Proceedings Volume 4424

ECLIM 2000: 26th European Conference on Laser Interaction with Matter

Milan Kalal, Karel Rohlena, Milan Sinor
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Proceedings Volume 4424

ECLIM 2000: 26th European Conference on Laser Interaction with Matter

Milan Kalal, Karel Rohlena, Milan Sinor
View the digital version of this volume at SPIE Digital Libarary.

Volume Details

Date Published: 23 April 2001
Contents: 7 Sessions, 126 Papers, 0 Presentations
Conference: 26th European Conference on Laser Interaction with Matter (ECLIM 2000) 2000
Volume Number: 4424

Table of Contents

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Table of Contents

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  • Inertial Confinement Fusion
  • High-Power Laser Facilities
  • Plasma Diagnostics and Laser and Target Technologies
  • Theory and Simulation
  • Hydrodynamic Instabilities and Energy Transfer in Laser-Produced Plasmas
  • Intense Radiation and Particle Sources
  • Nonfusion and Material Applications
Inertial Confinement Fusion
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Recent results of a study on the injected entropy approach to the ignition of high-gain targets
Angelo Caruso, Carmela Strangio
The most recent results on the injected entropy method to the ignition of high gain targets are presented. The base of the method is the ignition of high gain targets by energy injection in the final stages of the fuel implosion. In this scheme most of the energy needed to form the ignition spark is still provided by the work of the imploding target itself, as in the standard ICF scheme. The injected energy is used to set on a higher adiabat that small portion of the fuel destined to become the ignition spark. After a short analytical introduction to the method, the result of extensive numerical simulations by a 2D code are presented. The considered cases refer to imploding cylinders of finite length. The additional energy was injected axially by one or two opposing beams, whereas the acceleration stage of the cylindrical low-entropy implosion was assumed driven by a different driver. Heavy ion beams, soft x-rays and laser generated light ion beams were considered as vectors for the entropy injection. Issues related to the feasibility of these generators are discussed. The study was made for various initial conditions leading to different ignition modes and burn propagation.
Plasma shells compression on Angara-5-1
E. V. Grabovsky, S. L. Nedoseev, G. M. Oleynic, et al.
Appearance of generators of electric power of pulse duration of about 100 ns opened new possibilities in classic Z- pinches. First, it is connected with new level of power of this generators. Second, it has become possible to use loads of another size and densities. One of the new tasks studied on powerful installations is generation is generation of pulses of soft x-ray radiation for thermonuclear fusion research. The models of target ignition, developed on systems of laser initiation, determined the nanosecond time as a characteristic time scale of radiation pulse. A program of fast liner compression is developing in TRINITI on Angara 5-1 installation- an 8 module pulse generator of max power of 9TW, pulse rise time of 90 ns, load peak current of 4 MA. The main aim of the program was to investigate a way to create a source of soft x-ray radiation of high intensity for thermonuclear fusion and fundamental research work. A conception of double liner were proposed as a perspective way to ensure a dynamic hohlraum for thermonuclear target irradiation.
Nike direct-drive ICF program
A. N. Mostovych, Yefim Aglitskiy, Stephen E. Bodner, et al.
The Nike program coordinates experimental and theoretical efforts to evaluate and verify the physics base needed to proceed with direct-drive inertial confinement fusion. The program emphasizes the use of KrF laser drivers because of their demonstrated ultra-smooth target illumination and high absorption efficiency but is also applicable to short- wavelength glass laser drivers. Currently, the Nike program is concentration on the problem of increasing the gain of direct-drive target designs while simultaneously minimizing the growth of hydrodynamic instabilities. Advanced target design have been identified which achieve low isentropic compression while reducing RT instability through the use of tuned soft x-ray or shock preheating of the target ablator. Experiments measure the growth and saturation of the ablative RT instability and its modification as a result of tuning of the ablator isentrope and variations in laser imprinting. The important fundamental processes are also investigated in individual experiments to measure the emission and transport of x-ray radiation, the equations-of- state of deuterium, foams, and other relevant materials, as well as the acceleration of cryogenic filled foams.
Symmetry experiments on Omega with LMJ-like multiple beam cone irradiation
Andre L. Richard, J. P. Jadaud, Nicolas Dague, et al.
We carried out a set of experiments on the Omega laser facility at Rochester with Laser MegaJoule like indirect drive irradiation. We studied the irradiation non-uniformity with the foam ball radiography technique and the implosion symmetry with (D2 + Argon) filed capsules core emission. Cylindrical 'Nova scale 1' thin wall hohlraums were used. Forty of the Omega beams, arranged in three cones on each side of the hohlraum were used to create the x-ray drive. Eight additional beams were used on a Ti source to radiograph the foam balls. The shaped laser pulse was about 3 ns duration. The radiation drive was measured on each shot. The images were recorded with a 5 micrometers resolution Gated X-ray Imager coupled to a CCD camera.
Omega experiments and preparation for direct-drive ignition on NIF
Stanley Skupsky, Robert L. McCrory Jr., R. E. Bahr, et al.
Direct-drive laser-fusion ignition experiments rely on detailed understanding and control of irradiation uniformity, the Rayleigh-Taylor instability, and target fabrication. LLE is investigating various theoretical aspects of a direct-drive NIF ignition target based on an 'all-DT' design: a spherical target of approximately 3.5-mm diameter, 1 to 2 micrometers of CH wall thickness, and an approximately 350-micrometers DT-ice layer near the triple point of DT. OMEGA experiments are designed to address the critical issues related to direct-drive laser fusion and to provide the necessary data to validate the predictive capability of LLE computer codes. The cryogenic targets planned for OMEGA are hydrodynamically equivalent to those planned for the NIF. The current experimental studies on OMEGA address all of the essential components of direct- drive laser fusion: irradiation uniformity and laser imprinting, Rayleigh-Taylor growth and saturation, compressed core performance and shell-fuel mixing, laser- plasma interactions and their effect on target performance, and cryogenic target fabrication and handling.
Model experiments of fast ignition with coaxial high-power laser beams
Katsumasa Fujita, A. Sunahara, Kazuo A. Tanaka, et al.
An imploded plasma core is irradiated by a 100 ps laser pulse in a model experiments of fast ignition. Additional laser pulses for drilling and heating are introduced co- axially with the laser beams for the implosion. The preformed imploded core is created by the 12 beams of 0.53 micrometers laser with the total energy of 800 J. The additional heating pluses contain 100 ps pulses separated by 300 ps at the wavelength of 1.06 micrometers with the total energy of 320J. The first pulse is intended for drilling the coronal pulses surrounding the core and the second is for addition heating of the core. We measured the imploded core additionally heated with 100 ps pulses.
Recent advances in indirect drive ICF physics at CEA
J. Tassart, Guy Bonnaud, Jean-Luc Bourgade, et al.
The objective of Target Physics Program at CEA is the achievement of ignition on the LMJ, a glass laser facility of 1.8 MJ which will be competed by 2008. They include theoretical work, experimental work and numerical simulations. An important part of experimental studies is made in collaboration with US DOE Laboratories: Lawrence Livermore National Laboratory, Los Alamos National Laboratory and the Laboratory for Laser Energetics at the University of Rochester. Experiments were performed on Phebus, NOVA and OMEGA; they included diagnostics developments. Recent efforts have been focused on Laser Plasma Interactions, hohlraum energetics, symmetry, ablator physics and hydrodynamic instabilities. Ongoing work prepare the first experiments on the LIL which is a prototype facility of the LMJ. They will be performed by 2002. Recent progress in ICF target physics allows us to precise laser specifications to achieve ignition with reasonable margin.
Prospect of laser fusion in the 21st century
Chiyoe Yamanaka
The Inertial Confinement Fusion has remarkably developed in these 30 years. In the 21st century we can scope the fusion energy for the civil use. After the cold war era, the value of ICF has shifted from the defense demand to the peaceful applications year by ear. The MJ laser systems are under construction expecting the ignition. However there are many problems in science and technology. The alternative way to use a PW short pule laser is aiming the fast ignition. On the way to the goal, we should contribute the various applications of high power lasers such as laboratory astrophysics, x-ray lasers, laser induced thunder and so on.
Nuclear fusion driven by Coulomb explosions of deuterium clusters
Jason Zweiback, Roland A. Smith, Thomas E. Cowan, et al.
We have examined the interaction of deuterium clusters with high intensity, ultrafast laser radiation. Upon irradiation a hot plasma is created with a sufficient temperature to produce nuclear fusion. We have seen that larger clusters produce more fusion neutrons than small er clusters, consistent with a Coulomb explosion model. Fusion yields is currently limited by propagation effects. Using interferometric imaging we have examined the laser propagation and found that the laser energy is absorbed before it penetrates to the center of the gas jet.
High-Power Laser Facilities
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Vulcan upgrade: a petawatt laser facility for experiments at 1021 Wcm-2
Christopher B. Edwards, Ric M. Allott, J. L. Collier, et al.
The Vulcan Nd:glass laser facility at RAL delivers up to 100TW 0.8 ps from its ultra-short pulse beamline and up to 2.5kJ in 8 beams in 'long pulse' mode. It runs parallel operations to two target areas fora wide ranging science program for UK university and EU researchers and their collaborators. In March 1999, funding was awarded by the Engineering and Physical Sciences Research Council for the upgraded of Vulcan's ultrashort beam lie to 1PW as the first phase of a major enhancement program.
Status and overview of research programs at LULI 2000
Victor Malka, F. Amiranoff, Claude J. Chenais-Popovics, et al.
Since its creation, LULI has given an important contribution to laser plasma physics and Inertial Confinement Fusion studies. We will review some major results obtained these last two years with a 600 ps laser chain and with the recent 100-TW, 300fs ultra-intense laser chain. These result cover a wide spectrum of laser plasma physics research such as laser plasma interaction, laser plasma acceleration, fast ignitor, atomic processes in dens plasmas, shock waves generation and x-rays laser.
PHELIX: a petawatt high-energy laser for heavy ion experiments
M. Roth, Bruno Becker-de Mos, R. Bock, et al.
The unique combination of an intense heavy ion beam accelerator and a high energy laser opens the possibility of exploring new physics taking advantage of the synergy of both facilities. A variety of new fields can be addressed with this combination in plasma physics, atomic physics, nuclear- and astro-physics as well as material research. In addition, using CPA-technology, laser pulses with a pulse power of up to a petawatt opens the door to explore the regime of fully relativistic plasmas. Therefore the Gesellschaft fuer Schwerionenforschung is augmenting the current high intensity upgrade of the heavy ion accelerator facility with the construction of PHELIX. Designed with two pulse-generating front ends and send to multiple experimental areas PHELIX will serve as a highly versatile laser system for various applications. In this report, we present the design of the laser system and some key experiments that can be performed with this combination for the first time.
Current status of advanced photon research program at JAERI
Takashi Arisawa, Akira Nagashima, Eisuke J. Minehara, et al.
