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  • 1
    Electronic Resource
    Electronic Resource
    Direct drive acceleration of planar liquid deuterium targets : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2089-2094 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Nike laser (∼2–3 kJ, ∼1014 W/cm2) has been used to ablatively accelerate planar liquid deuterium targets. These experiments are designed to test some aspects of a high gain direct drive target design. The target consists of a low-density foam that is filled with liquid deuterium and covered with a thin polyimide membrane. The measured target trajectory agrees well with one-dimensional (1D) simulations. The growth of the areal mass modulations were measured with a new, 1.26 keV x-ray backlighter. The modulations appear later and grow to a smaller amplitude when the foot of the laser pulse is made spatially smoother. A thin layer of gold on the front of the target reduces the modulations. The results are compared with 2D modeling.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873498
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  • 2
    Electronic Resource
    Electronic Resource
    Effects of thin high-Z layers on the hydrodynamics of laser-accelerated plastic targets : Review,Tutorial and Invited Papers from the 43rd Annual Meeting of the APS Division of Plasma Physics (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 2234-2243 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experimental results and simulations that study the effects of thin metallic layers with high atomic number (high-Z) on the hydrodynamics of laser accelerated plastic targets are presented. These experiments employ a laser pulse with a low-intensity foot that rises into a high-intensity main pulse. This pulse shape simulates the generic shape needed for high-gain fusion implosions. Imprint of laser nonuniformity during start up of the low intensity foot is a well-known seed for hydrodynamic instability. Large reductions are observed in hydrodynamic instability seeded by laser imprint when certain minimum thickness gold or palladium layers are applied to the laser-illuminated surface of the targets. The experiment indicates that the reduction in imprint is at least as large as that obtained by a 6 times improvement in the laser uniformity. Simulations supported by experiments are presented showing that during the low intensity foot the laser light can be nearly completely absorbed by the high-Z layer. X rays originating from the high-Z layer heat the underlying lower-Z plastic target material and cause large buffering plasma to form between the layer and the accelerated target. This long-scale plasma apparently isolates the target from laser nonuniformity and accounts for the observed large reduction in laser imprint. With onset of the higher intensity main pulse, the high-Z layer expands and the laser light is transmitted. This technique will be useful in reducing laser imprint in pellet implosions and thereby allow the design of more robust targets for high-gain laser fusion. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1464541
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  • 3
    Electronic Resource
    Electronic Resource
    Measurements of laser-imprinted perturbations and Rayleigh–Taylor growth with the Nike KrF laser : The 38th annual meeting of the Division of Plasma Physics (DPP) of the American Physical Society (1997)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 4 (1997), S. 1969-1977 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Nike is a 56 beam Krypton Fluoride (KrF) laser system using Induced Spatial Incoherence (ISI) beam smoothing with a measured focal nonuniformity 〈ΔI/I〉 of 1% rms in a single beam [S. Obenschain et al., Phys. Plasmas 3, 1996 (2098)]. When 37 of these beams are overlapped on the target, we estimate that the beam nonuniformity is reduced by 37, to (ΔI/I)≅0.15% (excluding short-wavelength beam-to-beam interference). The extraordinary uniformity of the laser drive, along with a newly developed x-ray framing diagnostic, has provided a unique facility for the accurate measurements of Rayleigh–Taylor amplified laser-imprinted mass perturbations under conditions relevant to direct-drive laser fusion. Data from targets with smooth surfaces as well as those with impressed sine wave perturbations agree with our two-dimensional (2-D) radiation hydrodynamics code that includes the time-dependent ISI beam modulations. A 2-D simulation of a target with a 100 Å rms randomly rough surface finish driven by a completely uniform beam gives final perturbation amplitudes similar to the experimental data for the smoothest laser profile. These results are promising for direct-drive laser fusion.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872560
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  • 4
    Electronic Resource
    Electronic Resource
    The Nike KrF laser facility: Performance and initial target experiments (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2098-2107 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Krypton-fluoride (KrF) lasers are of interest to laser fusion because they have both the large bandwidth capability ((approximately-greater-than)THz) desired for rapid beam smoothing and the short laser wavelength (1/4 μm) needed for good laser–target coupling. Nike is a recently completed 56-beam KrF laser and target facility at the Naval Research Laboratory. Because of its bandwidth of 1 THz FWHM (full width at half-maximum), Nike produces more uniform focal distributions than any other high-energy ultraviolet laser. Nike was designed to study the hydrodynamic instability of ablatively accelerated planar targets. First results show that Nike has spatially uniform ablation pressures (Δp/p〈2%). Targets have been accelerated for distances sufficient to study hydrodynamic instability while maintaining good planarity. In this review we present the performance of the Nike laser in producing uniform illumination, and its performance in correspondingly uniform acceleration of targets. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871661
