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  • 1
    Digitale Medien
    Digitale Medien
    Electron–anode interactions in particle-in-cell simulations of applied-B ion diodes (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 3369-3387 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Particle-in-cell simulations of applied-B ion diodes using the QUICKSILVER code [D. B. Seidel et al., in Proceedings of the Europhysics Conference on Computational Physics, Amsterdam, 1990, edited by A. Tenner (World Scientific, Singapore, 1991), p. 475] have been augmented with Monte Carlo calculations of electron–anode interactions (reflection and energy deposition). Extraction diode simulations demonstrate a link between the instability evolution and increased electron loss and anode heating. Simulations of radial and extraction ion diodes show spatial nonuniformity in the predicted electron loss profile leading to hot spots on the anode that rapidly exceed the 350 °C–450 °C range, known to be sufficient for plasma formation on electron-bombarded surfaces. Thermal desorption calculations indicate complete desorption of contaminants with 15–20 kcal/mole binding energies in high-dose regions of the anode during the power pulse. Comparisons of parasitic ion emission simulations and experiment show agreement in some aspects, but also highlight the need for better ion source, plasma, and neutral gas models. © 1999 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.873576
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  • 2
    Digitale Medien
    Digitale Medien
    Ion divergence in magnetically insulated diodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2175-2182 
    Details
    ISSN: 1089-7674
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Magnetically insulated ion diodes are being developed to drive inertial confinement fusion. Ion beam microdivergence must be reduced to achieve the very high beam intensities required to achieve this goal. Three-dimensional particle-in-cell simulations [Phys. Rev. Lett. 67, 3094 (1991)] indicate that instability-induced fluctuations can produce significant ion divergence during acceleration. These simulations exhibit a fast growing mode early in time, which has been identified as the diocotron instability. The divergence generated by this mode is modest, due to the relatively high-frequency ((approximately-greater-than)1 GHz). Later, a low-frequency low-phase-velocity instability develops with a frequency that is approximately the reciprocal of the ion transit time. This instability couples effectively to the ions, and can generate unacceptably large ion divergences ((approximately-greater-than)30 mrad). Linear stability theory reveals that this mode has structure parallel to the applied magnetic field and is related to the modified two-stream instability. Measurements of ion density fluctuations and energy-momentum correlations have confirmed that instabilities develop in ion diodes and contribute to the ion divergence. In addition, spectroscopic measurements indicate that lithium ions have a significant transverse temperature very close to the emission surface. Passive thin-film lithium fluoride (LiF) anodes have larger transverse beam temperatures than laser-irradiated active sources. Calculations of the ion beam source divergence for the LiF film due to surface roughness and the possible loss of adhesion and fragmentation of this film are presented. © 1996 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.871672
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  • 3
    Digitale Medien
    Digitale Medien
    Diagnosing plasma conditions in light ion beam fusion experiments using inner-shell x-ray line emission (abstract)a) : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 564-564 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Kα emission spectroscopy is an important diagnostic technique used for plasmas created in intense light ion beam experiments.b),c) Emission lines can be produced as 2p electrons drop down to fill 1s vacancies created by the ion beam. Bailey et al.b) reported the first spectroscopic measurements of Kα x-ray satellites in intense proton beam experiments on PBFA-II at Sandia. Kα emission spectra have also recently been observed in intense Li-beam experiments on PBFA-II.d) Two approaches are used to analyze time-integrated x-ray spectra. In the first, CRE calculations are performed to compute synthetic time-integrated spectra using plasma conditions predicted from radiation-hydrodynamic simulations. In the second approach, plasma conditions are deduced from Kα satellite line intensity ratios measured from the highest ionization stages observed in the experiments. Results will be presented from our analysis of recent PBFA-II x-ray spectra. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146353
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  • 4
    Digitale Medien
    Digitale Medien
    High-accuracy time- and space-resolved Stark shift measurements (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. 1009-1014 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Stark-shift measurements using emission spectroscopy are a powerful tool for advancing understanding in many plasma physics experiments. We use simultaneous two-dimensional space- and time-resolved spectra to study the electric field evolution in the 20 TW Particle Beam Fusion Accelerator II ion diode acceleration gap. Fiber optic arrays transport light from the gap to remote streaked spectrographs operated in a multiplexed mode that enables recording time-resolved spectra from eight spatial locations on a single instrument. Design optimization and characterization measurements of the multiplexed spectrograph properties include the astigmatism, resolution, dispersion, and sensitivity. A semiautomated line-fitting procedure determines the Stark shift and the related uncertainties. Fields up to 10 MV/cm are measured with an accuracy ±2%–4%. Detailed tests of the procedure confirm that the uncertainty in the wavelength-shift error bars is less than ±20%. Development of an active spectroscopy probe technique that uses laser-induced fluorescence from an injected atomic beam to obtain three-dimensional space- and time-resolved measurements of the electric and magnetic fields is in progress. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147826
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  • 5
    Digitale Medien
    Digitale Medien
    Target diagnostics for intense lithium ion hohlraum experiments on Particle Beam Fusion Accelerator II : Proceedings of the tenth topical conference on high temperature plasma diagnostics (1995)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 66 (1995), S. 511-514 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A review of the diagnostics used at Sandia National Laboratories to measure the parameters of intense lithium ion-beam hohlraum target experiments on Particle Beam Fusion Accelerator II will be presented. This diagnostic package contains an extensive suite of x-ray spectral and imaging diagnostics that enable measurements of target temperature and x-ray output. The x-ray diagnostics include time-integrated and time-resolved pinhole cameras, energy-resolved one-dimensional streaked imaging diagnostics, time-integrated and time-resolved grazing incidence spectrographs, a transmission grating spectrograph, an elliptical crystal spectrograph, a bolometer array, an 11- element x-ray diode array, and an 11-element PIN diode detector array. The incident Li beam symmetry and an estimate of incident Li beam power density can be measured from ion beam-induced characteristic x-ray line emission and neutron emission. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1146334
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  • 6
    Digitale Medien
    Digitale Medien
    In situ gettering of edge-defined film-fed growth silicon in a CO ambient (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 77 (1995), S. 371-377 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: Edge-defined film-fed growth (EFG) Si grown with carbon monoxide (CO) added to the Ar ambient during crystal growth yields solar cells with higher efficiencies than when grown without CO. This increase in cell efficiency is not fully understood. Surface photovoltage, deep-level transient spectroscopy, Fourier transform infrared spectroscopy, scanning electron microscopy, and transmission electron microscopy were used to determine the minority carrier diffusion lengths, impurity distributions, and defect structures in uncontaminated, Cr contaminated, and V contaminated EFG material grown with and without CO added to the Ar ambient. We conclude that "SiC-like'' complexes in the near-surface region of the CO ambient material act as gettering sites during crystal growth, and that this gettering action results in lower bulk impurity levels and higher solar cell efficiencies. © 1995 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.359332
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  • 7
    Digitale Medien
    Digitale Medien
    Impedance of an annular-cathode indented-anode electron diode terminating a coaxial magnetically insulated transmission line (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 63 (1988), S. 681-688 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The impedance of a diode having an annular cathode and indented anode that terminates a coaxial MITL (magnetically insulated transmission line) is measured and compared with a semiempirical model developed from calculations made using the magic code. The measurements were made on the 16-Ω electron accelerator HELIA (high-energy linear induction accelerator) operating at 3 MV. The model agrees with the measurements within the 10% measuring error and shows that the diode operates in either a load- or line-dominated regime depending on AK (anode-cathode) gap spacing. In the load-dominated regime, which corresponds to small AK gaps, the diode impedance is controlled by an effective anode-cathode gap, and the flow is approximately axial. In the line-dominated regime, which corresponds to large AK gaps, the impedance is independent of the AK gap and corresponds to the impedance associated with the minimum current solution of the MITL, with the flow becoming more radial as the AK gap is increased.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.340057
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  • 8
    Digitale Medien
    Digitale Medien
    Coupling of radiation and hydrodynamics in a Z-pinch plasma (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1939-1945 
    Details
    ISSN: 1089-7550
    Quelle: AIP Digital Archive
    Thema: Physik
    Notizen: The relationship between hydrodynamics and radiative energy loss from a gas puff Z pinch was studied using helium, krypton, and a helium–krypton mixture. The results show that radiation cooling enables the magnetic field to compress the plasma to a higher electron density and a smaller final radius. The data are consistent with a simple model describing the thermalization of the plasma on the axis of the pinch. The spectrum of the krypton radiation from the mixture was harder than from the pure krypton pinch. This may be important for application of the Z pinch as a radiation source.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.337193
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  • 9
    Digitale Medien
    Digitale Medien
    Absorption spectroscopy of a laser-produced plasma (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2197-2197 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: Pin plasma sources are used as x-ray backlights for an Al plasma produced by focusing 1.06-μm laser light to irradiances of 1012 W/cm−2. Spatially resolved absorption features of the helium- like states of ionization of the plasma allow ground-state densities of the helium and hydrogenlike stages to be measured. Comparison with simulations indicates the need for realistic opacity effects to produce a high enough state of ionization for the plasma temperature. Work performed under the auspices of the U.S. DOE by the Lawrence Livermore National Laboratory under Contract No. W-7405-ENG-48.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1138732
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  • 10
    Digitale Medien
    Digitale Medien
    Absorption spectroscopy characterization measurements of a laser-produced Na atomic beam : 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. 354-357 
    Details
    ISSN: 1089-7623
    Quelle: AIP Digital Archive
    Thema: Physik , Elektrotechnik, Elektronik, Nachrichtentechnik
    Notizen: A pulsed Na atomic beam source developed for spectroscopic diagnosis of a high-power ion diode is described. The goal is to produce a ∼1012-cm−3-density Na atomic beam that can be injected into the diode acceleration gap to measure electric and magnetic fields from the Stark and Zeeman effects through laser-induced fluorescence or absorption spectroscopy. A ∼10 ns full width at half-maximum (FWHM), 1.06 μm, 0.6 J/cm2 laser incident through a glass slide heats a Na-bearing thin film, creating a plasma that generates a sodium vapor plume. A ∼1 μs FWHM dye laser beam tuned to 5890 Å is used for absorption measurement of the Na I resonant doublet by viewing parallel to the film surface. The dye laser light is coupled through a fiber to a spectrograph with a time-integrated charge-coupled-device camera. A two-dimensional mapping of the Na vapor density is obtained through absorption measurements at different spatial locations. Time-of-flight and Doppler broadening of the absorption with ∼0.1 Å spectral resolution indicate that the Na neutral vapor temperature is about 0.5–2 eV. Laser-induced fluorescence from ∼1×1012 cm−3 Na I 3s-3p lines observed with a streaked spectrograph provides a signal level sufficient for ∼±0.06 Å wavelength shift measurements in a mock-up of an ion diode experiment. © 1997 American Institute of Physics.
    Materialart: Digitale Medien
    URL: http://dx.doi.org/10.1063/1.1147828
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