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ABSTRACT: Ultrafast, two-dimensional x-ray imaging is an important diagnostics for the inertial fusion energy research, especially in investigating implosion dynamics at the final stage of the fuel compression. Although x-ray radiography was applied to observing the implosion dynamics, intense x-rays emitted from the high temperature and dense fuel core itself are often superimposed on the radiograph. This problem can be solved by coupling the x-ray radiography with monochromatic x-ray imaging technique. In the experiment, 2.8 or 5.2 keV backlight x-rays emitted from laser-irradiated polyvinyl chloride or vanadium foils were selectively imaged by spherically bent quartz crystals with discriminating the out-of-band emission from the fuel core. This x-ray radiography system achieved 24 μm and 100 ps of spatial and temporal resolutions, respectively.
The Review of scientific instruments 10/2010; 81(10):10E529. · 1.52 Impact Factor
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ABSTRACT: We simulated the plasma expansion of the cone wall due to the pre-pulse irradiation in fast-ignition experiments. Our radiation hydrodynamic simulations show the temporal evolution of the pre-formed plasma inside the cone. At the onset of the pre-pulse, collision within the expanding plasma near the cone axis generate a plasma jet. At the later stage of the pre-pulse the large density shelf above the critical density of 1.06 μm wavelength laser is formed near the tip inside the cone, and subsequently this critical density surface moves away from the inner surface of the cone tip. Our simulation gives roughly 80μm shift of the critical density surface under the typical pre-pulse condition of LFEX laser at Osaka University for 45 deg open angle cone. This shift of the critical density can reduce the energy coupling between the heating laser and the imploded core.
Journal of Physics Conference Series 09/2010; 244(2):022079.
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ABSTRACT: The success of fast ignitor scheme will ultimately relies on the efficient generation and propagation of enormous number of high-energy charged particles. Particle-in-cell simulations aimed at improving the coupling efficiency of input laser energy deposited to a compressed core by using a double cone are described. Quasistatic magnetic fields generated at the vacuum layer inside the double cones are found to play an important role in confining the high energy electrons. The double cones result in the confinement and focusing of about 15% of the input energy for deposition in the compressed core.
Journal of Physics Conference Series 09/2010; 244(2):022030.
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ABSTRACT: The fast ignition scheme is one of the most fascinating and feasible ignition schemes for the inertial fusion energy. At ILE
Osaka University, FIREX (Fast Ignition Realization Experiment) project is in progress. Implosion experiments of the cryogenic
target are scheduled in near future. There are two key issues for the fast ignition. One is controlling the implosion dynamics
to form high density core plasma in non-spherical implosion, and the other is heating the core plasma efficiently by the short
pulse high intense laser. The time and space scale in the fast ignition scheme vary widely from initial laser irradiation
to solid target, to relativistic laser plasma interaction and final fusion burning. The numerical simulation plays an important
role in demonstrating the performance of the fast ignition, designing the targets, and optimizing laser pulse shapes for the
scheme. These all the physics are desired to be self-consistently described. In order to study these physics of FI, we have
developed “Fast Ignition Integrated Interconnecting code” (FI3), which consists of collective Particle-in-Cell (PIC) code
(FISCOF1D/2D), Relativistic Fokker-Planck with hydro code (FIBMET), and two-dimensional Arbitrary-Lagrangian-Eulerian (ALE)
radiation hydrodynamics code (PINOCO). Those codes are sophisticated in each suitable plasma parameters, and boundaries conditions
and initial conditions for them are imported/exported to each other by way of DCCP, a simple and compact communication tool
which enable these codes to communicate each other under executing different machines. The feature of the FI3 code, and a
numerical result of integrated simulation are shown. This simulation system can be applied for particle acceleration and other
applications.