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  • 5
    Electronic Resource
    Electronic Resource
    X-ray imaging of targets irradiated by the Nike KrF laser : 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. 1099-1102 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Foil targets irradiated by the Naval Research Laboratory Nike KrF laser were imaged in the x-ray region with two-dimensional spatial resolution in the 2–10 μm range. The images revealed the smoothness of the emission from target and backlighter foils, the acceleration of the target foils, and the growth of Rayleigh–Taylor instabilities that were seeded by patterns on the irradiated sides of CH foils.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1147796
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  • 6
    Electronic Resource
    Electronic Resource
    Large area electron beam pumped krypton fluoride laser amplifier (1997)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 68 (1997), S. 2357-2366 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Nike is a recently completed multi-kilojoule krypton fluoride (KrF) laser that has been built to study the physics of direct drive inertial confinement fusion. This paper describes in detail both the pulsed power and optical performance of the largest amplifier in the Nike laser, the 60 cm amplifier. This is a double pass, double sided, electron beam-pumped system that amplifies the laser beam from an input of 50 J to an output of up to 5 kJ. It has an optical aperture of 60 cm × 60 cm and a gain length of 200 cm. The two electron beams are 60 cm high × 200 cm wide, have a voltage of 640 kV, a current of 540 kA, and a flat top power pulse duration of 250 ns. A 2 kG magnetic field is used to guide the beams and prevent self-pinching. Each electron beam is produced by its own Marx/pulse forming line system. The amplifier has been fully integrated into the Nike system and is used on a daily basis for laser-target experiments. © 1997 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1148118
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  • 7
    Electronic Resource
    Electronic Resource
    Generation of a large diameter intense relativistic electron beam for the triaxial relativistic klystron amplifier (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 3488-3493 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We built and tested a new electron beam generator that is capable of generating a 66 cm diameter annular intense relativistic electron beam of energy of 450 keV and current of 60 kA. The new generator incorporates a coaxial-to-triaxial mode converter which allows us to generate and (in the future) to propagate the electron beam between two coaxially grounded conductors. We designed the beam transport system to minimize the axial magnetic energy needed to confine the electron beam. An even lower impedance device can be built by scaling up the size, generating a higher electron beam current. This beam geometry (sheet beam) is useful for efficient generation of high power microwaves. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1145459
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  • 8
    Electronic Resource
    Electronic Resource
    Externally modulated intense relativistic electron beams (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 3353-3379 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The physics of modulation of an intense relativistic electron beam by an external microwave source is studied in this paper via experiment, theory, and simulation. It is found that the self-fields of the electron beam, in general, intensify the current modulation produced by the external source. The linear and nonlinear theory, together with the simulation, show that the classical klystron description in the drift tube region is substantially modified by the beam's high density. In the modulating gap, electron bunches may be generated instantaneously without the necessity of propagating the beam through a long drift tube. These properties, which have no counterparts in low-density beams, lead to the generation of large amplitude, coherent, and monochromatic current modulation on an intense beam. The excellent amplitude stability and the phase-locking characteristics (〈2°) of the modulated current, demonstrated in experiments, open new areas of research in high-power microwave generation and compact particle accelerators.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341521
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  • 9
    Electronic Resource
    Electronic Resource
    Behavior of high-voltage gaps in the presence of large space-charge fields (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 1460-1465 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: It is shown in this paper that a high-voltage gap exhibits a nonlinear capacitance behavior in the presence of large space-charge fields. The existence of this nonlinear capacitor is quasi dc in nature and does not result from transit time effects, i.e., high-frequency effects. This nonlinear behavior can be used to tailor the shape of bunched intense relativistic electron beams.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336076
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  • 10
    Electronic Resource
    Electronic Resource
    Generation of a high-power rf pulse in a rectangular waveguide (1987)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 58 (1987), S. 58-59 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High-power rf radiation with a frequency of 800 MHz was extracted from a modulated intense relativistic electron beam into a rectangular waveguide. The rf extraction was limited to a rf power below 500 MW. Problems which prevent generation of higher power were identified and solutions offered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139567
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