Under the Advanced Photon Research program, an ultra short pulse/high peak power laser (HPPL), x-ray laser (XRL) and free electron laser (FEL) have been developed since 1997 at Japan Atomic Energy Research Institute. For high peak power laser development a new method relating to the wave front detection based on Fresnel equation fitting and second harmonics generation are applied to the developed 100TW Ti:sapphire laser with 18.9fs pulse width. Further development towards 500TW-peak power is also carried out. Wave front compensation system using a photo refractive crystal with a novel external feedback loop to correct distorted wave front was successfully applied to high repetition rate all solid state Ti:Sapphire laser system that showed excellent focusability. For the development of compact and practical x-ray lasers a transition gain type x- ray lasing is studied using a pair of double pulsed glass lasers of 10J with 1ps pulse width and efficient laser oscillation for Ne-like Ti, Ni-like Ag, and Ni-like Sn were confirmed in the preliminary study. Energy consumed for these laser oscillations was less than that obtained by the conventional methods. Superconducting linac based FEL recorded an average power over 2kW in far IR region after succeeding in the generation of high peak and short pulse bunched electron beam, and energy recovering technique for electron beam by making use of superconducting system is now constructed for further higher power which could also lead to the technologies related to the shorter wavelength region. The above new light sources are ready for applying the experiments such as laser induced particle acceleration, high field physics, photochemistry, and the related simulation studies using massive parallel scalar computer are also made.
Powerful iodine two-pass amplifier on the Iskra-5 facility
V. I. Annenkov, Y. Gaidash, I. Galahov, et al.
Experimental results of the laser pulse amplification research of the powerful iodine two-pass amplifier on 'Iskra-5' facility are presented in this report. Input and output of radiation in the two-pass amplifying scheme were realized in the far field through spatial filter. The amplifier with 8m active length and 30 by 30 cm2 aperture was used. This amplifier was pumped by electro- discharge sources of multiple operations. The 400 mm- diameter liquid saturable absorber was used as optical shutter in the two-pass scheme. It is shown that for less than 1 J energy of input laser pulse, the energy of output pulse is 1 kJ. The obtained experimental data are satisfactory agreed with results of theoretical model This mode is based on the rate equations of laser pulse propagation along active medium without regard of energy losses and relaxation of excited iodine sublevels.
Design of 60-kJ SG-III laser facility and related technology development
Hansheng Peng, Xiaomin Zhang, X. F. Wei, et al.
The SG-III laser facility has been proposed to produce 1-ns, 60-kJ blue light pulses for IC Application at China Academy of Engineering Physics. The baseline design suggests that the SG-III be a 64-beam laser facility grouped into eight bundles with clear optical apertures of 30cm by 30cm. The facility consists of multiple subsystems, including the front end, preamplification and injection section, main amplifiers, beam transport and alignment system, switchyard, target area, integrated computer control, and beam diagnostics. The amplifier column in each bundle contains eight beamlets stacked 4 high by 2 wide. Great progress has been made in developing key laser technologies, such as integrated fiber optics, binary optics, adaptive optics, four-pass amplification, large aperture plasma electrode switches, rapid growth of KDP, brand-new laser glass, long flashlamps, precision manufacturing of large optics and metallized self-heating capacitors. Codes have been developed and numerical simulations have been conducted for the optical design of the facility. The design of the Technical Integration Line of 2 by 2 segmented array as a prototype module of SG-II has been optimized and the construction will soon get started.
Six-beam high-power KrF excimer laser system with energy of 100 J/23 ns
Yusheng Shan, Naiyan Wang, Weiyi Ma, et al.
In the ICF research, KrF laser is considered to be a promising candidate for the reactor driver due to its short wavelength, wide bandwidth, high efficiency, scalability, and advantages of UV laser in laser-plasma coupling. This paper describes some performance of 100J level multistage KrF laser system 'Heaven-I'. This high power KrF excimer laser system is under development in China Institute of Atomic Energy.
Activities of developing high-power KrF lasers for studying laser plasmas interaction physics at CIAE
Naiyan Wang, Yusheng Shan, Weiyi Ma, et al.
One group of China Institute of Atomic Energy is now developing high-power KrF laser systems for Inertial Confinement Fusion and laser plasmas interaction researches. During the past few years, we have built a six-beam high- power KrF excimer laser facility with energy of 100J/23ns and a target chamber.
Plasma Diagnostics and Laser and Target Technologies
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Warm dense plasma characterization by x-ray Thomson scattering
Otto L. Landen, S. H. Glenzer, Robert C. Cauble, et al.
We describe how the powerful technique of spectrally resolved Thomson scattering can be extended to the x-ray regime, for direct measurements of the ionization state, density, temperature, and the microscopic behavior of dense cool plasmas. Such a direct measurement of microscopic parameters of solid density plasmas could eventually be used to properly interpret laboratory measurements of material properties such as thermal and electrical conductivity, EOS and opacity. In addition, x-ray Thomson scattering will provide new information on the characteristics of hitherto difficult to diagnose Fermi degenerate and strongly coupled plasmas.
Introduction of tritium into polymer structure of shell targets: isotope exchange and degradation of polymer
Yury A. Merkul'ev, Sergey A. Startsev
The obtained worldwide results of experimental and theoretical study of processes of an isotope exchange of deuterium on tritium in polymers and organic compounds by Wilzbach method, named sometimes the method of tracing of organic compounds by tritium, and also processes of changing of chemical properties of these compounds under effect of radiation from tritium beta decay were carefully analyzed. The physical reasons explaining discrepancies in experimental results and conclusions authors are found.
Gained experience in production of wide-aperture optical elements using KDP and DKDP crystal rapid growth technology
Viktor I. Bespalov, Vladimir I. Bredikhin, V. P. Ershov, et al.
Optical elements made of KDP, DKDP crystals are up to now among the most expensive and significant ones in high-power laser systems with frequency conversion into higher harmonics. Only some companies have mastered such production technology of optical elements with the aperture size up to 40 by 40 cm. The production is characterized by very long cycles of crystal growth and large waste at manufacturing optical elements, which leads to an extremely high price of the products. An alternative technology based on rapid technology of profiled growth of crystal products and the technology of optical diamond micromilling by means of ISM- 600 machines are developed now at the Institute of Applied Physics RAS. The cycle duration of the crystal product growth reduces tens times, cutting of te grown product into optical elements proves to be practically wasteless. This leads to reduction of product growth reduces tens times, cutting of the grown product into optical elements proves to be practically wasteless. This leads to reduction of product cost and significant shortening of product cycle duration. The quality of crystal growth and optical processing is consistent with the requirements of optical systems. This together with the described applied technologies has permitted to manufacture optical elements for a series of high-power lasers.
Methods and control-driving devices for high-precision remote alignment of multichannel high-power laser facility
A. V. Charukhchev, Victor N. Chernov, A. F. Aushev, et al.
The results of work on creation of a system for remote control alignment of high-power multichannel Nd·glass laser systems, being created in VNIIEF and NlffiF A, are presented. Methods and principles of alignment, high·accuracy driving units for mirrors tilts and pinholes travels, CCD-sensor capable of accepting weak radiation fluxes with a wavelength A.=l,053 μmare considered.
Front end of the high-energy Nd:glass laser fusion system with shaped nanosecond laser pulses
Victor N. Chernov, Alexander V. Charukchev, Roman F. Kurunov, et al.
The design and performance of front end system for the upgrade six-channel Nd:glass laser facility PROGRESS are presented. The system consists of a single-mode Q-switch Nd:YLF master oscillator, pulse shaping system and preamplifier. The pulse shaping system comprises a LiTaO3 electro optic deflector pair driven by high-voltage generators on drift step recovery diodes. The system produces the shaped laser pulses in 1-10 nanosecond duration range. In one-pass preamplifier including a sequence of Nd:glass rod amplifiers with output aperture of 30mm the shaped pulses are amplified up to 5 J energy level.
Laser-radiation volume absorber and x-ray converter based on low-density beryllium
N. G. Borisenko, Vladimir V. Gorlevsky, A. I. Gromov, et al.
In the past few years much attention has been paid to studying the laser interaction with low-density polymer sub- critical media formed as the external target layers, which provided more symmetric heating and compression of the target internal shell. Beryllium foam is discussed, as a new type of a low-density media typical of high stability at low specific weight. Moreover, there is a feasibility to produce the beryllium doped by heavy element with its controlled distribution over the deposited layer. The developed technique allows one to use nano-crystal beryllium and low- density beryllium doped by heavy element with its controlled distribution over the deposited layer. The developed technique allows one to use nano-crystal beryllium and low- density beryllium for laser targets.
Semiconductor closed switch based on reverse switched dinistors: new type of switch for pulse power systems of Nd-glass lasers
V. G. Bezuglov, Igor V. Galakhov, S. L. Logutenko, et al.
We describe the operating principle, design and test results for the high-power semiconductor switch which based on the assembly of reverse switched dinistors. This switch has the following operating parameters: (i) operating voltage -25kV, (ii) peak operating current - up to 200kA, (iii) maximum transferred charge - up to 70C. The switch is intended for use by pulse power systems of Nd:glass lasers. The features of switch modes at such banks are discussed.
Multichannel system for measuring of radiation energy of power pulse lasers
Vladimir V. Il'in, Vladimir M. Komarov, A. V. Rubanov, et al.
Multichannel calorimetric system for measuring of energy of power pulse lasers is described. It consists of array of calorimetric detectors, communication cables and AD- converter plug-in personal/industrial computer. It measures energy of laser radiation from 0.1 mJ to 0.1 J the pulse duration range over 10-1-10-12 sec.
Picosecond flashlamp pumped Nd:YAG laser using all-solid-state passive pulse control
Vaclav Kubecek, Jens Biegert, Jean-Claude M. Diels, et al.
We demonstrated that a simple flashlamp pumped Nd:YAG laser, with the insertion of solid state passive elements, can be made a source of trains of high power picosecond pulses with accurate pulse to pulse reproducibility. The combination of passive negative feedback using GaAs together with semiconductor quantum well saturable absorber in an actively mode-locked Nd:YAG laser led to generation of stretched 200 ns long trains with pulsewidth of 42 ps. Cavity dumping resulted in single pulses at energies of 500 (mu) J with a nearly Gaussian spatial profile at repetition rate of 5 Hz. Without passive negative feedback, stable 75 ns long trains of pulses with pulsewidth of 52 ps were generated.
High-intensity pulse generation by saturated amplification of Stokes pulse with steep leading edge
Kenji Kuwahara, Eiichi Takahashi, Yuji Matsumoto, et al.
We have developed a new technique for high intensity short pulse generation. It consists of a steep pulse generation and a saturated amplification. Stimulated Brillouin scattering by a broad-band oscillator pulse was used to generate the steep Stokes pulse. The Stokes pulse was amplified by discharge type KrF laser amplifier under strongly saturated condition. The pulse shortening by the amplification was confirmed.
Possibility of target fabrication from beryllium deuteride (foaming technique)
Valeriy M. Dorogotovtsev, Nikolay A. Chirin, Vladimir V. Gorlevsky, et al.
We have developed a new method of fabrication of spherical shell laser targets of beryllium deuteride. The targets possess sufficient strength and long lifetime in deuterium- tritium mixture. The method is based on the original technology of producing the BeD2 and BeDT layers developed at Bochvar Institute, and a high-temperature technique of shell formation from fast decomposed matters developed at Lebedev Physical Institute. The performed investigation has shown that beryllium deuteride possesses all the properties necessary for a spherical target: the hydrogen isotopes permeability comparable to the permeability of a quartz glass, and the tensile strength higher than that of polymers.
X-ray streak-camera measurements on the ISKRA facilities
Vasili M. Murugov, Valeri P. Lazarchuk, Sergei I. Petrov, et al.
This paper presents the results of development of x-ray streak cameras, calibration test beds and methods for calibration of streak cameras and elements of x-ray optical schemes, procedures for recording a number of plasma parameters. We describe methods for streak photography of laser-produced plasma x-ray emission in experiments with various targets conducted on the facilities ISKRA-4 and ISKRA-5. These methods allow to make time-resolved records of the continuos plasma x-ray emission in various spectral ranges, to sweep in time line x-ray emission, to make simultaneous records of several plasma images in various spectral ranges, to make simultaneous records of several cross-sections of an object with subsequent reconstruction of a number of its 2D images at various moments of time with ps time resolution. By using these methods it is possible to control target irradiation uniformity in time, to study the dynamics of the microsphere implosion and outwardly blowing plasma corona, to determine the lifetime of the imploded core, to investigate the time evolution of electron temperature and to study the mixing processes of materials of various densities in multilayered targets.
Diagnostics of laser beam temporal dispersion on the ISKRA-5 multichannel facility
Alexei V. Senik, Andrey G. Kravchenko, Vasili M. Murugov
A twelve-channel system is described, intended for recording the laser radiation temporal parameters and dispersion on the ISKRA-5 laser facility. These measurements are needed for synchronous delivery of all twelve laser beams at the target with a minimal difference in the arrival time.
Phase and polarization distortions of high-power laser radiation passing through the optics of the wide-aperture spatial filter
Roman F. Kurunov, Anatoly A. Malkov, Vladimir G. Smirnov, et al.
The mechanical stresses in the lens material originated from the atmospheric pressure effect produce additional phase distortions of the light wave and the outflow of a part of the light energy to the orthogonal polarization through the stress-optical effect mechanism. We used the two-step algorithm is the stress analysis of the lens, the second- optical calculations using the strain field obtained on the first step. The obtained results show that in case of the lens tight fixing the phase and polarization distortions lie within acceptable limits.
Express method for estimating surface resistance of optical components to laser-induced damage
Vladmir S. Sirazetdinov, V. N. Alekseev, A. V. Bessarab, et al.
The study describes a method that, with a series of experimental data obtained from a single sample, allows not only to estimate the threshold fluences but to take into account statistical nature of surface-damage. In a number of experimental situations this method makes it possible to estimate damaging fluences even from the result of a singular exposure of the studied surface. Estimated threshold. Fluences for various optical elements are presented: K8-glass, experimental phosphate laser glass KGSS-0180, high-reflecting and anti-reflecting thin-film coating of elements. Half-height duration of 1.06 micrometers - radiation pulse of 4 ns and irradiation spot of approximately 4 mm in diameter were used in the experiment.
Phase conjugation under broadband three-wave mixing in a nonlinear crystal
Victor I. Sokolov, Michael I. Pergament, A. M. Nugumanov, et al.
An approach is proposed to phase conjugation (PC) of broadband light that is a problem for traditional PC at stimulated Brillouin scattering. Experimental and simulation results of a work aimed to obtain a complex conjugated wave of a broadband laser beam in three-wave mixing in a nonlinear crystal are presented. It is demonstrated by direct wavefront measurements that in mixing of the broadband first harmonic signal wave with the single- frequency second harmonic pump wave having quasi-plane wavefront the arising broadband first harmonic idler wave has a wavefront complex conjugated to the one of the signal light.
Application of an x-ray framing camera in ICF diagnostic
Shu Huai Wen, Jinxiu Cheng, Cunbang Yang, et al.
A large area gated MCP x-rays framing camera was developed in China. The main performances of the camera are as follows: temporal resolution of approximately 60 ps, space resolution of 201p/mm, frame number of 12 and frame interval adjustable, and gated time jitter of 50ps. In ICF experiments, camera was used to diagnostic plasma movement at intense laser entrance hole sides of a Au plane target, x-rays energy transport along an axial direction in a cylindrical cavity, and so on. In recent laser direct driven implode experiment, the camera haws ben used to measure x- rays intensity emitted by a glass microballoon with time and space evolution, and hence to diagnostic implosion symmetry and fuels compression degree. Experimental results showed that the framing camera is in high stability and reliability, and has been a routinely important instrument in ICF experiments.
Geometry-compensated scintillator for low-yield ICF burn history measurements
Jianlun Yang, Shu Huai Wen, Genxing Wang, et al.
In ICF burn history measurements, a small thin cylinder- shaped plastic scintillator sheet is often used as a neutron-to-light converter so as to position it within several centimeters from the target, and a group of fibers of achromatic lens then relays the scintillator image through a slit to the S20 photo cathode of a streak camera outside the chamber. In this case, scintillating light from only the central narrow slit pat of the scintillator sheet is practically used by the streak camera, and the thickness of the scintillator is limited to 1-2 mm to give acceptable temporal dispersion.
Neutron time-of-flight ion temperature measurement of direct-drive implosions on SG-II laser facility
Jianlun Yang, Shu Huai Wen, Zhengyuan Tang, et al.
A geometry-compensated shallow cup-shaped ST1422 plastic scintillator neutron time-of-flight (nTOM) detector has been designed and used on SG-II laser facility to diagnostic inertial confinement fusion (ICF) ion temperature in direct- drive implosions with yields of 108-109 DT neutrons. The measurement system consists of a shallow cup-shaped ST1422 fast plastic scintillator with a thickness of 5mm and full effective volume of 170cm3 placed at a distance of 5.25m from the target, a microchannel plate photomultiplier tube, a piece of coaxial cable with a length of 10m, and a transient oscilloscope with a bandwidth of 4.5GHz. The rise- time and FWHM of the temporal response function are 390ps and 1.47ns, respectively. Measured result for several shots are presented.
Theory and Simulation
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Rapid fuel layering inside moving free-standing ICF targets: physical model and simulation code development
I. V. Aleksandrova, S. V. Bazdenkov, V. I. Chtcherbakov
In this report, we discuss the physical concept and the results of mathematical modeling of free-standing target layering for inertial confinement fusion, including the detailed descriptions of the heat transfer and layer symmetrization mechanisms.
Modeling with backscatter and transmitted light of high-power smoothed beams with pF3D: a massively parallel laser plasma interaction code
R. L. Berger, L. M. Divol, S. H. Glenzer, et al.
Using the 3D wave propagation code, F3D, Berger et al., Phys. Plasmas 5,4337, and the massively parallel version pF3D, we have computed the transmitted and reflected light for laser and plasma conditions in experiments that simulated ignition hohlraum conditions. The frequency spectrum and the wavenumber spectrum of the transmitted light are calculated and used to identify the relative contributions of stimulated forward Brillouin and self- focusing in hydrocarbon-filled balloons, commonly called gasbags. The effect of beam smoothing, smoothing by spectral dispersion and polarization smoothing, on the stimulated Brillouin backscatter from Scale-1 NOVA hohlraums was simulated with the use of nonlinear saturation models that limit the amplitude of the driven acoustic waves. Other experiments on CO2 gasbags simultaneously measure at a range of intensities the SBS reflectivity and the Thomson scatter from the SBS-driven acoustic waves that provide a more detailed test of the modeling. These calculations also predict that the backscattered light will be very nonuniform in the near field which is important for specifying the backscatter intensities to be tolerated by the National Ignition Facility laser system.
Application of solitons to the study of laser propagation into a thermonuclear plasma in the inertial confinement fusion
J. F. Miramar Blazquez
In this work we study the laser propagation in a thermonuclear plasma corresponding to implosion of Deuterium-Tritium pellets in the Inertial Confinement Fusion, by injecting energy provided by high power laser devices into a quiescent plasma and generating solitons. Having in mind that the electric field inside of plasma can be studied by means of a particular Non Linear Schrodinger Equation, we solve this equation as an inverse problem using the Inverse Scattering Transform method, that is a 2 by 2 eigenvalue problem, known as AKNS scheme, developed by Ablovitz, Kamp, Newell and Shabat. We obtain the pseudo potentials q and r if we suppose that the eigenvalue is invariant in time, and is representative of wave eigenvector, obtaining a solution that has a structure of soliton type. In the process, one change of variable for space and another for time are applied, and the relation between the pseudo potentials is given by r equals -q. Discretization of Non Linear Schrodinger Equation, solved by Inverse Scattering Transform are give by Ablovitz et al. These solitons are generated near critical layer where w0 approximately equals wp, being w0 the laser frequency and wp the plasma frequency, exhibit a change in electronic density profile and are caused by ponderomotive force of laser radiation. The electronic density is a function of mean square of electric field. The dispersion relation is representative of an inhomogeneous plasma. Finally, the electric field is obtained as a function of space and time, showing a structure of soliton type.
Ab initio calculations of hydrogen in the dissociation regime
P. Blottiau, J. Clerouin, S. Bagnier
Deuterium Hugoniot recently obtained by NOVA-laser shock in the 70-210 GPa pressure range around one g/cm3, is up to now, only reproduced by M. Ross phenomenological model and some chemical models.
Hydrodynamic stability of ablation fronts: linear perturbation of a self-similar solution
Carine Boudesocque-Dubois, Jean-Marie Clarisse, Serge Gauthier
As is well-known, the efficiency of pellet implosions in inertial confinement fusion is strongly limited by several hydrodynamic instabilities. Among them, the ablation front instability plays a major role. Being the object of a continuing interest since the pioneering works of the 1970s, this instability is often referred to as the 'ablative Rayleigh-Taylor instability'. However, due to the physical processes in effect, this instability is probably closer to flame front instabilities than to classical Rayleigh-Taylor as stressed by Bychkov et al. Models proposed for this instability almost always assume steady flow, either using discontinuous thermal front approximation or accounting for thermal diffusion. Low Mach number approximation for which the unperturbed pressure profile is uniform, is also commonly used.
New direct-drive radiation preheated high-gain target designs for laser fusion
Denis G. Colombant, J. H. Gardner, Andrew J. Schmitt, et al.
A new target design has been proposed which displays a high gain at 1.3 MJ laser energy and improved Rayleigh-Taylor stability with a KrF laser system. The laser contrast ratio in this case is around 250 and the laser pulse lengths is around 28 ns. For a system like NIF, where the contrast ratio is limited to about 100, where no zooming is planned, where the laser pulse length is limited to less than 20 ns and 1/3 micrometers is the laser light wavelength, we have looked at targets using radiation preheat. We have designed targets for this application and investigated more fully the trade- off between gain and stability.
