Search Results - (Author, Cooperation:D. Rose)
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1Latest Papers from Table of Contents or Articles in PressS. A. Stern ; F. Bagenal ; K. Ennico ; G. R. Gladstone ; W. M. Grundy ; W. B. McKinnon ; J. M. Moore ; C. B. Olkin ; J. R. Spencer ; H. A. Weaver ; L. A. Young ; T. Andert ; J. Andrews ; M. Banks ; B. Bauer ; J. Bauman ; O. S. Barnouin ; P. Bedini ; K. Beisser ; R. A. Beyer ; S. Bhaskaran ; R. P. Binzel ; E. Birath ; M. Bird ; D. J. Bogan ; A. Bowman ; V. J. Bray ; M. Brozovic ; C. Bryan ; M. R. Buckley ; M. W. Buie ; B. J. Buratti ; S. S. Bushman ; A. Calloway ; B. Carcich ; A. F. Cheng ; S. Conard ; C. A. Conrad ; J. C. Cook ; D. P. Cruikshank ; O. S. Custodio ; C. M. Dalle Ore ; C. Deboy ; Z. J. Dischner ; P. Dumont ; A. M. Earle ; H. A. Elliott ; J. Ercol ; C. M. Ernst ; T. Finley ; S. H. Flanigan ; G. Fountain ; M. J. Freeze ; T. Greathouse ; J. L. Green ; Y. Guo ; M. Hahn ; D. P. Hamilton ; S. A. Hamilton ; J. Hanley ; A. Harch ; H. M. Hart ; C. B. Hersman ; A. Hill ; M. E. Hill ; D. P. Hinson ; M. E. Holdridge ; M. Horanyi ; A. D. Howard ; C. J. Howett ; C. Jackman ; R. A. Jacobson ; D. E. Jennings ; J. A. Kammer ; H. K. Kang ; D. E. Kaufmann ; P. Kollmann ; S. M. Krimigis ; D. Kusnierkiewicz ; T. R. Lauer ; J. E. Lee ; K. L. Lindstrom ; I. R. Linscott ; C. M. Lisse ; A. W. Lunsford ; V. A. Mallder ; N. Martin ; D. J. McComas ; R. L. McNutt, Jr. ; D. Mehoke ; T. Mehoke ; E. D. Melin ; M. Mutchler ; D. Nelson ; F. Nimmo ; J. I. Nunez ; A. Ocampo ; W. M. Owen ; M. Paetzold ; B. Page ; A. H. Parker ; J. W. Parker ; F. Pelletier ; J. Peterson ; N. Pinkine ; M. Piquette ; S. B. Porter ; S. Protopapa ; J. Redfern ; H. J. Reitsema ; D. C. Reuter ; J. H. Roberts ; S. J. Robbins ; G. Rogers ; D. Rose ; K. Runyon ; K. D. Retherford ; M. G. Ryschkewitsch ; P. Schenk ; E. Schindhelm ; B. Sepan ; M. R. Showalter ; K. N. Singer ; M. Soluri ; D. Stanbridge ; A. J. Steffl ; D. F. Strobel ; T. Stryk ; M. E. Summers ; J. R. Szalay ; M. Tapley ; A. Taylor ; H. Taylor ; H. B. Throop ; C. C. Tsang ; G. L. Tyler ; O. M. Umurhan ; A. J. Verbiscer ; M. H. Versteeg ; M. Vincent ; R. Webbert ; S. Weidner ; G. E. Weigle, 2nd ; O. L. White ; K. Whittenburg ; B. G. Williams ; K. Williams ; S. Williams ; W. W. Woods ; A. M. Zangari ; E. Zirnstein
American Association for the Advancement of Science (AAAS)
Published 2015Staff ViewPublication Date: 2015-10-17Publisher: American Association for the Advancement of Science (AAAS)Print ISSN: 0036-8075Electronic ISSN: 1095-9203Topics: BiologyChemistry and PharmacologyComputer ScienceMedicineNatural Sciences in GeneralPhysicsPublished by: -
2Articles: DFG German National LicensesStaff View
ISSN: 0006-3061Source: Elsevier Journal Backfiles on ScienceDirect 1907 - 2002Topics: BiologyChemistry and PharmacologyType of Medium: Electronic ResourceURL: -
3Articles: DFG German National LicensesOttinger, P. F. ; Rose, D. V. ; Neri, J. M. ; Olson, C. L.
