laser-irradiated targets with high X-ray conversion efficiency
Authors: Bazylev B.N. , Romanov G.S. , Smetannikov A.S. , Tolkach V.I. , Burdonskii I.N. , Gavrilov V.V. , Gol'tsov A.Yu. , Zhuzhukalo E.V. , Koval'Skii N.G. , Kondrashov V.N. , Pergament M.I. , Koshevoj M.O. , Rupasov A.A. , Shikanov A.S.
Published: March 2009

Results of experimental and computational investigations devoted to energy transfer mechanisms and X-ray conversion efficiency in laser-produced plasma are presented and discussed. The layers of different thicknesses and diameters deposited on the plane mylar substrate were irradiated by the focused beam of Nd:glass laser. Spectrally, temporally, and spatially resolved measurements of soft X-ray emission have been carried out at power densities of 1013-1014 W/cm2. The conditions of “re-emission” zone formation have been established. Radiative heat conductivity is shown to be the important energy transfer mechanism in the experimental conditions under investigation.
Hydrodynamic instability and target design
Authors: Lebo I.G. , Rozanov V.B. , Tishkin V.F.
Published: March 2009

The development of hydrodynamic instability (HDI) in laser targets is studied by means of 2D numerical code “ATLANT.” The scaling of HDI development for the condition of “DELFIN-1” laser setup experiments is derived. It is shown that there is the possibility to improve the shell compression condition for the case of long-wave perturbation of laser flux (determined by particular target irradiation geometry) by using the shell with “relief.”
Inelastic electron–ion scattering in hot and dense plasmas
Authors: Blancard C. , Dubau J.
Published: March 2009

An atomic model to describe the density and temperature effects on inelastic electron-ion collisions in dense plasmas is presented. This model has been used for Na-like iron to compute the optically allowed and forbidden collision rates from the ground configuration 1s2 2s2 2p6 3s to the 1s2 2s2 2p6 41 excited levels with l = 0,1,2. The focus is on temperature and density ranges 100–300 eV and 1022–1024 cm-3.
Investigation of iodine laser interaction of intensities Iλ2 ~ 1013–1015 Wcm–2μm2 with aluminum targets
Authors: Mróz W. , Parys P. , Wolowski J. , Woryna E. , Králiková B. , Krása J. , Láska L. , Mašek K. , Skála J. , Rohlena K.
Published: March 2009

The results of an experimental investigation of iodine laser interaction with Al targets obtained on the laser system PERUN (λ = 1.315 μm, E < 50 J, τ ∼ 350 ps) by means of corpuscular diagnostics, are presented. Ion velocity distributions, angular distributions, and electron temperature were determined. The plasma electron temperature Te ∼ 550 ± 100 eV was weakly dependent on laser intensity in the range Iλ2 ∼ 1014-1015 Wcm-2 μm2. Maximal velocity (energy) for the Al ions was estimated as V ∼ 9 × 107 cm/s (∼ 110 keV) and the maximal measured charge state was z = 13. It was shown that the diameter of the area emitting high energy ions is a few times larger than the focus diameter (80 μm), which indicates a strong influence of lateral heat transport on plasma parameters. The hot electron temperature Te.h was estimated to be in the range 6–10 keV. On the basis of Langmuir probe measurements, the electron temperature of expanded Al plasma at a distance of about 100 cm was estimated to be Te ∼ 3 eV
Generation of nanosecond soft X-ray pulses as a result of interaction of the Nd: glass laser radiation with gas puff targets
Authors: Fiedorowicz H. , Bartnik A. , Patron Z. , Parys P.
Published: March 2009