Single electron model of second and third harmonic generation on solid surfaces
K. Gal, S. Varro
Recent experiments have shown that second and third harmonics generated in laser plasmas on solid surfaces preserve the polarization of the incoming laser beam. This contradicts to most theories according to that the polarization of even harmonics should be p-polarized for p- and s-polarized laser beams as well. In the present work a theoretical model of harmonic generation at surfaces having large density gradient is developed, and applied to explain the experimentally observed polarization dependence of the harmonics on that of the fundamental beam.
Azimuthal radiation asymmetry around the LMJ capsule
Jean Giorla, F. Poggi, D. Paillard, et al.
In indirect drive configuration, the Laser MegaJoules 60 quads induce an azimuthal asymmetry of the hohlraum lighting, which can be reduced using an elliptical focal spot. This paper deals with the characterization of the spot size according to both the azimuthal symmetry and the passing-through Laser Entrance Hole criteria. We have investigated the acceptable domain of laser spot sizes for various possible LMJ configurations. The, we have quantified the azimuthal asymmetry decrease due to the elliptical spot elongation.
Full-through laser cutting process simulation
Markus S. Gross, Ian Black, W. H. Mueller
This paper describes the implementation and numerical evaluation of a transient 3D computer simulation of the CO2 laser cutting process. Utilizing Crank-Nicolsen-Finite- Difference equations for the solution of the Fourier heat transfer equation with Newtonian convection, the temperature distribution is predicted. For high accuracy the mesh is of non-equidistant nature, following a Weibull Distribution for the grid spacing. A parallel computation solver is used, based on Divide-and-Conquer Gaussian elimination for banded matrices, to calculate the nodal temperatures using a cluster of two HP J5000 workstations. Included in the solution is the behavior of the material during phase change, while the open structure of the developed software allows incorporation of effects such as surface oxidation, radiation and limited convective flow. The main area of interest is the cutting capability with respect to varying material thickness, cutting speed, power of the laser, laser mode, focal spot diameter and material properties, as well as the effect of these parameters on the quality of the cut.
Nonequilibrium pulsed plasma: ICF target, neutron, and x-ray sources applications
Sergei Yu. Gus'kov
The approaches based on the properties of nonequilibrium pulsed plasmas to develop ICF target design and some ICF application problems are discussed. The methods of the creation of pulsed plasmas with essential properties on the laser radiation absorption and the emission of soft x-ray, fast ions and thermonuclear neutrons are proposed. Theoretical and experimental results are presented on the following fields: 1) laser-produced plasma of porous matter of light elements as a direct ICF target absorber smoothing the laser energy deposition nonuniformities; 2) laser- produced plasma of the composed materials which are the porous medium of light elements with a distribute solid clusters of heavy elements as a wide-range x-ray converter of the ICF target at the direct irradiation by laser beams; 3) laser-produced plasma of regularly volume-structured matter consisting of an ensemble of alternate thin layers of high and low density material containing a thermonuclear fuel or an ensemble of microshells in contact with an one another mode of a material contain such a fuel as a high power neutron source with the intensity more than 1010 DT neutron per one joule of laser energy; 4) high-power- laser-produced plasma of thin foil as a source of light Mev- ions for the direct ignition of ICF target.
Direct ignition of DT and DD fuels by laser-produced plasma flow
Angelo Caruso, Sergei Yu. Gus'kov, Vladislav B. Rozanov, et al.
The direct ignition of the compressed DT and DD fuels of ICF targets by the light ions of laser-produced plasma flows is proposed. Plasma flow, with necessary parameters, is generated as result of laser-produced thermal explosion of a thin separate foil, placed near ICF target. The foil thickness must be less than energy deposition length of the fast electrons inside the produced plasma. It ensures the volume explosion of such a target-generator along all of its thickness in the process of multiple fast electron crossings of the foil. In such a condition the light ions energy may be controlled at the optimal laser energy coupling in the target-generator. Direct ignition method by laser-produced plasma flow is more preferable in comparison with the method by laser-produced fast electrons beam on the reason that the complex procedure of a boring of ICF target plasma does not need.
Rare gas cluster explosion in an intense laser field
Kenichi Ishikawa, Thomas Blenski
We study rare gas cluster explosion in an intense, femtosecond laser pulse using Monte Carlo particle dynamics simulations. The obtained dependence of ion energy on ion charge is approximately quadratic for lower charge states and linear for higher ones. This behavior, also observed in experiments, can be entirely explained on the basis of the Coulomb explosion mechanism. Our results also show that electron impact ionization plays only a minor role in ionization.
Instabilities of high-intensity linearly polarized laser light in a plasma
Moma S. Jovanovic, Kunioki Mima, Milos M. Skoric, et al.
An attempt to solve a fully nonlinear system of fluid and Maxwell equations for 1D propagation of linearly polarized relativistic intensity laser light in a uniform underdense plasma is presented. Linearly-polarized light induces longitudinal modes. Thus electronic parametric and other instabilities appear coupled with each other. We find competing relativistic forward- and backward-Raman scattering, saturated to incoherently broadened spectra via unique cascade and photon condensation mechanisms. Moreover, our code is extendable to other parametric instabilities such as stimulated Brillouin scattering, as well as to 2D treatment of e.g. laser self-focusing and filamentation.
Numerical simulation of shockwave by KrF laser ablation
Susumu Kato, Kaori Kato, Takayuki Aoki, et al.
Hydrodynamic simulation code that is based on the cubic interpolated pseudo-particle scheme and the model of the equation of state is developed to analyze the hydrodynamic instabilities in the inertial confinement fusion. Ablation structure, shockwave, and the hydrodynamic instabilities by KrF laser were investigated by the 1D and 2D hydrodynamic simulation.
Application of a high-power KrF laser for the study of supersonic gas flows and the development of hydrodynamic instabilities in layered media
The design of a miniature laser shock tube for the study of a wide range of hydrodynamic phenomena in liquids at pressures greater than 10 kbar and supersonic flows in gases with large Mach numbers is discussed.
Numerical model of two-beam laser heating and compression of spherical shell targets with low-density coating
A. B. Iskakov, Ivan G. Lebo, Vladislav B. Rozanov, et al.
The construction of powerful multi-beam Nd-laser facilities with pulse energy of 1-2 MJ for the demonstration of 'ignition' in thermonuclear targets is in progress in USA and France. The projects of such facility are also developed in Russia. Such facility is supposed to be built for a few stages. At the intermediate stage it will operate only with a few beams and high symmetry of the spherical target irradiation might not be obtained. The report present the results of 2D beam powerful Nd-laser with energy 100 kJ and pulse duration of 3 ns. On the basis of our simulation we obtained that in case of appropriate profile of laser irradiation of the targets with adjusted thickness relief one can get relatively high neutron yield at the given laser energy.
Neutron yield in conic targets with additional laser fuel heating
The compression and the thermonuclear energy release in conic targets with additional laser heating are calculated. It is shown that irradiation of conic targets with a compound KrF laser pulse with energy 300-400 kJ can provide a neutron yield of >= 1016 per shot and, accordingly, target energy gain coefficients above 0.1. As a result, it is possible to create the high repetition rate thermonuclear neutron source with yield 1016-1017 per shot on the basis of UV-laser.
Development of Rayleigh-Taylor instability in a shell of an incompressible fluid in presence of ablation
Ivan G. Lebo, Vladislav B. Rozanov, Roman V. Stepanov
We introduce the model of growth of the small perturbations on the boundaries of an incompressible fluid shell with accounting for the ablation effect. Basing on this model we consider the following problems: (i) Behavior of perturbations at 'thin' and 'thick' shell; (ii) Development of perturbations at the outer boundary for different regimes of outer pressure; (iii) Development of RTI at a corresponding unstable boundary in cases of the shell compression and expansion, for the work of external forces is equal for both cases; (iv) The effect of ablation on the RTI development process.
Convective instability of radiatively cooling self-similar implosions
Masakatsu Murakami, Katsunobu Nishihara
The linear convective instability of imploding gaseous masses is investigated with a self-similar solution, which takes radiation heat conduction into account. The solution shows that the implosion process continuously transits from initial adiabatic regime to consequent non-adiabatic regime, where the mechanical compression work and the radiation loss balance such that the Péclet number of the system is kept constant. The transition accompanies the decrease in the polytropic index, r d(logp)/d(log p) where p and p are respectively the pressure and density, with the adiabatic index i( r) as its initial vaiue. As a result of the radiative cooling, the fluid becomes unstable to convective modes, when the criterion for instability, d(p/pT)/dr <0, is fulfilled in the core. The spatial and temporal dependence of the perturbations are presented.
Anomalous absorption of linearly polarized laser pulse in overdense plasma
Tatsufumi Nakamura, Susumu Kato, Toshikazu Kato
Anomalous absorption of an intense short laser pulse in overdense plasmas is analyzed. A diffusion equation describing the time evolution of the electron distribution function is derived. From the equation it is shown that the electron distribution function becomes anisotropic in the momentum space, which gives rise to the absorption of the energy. The diffusion is dominant in px direction rather than pz direction. In pz direction, however, the drift term is contained resulting for the longitudinal component of the J X B force, which has ben neglected but is important for the intense laser case. The absorption coefficient and skin depth is obtained for the ASE regime. The absorption coefficient increases in time starting from the well-known absorption coefficient for a lower intensity laser pulse.
Numerical simulation of plasma implosion due to radiation heating of the inlet hole walls of hohlraum target
V. A. Gasilov, A. Y. Krukovskii, T. P. Novikova, et al.
This paper deals with a numerical simulation of the behavior of asthma flows produced when heating the inlet hole walls of hohlraum target by x-ray radiation. Results of 1D numerical calculation are presented for ablation plasma flows interaction with internal transverse magnetic field or with subcritical plasma contained in the target cavity. The calculations confirm the possibility of plasma flows suppression during the time of laser-pulse action.
Supra-thermal energetic electron jets by intense laser pulse in inhomogeneous plasma
K. Satou, T. Okada, Aleksandr A. Andreev
High energy electron jets are produced by the interaction of high-intense laser pulse with various density plasmas. With t e progress of short-pulse multiterawatt laser, it has become possible to produce MeV electron in a plasma. These electrons can be used to apply fusion energy research, particle acceleration, and x-ray source development. 3D particle-in-cell simulations were performed to produce supra thermal electrons. We studied the interaction of P-polarized shaped laser pulse with solid foil targets. In this case an interaction of a main part of laser pulse extremely enhanced energy of fast escaped electrons at some conditions. Proposed mechanism of electron acceleration by laser wave in such plasmas raises electron energy up to 10 MeV for laser intensity more than 1019W/cm2. Conversion coefficient of laser energy to electron one strongly depends on laser intensity.
Enhancement of electron acceleration in laser wakefields by a perpendicularly propagating laser beam
V. Petrzilka, J. A. Tataronis, L. Krlin
By numerical modeling of the test particle motion of an ensemble of relativistic electrons in a longitudinal laser wakefield, we show in the present contribution that a strong enhancement of electron acceleration and trapping in the wakefield arises in the presence of a perpendicularly propagating transverse laser beam. Ripple of the wakefield amplitude reduces the acceleration enhancement. Effects of phase randomization of the transverse laser field are explored as well.
Rayleigh-Taylor instability of ablation fronts with arbitrary Froude numbers
A. R. Piriz
The Rayleigh-Taylor instability of an ablation front has been studied by means of a new analytical model. It is valid for the regime with large and intermediate Froude numbers but it is well behaved also for Fr <EQ 10-2. The model is not limited by a particular approximation for the unperturbed corona profiles. For this, it is suitable to be used with the profiles given by accurate 1D simulations. Besides, it applies to other deflagrations such as laminar flames.
Classical and nonclassical (thermally stabilized) Rayleigh-Taylor analysis in a corona
J. Ramirez, J. Sanz, R. Ramis, et al.
A transition regime in a 2D liquid-gas interface is identified from basic R-T formulation. Characteristic times, mode generation and mode interactions are studied. Results are well compared to the ones from a different hydrodynamic computer code. Then a nonlinear model of the ablative R-T instability is used to include mass evaporation rate and thermal stabilization. A specific solver for the Laplace equation is used. Results are compared to the ones from the previous formulation. Specific attention is given to bubbles.
Calculation of optical characteristics of nonequilibrium plasma
E. M. Ivanov, Vladislav B. Rozanov, G. A. Vergunova
A collisional-radiative model has bene developed to calculate the physical and optical characteristics of thermodynamical nonequilibrium plasma. The mean charge of plasma ions, the ionization-state density, radiative energy losses, line ratios, the opacities and the emissivities have been calculated for the steady-state optically transparent plasma, which contains aluminum or copper multi charged ions, in a broad range of plasma densities and temperatures. The comparison shows that our result agree satisfactorily with the calculation results of other authors and with the experimental data.
Nonlinear propagation of a randomized laser beam: plasma-induced smoothing and scattering instabilities
Andrei V. Maximov, Wojciech Rozmus, Clarence E. Capjack, et al.
The instability of hot spots leading to angular spreading and frequency broadening of a spatially randomized laser beam has a much lower threshold for collisional plasmas compared to the collisionless regime. The plasma-induced spatial and temporal incoherence in forward-propagating light is consistent with the forward stimulated Brillouin scattering (SBS). It also serves to reduce the reflectivity of backward SBS. The interaction of randomized beams with collisional plasmas produces the angular and frequency spectra of transmitted light that are much broader and smoother than in the collisionless regime.
Analytical atomic hydrogenic model for calculation of plasma optical properties
J. G. Rubiano, R. Rodriguez, J. M. Gil, et al.
The screened hydro genic model and analytical potentials are tools widely used for atomic calculation of dense plasma physics. In this paper we present a method to obtain screened hydro genic energy levels and wave function from analytical potentials for ions. Atomic data obtained using this model are compared satisfactorily with result of more sophisticated self-consistent codes.
Analytical potential for excited configurations
R. Rodriguez, J. G. Rubiano, J. M. Gil, et al.
An analytical potential for excited configurations, obtained from an analytical one for ground configuration, is presented in this work. With this potential we calculate several atomic properties of special relevance. The results are compared with those obtained with a self consistent method.
High-order harmonics and trains of subfemtosecond pulses generated from an ultrathin foil
Bai-fei Shen, Jurgen Meyer-ter-Vehn
The nonlinear propagation of two high-intensity laser pluses of circular polarization in thin foil targets is investigated theoretically and by simulation. The two laser pulses illuminate a foil normally from both sides and create a spatially confined relativistic election plasma. The solutions depend on the phase relation of the two laser pulses. High order harmonics are found when frequencies and/or polarizations of the two pulses differ. The harmonics compound to a train of sub-femto-second pulse in the time domain. Under certain conditions, an instability occurs and can destroy the foil. Energetic electrons are produced due to the instability.
X-rays from irradiation of large clusteres by superintense laser pulses
M. B. Smirnov, Vladimir P. Krainov
Irradiation of large clusters by a super-intense femtosecond laser pulse leads to formation of an extremely excited medium. This heating of cluster conducting electrons allows one to reach the maximum excitation of the matter excluding explosions. This mater present an ideal plasma consisting of conducting electrons and multi charged ions only. The problem under consideration is studied both experimentally and also theoretically on the basis of various numerical models.
Symmetry calculations for greenhouse ICF targets irradiated by a small number of laser beams
Sergei Yu. Gus'kov, Nikolai V. Zmitrenko, Vladislav B. Rozanov, et al.
In this paper we consider the symmetry of the deposited energy distribution for the case the number of laser beams to be small in the direct compression open GH scheme. We investigate the dependence of asymmetry on the geometry of irradiation, laser intensity profile in a beam and the properties of absorber. Our calculations show that one may obtain the asymmetry at the level not worse than 2-3 percent for Gaussian beams. The magnitude of asymmetry may be written as an integral representation. For 2-beams irradiation it gives conditions for the laser beam profile or absorber.
Resonant instability of laser speckles in a semicollisional underdense plasma
A. V. Brantov, V. Yu. Bychenkov, V. T. Tikhonchuk, et al.
Instability of a nonlinear laser filament formed due to cumulative effect of the ponderomotive and thermal self- focusing has been investigated in a weakly collisional underdense plasmas. This instability corresponds to the near-forward stimulated Brillouin scattering with excitation of a waveguide electromagnetic mode coupled to a localized supersonic density perturbation. Comparison with the collision-less ponderomotive case demonstrates a significant reduction of the instability threshold and a modification of its characteristics due to nonlocal thermal effects.
Possibility of highly symmetrical compression of GH targets by two laser beams
Sergei Yu. Gus'kov, Vladislav B. Rozanov, Roman V. Stepanov, et al.
A possibility of a uniform irradiation, heating, and stable compression of a 'laser greenhouse' type target by two-beam irradiation by means of a low-density foam-like structured absorber of the laser radiation.
Hydrodynamic instabilities and turbulent mixing at the laser target compression
Vladislav B. Rozanov, Nikolai V. Zmitrenko
An understanding of hydrodynamics instability development is a key element in the studies of the ICF target robustness. All the perspective target design proposals are close to a limit when these instabilities leave out an ignition. It concerns both a direct and an indirect drive design. SO, the evaluation of the perturbation amplitudes of the mixing zone size is the principal ones. At the present work the basic ideas to predict the scales of a turbulent mixing in the laser targets are formulated. These ideas are based on the knowledge of the individual perturbation development and a co-evolution of a set of such the perturbation.This approach is different from a standard harmonic analysis, it takes into account a character of a geometry and it is based in the numerical and experimental results of the hydrodynamics instabilities investigations.
Hydrodynamic Instabilities and Energy Transfer in Laser-Produced Plasmas
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Dimensionality dependence of late time evolution of Rayleigh-Taylor and Richtmyer-Meshkov instabilities
O. Sadot, Dan Oron, D. Kartoon, et al.
Using a statistical mechanics bubble competition model, Alon et al, have shown that the 2D Rayleigh-Taylor (RT) mixing zone bubble and spike fronts evolves. The Richtmyer-Mechkov mixing zone fronts have been found to evolve also.
Experimental observation of the Langmuir decay instability associated with the stimulated Raman scattering
S. Depierreux, C. Labaune, Hector A. Baldis, et al.
An experiment is performed which definitely demonstrates the occurrence of the Langmuir decay instability in the laser plasma interaction. Stimulated Raman scattering is used as a source of well-defined electron plasma waves. Both products of the instability are observed simultaneously using Thomson scattering of a short wavelength probe beam. Resolution of the Thomson scattering measurements in wavelength, wavenumber, time and space allow an unambiguous identification of the ion acoustic waves. Spatial and temporal correlation of these ion acoustic waves with the stimulated Raman scattering activity is observed whereas they appear to be anticorrelated in time and space with the stimulated Brillouin scattering activity.
Numerical analysis of spherically convergent Rayleigh-Taylor experiments
D. Galmiche, C. Cherfils, S. Gail Glendinning, et al.
In the frame of a CEA/US DOE collaboration, radiation driven spherically convergent experiments were performed on the Nova laser in order to measure the Rayleigh-Taylor growth at the ablation front. Numerical simulations using het 2D Lagrangian code PCI2 have correctly reproduced experiments in moderate convergent geometry. Experiments have addressed convergence ratios up to 4 by considering larger capsules, larger hohlraum and longer laser pulses. Numerical analysis of these high convergence implosions is presented, and the effect of convergence on the Rayleigh-Taylor growth is investigated.
Lateral heat transfer and pressure profile smoothing in laser-irradiated low-density targets
A. E. Bugrov, I. N. Burdonskiy, V. V. Gavrilov, et al.
The interaction of powerful laser pulses with low-density materials is experimentally studied following our earlier experiments on 'Mishen' facility. Porous or foam-like materials considered as very important and suitable components of advanced ICF target designs. The low-density media seem to be very helpful for some other research programs of great importance including modeling of astrophysical phenomena, realization of x-ray lasers, determination of the EOS for matter in a multimegabar range.
Absorption and transformation of laser energy in picosecond laser-plasma experiments at intensity of 1016 to 1019 W/cm2
Vladimir G. Borodin, Alexander V. Charukchev, Victor N. Chernov, et al.
The interaction of a 1053 nm picosecond laser pulse with a solid target for focused intensities of up to 1019 W/cm2 are studied by measurements of the absorption of the laser light in the plasma and by measurements of the production of hard x-rays. Absorption measurements are made by collecting the scattered light in set of calorimeters. Light scattered in backward and specular directions is collected separately. Measurements are presented for both high and low Z targets. Hard x-ray spectrum in range 15-1000 keV and hot electron production in range 1-22 MeV are measured using a multichannel filter/scintillator and filter/semiconductor spectrometers. Spatial parameters of fast ions are studied.
Time-resolved studies of parametric instabilities in laser-produced plasmas of near-critical density
A. E. Bugrov, I. N. Burdonskiy, V. V. Gavrilov, et al.
In the context of research on laser interaction with ultra low-density porous media, comparative experiments with thin, burning through plastic foils have been carried out. The structure of backscattered spectra near the laser fundamental frequency was observed and analyzed taking into account the simultaneously temporally and spectrally resolved measurements of the second harmonic emissions. Parametric instabilities responsible for the emissions are identified.
Experimental and numerical study of transverse inhomogeneities in plasma expansion
A. B. Iskakov, Ivan G. Lebo, Jiri Limpouch, et al.
The impact of a laser prepulse on the expansion of plasma heated by a strongly non-0uniform main laser pulse is studied experimentally by a side-on shadowgraphy. Our numerical simulations reproduced well the qualitative features of the observed plasma expansion and the smoothing effect of the prepulse .The numerical model identifies sharp contact boundaries between the colliding plasma streams, that are only gradually relaxed with the advancing time.
Ablation front Rayleigh-Taylor instability experiments in indirect drive at Phebus facility
Andre L. Richard, B. Meyer, P. Salvatore, et al.
Experiments were performed in indirect drive at the Phebus laser facility to study the ablation front Rayleigh-Taylor instability. Brominated plastic targets with sinusoidal modulations were accelerated with a temporally shaped soft x-ray pulse created in a hohlraum. The growth of the perturbations was observed by face-on radiography using a new Wolter-like microscope and the acceleration was derived from separate side-on velocity measurements.
Advanced model for SBS of a randomized laser beam and application to polarization smoothing experiments with preformed underdense plasmas
V. T. Tikhonchuk, Julien Fuchs, C. Labaune, et al.
A model is presented, which describes the stimulated Brillouin scattering (SBS) of a randomized laser beam interacting with an underdense, expanding plasma. The model accounts for the self-focusing of speckles in the regime where plasma heating has an important effect on speckle self-focusing and on SBS threshold and reflectivity. The model exhibits a good agreement with SBS levels measured at the LULI multi-beam facility for a broad range of the laser and plasma parameters and both types of beam smoothing - RPP and polarization smoothing (PS). The model and experiments confirm that eh PS technique allows to control the SBS level more efficiently than RPP.
Measurement of preheat due to fast electrons in laser implosions
Barukh Yaakobi, Christian Stoeckl, Thomas R. Boehly, et al.
The emission of hard x-rays, coincident with 3(omega) L/2 emission, has been measured in laser-interaction experiments on the OMEGA laser system, indicating fast electrons due to the two-plasmon-decay instability. The purpose of the present experiment was to determine the preheat level due to these electrons. In a calibration experiment a flat target containing titanium and vanadium layers was irradiated and the preheat was determined using two signatures: the intensity of K(alpha) lines from the high-Z target layers and the spectrum of hard x-rays measured by an array of BaF2 scintillation detectors. The intensity of both signals can be directly related to the preheat energy; therefore, the two preheat measurements can be cross calibrated. This comparison lends support to the determination of preheat in spherical target experiments, where only the hard x-ray diagnostic is available. For CH shell implosions and square laser pulses the preheat energy deposited in the target amounts to approximately 0.1 percent of the laser energy. The maximum rise in temperature due to the preheat is approximately 10 eV. Finally, the temperature of fast electrons is deduced from the measured spectrum of MeV protons accelerated from the surface of the target; the result agree with the temperature deduced from hard x-rays, namely, T approximately 100 to 200 keV.
Rayleigh-Taylor instability in a stratified gas flow initiated by the compression waves
S. G. Zaytsev, V. V. Krivets, S. N. Titov, et al.
The quantitative characteristics of process of excitation and development of turbulence in the mixing zone between the non-reacted hydrogen-oxygen mixture and inert gases were under the investigation. The accelerated motion is created by compression waves generated by a flame front, expanding in a combustible mixture. The experimental study includes definition of the mixing zone evolution during its motion along the channel with acceleration and subsequent deceleration.
Intense Radiation and Particle Sources
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Soft x-ray emission from a double-stream gas puff target irradiated by a nanosecond laser pulse
In this work a double stream ga puff target was applied in experiments connected with a laser plasma soft x-ray source. The results of the gas puff target density measurements was presented. The experimental results of x-ray measurements concern two experiments. The first one was performed in the Institute of Optoelectronics using 1 ns Nd:glass laser. In this experiment soft x-ray radiation around 1 keV and 3 keV was investigated. The measurements were performed using an x-ray pinhole camera, a flat crystal spectrograph and a soft x-ray photodiode. The second experiment was performed in the Institute for Plasma Physics using a 27 ns KrF laser. In this experiment EUV radiation of the wavelength around 13 nm from the gas puff plasma was measured using a multilayer mirror combined with an x-ray detector. In both experiments it was shown that the emission from the plasma created in the double stream gas puff target was even an order of magnitude higher than in a case of using the ordinary gas puff target.
Investigation of an EUV emission from a double-stream gas puff target irradiated by a nanosecond laser pulse
Andrzej Bartnik, Henryk Fiedorowicz, Susumu Yamagami, et al.
A double stream gas puff was proposed as a target for a laser pulse in a soft x-ray source, to overcome a problem of 3D gas flow outside the sonic nozzle. In a case of the sonic nozzle the gas density drops dramatically with a distance from the nozzle outlet. The double stream gas puff target is created by an injection of high Z gas into a hollow stream of low Z gas. Such a solution allows to decrease an x-ray absorption in cold gas and to keep the inner gas at a relatively high density on a distance up to 2mm from the nozzle outlet. Also in this case plasma emitting soft x-rays created by the laser pulse on the distance over 1mm from the nozzle outlet would not destroy it.
Propagation issues and fast particle source characterization in laser-plasma interactions at intensities exceeding 1019 W/cm2
M. Borghesi, H. D. Campbell, M. Galimberti, et al.
A series of experiments recently carried out at the Rutherford Appleton Laboratory investigated various aspects of the laser-plasma interaction in the relativistic intensity regime. The propagation of laser pulses through preformed plasmas was studied at intensities exceeding 1019 W/cm2. The transmission of laser energy through long scale underdense plasmas showed to be inefficient unless a plasma channel is preformed ahead of the main laser pulse. The study of the interaction with overdense plasmas yielded indication of propagation oat densities above the critical density, possible due to relativistic effects. The production of fast particles during the interaction with solid density targets was also investigated. The measurements revealed the presence of a small-sized directional source of multi-MeV protons, which was not observed when a plasma was preformed at the back of the solid target. The properties of the source are promising in view of its use in radiographic imaging of dense matter, and preliminary test were carried out.
High-energy ions produced from cluster explosions
M. Eloy, R. Azambuja, J. T. Mendonca, et al.
We report on simulations of atomic cluster explosions upon interaction with high-intensity femtosecond laser pulses. By using a 2D and 3D fully relativistic PIC code we investigate the dynamics of hydrogen and argon cluster explosions providing information about the time-resolved ion energy spectra, for different laser intensities. Multi-cluster systems are also studied and the influence of cluster distribution in ionic energy spectra is shown. Results indicate that MeV ions are produced through Coulomb explosion of the atomic clusters and the possibility of capturing most of these ions with a specially designed magnetic focusing system is discussed.
Development of x-ray photoelectron microscopic system with a compact x-ray source
Chiemi Fujikawa, Naohiro Yamaguchi, Tadayuki Ohchi, et al.
We have constructed an x-ray photoelectron microscopic system with x-rays form laser-produced plasma as a source. X-rays involving amplified spontaneous emissions at 15.47 nm were collected by a Schwarzschild mirror coated with Mo/Si multilayers for 15.47 nm x-ray. As preliminary results, Ga 3d and As 3d electrons emitted form a GaAs wafer were observed in the photoelectron spectrum taken by 1 min accumulation.
X-ray spectroscopy of laser-heated CF2-foils
Matthias Geissel, R. Bock, Anatoly Ya. Faenov, et al.
At the Z6 experimental area of the Gsesellshaft fur Schwerionenforschung in Darmstadt experiments with the nhelix laser facility were carried out to determine the plasma parameter sch as temperature, degree of ionization and expansion dynamics for laser heated targets, which are used for the ion beam-plasma-interaction experimental series. Spatially resolved x-ray spectroscopy with spherically bent mica crystals showed well collimated jets of He- and H-like ions emerging out of the front and rear surface of the target with energies in the MeV range.
High-order harmonic generation and attosecond pulse production from a linear chain of ions
R. Numico, Danilo Giulietti, Antonio Giulietti, et al.
The high order harmonic generation process due to the interaction of a multi-well quantum system with an intense laser field is examined. A plateau extension up to a photon energy of Ip + 8Up and the generation of attosecond pulses are evidenced. The influence of the intermediate ions on the conversion efficiency and on the plateau extension is studied.
Concept of the high-energy photon emission from the wire array Z-pinch
P. Kubes, J. Kravarik, D. Klir, et al.
Z-pinches are the laboratory sources of x-rays offering a large variety of diverse applications. As a discharge load, the liners and the fibers are often used.
Coherent short-wavelength radiation via picosecond Nd:glass lasers
Hiroto Kuroda, Tsuneyuki Ozaki, Atsushi Ishizawa, et al.
We review the present status of our research on the generation of coherent soft x-ray radiation using high- intensity picosecond Nd:glass laser pulses. We adopt two completely different methods for this purpose, that is high- harmonic generation from solid-vacuum interfaces, and longitudinally pumped transient collisional excitation Ni- like Mo x-ray laser. Unexpected jetlike structures are observed in the visible emission of the longitudinally- pumped molybdenum plasma, extending over a length of several millimeters. Efficiency of harmonic generation from near- solid density plasma is found to increase by a factor of 2 to 3 when using prepulses.
Generation of high-charge-state ions from CO2 laser-produced plasma
K. N. Makarov, S. V. Khomenko, S. G. Nischuk, et al.
The measurement results are presented for angular dependency of the CO2 laser produced plasma parameters at power density of 4 by 1013W/cm2 and laser pulse duration of 14 ns. 2D numerical simulations are in sufficiently good agreement with experiment. It is shown that the light pressure effects on plasma expansion dynamics and the number of particles generated at the target normal direction.
Electron source produced in the self-modulated laser wake field regime
Victor Malka, J. Faure, J. R. Marques, et al.
In this article, we report on experimental electron spectra generated by SMLWF in the ultra-relativistic regime a0 > 1, where a0 is the normalized vector potential of the laser. For the first time, we have observed that in our range of parameters the maximum electron energy increases when the electron density decreases. A maximum of 70 MeV was observed for ne/nc equals 1.5 percent.
Soft x-ray emission from Ar clusters heated by ultrashort laser pulse
Tomas Mocek, Cheon Min Kim, H. J. Shin, et al.
We report soft x-ray spectra produced by the interaction of 25-100 fs laser pulses at an intensity of up to 7 by 1016 W/cm2 with cryogenically cooled Ar gas jet. New spectral lines from Ar8+, Ar9+ and Ar10+ charge states appeared with decreasing pre- expansion gas temperature. Nonlinear increase of X-ray line emission from Ar7+, Ar8+ and Ar9+ was observed with cooling, which saturated below certain temperature. The change in x-ray spectrum is attributed to efficient collisional heating and collisional ionization of growing small-to-medium sized Ar clusters from the cooled jet. When the laser pulse was extended to 100 fs we have observed considerably stronger emission on lines from high charge states, such as Ar8+, Ar9+ and Ar10+ which suggests that resonance absorption condition could be reached for the 100-fs pulse.
Femtosecond laser-produced plasmas as x-ray sources
Hidetoshi Nakano, Tadashi Nishikawa, Naoshi Uesugi, et al.
Femtosecond laser-produced plasma are bright ultrafast x-ray sources. Since the short x-ray pulses from such plasmas are synchronized to laser pulses, femtosecond laser-produced plasmas are important sources to probe the ultrafast response of optically excited materials. Conversion efficiency has to be improved so that laser-produced parameters, as a prepulse, one can improve x-ray emissions from laser-produced plasma. We report here the result of experimental and theoretical investigations of the line x- ray emissions form aluminum plasma created by a pair of femtosecond laser pulses in order to show the optimum energy conversion into selected x-ray lines.
Intense ion beams accelerated by petawatt-class lasers
Markus Roth, Thomas E. Cowan, Curtis G. Brown, et al.
The LLNL Petawatt Laser has achieved focused intensities up to 6 by 1020 W/cm2. IN plasmas created by this laser, the quiver energy of target electrons exceed several MeV. Recent experiments revealed an intense, collimated beam of high-energy is converted into protons which leads to an energy content of 30J in a pulse of less than 10 ps. The beam shows a broad particle energy spectrum with a sharp cut off and an almost mono-energetic part above 55 MeV. With their short pulse duration, high particle energy and large luminosity these beams are promising candidates in numerous applications, such as short-pulse injectors for laser accelerators or as the ignitor for fast ignition ICF. Using intense proton beams the fast ignitor concept may also become more attractive in heavy-ion fusion due to the possibility to work with indirectly driven targets. Finally, the acceleration is not restricted to protons and the use of tailored target surfaces may allow to accelerate more massive ions to similar energy per nucleon.
Gamma-ray generation in the picosecond-laser plasma with taking into account the prepulse influence
V. S. Belyaev, G. A. Vergunova, Sergei Yu. Gus'kov, et al.
The picosecond laser pulse interaction with different targets was studied on the NEODIM installation. THE processes in laser-produced plasma were considered theoretically and by numerical calculations by RAPID-SP and RADIAN codes with taking into account the pre-pulse with energy contrast of the factor 103-104. Interpretation of the experiments, estimations and numerical results for plasma and electromagnetic fields parameters, fast electron and (gamma) -radiation are presented in this work.
Point x-ray source driven by laser
Andrei S. Shikanov, Yuri V. Korobkin, A. S. Kishinez, et al.
Investigation of spectral, spatial and temporal characteristics of a monochomatic point x-ray source of photon energy approximately 5 keV has been carried out. The source was set up using a laser produced titanium or aluminum plasma as a cathode and a point-tip titanium anode. Parameters of x-ray radiation in Ti K-shells are 1) spectral brightness of approximately 1021 photons/cm2.sec.sr.keV, 2) spatial size approximately 250 microns, and 3) x-ray pulse duration less than 20 ns. It is experimentally provided that in case of appropriate choice of accelerating voltage the radiation spectrum is practically monochromatic and represented by characteristics lines of the anode's material.
Influence of external magnetic and electric fields on properties of an ion beam emitted from laser-produced plasma
Jerzy Wolowski, Luigi Celona, Giovanni Ciavola, et al.
The experimental results of investigations on influence of external magnetic and electric fields on characteristics of ion stream emitted from a plasma produced by the Nd:glass performed at IPPLM, Warsaw are presented. A negatively biased target up to -15 kV and a magnetic field up to 0.45 T were used in the experiment. A set of ion collectors and an electrostatic cylindrical ion energy analyzer located at small angles with respect to the laser beam axis and at large distances from the target were applied for ion measurements. The effect of an external magnetic field is essential to plasma expansion but the effect of the retarding potential of the target is very weak in our experimental conditions. The presented results relate only to tungsten plasma. The aim of the studies was to prove a possibility of optimization of ion beam parameters from laser-produced plasma for particular application as a Laser Ion Source coupled with the Electron Cyclotron Resonance ion source for particle accelerators.
Production of highly ionized plasma by microdot array irradiation and its application to compact x-ray lasers
Naohiro Yamaguchi, Chiemi Fujikawa, Kazunobu Okasaka, et al.
Plasma production and expansion by the irradiation of an array of small spot have been investigated from a point of view of soft x-ray laser generation. The expansion nature of highly ionized ions produced by the micro-dot array irradiation method has ben measured and compared with that by the simple line irradiation. Spatial distribution of gain coefficient of the Li-like Al ion transition lines have also been measured. It has been clarified that rapid expansion and efficient cooling are achieved in plasmas produced by the micro-dot array irradiation method.
Nonfusion and Material Applications
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Supernova remnant simulation experiments on VULCAN
N. C. Woolsey, Y. Abou Ali, R. Evans, et al.
The VULCAN laser at the Central Laser Facility has been used for laboratory simulations of collision-less astrophysical shocks. By ensuring that the experiment exhibit similar values of key dimension-less parameters to those in supernova remnants the hydrodynamics and magnetic field of the experiment are scaled to those of SNR. This enables some of the most challenging aspects of shock behavior to be tested directly against experiment. The experiments provide dat against which to test current theory. Collision-less shock formation, and plasma interaction of two counter- propagating colliding foils permeated by a strong magnetic field are discussed.
Aluminium K-shell emission of laser-generated hot plasma at solid density in high spectral and subpicosecond time resolution
U. Andiel, Klaus Eidmann, Roberto C. Mancini, et al.
We focused ultra short frequency doubled laser pulses on solid AL targets with a thin surface layer of carbon as tamper material. Iso choric heating of aluminum can be achieved this way. We are investigating the K-shell emission by means of a high resolution von Hamos crystal spectrometer. The spectra show line broadening and shifting compared to low density plasma emission. From spectral analysis an electron temperature of (200-400)eV at an electron density close to solid sate are determined. Time resolved spectra are detected by coupling a conical crystal to a sub-ps x-ray streak camera in accumulation mode, providing a time resolution of 0.9 ps when averaging over a large number of laser shots. K-shell line durations in the range of (1-2) ps are observed this way.
Time-resolved x-ray spectra from laser-generated high-density plasmas
U. Andiel, Klaus Eidmann, Klaus-Juergen Witte
We focused frequency doubled ultra short laser pulses on solid C, F, Na and Al targets, K-shell emission was systematically investigated by time resolved spectroscopy using a sub-ps streak camera. A large number of laser shots can be accumulated when triggering the camera with an Auston switch system at very high temporal precision. The system provides an outstanding time resolution of 1.7ps accumulating thousands of laser shots. The time duration of the He-(alpha) K-shell resonance lines was observed in the range of (2-4)ps and shows a decrease with the atomic number. The experimental results are well reproduced by hydro code simulations post processed with an atomic kinetics code.
Application of highly nondegenerate cascaded four-wave mixing to high-order harmonic generation
H. Crespo, J. T. Mendonca, A. Guerreiro
We propose to use nondegenerate cascaded four-wave mixing processes for efficient high order harmonic generation in plasmas and dielectrics. A simple model is used to estimate the temporal duration and maximum order of the generated harmonics for both a typical laser-produced plasma and glass slide. In the plasma case, we expect considerable pulse compression, with the production of sub-femtosecond pulses starting from the 8th harmonic.
Characterization of ionization fronts by photon acceleration
Jose M. B. Dias, N. C. Lopes, G. Figueira, et al.
New results from the interaction of ultra short laser pulses with ionization fronts are presented. The frequency up- shifts, due to photon acceleration, were obtained in a co- and counter propagation scheme. The different levels of frequency up-shift observed give us not only the overall plasma density but also information about the fine structure of the ionization font. The correlation between the interaction lengths for co- and counter-propagation, with the longitudinal and transverse dimensions of the ionization front is also discussed. Those result clearly show the capability of using photon acceleration phenomena to fully characterize a relativistic ionization front.
Laser-generated weak shock wave propagation dynamics in the solids
Angelo Caruso, Sergei Yu. Gus'kov, I. Ya. Doskach, et al.
The processes of the weak shock wave generation and propagation in the solid targets are studied by analytical and numerical methods. The impact of the laser pulse with wavelength (lambda) equals 1.06 micrometers and the pulse intensity I equals 1010-1012W/cm2 was considered as a wave source. The resulting wave with pressure about 1-100kBar is studied in a solid medium 0.5-1 mm thick. The results of modeling compared with experimental data shows correctness of hydrodynamical approximations for a given problem.
Gamma-ray measurements in relativistic interaction with underdense plasmas
M. Galimberti, Antonio Giulietti, Danilo Giulietti, et al.
Fast electrons generated during laser-plasma interactions at relativistic intensities can be studied directly using electron spectrometers, or indirectly, detecting the gamma- ray bremsstrahlung radiation generated by the interaction of these electrons with matter. In a recent experiment carried out at the Rutherford Appleton Laboratory using the Vulcan laser, the propagation of a 75 H, 1 ps Chirped Pulse Amplified pulse (CPA) in a preformed plasma channel was studied using a variety of diagnostic techniques. High energy gamma ray detectors based on NaI(Tl) scintillator coupled to photomultipliers were used to detect bremsstrahlung emission from accelerated electrons. The gamma-ray yield was studied for different plasma channel conditions by varying the delay between the channel forming pulse and the main CPA pulse. These result are correlated with the interferometric images of the plasma interaction region.
Time evolution of colliding laser-produced magnesium plasmas
S. S. Harilal, L. Aschke, T. Atwee, et al.
Fast photography is used to investigate expansion dynamics of colliding laser produced magnesium plasmas. A ruby laser pulse is split into two beams by the help of a movable glass wedge and focused onto two magnesium targets placed at 90 degrees to each other. The intensity ratio of the two laser beams is 7:1 that created hot and cold plasmas on the target surfaces. A collision region is observed 6 ns after the laser maximum and its emission is found to increase with time.
Influence of laser irradiance and helium ambient on the expansion of laser-produced carbon plasma
S. S. Harilal, C. V. Bindhu, V. P. N. Nampoori, et al.
The emission features of laser ablated carbon plasma plume generated in helium ambient have been investigated with time resolved plasma diagnostic technique. At lower irradiance levels only a slowly propagating C2 component is seen. At higher irradiance levels, emission from C2 shows a twin peak distribution in time. The present results also show that the helium ambient pressure and laser irradiance has opposite effects on the time of flight profiles of C2 species. A simple adiabatic expansion model appears to provide a good description of the plume range and this may provide useful for scaling deposition experiments in terms of pressure and laser irradiance.
Preliminary results on the EOS of water in the megabar range
Eugene A. Henry, Dimitri Batani, A. Morelli, et al.