[S.l.] : American Institute of Physics (AIP)
Published 1992Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Light-ion inertial confinement fusion requires beam transport over distances of a few meters for isolation of the diode hardware from the target explosion and for power compression by time-of-flight bunching. This paper evaluates ballistic transport of light-ion beams focused by a solenoidal lens. The ion beam is produced by an annular magnetically insulated diode and is extracted parallel to the axis by appropriate shaping of the anode surface. The beam propagates from the diode to the solenoidal lens in a field-free drift region. The lens alters the ion trajectories such that the beam ballistically focuses onto a target while propagating in a second field-free region between the lens and the target. Ion orbits are studied to determine the transport efficiency ηt (i.e., the fraction of the beam emitted from the diode which hits the target) under various conditions relevant to light-ion inertial confinement fusion. Analytic results are given for a sharp boundary, finite thickness solenoidal lens configuration, and numerical results are presented for a more realistic lens configuration. From the analytic results, it is found that ηt can be in the range of 75%–100% for parameter values that appear to be achievable. Numerical results show that using a more realistic magnetic-field profile for the lens yields similar values of ηt for small radius diodes but significantly reduced values of ηt for large radius diodes. This reduction results from the radial gradient in the focusing field at larger radius.Type of Medium: Electronic ResourceURL: -
4Articles: DFG German National LicensesOliver, B. V. ; Genoni, T. C. ; Rose, D. V. ; Welch, D. R.
[S.l.] : American Institute of Physics (AIP)
Published 2001Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The effect of backscattered electrons on space-charge limited currents of cylindrical (coaxial) diodes with anode center conductors is studied. The scattered electrons are parametrized by a fractional current density α and fractional energy β of the incident electrons. For bipolar flow, current enhancement factors of 2.5 are calculated for α, β(similar, equals)0.5. Comparison of the model equations to one-dimensional particle-in-cell simulations with fully integrated Monte Carlo scattering algorithms demonstrates very good agreement for a range of energies and anode materials. In the absence of backscattering, the bipolar diode impedance decreases for increasing ratio of cathode to anode radius rc/ra for ratios greater than about 20. © 2001 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
5Articles: DFG German National LicensesOttinger, P. F. ; Young, F. C. ; Stephanakis, S. J. ; Rose, D. V. ; Neri, J. M. ; Weber, B. V. ; Myers, M. C. ; Hinshelwood, D. D. ; Mosher, D.
[S.l.] : American Institute of Physics (AIP)
Published 2000Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Ion beam self-pinched transport (SPT) experiments have been carried out using a 1.1-MeV, 100-kA proton beam. A Rutherford scattering diagnostic and a LiF nuclear activation diagnostic measured the number of protons within a 5 cm radius at 50 cm into the transport region that was filled with low-pressure helium. Time-integrated signals from both diagnostics indicate self-pinching of the ion beam in a helium pressure window between 35 and 80 mTorr. Signals from these two diagnostics are consistent with ballistic transport at pressures above and below this SPT pressure window. Interferometric measurements of electron densities during beam injection into vacuum are consistent with ballistic transport with co-moving electrons. Interferometric measurements for beam injection into helium show that the electron density increases quadratically with pressure through the SPT window and roughly linearly with pressure above the SPT window. The ionization fraction of the helium plateaus at about 1.5% for pressures above 80 mTorr. In the SPT window, the electron density is 3 to 20 times the beam density. Numerical simulations of these beam transport experiments produce results that are in qualitative agreement with the experimental measurements. © 2000 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
6Articles: DFG German National LicensesYoung, F. C. ; Hubbard, R. F. ; Lampe, M. ; Neri, J. M. ; Ottinger, P. F. ; Stephanakis, S. J. ; Slinker, S. P. ; Hinshelwood, D. D. ; Rose, D. V. ; Olson, C. L. ; Welch, D. R.