12/2009: pages 243-250;
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ABSTRACT: Particle-in-cell simulations aimed at improving the coupling efficiency of input laser energy deposited to a compressed core by using a double cone are described. It is found that the number of high-energy electrons escaping from the sides of the cone is greatly reduced by the vacuum gap inside the wing of the double cone. Two main mechanisms to confine high-energy electrons are found. These mechanisms are the sheath electric field at the rear of the inner cone wing and the quasistatic magnetic field inside the vacuum gap. The generation mechanism for the quasistatic magnetic fields is discussed in detail. It is found that the quasistatic fields continue to confine the high-energy electrons for longer than a few picoseconds. The double cones provide confinement and focusing of about 15% of the input energy for deposition in the compressed core.
Physical Review Letters 07/2009; 102(24):245001. · 7.37 Impact Factor
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ABSTRACT: When a weak probe laser pulse is injected into a wakefield excited by a short high-intensity pump laser pulse, the probe pulse will be Raman scattered by the wakefield. It is possible to determine the density profile from the spectrum of this forward Raman scattered probe laser [
R. E. Slusher and C. M. Surko, Phys. Fluids 23, 472 (1980)
]. In this paper, an analytical solution for the multiple sidebands of the forward Raman scattering of the probe laser pulse is presented. These multiple sidebands are connected with the steepening of density perturbation of the wakefield. More detailed information of the laser wakefield can be obtained from these multiple sidebands. The propagation of the probe pulse in wakefields is studied with one-dimensional particle-in-cell (PIC) simulations. The analytical solution and the results of PIC simulations are consistent with each other and other experiments.
Physics of Plasmas 09/2008; 15(9):093107-093107-6. · 2.15 Impact Factor
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ABSTRACT: Electron energy characteristics generated by the irradiation of ultraintense laser pulses onto solid targets are controlled by using cone targets. Two parameters characterizing the laser-cone interaction are introduced, which are cone angle and the ratio of the laser spot size to the cone tip size. By changing these parameters, the energy absorption rate, laser irradiance at the cone tip, and electron acceleration at the cone tip and side wall are controlled. The optimum cone targets for fast ignition are 30° cone angle with double-cone geometry, and a tip size comparable to the core size, with the irradiation of a laser pulse with a spot size of about four times the cone tip size. Cone targets have the possibility to enhance the maximum energy of laser-accelerated protons by using a smaller angle cone depending on the laser f-number.
Physics of Plasmas 10/2007; 14(10):103105-103105-7. · 2.15 Impact Factor
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ABSTRACT: Fast electrons are effectively generated from solid targets of
cone-geometry by irradiating intense laser pulses, which is applied to
fast ignition scheme. For realizing optimal core heating by those
electrons, understanding the characteristics of electrons emitted from
cone targets is crucial. In this paper, in order to understand the
generation and transport processes of hot electrons inside the cone
target, two-dimensional (2D) particle-in-cell (PIC) simulations were
carried out. It is shown that hot electrons form current layers which are
guided by self-generated surface magnetic field, which results in
effective energy transfer from laser pulse to hot electrons. When the hot
electrons propagate through the steep density gradient at the cone tip,
electrostatic field is induced via Weibel instability. As a result, hot
electrons are confined inside and emitted gradually from the target, as an
electron beam of long duration. Energy spectrum and temporal profile of
hot electrons are also evaluated at the rear side of the target, where the
profile of rear side plasma is taken from the fluid code and the result is
sent to Fokker-Planck code.
Laser and Particle Beams 02/2006; 24(01):5 - 8. · 1.62 Impact Factor
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ABSTRACT: Multi-MeV electron generation by ultraintense laser pulses plays a major role in fast ignition laser fusion and related high energy density science. This Letter discloses a unique feature of relativistic electron motion and self-induced electromagnetic fields which depend upon laser incident angle and intensity. When the incident angle is larger than the critical value (theta> or =thetacr), despite an MeV electron being injected obliquely into the target, the high energy electron is decoupled from the bulk of the plasma and transported along the surface by the structured electron motion guided by the surface quasistatic electromagnetic field. The surface electromagnetic field and fast-electron density and current profiles are sustained as a quasisteady state by the intense laser irradiation. The analytical structures of the field and electron density agree reasonably well with 2D particle in cell simulation results.
