Search Results - (Author, Cooperation:D. P. Murphy)
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1Latest Papers from Table of Contents or Articles in PressH. Palike ; M. W. Lyle ; H. Nishi ; I. Raffi ; A. Ridgwell ; K. Gamage ; A. Klaus ; G. Acton ; L. Anderson ; J. Backman ; J. Baldauf ; C. Beltran ; S. M. Bohaty ; P. Bown ; W. Busch ; J. E. Channell ; C. O. Chun ; M. Delaney ; P. Dewangan ; T. Dunkley Jones ; K. M. Edgar ; H. Evans ; P. Fitch ; G. L. Foster ; N. Gussone ; H. Hasegawa ; E. C. Hathorne ; H. Hayashi ; J. O. Herrle ; A. Holbourn ; S. Hovan ; K. Hyeong ; K. Iijima ; T. Ito ; S. Kamikuri ; K. Kimoto ; J. Kuroda ; L. Leon-Rodriguez ; A. Malinverno ; T. C. Moore, Jr. ; B. H. Murphy ; D. P. Murphy ; H. Nakamura ; K. Ogane ; C. Ohneiser ; C. Richter ; R. Robinson ; E. J. Rohling ; O. Romero ; K. Sawada ; H. Scher ; L. Schneider ; A. Sluijs ; H. Takata ; J. Tian ; A. Tsujimoto ; B. S. Wade ; T. Westerhold ; R. Wilkens ; T. Williams ; P. A. Wilson ; Y. Yamamoto ; S. Yamamoto ; T. Yamazaki ; R. E. Zeebe
Nature Publishing Group (NPG)
Published 2012Staff ViewPublication Date: 2012-08-31Publisher: Nature Publishing Group (NPG)Print ISSN: 0028-0836Electronic ISSN: 1476-4687Topics: BiologyChemistry and PharmacologyMedicineNatural Sciences in GeneralPhysicsKeywords: *Altitude ; Atmosphere/chemistry ; Calcium Carbonate/*analysis ; *Carbon Cycle ; Carbon Dioxide/analysis ; Diatoms/metabolism ; Foraminifera/metabolism ; Geologic Sediments/chemistry ; Global Warming/history/statistics & numerical data ; History, 21st Century ; History, Ancient ; Marine Biology ; Oxygen/metabolism ; Pacific Ocean ; Seawater/*chemistry ; TemperaturePublished by: -
2Articles: DFG German National LicensesMeger, R. A. ; Blackwell, D. D. ; Fernsler, R. F. ; Lampe, M. ; Leonhardt, D. ; Manheimer, W. M. ; Murphy, D. P. ; Walton, S. G.
[S.l.] : American Institute of Physics (AIP)
Published 2001Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The use of moderate energy electron beams (e-beams) to generate plasma can provide greater control and larger area than existing techniques for processing applications. Kilovolt energy electrons have the ability to efficiently ionize low pressure neutral gas nearly independent of composition. This results in a low-temperature, high-density plasma of nearly controllable composition generated in the beam channel. By confining the electron beam magnetically the plasma generation region can be designated independent of surrounding structures. Particle fluxes to surfaces can then be controlled by the beam and gas parameters, system geometry, and the externally applied rf bias. The Large Area Plasma Processing System (LAPPS) utilizes a 1–5 kV, 2–10 mA/cm2 sheet beam of electrons to generate a 1011–1012 cm−3 density, 1 eV electron temperature plasma. Plasma sheets of up to 60×60 cm2 area have been generated in a variety of molecular and atomic gases using both pulsed and cw e-beam sources. The theoretical basis for the plasma production and decay is presented along with experiments measuring the plasma density, temperature, and potential. Particle fluxes to nearby surfaces are measured along with the effects of radio frequency biasing. The LAPPS source is found to generate large-area plasmas suitable for materials processing. © 2001 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
3Articles: DFG German National LicensesFernsler, R. F. ; Manheimer, W. M. ; Meger, R. A. ; Mathew, J. ; Murphy, D. P. ; Pechacek, R. E. ; Gregor, J. A.
