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  • 1
    Electronic Resource
    Electronic Resource
    Thermonuclear burn time and duration in laser-driven high-aspect-ratio targets (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 945-947 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thermonuclear burn time and burn duration in ablatively driven high-aspect-ratio targets have been measured. While the observed burn times were in agreement with results of a one-dimensional hydrodynamic simulation, the observed burn durations were excessively long.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.101731
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  • 2
    Electronic Resource
    Electronic Resource
    Soft x-ray spectra of highly ionized elements with atomic numbers ranging from 57 to 82 produced by compact lasers (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1923-1930 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: X-ray emission spectra in the spectral range of 2–13 nm from 19 kinds of material with high atomic numbers (lanthanum through lead) were recorded with a grazing incidence spectrometer equipped with a microchannel plate detector. There is an intense, narrow spectral band in these spectra which shifts toward shorter wavelength and becomes weak in intensity with increasing atomic number. The materials were irradiated either by a 4 J/35 ns slab Nd:glass laser or by a 0.5 J/8 ns Nd:YAG laser. The absolute photon intensities of the spectra were determined with an absolutely calibrated charge coupled device camera. The peak spectral brightness of the emission at the peak intensity of the spectral band for lanthanum plasma was estimated to be 2.1×1016 photons/s/mm2/mrad2 in 0.1% bandwidth. The origin of the narrow, intense spectral bands in the recorded spectra and their dependence on target materials and laser wavelength are interpreted.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356339
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  • 3
    Electronic Resource
    Electronic Resource
    Direct-drive hydrodynamic instability experiments on the GEKKO XII laser (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 4079-4089 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Hydrodynamic instabilities, such as the Rayleigh–Taylor (R–T) instability, play a critical role in inertial confinement fusion as they finally cause fuel-pusher mixing that potentially quenches thermonuclear ignition. Good understanding of the instabilities is necessary to limit the mixing within a tolerable level. A series of experiments has been conducted on the GEKKO XII laser facility [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] to measure hydrodynamic instabilities in planar foils directly irradiated by 0.53 μm laser light. It has been found that (1) the imprint is reasonably explained by an imprint model based on the equation of motion with the pressure perturbation smoothed by the cloudy-day effect, and (2) the experimental R–T growth rate is significantly reduced from the classical growth rate due probably to ablative stabilization enhanced by nonlocal heat transport. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872528
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  • 4
    Electronic Resource
    Electronic Resource
    Kinetic effects on the electron thermal transport in ignition target design (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 3420-3424 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Preheating is one of the most critical issues in laser fusion, because of significant reduction of volume compression. The nonlocal heat transport in an ablative plasma is found to play an important role in the preheating under high intensity laser irradiation. Namely, the electron heat transport should be described by the Fokker–Planck (FP) equation in the fluid implosion code. The Spitzer–Härm (SH) thermal conduction model is not applicable because the electron mean free path is comparable to the temperature scale length. The numerical simulations of the implosion with the FP heat transport have been carried out for the fast (high entropy) implosion mode in which the implosion velocity reaches as high as 6×107 cm/s. In the fast implosion, the required laser energy for ignition can be reduced. It is found in the simulation that the isentrope in the FP simulation code is higher by two to four times than that in the flux limited SH simulation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871592
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  • 5
    Electronic Resource
    Electronic Resource
    Recent progress of implosion experiments with uniformity-improved GEKKO XII laser facility at the Institute of Laser Engineering, Osaka University (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2077-2083 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The irradiation uniformity of the GEKKO XII laser [C. Yamanaka et al., IEEE J. Quantum Electron. QE-17 1639 (1981)] has been improved by using partially coherent light with angular spectral dispersion and by improving power balance among the beams. Implosion experiments with the uniformity-improved GEKKO XII have been carried out in order to demonstrate stable formation of the hot spark. The isentrope of the compressed pellet shell is controlled by adding a prepulse to enhance the ablative stabilization of the Rayleigh–Taylor instability. The implosion dynamics has been investigated by x-ray imaging and neutron diagnostics. The experimental results are compared with the mix model prediction based on the one-dimensional hydrodynamic simulation. The degradation of neutron yield is attributed to the low-mode asymmetry. Finally, recent results of planer target experiments on the ablative stabilization of the Rayleigh–Taylor instability are also presented. The observed linear growth rate was about 50% of the classical growth rate and was lower than that of the theoretical prediction, based on the Takabe formula combined with the one-dimensional simulation. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872005
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  • 6
    Electronic Resource
    Electronic Resource
    Study of indirectly driven implosion by x-ray spectroscopic measurements (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 2063-2074 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Fusion pellet implosion by laser-generated x rays was investigated by means of time-integrated spectroscopic measurements. Deuterium fuel was seeded with a small amount of Ar in order to determine the electron temperature and the density of the compressed fuel from, respectively, the emission intensity ratio and the broadening of the Lyβ (Ar17+1s-3p) and Heβ (Ar16+1s2-1s3p) lines. Comparison of the observed results with volume-averaged temperatures and densities obtained from one-dimensional (1-D) fluid-dynamic simulations showed large discrepancies at maximum compression. One possible explanation is that the fuel is stably compressed until the beginning of pusher deceleration by collision with a reflected shock wave from the pellet center, and that further compression during the deceleration phase is terminated in particular for heavy stagnation cases. Similar results were obtained for fusion output. Experimentally obtained neutron yields were close to those from the 1-D simulations at the beginning of the deceleration but a factor of 10–100 less than those expected at maximum compression. These results were examined in terms of shell disintegration in the acceleration phase and pusher–fuel mixing at the contact surface in the deceleration phase due to growth of initial perturbations of the pellet resulting from fluid instabilities. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871293
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  • 7
    Electronic Resource
    Electronic Resource
    Relativistic phase fluctuations of beat wave accelerators and wakeless triple solitons (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 1866-1871 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The coupled wave equations for two incident laser beams, their cascade beams, and a relativistic electron plasma wave are numerically analyzed to show phase fluctuations of the acceleration field. It is found that the phase fluctuations are induced by the relativistic nonlinear shift of the plasma frequency together with the electromagnetic pump wave depletion. When the phase fluctuations become significant, the accelerated particle energy is reduced strongly. The triple-soliton concept, which is proposed to overcome the above difficulties, is also numerically investigated. In particular, effects of the relativistic nonlinearity and the frequency mismatch are discussed. The numerical analysis clarified that the appropriate initial frequency mismatch cancels the relativistic nonlinearity, as indicated by McKinstrie and DuBois [Phys. Rev. Lett. 57, 2022 (1986)] and the triple-soliton propagates for a long distance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.858919
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  • 8
    Electronic Resource
    Electronic Resource
    Hydrodynamic instability in an ablatively imploded target irradiated by high power green lasers (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2875-2883 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Time evolution of the ablation front displacement between concave and convex regions of a surface corrugated spherical target was observed by flash x-ray radiography. The results are compared with calculations based on the linearized fluid equation combined with a one-dimensional simulation to describe the ambient fluid motion. In the analysis, perturbation of the fluid is scaled up to kδ∼2π (k is the perturbation wavenumber and δ is the perturbation amplitude) for the acceleration phase with perturbation mode numbers of l=20 and 30. The practical perturbation of the target requires a relaxation time to form the nominal eigenstate of the Rayleigh–Taylor instability, which results in time delay of instability growth onset.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866996
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  • 9
    Electronic Resource
    Electronic Resource
    Scalings of implosion experiments for high neutron yield (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2884-2893 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of experiments focused on high neutron yield has been performed with the Gekko-XII green laser system [Nucl. Fusion 27, 19 (1987)]. Deuterium–tritium (DT) neutron yield of 1013 and pellet gain of 0.2% have been achieved. Based on the experimental data from more than 70 irradiations, the scaling laws of the neutron yield and the related physical quantities have been studied. Comparison of the experimental neutron yield with that obtained by using a one-dimensional fluid code has led to the conclusion that most of the neutrons produced in the stagnation phase of the computation are not observed in the experiment because of fuel–pusher mixing, possibly induced by the Rayleigh–Taylor instability. The coupling efficiency and ablation pressure have been calculated using the ion temperature measured experimentally. A coupling efficiency of 5.5% and an ablation pressure of 50 Mbar have been obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866997
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  • 10
    Electronic Resource
    Electronic Resource
    Single spatial mode experiments on initial laser imprint on direct-driven planar targets (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1734-1744 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Flat plastic targets were directly irradiated and accelerated by partially coherent light from the GEKKO XII laser [Yamanaka et al., IEEE J. Quantum Electron. QE-17, 1639 (1981)] with the wavelength of 0.53 μm in order to investigate initial laser imprinting. The growth of the perturbation imprinted on the target by an initial foot pulse modulated with a single spatial frequency was observed by the face-on x-ray backlight technique. Imprint levels produced by the foot beam with a stationary intensity modulation of the illumination profile and with a dynamically changing modulation were successfully obtained by an image relay technique and the improved two-wavelength Young's interference method. Simple analytic models are proposed and compared with the experimental results. Stationary imprinting with perturbation wavelength longer than the target thickness is found to be well described by a simple incompressible model. The dynamic dependence of the imprint on the time scale of the temporal illumination profile is found to be qualitatively explained by linear perturbation analysis. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1467656
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