[S.l.] : American Institute of Physics (AIP)
Published 1994Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The interaction of intense proton beams with low-pressure (0.25 to 4 Torr) background gases is studied to evaluate beam-current neutralization during transport. Electrons to neutralize the beam are provided by beam-induced ionization of the gas. In experiments with 1 MeV, 1 kA/cm2 protons, net currents outside the beam envelope and electron densities within the beam envelope are measured for helium, neon, argon, and air. Net-current fractions are 2% to 8% and ionization fractions are 0.6% to 5% for 5 to 7 kA beams. Simulations of the experiments for helium and argon suggest that fast electrons play an important role in generating a significant fraction of the return current in a halo outside the beam. As a result, net currents inside the beam may be larger than inferred from magnetic-field measurements outside the beam. Ions at the head of the beam are observed to lose more energy than expected from collisional energy losses in the background gas.Type of Medium: Electronic ResourceURL: -
7Articles: DFG German National LicensesRose, D. V. ; Guillory, J. U. ; Beall, J. H.
[S.l.] : American Institute of Physics (AIP)
Published 2002Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: A spatially independent beam stability model [W. K. Rose et al., Astrophys. J. 280, 550 (1984)] is compared with one-dimensional particle-in-cell (PIC) simulations. The model uses rate equations to evaluate the coupling of longitudinal waves created by beam-plasma instabilities. Equilibrium solutions of the stability model are examined and wave energies from the model are compared with PIC simulations. The PIC simulations enable the stability model to be benchmarked and to explore the temporal evolution of the background plasma electron energy distribution, a capability not presently treated in the stability model. The generation of hot plasma electron tails is examined in the PIC simulations. The scalable, spatially independent model can be used in laboratory and astrophysical parameter regimes while numerical constraints limit the parameter regimes treatable in the PIC simulations. © 2002 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
8Articles: DFG German National LicensesRose, D. V. ; Genoni, T. C. ; Welch, D. R.
[S.l.] : American Institute of Physics (AIP)
Published 2002Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: A steady-state analytic model of beam erosion is presented and compared with two-dimensional hybrid particle-in-cell simulations of 100 MeV to 2 GeV proton beams propagating in a dense background gas. The analytic model accounts for nonzero beam erosion front velocities and the finite energies of beam particles radially exiting the beam through a single parameter. The model is in agreement with the simulation results for a single value of this parameter over the beam energy ranges considered. © 2002 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
9Articles: DFG German National LicensesOliver, B. V. ; Ottinger, P. F. ; Rose, D. V.