[S.l.] : American Institute of Physics (AIP)
Published 1998Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: An analysis is presented for the production of weakly ionized plasmas by electron beams, with an emphasis on the production of broad, planar plasmas capable of reflecting X-band microwaves. Considered first in the analysis is the ability of weakly ionized plasmas to absorb, emit and reflect electromagnetic radiation. Following that is a determination of the electron beam parameters needed to produce plasmas, based on considerations of beam ionization, range, and stability. The results of the analysis are then compared with a series of experiments performed using a sheet electron beam to produce plasmas up to 0.6 m square by 2 cm thick. The electron beam in the experiments was generated using a long hollow-cathode discharge operating in an enhanced-glow mode. That mode has only recently been recognized, and a brief analysis of it is given for completeness. The conclusion of the study is that electron beams can produce large-area, planar plasmas with high efficiency, minimal gas heating, low electron temperature, high uniformity, and high microwave reflectivity, as compared with plasmas produced by other sources. © 1998 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
4Articles: DFG German National LicensesPeyser, T. A. ; Antoniades, J. A. ; Myers, M. C. ; Lampe, M. ; Pechacek, R. E. ; Murphy, D. P. ; Meger, R. A.
[S.l.] : American Institute of Physics (AIP)
Published 1991Staff ViewISSN: 1089-7623Source: AIP Digital ArchiveTopics: PhysicsElectrical Engineering, Measurement and Control TechnologyNotes: A multi-element segmented concentric Faraday collector has been developed for measuring the time evolution of the beam half-current radius (a1/2) of an intense relativistic electron beam. Each collector segment measures the total current within its radius. The data analysis procedure fits the data from all five segments at a given time to a prescribed beam profile and calculates a1/2 from the parameters of the fitted curves. The effect of beam centroid offsets on the data analysis was investigated numerically. Beam centroid offsets as large as half the beam radius produce only a 10% error in the experimental measurement of a1/2. The use of a thin graphite overlayer followed by range-thick stainless steel reduces scattering from one collector element to the next. The instrument has been used extensively on the SuperIBEX relativistic electron beam accelerator for measurement of the half-current radius as a function of time. Radius variations in excess of 4:1 have been measured over the duration of the beam pulse for beams with 5-MeV energy, 20-kA peak current and 1-cm final half-current radii.Type of Medium: Electronic ResourceURL: -
5Articles: DFG German National LicensesMurphy, D. P. ; Peyser, T. A. ; Pechacek, R. E.
[S.l.] : American Institute of Physics (AIP)
Published 1994Staff ViewISSN: 1089-7623Source: AIP Digital ArchiveTopics: PhysicsElectrical Engineering, Measurement and Control TechnologyNotes: A compact, four-way, optical image splitter is described which maintains equal intensity and equal optical path length in each arm of the apparatus. The four output beams are parallel with the input light beam.Type of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesMyers, M. C. ; Fernsler, R. F. ; Meger, R. A. ; Antoniades, J. A. ; Murphy, D. P. ; Hubbard, R. F.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: An intense relativistic electron beam injected into dense gas characteristically propagates in a self-pinched mode but is susceptible to the resistive hose instability. This convective instability typically leads to large amplitude beam motion and the disruption of propagation. Theory and computation suggest that, although resistive hose cannot be completely suppressed, its convective growth can be reduced by varying the average betatron oscillation frequency from head to tail in the beam pulse. We report here on experiments designed to implement this variation by tailoring the beam emittance using an ion-focused regime "conditioning'' cell. Conditioning effectiveness is assessed by using measured beam quantities to evaluate a detuning parameter η(t). This information is correlated with beam propagation measurements to determine the optimum conditioning for resistive hose suppression.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesMurphy, D. P. ; Myers, M. C. ; Weidman, D. J. ; Antoniades, J. A. ; Fernsler, R. F. ; Meger, R. A.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The propagation of intense, relativistic electron beams in air is subject to the resistive hose instability. Conditioning the beam prior to injecting it into the air can extend its range by reducing the hose growth rate and by reducing the initial spatial perturbations that seed the hose instability. Experiments have been performed using the SuperIBEX accelerator (Ipeak=10–30 kA, E=4.5 MeV, 40 ns full width at half-maximum) to develop conditioning cells that suppress the hose. This paper describes the performance of an active wire Bθ cell that is used in conjunction with an ion focused regime (IFR) cell. The IFR cell detunes the instability by producing a head-to-tail radius taper on the beam. The wire cell maintains this radius taper while producing an emittance taper that is necessary to suppress the hose growth. In addition, the wire cell reduces the initial beam perturbations through the anharmonic centering force associated with the wire current and its azimuthal magnetic field Bθ. The ability of the Bθ cell to reduce the beam offset with a minimal increase in the beam radius gives it several advantages over the use of a simple, thick scattering foil to perform the radius taper to emittance taper conversion. The SuperIBEX beam propagation distance, in terms of the betatron oscillation scale length, was extended to ∼10λβ using these cells. © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesMyers, M. C. ; Antoniades, J. A. ; Meger, R. A. ; Murphy, D. P. ; Fernsler, R. F. ; Hubbard, R. F.