In recent years, shock waves driven by high power lasers have become a reliable tool for the study of the equation of state (EOS) of material sin the Megabar pressure range, where they become strongly correlated, degenerate, dense plasmas. The EOS of water at very high pressures plays a very important role in astrophysics. In particular, the large magnetic field measured on Uranus and Neptune by Voyager 2 is assumed to be generated in the 'ice' layers where pressures up to 6 Mbar are reached. Recent calculations predict an insulator-metallic phase transition of water in this regime. Here, we present some preliminary results form a recent experiment on water EOS performed with the laser PHEBUS and funded by the European Union in the framework of the 'Access to Large Scale Facilities' program. In the experiment, structured targets made of an Aluminium step followed by a water layer are irradiated by the laser at an intensity approximately equals 4.1014 W.cm-2 to generate a shock wave. Velocities are measured in the two materials using a VISAR interferometric diagnostic for water, and a streak camera to measure target emission for Al. EOS points for water are obtained with the impedance mismatch method using Al EOS as a reference. Water reflectivity was also measured.
Laser-produced pair production in vacuum and Hawking-Unruh radiation
Heinrich Hora, Reynaldo Castillo, Wai-Kin Chan, et al.
Laser generated electron-positron pair production is under discussion in the literature form 1969 and large numbers of positrons have been measured since a few years. For electron-positron pair production in vacuum due to vacuum polarization as predicted by Heisenberg 1934, again much higher laser intensities around 1028W/cm2 are necessary which may be available within a number of years. For these cases the similar electron acceleration by gravitation near black holes at Hawking-Unruh radiation have been discussed since 1985 by McDonald. These conditions are considered in view of the earlier work on pair production, change of statistics for electrons at relativistic black body radiation and an Einstein-recoil mechanism with a consequence of a physical foundation of the fine structure constant.
Investigation of optical-field ionized plasmas by Thomson scattering
C. Michael Jost, Ernst E. Fill
Using Thomson scattering of laser light we have studied optical-field ionized Hydrogen and Deuterium plasmas with respect to electron density, electron temperature and ion temperature. The plasmas were created by focusing 120 fs, 790 nm pulses of our Hz ATLAS Ti:sapphire laser system to intensities of up to 7 X 1016 W/cm2. The measurements were performed for linear and elliptic polarization of the ionizing laser light. We find that the ion temperatures for Deuterium and Hydrogen are not identical, whereas the corresponding electron temperatures show no significant difference. Considering standard theory for optical-field ionization we would expect much higher electron temperatures for elliptic than for linear laser polarization. But for Deuterium the electron temperature for elliptic polarization. With increasing particle density ionization defocusing of the laser beam and heating of the electrons due to inverse bremsstrahlung gain in significance.
Optical diagnostics of evacuated polyacetal capillary discharge
Milan Kalal, Miroslav Vrbova, Alexandr Jancarek, et al.
In this paper our new capillary discharge device built for the soft x-ray laser studies is described and the first experimental results obtained from electrical, optical and UV diagnostics together with code simulations are presented.
Determination of energy spectrum of laser-created heavy ions from their implantation depth profile in a metallic substrate
Josef Krasa, Leos Laska, Karel Rohlena, et al.
The energy spectrum of heavy ions emitted from laser- produced plasmas was determined by the use of a technique relying on the implantation of plasma ions into a substrate located close to the plasma. Ion energy spectra were reconstructed from depth profiles of the implanted ions measured by standard Rutherford back-scattering technique employing 2 MeV alpha particles scattered at 170 degrees laboratory angle. The energy spectra of Ag, Au, and Pb ions, implanted into aluminium or steel foils, are presented. A review of another techniques for ion energy spectrum measurement is presented and their limitations are compared.
Simulation study of short-pulse laser energy conversion to x-ray line emission
Jiri Limpouch, A. B. Iskakov, Aleksandr A. Andreev, et al.
Line x-ray emission from short-pulse laser-produced plasmas is studied via 1D and 2D hydrodynamics models coupled with planar atomic physics post-processor. Laser energy conversion efficiency to He-(alpha) line emission is shown to be significantly enhanced when laser prepulse precedes the main pulse at an optimum pulse separation. The calculated optimum pulse separation of 1.5-2 ns as well as emitted energy and spectra compare well with the experiment.
Line x-ray emission from Al targets irradiated by high-intensity variable-length laser pulses
Jiri Limpouch, Oldrich Renner, E. Krousky, et al.
The absolutely calibrated K-shell spectra emitted form short-living aluminum plasma at laser intensities of 5 by 1015- 4 by 1018 W/cm2 are reported. The experiments performed with the constant energy, variable-length laser pulse are modeled by the 1D hydrodynamics code including non-linear resonance absorption of the laser radiation, fast electron acceleration and energy transfer into the target. The characteristic features of the measured and the post- processed spectra are outlined; the scaling rules for the conversion efficiency of the laser radiation into the line x-ray emission are discussed.
Near-10-MeV ion acceleration in the forward direction and isotope production with a high-intensity laser
Anatoly M. Maksimchuk, Koshichi Nemoto, S. Banerjee, et al.
High energy protons with the energy up to 10 MeV were accelerated in the forward direction using a tabletop laser with focusing intensity of 6 X 1018W/cm2. When a deuterated polystyrene was deposited on a front surface of a Mylar film and a boron sample was placed behind the laser target we observed the production of approximately 105 atoms of positron active isotope 11C from the reaction 10B(d,n)11C. The activation results suggest that deuterons were accelerated from the front surface of the laser target.
Results of investigation of x-ray emission from laser-produced plasma by the developed acquisition system
T. Pisarczyk, Andrzej Kasperczuk
In this paper we present some results of investigation of x- ray emission form laser produced-plasma obtained by means of acquisition system for x-ray pictures imaging. The acquisition system allows for 2D registration of plasma emitted radiation in the energetic range 0.1-10 keV. This system was designed within the frames of a research project of the State Committee for Scientific Research of the Polish Government No. 8 T11B007 09 specially for the needs of IPPLM experiments connected with active x-ray laser mediums within the frame of a research work: 'Laser Plasma in the magnetic fields.'
Intensity distribution of the focal lines of the prepulse and mainpulse at the solid target surface
A. R. Praeg, Tomas Mocek, Bedrich Rus, et al.
At the Prague Asterix Laser System (PALS) of the Academy of Sciences of Czech Republic the former Asterix IV iodine laser of the Max-Planck-Institut fur Quantenoptik is currently re-installed. For the soft x-ray laser experiments that will be performed in the near future a well defined focal line at the position of the target surface is important. Applying the prepulse technique there are two possibilities, either the main beam a d the prepulse beam are focused by the same focusing optics or the two different beams are focused by two optical systems separately. It is important to characterize the physical properties of the both line foci, i.e. their intensity distribution in two dimensions, since their energy ratio is giving only a mean value and not the actually existing non-uniformities along or across the focal line. By using two different focusing optics it is possible that the two lien foci do not have exactly the same width at full-width-half-maximum. In order to realize a well defined prepulse line focus it is important to measure the exact intensity distribution in two dimensions. We concept a method to obtain quantified 2D focal images and we present preliminary experimental results using a cylindrical lens array as well as using only a single cylindrical lens in combination with a spherical focusing lens.
Laser-induced satellites in emission of hydrogenic aluminum
Oldrich Renner, Olivier Peyrusse, P. Sondhauss, et al.
The analysis of the fine structure observed in spectra of hydro genic aluminum emitted from a constrained-flow plasma indicates the presence of the laser-induced satellites. The measured profiles of the Al Lyman line (beta) exhibit peaks in the wings consistent with theoretical predications of the spectral line modification by strong single-frequency electric fields. The experimental identification of laser satellites opens up significant applications in the diagnosis of transient plasmas submitted to external oscillating fields.
Sub-angstrom study of plasma x-ray emission by transmission grating spectrometer
Alexander A. Rupasov, S. Sailaja, V. Arora, et al.
A simple XUV transmission grating spectrography operating in the wavelength range of 3-90 angstrom with sub-angstrom resolution without using any XUV imaging optics is described. This is based on a free-standing gold microstructure grating of 2000 angstrom period in normal incidence geometry. A spectral resolution of 0.6 angstrom is obtained by optimizing the slit aperture, the source to grating and the grating to detector distances. Electron temperature deduced form analysis of the spectrum of a laser produced magnesium plasma using a plasma spectroscopic code are consistent with theoretical considerations.
Femtosecond, picosecond, and nanosecond laser microablation: laser plasma and crater investigation
Alexandre F. Semerok, Beatrice Salle, Jean-Luc Lacour, et al.
Crater shapes and plasma plume expansion in the interaction of sharply focused laser beams with metals in air at atmospheric pressure were studied. Laser ablation efficiencies and rates of plasma expansion were obtained. The best ablation efficiency was observed with femtosecond laser pulses. It was found that for nanosecond pulses the laser beam absorption, its scattering and reflection in plasma were the limiting factors for efficient laser ablation and precise material sampling with sharply focused laser beams. The experimental results obtained were analyzed with relation to different theoretical models of laser ablation.
Material properties experiments using the AWE HELEN laser
P. C. Thompson, S. D. Rothman, A. M. Evans, et al.
The AWE 1 TW Nd-glass laser HELEN has been used for a number of studies of material properties. Here we discuss measurement of preheat in our high pressure Hugoniot studies and present results for the principal Hugoniot of triacrylate foam at pressures up to 1 Mb. Michelson interferometer results demonstrate spallation in shocked aluminum enabling us to quantify the spall thickness and strength. High resolution spectral data has been obtained from niobium samples in which the M-shell approaches full occupancy.
Experimental investigation of light bullets generated by interaction of intense picosecond laser pulses with plasma
Nadja Vogel, N. Kochan
Generation of an extremely stable light bullets in a preformed plasma near critical density has been observed experimentally. Optical probing measurements indicate the formation of pulsating channels, typically of about 5 micrometers in diameter, directed towards a heating laser beam, as well as a disconnected massive plasm block moving also towards a laser beam.
Holography of fast moving objects with nanosecond laser pulses
M. Werdiger, S. Eliezer, S. Maman, et al.
When a high power laser irradiates a thin foil, its back surface is accelerated to several km/sec. Due to hydrodynamic instabilities the foil is broken into pieces. This ejected material form an Aluminum target was recorded, using off-axis holography technique. The main laser that generates the shock wave, is a Nd:YAG laser system with a wave length of 1.06 micrometers , pulse duration of 7.5 ns and irradiance in the range (1.4-2.4) by 1013 W/cm2. The hologram is produced by splitting a frequency doubled beam of an additional laser, synchronized with the main laser. One part of it is used as the object beam and the second part serves as the reference beam to the hologram.
Properties of high-z plasma produced by 1-picosecond laser pulse
Eugeniusz Woryna, Jan Badziak, Josef Krasa, et al.
The results of investigation of ion emission from various solid targets, irradiated with an intense 1-ps laser pulse are reported. The ion measurements were based on the time- of-flight method and were performed with the use of ion collectors and electrostatic ion-energy analyzer. The emission of highly-charged heavy ions is demonstrated for the first time for a plasma produced with an ultrashort laser pulse. Ion collector signals show two groups of ions existence of which corresponds to different mechanisms of their generation. Ion yield depends essentially on the laser beam focusing conditions. A production of intense streams of highly charged, high energy ions was observed.