[S.l.] : American Institute of Physics (AIP)
Published 1996Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The ionization of gas by intense (MeV, kA/cm2) ion beams is investigated for the purpose of obtaining scaling relations for the rate of rise of the electron density, temperature, and conductivity of the resulting plasma. Various gases including He, N, and Ar at pressures of order 1 torr have been studied. The model is local and assumes a drifting Maxwellian electron distribution. In the limit that the beam to gas density ratio is small, the initial stage of ionization occurs on the beam impact ionization time and lasts on the order of a few nanoseconds. Thereafter, ionization of neutrals by the thermal electrons dominates electron production. The electron density does not grow exponentially, but proceeds linearly on a fast time scale tth=U/(vbρ dE/dx) associated with the time taken for the beam to lose energy U via collisional stopping in the gas, where U is the ionization potential of the gas, vb is the beam velocity, ρ is the gas mass density, and dE/dx is the mass stopping power in units of eV cm2/g. This results in a temperature with a slow time dependence and a conductivity with a linear rise time proportional to tth. © 1996 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
10Articles: DFG German National LicensesStaff View
ISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Numerical simulations of grad-B drifting, high-current, relativistic electron beams are presented. The simulations use a hybrid fluid/particle-in-cell code to study the net-current and conductivity evolution for 200 to 900 kA, 1.3 MeV annular electron beams in a background gas of nitrogen (N2) at pressures of 1–60 Torr. Optimum guide-wire current and gas pressure for efficient beam transport are found from the simulations to be ∼40 kA and ∼5–15 Torr of N2, respectively, with energy transport efficiencies as high as 80% for transport distances up to 200 cm. For beam currents and/or gas pressures near the high end of the ranges considered, large net currents significantly alter the magnetic-field profile and result in decreased transport efficiency. Transport efficiencies up to 90% are also found for a self-pinched transport mode in the 1–15 Torr N2 range with no wire current. © 2001 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
11Articles: DFG German National LicensesOliver, B. V. ; Ottinger, P. F. ; Rose, D. V. ; Hinshelwood, D. D. ; Neri, J. M. ; Young, F. C.
[S.l.] : American Institute of Physics (AIP)
Published 1999Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Electron density measurements from previous ion-beam-induced gas ionization experiments [F. C. Young et al., Phys. Plasmas 1, 1700 (1994)] are re-analyzed and compared with a recent theoretical model [B. V. Oliver et al., Phys. Plasmas 3, 3267 (1996)]. Ionization is produced by a 1 MeV, 3.5 kA, 55 ns pulse-duration, proton beam, injected into He, Ne, or Ar gas in the 1 Torr pressure regime. Theoretical and numerical analysis indicates that, after an initial electron population is produced by ion beam impact, ionization is dominated by the background plasma electrons and is proportional to the beam stopping power. The predicted electron density agrees with the measured electron densities within the factor of 2 uncertainty in the measurement. However, in the case of Ar, the theoretically predicted electron densities are systematically greater than the measured values. The assumptions of a Maxwellian distribution for the background electrons and neglect of beam energy loss to discrete excitation and inner shell ionization in the model equations are considered as explanations for the discrepancy. © 1999 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
12Articles: DFG German National LicensesStaff View
ISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: The self-pinched transport of intense ion beams in low-pressure background gases is studied using numerical simulations and theoretical analysis. The simulations are carried out in a parameter regime that is similar to proton beam experiments being fielded on the Gamble II pulsed power generator [J. D. Shipman, Jr., IEEE Trans. Nucl. Sci. NS-18, 243 (1971)] at the Naval Research Laboratory. Simulation parameter variations provide information on scaling with background gas species, gas pressure, beam current, beam energy, injection angles, and boundaries. The simulation results compare well with simple analytic scaling arguments for the gas pressure at which the effective net current should peak and with estimates for the required confinement current. The analysis indicates that the self-pinched transport of intense proton beams produced on Gamble II (1.5 MeV, 100 kA, 3 cm radius) is expected to occur at gas pressures between 30 and 80 mTorr of He or between 3 and 10 mTorr of Ar. The significance of these results to ion-driven inertial confinement fusion is discussed. © 1999 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
13Articles: DFG German National LicensesWelch, D. R. ; Rose, D. V. ; Oliver, B. V. ; Genoni, T. C. ; Clark, R. E.