A new method of generation of nanosecond soft X-ray pulses with a photon energy around 1 keV is presented. X-rays are generated in a high-temperature plasma, which is created as a result of the interaction of Nd:glass laser radiation with a gas puff target. The target was obtained by puffing a small amount of gas through the nozzle into the vacuum chamber by means of a pressure electromagnetic valve. The pulses of laser radiation, with pulse duration of 1 ns and energy up to 15 J, generated in the system of a high-power Nd:glass laser were used for the target heating. Spatial, spectral, and temporal measurements of X-ray emission have shown that the high-intensity soft X rays are generated as a result of the interaction of nanosecond pulses of Nd:glass laser radiation with the gas puff target. A high efficiency of X-ray generation is suggested to be related to the effect of condensation of the gas outflowing from the valve nozzle and, in effect, to the interaction of laser radiation with matter in a form of aerosol.
Subpicosecond X-ray diffraction
Authors: Wark J.S. , He H.
Published: March 2009

With the advent of ultrashort (subpicosecond) high-power lasers it is now possible to create intense bursts of X-rays with subpicosecond durations. An analysis of the temporal response of diffraction of such X-rays by crystals in both the dynamical and kinematic regime is presented. It is also shown that under certain conditions the temporal resolution can be determined by the response of the crystal.
Applications of the colliding shock lens
Authors: Michaelis M.M. , Lisi N. , Kuppen R. , Buccellato R. , Prause A.
Published: March 2009

The colliding shock lens is described briefly. Possible applications, industrial drilling and cutting, laser Q-switching and spatial filtering, ultrahigh-power applications, and “all gas lasers” are proposed. The time evolution, scaleability, and repetition rate operation are investigated.
New methods of X-ray spectroscopy of laser-produced plasmas with one-dimensional spatial resolution
Authors: Renner O. , Kopecký M. , Krouský E. , Förster E. , Missalla T. , Wark J.S.
Published: March 2009

Two novel high-dispersion, high-resolution spectroscopic methods are described. The properties of the vertical dispersion variants of the double-crystal spectrometer and the Johann spectrometer with a cylindrically bent crystal are discussed and compared with those of standard spectroscopic schemes. Preliminary experimental data demonstrate the good luminosity and extreme spectral and 1-D spatial resolution of these methods, which should prove useful in high-precision X-ray spectroscopic measurements of laser-produced plasmas.
Neutron penumbral imaging of inertial confinement fusion targets
Authors: Garçonnet J-P. , Delage O. , Schirmann D. , Bertin A. , Grenier G. , Guilpart B. , Rouyer A.
Published: March 2009

The first 14-MeV neutron images of imploded microballoons have been obtained on the Phébus laser facility at CEL-V. The sizes of the source have been measured, in direct-drive experiments, by means of a coded-aperture imaging system. The principle is to use a thick aperture with a diameter larger than that of the source to image the microballoon. The deconvolution of the recorded image allows one to reconstruct the image of the neutron source, and this technique allows one to obtain images at a lower neutron yield than with a conventional pinhole camera. The choice of the experimental conditions is a trade-off between the Phébus conditions, the spatial resolution, and the image reconstruction method that is related to the signalto-noise ratio. The sensitivity of the diagnostic is strongly dependent on the number of scintillator photons that are collected by the recording system. The neutron measurement threshold of our experimental setup is typically 2 × 1010 neutrons/shot for neutron source sizes of 800 μm.
Absolute brightness measurements at the LURE synchrotron with a bolometer and application to the absolute calibration of photodiodes and photocathodes
Authors: Reverdin C. , Troussel P. , Guern F. Le , Bourgade J.L. , Schirmann D. , Dalmasso J.M. , Gontier D. , Lidove G.
Published: March 2009

An electrically calibrated bolometer designed to measure VUV and soft X-ray radiation in tokamaks was installed at the end of the calibration beam line used by CEL-V at the LURE synchrotron. Low-noise electronics and an adequate data acquisition enabled absolute measurements of power densities as low as 1 μW/cm2. Power density measurements are presented. At the same location several soft X-ray detectors used in laser-plasma interaction studies were installed and their absolute calibration was performed (photocathodes, photodiodes, etc.). Calibration results are presented and compared with a Henke model for photocathode response.
High-power imploding plasma for the X-ray laser
Authors: Baksht R.B. , Datsko I.M. , Fedunin A.V. , Loskutov V.V. , Oreshkin V.I. , Russkich A.G. , Shishlov A.V.
Published: March 2009

