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  • Electronic Resource  (16)
  • 2000-2004  (5)
  • 1995-1999  (11)
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  • Electronic Resource  (16)
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  • 1
    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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  • 2
    Electronic Resource
    Electronic Resource
    Imprint reduction in a plasma layer preformed with x-ray irradiation (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1381-1391 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Indirect–direct-hybrid irradiation scheme has been proposed for suppressing the initial imprint of the laser irradiation nonuniformities. The target is irradiated by a low intensity x-ray radiation prior to the direct-drive laser pulse. The x-ray irradiation generates a plasma expansion layer on the target surface. The thermal smoothing effect is expected to take place in the preformed plasma when the direct-drive laser pulse comes onto the target, and then, the initial imprint can be significantly reduced. Planar target experiments on the indirect–direct-hybrid irradiation scheme were performed. The preformed plasma profile was measured by using x-ray side-on backlighting method. The reduction of the initial imprint was demonstrated by the indirect–direct-hybrid irradiation scheme on planar target experiments. The imprint is suppressed by a factor of 1.5–7 depending on x-ray preirradiation conditions. Results are in good agreement with the cloudy-day model with parameters derived from one-dimensional simulation. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455629
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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
    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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  • 5
    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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  • 6
    Electronic Resource
    Electronic Resource
    One- and two-dimensional fast x-ray imaging of laser-driven implosion dynamics with x-ray streak cameras : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 828-830 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: One- (1D) and two-dimensional (2D) x-ray imaging techniques with x-ray streak cameras have been developed and utilized for investigating implosion dynamics of laser fusion targets. Conventional streaked 1D images of the shell motion of the imploding target was recorded together with the time-resolved 2D multi-imaging x-ray streak images of the core shapes on the same x-ray streak camera. Precise comparison of the core dynamics between the experimental and simulation results was performed with an accuracy of 30 ps by fitting the trajectories of the x-ray emission from the imploding shell. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147700
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  • 7
    Electronic Resource
    Electronic Resource
    Ultrafast two-dimensional x-ray imaging with x-ray streak cameras for laser fusion research (invited) : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 745-749 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultrafast two-dimensional x-ray imaging is required for diagnosing laser-driven inertial confinement fusion plasmas. Image sampling technique with x-ray streak cameras can meet this requirement. Multi-imaging x-ray streak camera method (MIXS) with temporal and spatial resolutions of 10 ps and 15 μm, respectively, has been developed and successfully utilized for diagnosing the uniformity and heating process of the imploded core plasmas. The two-dimensional sampling-image x-ray streak camera method is also presented. Two types of spectroscopic applications of the MIXS have been developed recently. One is multichannel MIXS, which has three MIXS channels with various spectral responses for time-resolved two-dimensional temperature measurement of the plasmas. Another is monochromatic MIXS for temperature, density, and mixing measurement, in which monochromatic images with Bragg crystals are coupled to MIXS. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147690
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  • 8
    Electronic Resource
    Electronic Resource
    Time-resolved two-dimensional monochromatic imaging of laser-imploded plasma : Proceedings of the eleventh topical conference on high temperature plasma diagnostics (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 817-819 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: To prepare a new diagnostic tool for the laser-imploded plasma, we have developed a time-resolved, two-dimensional monochromatic imaging system that consists of a pinhole array, a flat diffraction crystal, and an x-ray streak camera without cathode slit. We have successfully reconstructed time-resolved two-dimensional images of an Ar resonance line emitted from an imploded plastic shell filled with D2/Ar mixture gas. The current system provides the temporal resolution of ∼24 ps and the spatial resolution of ∼16 μm for the direction perpendicular to the spectral dispersion. The spatial resolution parallel to the spectral dispersion is ≤27 μm, that depends on the crystal broadening and the spectral linewidth. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147697
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  • 9
    Electronic Resource
    Electronic Resource
    Development of wide-field, multi-imaging x-ray streak camera technique with increased image-sampling arrays : Papers from the thirteenth topical conference on high temperature plasma diagnostics (2001)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 72 (2001), S. 755-758 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: In order to enlarge the field of view of a multi-imaging x-ray streak (MIXS) camera technique [H. Shiraga et al., Rev. Sci. Instrum. 66, 722 (1995)], which provides two-dimensionally space-resolved x-ray imaging with a high temporal resolution of ∼10 ps, we have proposed and designed a wide-field MIXS (W-MIXS) by increasing the number of image-sampling arrays. In this method, multiple cathode slits were used on the photocathode of an x-ray streak camera. The field of view of the W-MIXS can be enlarged up to 150–200 μm instead of ∼70 μm for a typical MIXS with a spatial resolution of ∼15 μm. A proof-of-principle experiment with the W-MIXS was carried out at the Gekko-XII laser system. A cross-wire target was irradiated by four beams of the Gekko-XII laser. The data streaked with the W-MIXS system were reconstructed as a series of time-resolved, two-dimensional x-ray images. The W-MIXS system has been established as an improved two-dimensionally space-resolved and sequentially time-resolved technique. © 2001 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1319354
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  • 10
    Electronic Resource
    Electronic Resource
    Two-dimensional sampling-image x-ray streak camera for ultrafast imaging of inertial confinement fusion plasmas : Proceedings of the 12th topical conference on high temperature plasma diagnostics (1999)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 70 (1999), S. 620-623 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Ultrafast two-dimensional (2D) x-ray imaging with a temporal resolution better than 10 ps is of great importance in diagnosing the final stages of the imploded core plasmas of inertial confinement fusion (ICF) targets. The multi-imaging x-ray streak camera (MIXS) has been one of such imaging techniques. Recently, we have proposed another scheme, a 2D sampling-image x-ray streak camera method (2D-SIXS). In this scheme, a 2D image is sampled two dimensionally with a set of sampling points distributed regularly over the whole image on a cathode plate of an x-ray streak camera. The sampled image is streaked, and then, reconstructed to form the time-resolved 2D images like movie pictures. In this article, we report results of our proof-of-principle experiments of 2D-SIXS scheme performed at Gekko-XII glass laser system. A gold-coated spherical target was irradiated by three beams (0.53 μm) of Gekko-XII laser. Streaked data of 2D-SIXS were obtained and a series of time-resolved 2D x-ray images were successfully reconstructed. 2D-SIXS is suitable for very fast, short-lived, and small x-ray sources such as a hot spark in the ICF plasma as well as short-pulse-laser-produced plasmas. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149285
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