Physical Review Letters 12/2004; 93(26 Pt 1):265002. · 7.37 Impact Factor
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ABSTRACT: The magnetic field generation by a relativistic laser light irradiated on a thin target at the oblique incidence is investigated using a two dimensional particle-in-cell simulation. The surface magnetic field inhibits the electron transport towards the inside plasma, when an incident angle exceeds the critical angle, which depends on the laser and plasma parameters.
11/2004;
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ABSTRACT: It was reported that the fuel core was heated up to ~ 0.8 [keV] in the fast ignition experimentswith cone-guided targets, but they could not theoretically explain heating mechanisms and achievement of such high temperature. Thus simulations should play an important role in estimating the schemeperformance, and we must simulate each phenomenon with individual codes and integrate them under the Fast Ignition Integrated Interconnecting code project. In the previous integrated simulations, fast electronsgenerated by the laser-plasma interaction were too hot to efficiently heat the core and we got only 0.096 [keV] temperature rise. Including the density gap at the contact surface between the cone tip and theimploded plasma, the period of core heating became longer and the core was heated by 0.162 [keV], ~69% higher increment compared with ignoring the density gap effect.
11/2004;
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ABSTRACT: Physics of the inertial fusion is based on a variety of elements such as compressible hydrodynamics, radiation transport, non‐ideal equation of state, non‐LTE atomic process, and laser plasma interaction. In addition, implosion process is not in stationary state and fluid dynamics, energy transport and instabilities should be solved simultaneously. In order to study such complex physics, an integrated implosion code including all physics important in the implosion process should be developed. Before starting this work, an integrated code based on Hirt’s ALE method had been developed. But it needed sophisticated rezoning/remapping algorithm and less dissipative ALE method in hardly distorted mesh. In this work, we have developed 2‐D integrated implosion code based on CIP method which was described in ALE formation. In the IFE research, the fast ignition scheme is one of the epoch making new scheme. In the scheme, the formation of the high density core plasma is one of the problem to be solved. In this paper non‐spherical implosion for fast ignition is solved using the integrated code. © 2003 American Institute of Physics
AIP Conference Proceedings. 06/2003; 669(1):253-256.
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ABSTRACT: One of the most important issues studying the Inertial Confinement Fusion (ICF) is hydrodynamic instability such as RayleighTaylor instability and Richtmyer-Meshkov instability. Many works have been done to estimate the growth rate of the RayleighTaylor instability in laser-accelerated targets. But there are still uncertain parameters to make quantitative prediction of the instability. Especially, a spike and bubble saturation, Kelvin-Helmholtz instability, ablation, thermal conduction and so on complicate the matter in non-linear phase. In such a case, computational simulations play an important role as well as the experiments. For these simulations, the computational code must be stable in numerically, robust without distorted meshes and less dissipative. Also, sophisticated physical models should be considered. In the Institute of Laser Engineering, Osaka University, sophisticated 2-D Arbitrary Lagrangian-Eulerian hydrodynamics code, ILESTA-2D[1] have been developed for the study o...
02/1998;
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ABSTRACT: The energy distribution of the produced high energy electrons in the interaction of ultraintense picosecond laser pulses with high-Z solid targets is shown to be sensitive to the preformed plasma created by the prepulse and the amplified spontaneous emission pedestal. The created preformed plasmas, which are obtained by radiation hydrodynamic simulations for the present heating laser system at ILE, Osaka University, are seen to extend up to 30– 100 m just before the arrival of the main pulse. The dependences of the coupling efficiency of the laser energy to high energy electrons, and the energy spectra of these accelerated electrons, on this preformed plasma, are studied via a two-dimensional particle-in-cell simulation code. It is found that in a small preformed plasma case, J B heating is dominant and the produced electron temperature agrees well with Haines' scaling law Haines et al., Phys. Rev. Lett., 102, 045008 2009. While in a large preformed plasma case, in addition to J B heating and/or vacuum heating, other acceleration mechanisms, such as stochastic heating, can accelerate electrons to very high energies, carrying a significant fraction of input laser energy. Even after several picoseconds, the number of high energy electrons 0.5 MeV E 5 MeV generated in a small preformed plasma case can be several times larger than that of a large preformed plasma case. © 2010 American Institute of Physics.