The Al–Mg photoresonant X-ray laser scheme study was carried out on the 1.4-MA GIT-4 generator with a 1.7-cm separation between the liner axis and the Mg target. The radiation power in the pumping line was (2–3).109 W/cm and the radiation power within the 45–60–A range was 3.11010 W/cm. The Mg VI and MG VII lines were found by the grating spectrograph.
Nonlinear relativistic self-focusing of laser radiation in plasmas: Arbitrary intensity
Authors: Asthana M. , Maheshwari K.P. , Sodha M.S.
Published: March 2009

A paraxial theory of relativistic self-focusing of a Gaussian laser beam in plasmas, when the nonlinear part of the effective dielectric constant is arbitrarily large, is presented. The plasma is taken to be homogeneous without any density fluctuations being necessary. The approach of Akhmanov et al. based on the WKB and paraxial ray approximations has been followed. It is seen that the saturating nature of nonlinearity leads to two values of critical power of the beam (Pcrl and Pcr2) for self-focusing. When the power of the beam P lies between the two critical values (i.e., Pcr1 < P < Pcr2), the medium behaves as an oscillatory waveguide; the beam first converges and then diverges, converges again, and so on. For P > Pcr2 the beam first diverges, then converges, then diverges, and so on. Because the relativistic mechanism is instantaneous, the theory is applicable to the understanding of selffocusing of laser pulses also.
Radially convergent 30–100-μs e-beam-pumped Xe and Ne lasers
Authors: Bugaev A.S. , Koval N.N. , Lomaev M.I. , Mel'chenko S.V. , Ryzhov V.V. , Tarasenko V.F. , Turchanovsky I. Yu. , Fedenev A.V. , Shchanin P.M.
Published: March 2009

The design scheme of a radially convergent 30-, 70-, or 100-μs e-beam-pumped laser with 9 or 18 1 excited volume is described. Amplitude, temporal, and spectral characteristics of the laser output, as well as laser thresholds in (Ar–Xe, He–Ar–Xe, He–Ne–Ar, and He– Ne–Ar–H2) gas mixtures have been investigated. The distribution of the specific deposited energy over the laser chamber cross section has been calculated by the Monte Carlo method. The small signal gain and unsaturable loss values of the active medium were measured for a Penning plasma Ne laser at λ = 0.585 μm.
Production of a high-density, long scale-length iron plasma using a capillary discharge
Authors: Blyth W.J. , Woolsey N.C. , Wark J.S. , Young P.E. , Zigler A. , Rose S.J.
Published: March 2009

The production of a long scale-length plasma of electron density 1020–1021 cm-3, measuring 10 X 0.5 mm using a laser-heated capillary discharge is reported. X-ray spectroscopic measurements have been performed which show that the plasma constituents can be varied by changing the material that lines the exit slit of the device. The capillary thus provides a useful source of large underdense plasmas created from solid materials suitable for laser-plasma interaction studies. Numerical simulations consistent with spectroscopic studies suggest that temperatures up to about 700 eV were achieved following irradiation of these plasmas by high-power laser light.
Coherent backscattering in the soft X-ray region
Authors: Luccio A. , Matone G. , Miceli L. , Giordano G.
Published: March 2009

Coherent X rays can be produced by Compton scattering of laser light on a relativistic electron beam, whose current is periodically modulated by the same laser radiation in a suitable miniundulator. If electron and laser photon energy are properly matched, the modulated electron beam acts as a moving diffraction grating and the X rays show a high degree of coherence. A practical implementation of this scheme is shown.
Studies of relativistic wave–particle interactions in plasma-based collective accelerators
Authors: Williams R. L. , Clayton C. E. , Joshi C. , Katsouleas T. , Mori W. B.
Published: March 2009