[S.l.] : American Institute of Physics (AIP)
Published 1995Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Conducting tubes filled with neutral gas at pressures between 0.001 and 0.1 Torr can be used to transport, to center, and to reduce the transverse oscillations of high current ((approximately-greater-than)10 kA) electron beams. Electron impact ionization of the gas leads to partial neutralization of the beam space charge allowing self-focused beam transport and phase-mix damping of injected beam oscillations. In addition, the presence of conducting walls helps center the beam in the transport tube. High current beams, transported through a 1.3 m long tube, were centered to within one-tenth of the beam radius and input transverse oscillations were damped to submillimeter values without significant current loss or emittance growth. Beam transport properties are examined as a function of injected current, gas pressure, and cell geometry. Experimental results are compared with a theoretical model.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesMurphy, D. P. ; Pechacek, R. E. ; Taggart, D. P. ; Fernsler, R. F. ; Hubbard, R. F. ; Slinker, S. P. ; Meger, R. A.
New York, NY : American Institute of Physics (AIP)
Published 1992Staff ViewISSN: 1089-7666Source: AIP Digital ArchiveTopics: PhysicsNotes: High-current charged particle beams can be guided by reduced density channels. Such guiding occurs when the distribution of plasma currents in the density channel causes a net attractive force to be exerted on the beam. In particular, a relativistic electron beam (REB) injected parallel to a spatially offset, reduced density channel is pulled toward the channel. The force exerted on the beam is predicted to increase as the beam current increases and as the offset between the beam and the channel increases out to offsets equal to the channel radius. An experiment with a 1 MV, ≈10 kA beam was performed that demonstrates this effect.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesMurphy, D. P. ; Raleigh, M. ; Pechacek, R. E. ; Greig, J. R.
[S.l.] : American Institute of Physics (AIP)
Published 1987Staff ViewISSN: 1089-7666Source: AIP Digital ArchiveTopics: PhysicsNotes: The interaction of an intense relativistic electron beam (REB) with preformed channels in gaseous atmospheres has been analyzed in order to delineate the effects of reduced density, avalanche ionization, preexisting conductivity, and channel currents. The REB for these experiments was produced from a field emission diode driven by the (approximate)1.4 MV pulse from a pulse forming line. Relativistic electron beam currents up to (approximate)16 kA with current densities up to (approximate)2 kA/cm2 were achieved and the REB current was approximately a half sine wave of width 27 nsec (FWHM). Preformed channels in the atmosphere were created using laser-guided electric discharges. Current-carrying reduced density channels were produced by applying a second discharge to the reduced density channel produced by the first discharge. Reduced density (≤ρ0/80), nonconducting channels were produced by the absorption of radiation from a pulsed CO2 laser in ammonia gas at background pressures of (approximate)40 Torr (ρ0/20). The results show that reduced density had little effect on REB propagation except for a decrease in scattering until the density within the channel had been reduced to such a low level that the dominant mechanism by which conductivity is generated shifted from direct collisional ionization to avalanche ionization. Avalanche ionization in a uniform atmosphere increases the growth of REB instabilities but when it is limited to the reduced density channel region the REB was always repelled or expelled from the channel. Preexisting channel conductivity (σ≥0.1 S/m) also caused the REB to be repelled or expelled from the channel. The presence of a parallel channel current permitted the REB to be readily injected into the channel and guided along it with minimal losses. All of these effects and the thresholds at which they occurred are consistent with the present understanding of the interaction of intense REB's with gaseous atmospheres.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesANDREAS, B. G. ; GERALL, A. A. ; GREEN, R. F. ; MURPHY, D. P.
Provincetown, Mass., etc. : Periodicals Archive Online (PAO)
Published 1957Staff ViewISSN: 0022-3980Topics: PsychologyURL: