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  • 1
    Electronic Resource
    Electronic Resource
    High-purity ion beam production at high current densities with a liquid-helium-cooled series-field-coil extraction ion diode (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2926-2938 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Experiments are described in which a high-purity, high-power (0.15 TW, 1 MeV) proton beam is generated from an ion source consisting of H2 gas frozen onto a liquid-helium-cooled copper anode at 4.2 K in a series-field-coil extraction diode on the 0.7 TW HydraMITE-II accelerator. Peak anode proton current densities of 2 kA/cm2 were measured. This current density is a factor of 100 higher than those obtained in previous liquid-helium-cooled cryogenic diode experiments on small accelerators and is in the range required for high-power ion beam applications. Thomson parabola, Faraday cup, and carbon activation measurements indicate an ion beam proton fraction close to 100% for the cryogenic source, compared to 50–70% for the standard hydrocarbon anode tested. The cryogenic proton source is believed to consist of no more than a few monolayers of molecular hydrogen. The hydrogen-coated cryogenic anode shows a faster initial anode turn-on than other materials. However, source-limited emission from the thin hydrogen layer results in a somewhat longer current risetime, reduced ion diode efficiency, lower proton current enhancement over the Child–Langmuir limit, and a proton spectrum of lower average energy than for the hydrocarbon anode. Techniques to overcome these limitations are discussed. Cryogenic ion sources consisting of frozen N2, CH4, and Ne have also been studied. In each case, high intensity beams consisting predominantly of components of the refrigerated gas were produced.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349317
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  • 2
    Electronic Resource
    Electronic Resource
    Lithium niobate stress gauge current diagnostic for noninductive measurement of fast-rise-time multimegampere currents (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 68 (1990), S. 4917-4928 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Accurate modeling of load behavior in Z-pinch plasma radiation sources driven by high-current generators requires the measurement of fast-rise-time multimegampere currents close to the load. Conventional current diagnostics mounted in inductive cavities (such as B-dot loops and Rogowski coils) fail at small radius because of electrical breakdown produced by high dI/dt. In this paper, we describe the use of large-signal, nanosecond-time-resolution lithium niobate piezoelectric stress gauges to directly measure the magnetic pressure B2/2μ0=μ0I2/8π2r2 generated at radius r by a current I flowing in a radial transmission line. Current measurements have been performed at radius r=2.54×10−2 m on Sandia National Laboratories' Proto-II (10 TW) and SATURN (30 TW) gas puff Z-pinch experiments with maximum currents of 10.1 MA and dI/dt to 2.1×1014 A/s. Comparisons with Faraday rotation and B-dot current diagnostic measurements at large radius are presented. Bremsstrahlung noise problems unique to the SATURN gas puff source are discussed. For a Y-cut lithium niobate stress gauge on a pure tungsten electrode, current densities up to I/2πr=78 MA/m can be measured before the electrode yield strength and the piezoelectric operating stress limit are exceeded. Above the Hugoniot elastic limit of the electrode material, the dynamic range and accuracy of the diagnostic are greatly reduced, but it appears that the technique can be extended to higher current densities using an X-cut quartz piezoelectric element and a tungsten-sapphire electrode impedance stack.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347077
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  • 3
    Electronic Resource
    Electronic Resource
    Measurement of radiation symmetry in Z-pinch-driven hohlraums : 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. 2173-2181 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Z-pinch-driven hohlraum (ZPDH) [J. H. Hammer et al., Phys. Plasmas 6, 2129 (1999)] is a promising approach to high yield inertial confinement fusion currently being characterized in experiments on the Sandia Z accelerator [M. E. Cuneo et al., Phys. Plasmas 8, 2257 (2001)]. Simulations show that capsule radiation symmetry, a critical issue in ZPDH design, is governed primarily by hohlraum geometry, dual-pinch power balance, and pinch timing. In initial symmetry studies on Z without the benefit of a laser backlighter, highly-asymmetric pole-hot and equator-hot single Z-pinch hohlraum geometries were diagnosed using solid low density foam burnthrough spheres. These experiments demonstrated effective geometric control and prediction of polar flux symmetry at the level where details of the Z-pinch implosion and other higher order effects are not critical. Radiation flux symmetry achieved in Z double-pinch hohlraum configurations exceeds the measurement sensitivity of this self-backlit foam ball symmetry diagnostic. To diagnose radiation symmetry at the 2%–5% level attainable with present ZPDH designs, high-energy x rays produced by the recently-completed Z-Beamlet laser backlighter are being used for point-projection imaging of thin-wall implosion and symmetry capsules. © 2002 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1455002
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  • 4
    Electronic Resource
    Electronic Resource
    Efficient x-ray production from ultrafast gas-puff Z pinches (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 57 (1985), S. 830-833 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Proto-II accelerator has been used to implode krypton and xenon annular gas puffs. A significant fraction of the machine electrical energy was converted first to plasma kinetic energy and then to x rays when the plasma pinched on axis. Quantitative measurements using time-resolved bolometers have shown as much as 10% of the total radiation yield near 1 keV in Xe and 2 keV in Kr. We have compared this radiation yield to the predictions from one-dimensional magnetohydrodynamic code calculations. The implosions were also observed with both time-integrated pinhole cameras and spectrographs. No hard x-ray (E〉10 keV) output was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.334734
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  • 5
    Electronic Resource
    Electronic Resource
    Fast resistive bolometry : 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. 651-655 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Resistive bolometry is an accurate, robust, spectrally broadband technique for measuring absolute x-ray fluence and flux. Bolometry is an independent technique for x-ray measurements that is based on a different set of physical properties than other diagnostics such as x-ray diodes, photoconducting detectors, and P-I-N diodes. Bolometers use the temperature-driven change in element resistivity to determine the total deposited energy. The calibration of such a device is based on fundamental material properties and its physical dimensions. We describe the use of nickel and gold bolometers to measure x rays generated by high-power z pinches on Sandia's Saturn and Z accelerators. The Sandia bolometer design described herein has a pulse response of ∼1 ns. We describe in detail the fabrication, fielding, and data analysis issues leading to highly accurate x-ray measurements. The fundamental accuracy of resistive bolometry will be discussed. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149488
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  • 6
    Electronic Resource
    Electronic Resource
    Application of piezoelectric stress gauges to the measurement of pulsed ion and neutral beam power density (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. 949-949 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Fast-response piezoelectric stress gauges are potentially useful in a number of plasma physics diagnostic applications, but have received only limited development in this direction. Principal applications include the measurement of pulsed photon, electron, ion,b) and neutral beam power, and magnetic pressure.c) We will discuss the use of X-cut quartz and PVDF piezoelectric polymer stress gauges for measurement of ion power density on ion diode experiments. In our present work on the PBFA accelerator, we are attempting to quantify the ion and neutral particle flux in a parasitic beam which limits power coupling to the primary ion beam for light ion ICF experiments. Stress gauge data and hydrocode calculations related to this problem will be presented. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1146152
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  • 7
    Electronic Resource
    Electronic Resource
    Photoconducting x-ray detectors for Z-pinch experiments (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 1804-1806 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: We have used GaAs and GaAs:Cr photoconducting detectors (PCDs) to measure the absolute x-ray output from 1 to 10 keV from Z-pinch plasma radiation sources. We calibrated the detectors over the spectral range of 900–3000 eV and found the spectral response to be constant to within the accuracy of the measurements. The flat spectral response, increased sensitivity (compared with bolometers), and good time response of the PCDs, coupled with their reliability and long lifetimes, have allowed us to acquire absolute x-ray data of significantly higher quality than possible with resistive bolometers or x-ray diodes (XRDs). An added attraction of PCDs is their smooth saturation at high incident x-ray fluxes. Unlike other types of electrical x-ray detectors, this feature allows a PCD to operate over a wide range of incident x-ray powers (10–104 W/cm2 ). We present results from gas puff Z-pinch experiments on Proto-II and Supermite comparing PCD, XRD, and resistive bolometer performance.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1140118
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  • 8
    Electronic Resource
    Electronic Resource
    Radiation diagnostics for x-ray laser experiments on Proto-II (1986)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 57 (1986), S. 2195-2195 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: X-ray laser experiments on the Sandia Proto-II accelerator (10 TW, 40-ns FWHM, 0.125 Ω) use a wide array of radiation diagnostics. Precise x-ray measurements are difficult in the environment of a large pulsed power accelerator. Machine shock, EMP, and large x-ray fluences are significant problems. X-ray diodes and resistive bolometers provide excellent time-resolved information. Crystal and grazing-incidence grating spectrographs and x-ray pinhole cameras give time-integrated data. A recent major effort at Sandia has been the development of time-resolved x-ray pinhole cameras, crystal spectrographs, and grazing-incidence spectrographs. These diagnostics use microchannel plates or a scintillator and streak camera system to obtain time resolution. Precise alignment, nanosecond time resolution, and high spectral precision are all needed for successful x-ray laser experiments. We will present descriptions of the diagnostics and data taken on recent x-ray laser experiments. This work was supported by the U.S. DOE.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1138730
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  • 9
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    On a Neglected Aspect of the Theory of Risk Aversion (1971)
    Oxford : Periodicals Archive Online (PAO)
    Economic Inquiry. 9:2 (1971:Aug.) 211 
    Details
    ISSN: 0095-2583
    Topics: Economics
    URL: http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&res_dat=xri:pao:&rft_dat=xri:pao:article:b097-1971-009-02-000009
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  • 10
    Electronic Resource
    Electronic Resource
    On the mean ergodic theorem for weighted averages (1969)
    Springer
    Probability theory and related fields 13 (1969), S. 141-149 
    Details
    ISSN: 1432-2064
    Source: Springer Online Journal Archives 1860-2000
    Topics: Mathematics
    Notes: Summary Let (Ω, ⌆, P) be a probability space and let T be a measurable and measure preserving point transformation from Ω into Ω. Let f be a measurable and square integrable function on (Ω, ⌆, P), and let a N,k for N, K=0, 1, ... be such that $$\sum\limits_k {a_{N,k} = 1}$$ for all N. The authors investigate conditions on the a N,k 's such that the sequence $$\sum\limits_{k = 0}^\infty {a_{N,k} f(T^k )}$$ converges in mean square for all (Ω, ⌆, P, T) and f described above. The special cases T weakly mixing and T strongly mixing are also considered.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00537020
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