The interaction of externally injected charged particles (electrons) with plasma waves moving with a phase velocity that is very close to the speed of light is examined. Such plasma waves form the basis of at least three collective accelerator schemes: the plasma beat wave accelerator (PBWA), the plasma wake-field accelerator (PWFA), and the laser wake-field accelerator (LWFA). First, the electron trapping threshold, energy gain and acceleration length are examined using a 1-D model. This model elucidates how the final energies of the injected test electrons depend upon their injection and extraction phases and phase slippage. Phase energy diagrams are shown to be extremely useful in visualizing wave-particle interactions in 1-D. Second, we examine, using a two-dimensional model, the effects of radial electric fields on focusing or defocusing the injected particles depending upon their radial positions and phases in the relativistically moving potential well. Finally, we extend the model to 3-D so that the effect of injected particles' emittance on the acceleration process may be determined. This simple 3-D model will be extremely useful in predicting the electron energy spectra of several current experiments designed to demonstrate ultrahigh gradient acceleration of externally injected test particles by relativistic plasma waves.
Kinematical relations at nonlinear laser field: Free electron interactions
Authors: Körmendi F. F.
Published: March 2009

Kinematical relations of nonlinear interaction of laser beams with free charged particles are analyzed. General expressions are found for the number of scattered photons as a function of the number of simultaneously absorbed and/or emitted photons and the kinetic parameters of the charged particle-photon system. The results are applied to the processes of particle acceleration by lasers, frequency conversion, solitonic propagation, and others.
Thermal focusing instability in spherical targets for laser fusion
Authors: Sanz J. , Ibáñez F.
Published: March 2009

By using a linear analysis, a new type of thermal self-focusing instability without inverse bremsstrahlung absorption is analyzed. In the model it is assumed that part of the light is absorbed only at the critical surface and that the heat conduction is restricted to a layer on the target. Perturbations with wavelengths comparable to target radius are studied.
Characterization of self-generated intense electron beams in a plasma focus
Authors: Choi P. , Deeney C. , Herold H. , Wong C. S.
Published: March 2009

The parameters of self-generated electron beams have been measured and correlated to the dynamics of a 60 kV, 28 kJ plasma focus. The electron beam emission occurs in two periods: the first corresponds to the initial formation and disruption of the pinched plasma and terminates with the disruption of the plasma column, and the second period occurs after the breaking up of the focus plasma. The first period is characterized by high-energy electron beams, whereas in the second period the electron beams have lower average energies but higher currents. A relativistic electron beam is found to occur around the time of first compression, when the plasma is observed to be macroscopically stable, in contrast to measurements obtained from machines with similar energies but operating at lower voltages. The plasma X-ray emission is observed to be closely related to the electron beam characteristics. Possible mechanisms for the formation of the electron beams observed are discussed.
Fast compression of magnetic flux inside an imploding cylinder driven by laser beams
Authors: Choe W. H.
Published: March 2009

A method for the compression of magnetic flux inside a cylindrical liner imploded by laser beams is analyzed using a thin shell model. Simple scaling relations are derived for a number of key parameters. The potential of this scheme, as a fast-rising magnetic pulse generator, is explored based on the scalings obtained.
Optical ionization and heating of gases by intense picosecond KrF laser radiation
Authors: Offenberger A.A. , Blyth W. , Preston S.G. , Wark J.S. , Key M.H. , Dangor A.E. , Modena A. , Najmudin Z. , Djaoui A. , Key M.H.
Published: March 2009

We report on multiphoton ionization experiments using picosecond (ps) and sub-ps UV-laser radiation at focused intensities up to 1018 W/cm2. The experiments are concerned with determining the electron temperature of optically ionized gases produced by intense KrF lasers. Thomson scattering, stimulated Raman scattering (SRS), and X-ray emission measurements have been made and compared with modeling calculations of heating. A particular objective is to identify the respective roles of above-threshold ionization, nonlinear inverse bremsstrahlung absorption, and SRS in determining the temperature of the electrons. Results for 350-fs pulses are compared with previous measurements for 12-ps pulses (for which strikingly different behavior is observed). The importance of using subps, short-wavelength lasers to minimize electron temperature is confirmed.
Inertial fusion targets driven by cluster ion beam: The hydrodynamic approach
Authors: Eliezer S. , Martinez-Val J.M. , Deutsch C.
Published: March 2009

Cluster-driven inertial confinement fusion (ICF) is analyzed. A cluster is defined as a charged supermolecule with a charge of one (or of the order 1) and with a very high mass number A, so that Z/A « 1. The energy deposition range is shown to be very small (a few micrometers) for projectiles with a few tens of kev/a.m.u. A significant momentum transfer is therefore possible in its slowing down as it passes through matter. In this case, a high hydrodynamic efficiency seems evident. Three relevant models for cluster beam-target interactions are discussed: (1) the rocket model, where the ablation pressure (Pa) is much larger than the cluster beam direct pressure (II); (2) the hammer model, where Pa « II (in this case, two possibilities are discussed—an impact interaction between the beam and the target, and an impact interaction between one cluster and its absorption volume); (3) an intermediate model, where Pa ~II (in this regime, the hydrodynamic efficiency is maximum). Preliminary simulations were performed and the general features of the models were confirmed. Most relevant for ICF, it was found that approximately 75% of the beam energy is converted into X rays, so that the indirect drive is promising in this context.
Design of an ICF plant using a nuclear-driven solid-state laser
Authors: Lin L.-T.S. , Prelas M.A. , He Z. , Bahns J.T. , Stwalley W.C. , Miley G.H. , Petra M. , Batyrbekov E.G. , Shaban Y.R.
Published: March 2009

An ICF plant is designed to use nuclear-driven flashlamp-pumped solid-state lasers as fusion drivers. It is proposed to use a separated fission reactor with aerosol fuel to drive alkali metal excimer flashlamps as the pumping source for solid-state lasers. The first observation of nuclear-excited sodium excimer emission at 436 nm in a TRIGA reactor with 815 Torr of He-3 and 60 Torr of sodium vapor (at T = 924 K) is reported. The experiment demonstrates the feasibility of a nuclear-driven alkali metal excimer lamp. The compatibility of alkali metal excimers with different laser crystals is evaluated for driver efficiency. High overall laser efficiency ensures large fractional output power extraction from nuclear fusion by this plant. The suitability of laser crystals for the ICF plant is also presented.
Interaction of ion cluster beams with cold matter and dense plasmas
Authors: Deutsch C.
Published: March 2009

Arbitrarily heavy cluster ion beams (CIB) are examined for the purpose of driving directly or indirectly an ICF compression. This paper provides an overview of cluster production, and of their interaction with cold and hot matter. Fragmentation is also considered. Concepts and ideas of interest for further investigations are identified and delineated. A connection is made with a CIB interaction experiment planned at Orsay. It is conjectured that CIB should experience enhanced stopping when compared to their atomic counterparts under similar conditions.
Observation of Kα. X-ray satellites from a target heated by an intense ion beam
Authors: Bailey J. , Carlson A. L. , Chandler G. , Derzon M. S. , Dukart R. J. , Hammel B. A. , Johnson D. J. , Lockner T. R. , Maenchen J. , McGuire E. J. , Mehlhorn T. A. , Nelson W. E. , Ruggles L. E. , Stygar W. A. , Wenger D. F.
Published: March 2009

We have made the first observation of Kα X-ray satellites from a target heated by an intense ion beam. The satellites are produced when thermal ionization due to beam heating is accompanied by inner-shell ionization from beam ion impact. The Particle Beam Fusion Accelerator II was used to irradiate a conical aluminum target with a proton beam. The nominal beam parameters were 50–75 kJ in a 1-cm spot, 15–20-ns pulse length, and 4–5-MeV protons at peak power. An elliptical crystal X-ray spectrograph inside a 1000-kg tungsten shield was used to record the spectra. The peak ion stage reached by the aluminum target was +8. Collisional radiative calculations were performed, which indicate a peak electron temperature of 20–60 eV.
Atomic processes in ionic projectiles in plasma: End-of-the-range effects
Authors: Nardi E. , Zinamon Z.
Published: March 2009

The charge state and the level populations of ionic projectiles that are stopped in hydrogen plasma are calculated in the average ion model. It is shown that in available experimental systems the parameters can be chosen such that the end of the range will occur inside the plasma column. The predicted narrow region over which recombination occurs can be used as a check on plasma stopping-power theory and as a direct measurement of the range, using spectroscopic diagnostics.
Scaling laws for the effective charge of heavy ions penetrating gas or plasma targets
Authors: Peter Th.
Published: March 2009

Until now a theoretical derivation of scaling laws for the effective charge Zeff of heavy ions penetrating matter has been lacking, although for cold gaseous targets there are well-established empirical relations of the form Zeff/Zp = f (up/ZpγZtδ), where vp and Zp are, respectively, the velocity and nuclear charge of the projectile ion, Zt, is the nuclear charge of the target atoms, and γ and δ are the scaling exponents. We show that the scaling exponents may be derived from an investigation of loss and capture rates. The treatment is based on the Bohr-Lamb criterion. This very crude criterion yields γ = 2/3. Our analysis allows the formulation of a modified criterion, yielding γ = 0.528 for cold gas, which deviates by only 2% from the often-used empirical Betz formula. The dependence on Zt, in cold gas is oscillatory and cannot be described by a simple exponent δ. The treatment is also applied to a fully ionized plasma, resulting in Zerf/Zp = f (upZt0.27/Zp1.39).
Lasers pumped by heavy-ion beams
Authors: Ulrich A. , Busch B. , Eylers H. , Krötz W. , Miller R. , Pfaffenberger R. , Ribitzki G. , Wieser J. , Murnick D. E.
Published: March 2009

General aspects of the excitation of matter with heavy-ion beams are discussed. Lasers in the wavelength region between 1 and 3 μm in rare-gas mixtures pumped with 1.9-GeV xenon, 100-MeV sulphur, 3.6-MeV argon, and 3.3-MeV helium ions are described as examples for lasers pumped by heavy-ion beams. The beam power ranges from a few watts (dc) to about 1 MW during short pulses of about 1-ns length. Optical gain can be measured with an intracavity method. Data on the shape of the volume excited by a 100- MeV 32S beam are shown. An experimental setup for time-resolved optical spectroscopy in a wide wavelength region between a few nanometers and about 700 nm is described. Emission spectra of rare gases excited by heavy-ion beams are discussed and optical gain on ion lines and excimer bands is estimated for different target and beam parameters. Collisional processes in the target gas were studied by time-resolved optical spectroscopy. Population densities of selected 3p levels in Ne I, II, and IV and rate constants for collisional depopulation of excited levels were determined. Experiments planned at the heavy-ion synchrotron SIS at Gesellschaft für Schwerionenforschung in Darmstadt are discussed.
Frequency-dependent opacity calculations for high-Z plasma including l splitting
Authors: Rickert A. , Meyer-Ter-Vehn J.
Published: March 2009

Frequency-dependent opacities are determined for high-Z plasma taking into account splitting of the energy levels with orbital quantum number l. The energy levels are calculated with the help of the screened hydrogenic model generalized by Perrot for l splitting. Oscillator strengths for bound-bound and bound-free transitions are computed from hydrogenic wave functions with two different screened nuclear charges. The average atom model is used to determine the plasma state, with provision for continuum lowering and pressure ionization. Explicit results for extinction coefficients of gold plasma with ρ = 0.1 g/cm3 and T = 100−500 eV are compared with calculations neglecting l splitting. Considerably enhanced absorption at lower photon energies (50–300 eV) is obtained when taking l splitting into account. Planck and Rosseland mean opacities are also calculated and compared with data contained in the SESAME opacity library. Remarkable agreement is found without any artificial line broadening or band smearing.
Radiative transfer in Rayleigh–Taylor unstable ICF pellets
Authors: Pomraning G. C.
Published: March 2009

A formulation of radiative transfer is discussed describing energy flow in a turbulent mixture in the vicinity of a Rayleigh–Taylor unstable interface, as might be extant in an ICF pellet. Included in this discussion are (1) the method of smoothing and the Liouville master equation approaches in the case of Markovian statistics as the description of the fluid mixing, (2) the use of asymptotics to derive various limiting descriptions of the Markov model, (3) the use of the theory of alternating renewal processes to obtain an integral equation formulation for non-Markovian statistics, and (4) the reduction of this non-Markovian integral formulation to integro-differential equations of the generic transport form, with statistical effects represented by pseudoscattering terms.
Linear and electronic transport in strongly coupled binary ionic mixtures
Authors: Léger D. , Deutsch C.
Published: March 2009

This paper is devoted to a systematic investigation of linear transport properties in strongly coupled binary ionic mixtures of pointlike ions interacting solely through Coulomb interactions. The basic formalism rests upon suitable extensions of the Boltzmann–Ziman equation explained in this work. Validity conditions for the Lorentzian approximation are thoroughly discussed as well as entropy arguments. High temperature inelastic contributions are emphasized out.
High power laser system ISKRA V
Authors: Kirillov G. A. , Murugov V. M. , Punin V. T. , Shemyakin V. I.
Published: March 2009

The 12-beam, photodisssociative iodine laser system ISKRA V has been built for laser fusion research. In this article we describe the optical scheme, elements and parameters of the output radiation. Pulse power of 100 TW was achieved in the preliminary experiments.
Effects of multiple ionization on the Kα spectrum of aluminum in intense lithium beam experiments
Authors: Wang P. , MacFarlane J.J. , Moses G.A.
Published: March 2009

The effect of multiple ionization on Kα spectra is investigated for aluminum targets irradiated by intense lithium beams. Multiple ionization cross sections have been calculated using a formulation incorporating single-electron ionization probability in the binomial distribution. In contrast to conventional binary-encounter approximation (BEA) theory, the single-electron ionization probabilities for each atomic shell have been calculated using a combination of modified plane-wave Born approximation (MPWBA) and an empirical effective interaction radius which is dependent on both the target ion and the projectile. Our calculations show that the effect of multiple inner-shell ionization on aluminum Kα spectra observed in intense lithium beam experiments is important. Multiple ionization effects become less important as the target ionization state increases. Nevertheless, even for highly ionized species up through Be-like Al multiple ionization effects can be significant and must be considered in the analysis of spectra obtained in intense Li beam-plasma interaction experiments.
Heavy-ion beam focusing with a wall-stabilized plasma lens
Authors: Tauschwitz A. , Boggasch E. , Hoffmann D.H.H. , Jacoby J. , Neuner U. , Stetter M. , Stöwe S. , Tkotz R. , De Magistris M. , Seelig W.
Published: March 2009

Focusing of heavy-ion beams is an important issue for ion beam-driven inertial confinement fusion. For the experimental program to investigate matter at high energy densities at GSI, the application of a plasma lens has attractive features compared to standard quadrupole lenses. A plasma lens using a wall-stabilized discharge has been systematically investigated and optimized for this purpose. Different lenses were tested in several runs at the GSI linear accelerator UNILAC and at the SIS-synchrotron. A remarkably high accuracy and reproducibility of the focusing were found. The focal spot size was mainly limited by the beam emittance. A summary of experimental results and important limitations of the focal spot size is given.