[S.l.] : American Institute of Physics (AIP)
Published 2002Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: In heavy-ion inertial confinement fusion (HIF), an ion beam is transported several meters through the reactor chamber to the target. This standoff distance mitigates damage to the accelerator from the target explosion. For the high perveance beams and millimeter-scale targets under consideration, the transport method is largely determined by the degree of ion charge and current neutralization in the chamber. This neutralization becomes increasingly difficult as the beam interacts with the ambient chamber environment and strips to higher charge states. Nearly complete neutralization permits neutralized-ballistic transport (main-line HIF transport method), where the ion beam enters the chamber at roughly 3-cm radius and focuses onto the target. In the backup pinched-transport schemes, the beam is first focused outside the chamber before propagating at small radius to the target. With nearly complete charge neutralization, the large beam divergence is contained by a strong magnetic field resulting from roughly 50-kA net current. In assisted-pinched transport, a preformed discharge channel provides the net current and the discharge plasma provides nearly complete charge and current neutralization of the beam. In self-pinched transport, the residual net current results solely from the beam-driven breakdown of the ambient gas. Using hybrid particle-in-cell simulation codes, the behavior of HIF driver-scale beams in these three transport modes is examined. Simulations of neutralized ballistic transport, at a few-mTorr flibe pressure, show excellent neutralization given a preformed or photoionized (from the heated target) plasma. Two- and three-dimensional simulations of assisted-pinch transport in roughly 1-Torr Xe show the importance of attaining 〉1-μs magnetic diffusion time to limit self-field effects and achieve good transport efficiency. For Xe gas pressures ranging from 10–150 mTorr, calculations predict a robust self-magnetic force sufficient for self-pinched transport. The latest simulation results are presented and the important remaining issues for each transport scheme are discussed. © 2002 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
14Articles: DFG German National LicensesOttinger, P. F. ; Rose, D. V. ; Oliver, B. V.
[S.l.] : American Institute of Physics (AIP)
Published 1999Staff ViewISSN: 1089-7674Source: AIP Digital ArchiveTopics: PhysicsNotes: Two fluid equilibrium solutions for intense ion beam transport in low-pressure gas or vacuum are derived. The equilibria that are most relevant to beam transport have neutralizing electrons drifting in the same direction as the beam. These solutions require a small net positive charge within the beam channel to support an equilibrium radial electric field to allow the electrons to E×B drift axially. At the extremes of the domain of allowable solutions this electric field approaches zero and complete charge neutrality is achieved. In this case, two solutions are obtained. The first describes ballistic beam transport with complete neutralization of the beam current by the electrons, and the second describes pinched beam transport with no neutralizing electron current. Equilibria between these two extremes exhibit both a small net positive charge within the beam channel and partial current neutralization. © 1999 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
15Articles: DFG German National LicensesRose, D. V. ; Welch, D. R. ; Oliver, B. V. ; Clark, R. E.
[S.l.] : American Institute of Physics (AIP)
Published 2002Staff ViewISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: Dose-rate calculations for intense electron-beam diodes using particle-in-cell (PIC) simulations along with Monte Carlo electron/photon transport calculations are presented. The electromagnetic PIC simulations are used to model the dynamic operation of the rod-pinch and immersed-B diodes. These simulations include algorithms for tracking electron scattering and energy loss in dense materials. The positions and momenta of photons created in these materials are recorded and separate Monte Carlo calculations are used to transport the photons to determine the dose in far-field detectors. These combined calculations are used to determine radiographer equations (dose scaling as a function of diode current and voltage) that are compared directly with measured dose rates obtained on the SABRE generator at Sandia National Laboratories. © 2002 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
16Articles: DFG German National LicensesStaff View
ISSN: 1365-2389Source: Blackwell Publishing Journal Backfiles 1879-2005Topics: GeosciencesAgriculture, Forestry, Horticulture, Fishery, Domestic Science, NutritionNotes: Excess salts may be removed from soil by leaching, but ponding water on the soil's surface and allowing infiltration requires large quantities of water. During such leaching water flows preferentially through macropores between aggregates, while the flow within aggregates is much less. Consequently, solute within aggregates is removed much more slowly, thus decreasing overall leaching efficiency. For this reason intermittent ponding can be more efficient because it allows time for solute to diffuse to the surfaces of aggregates during the rest period and subsequently be removed in macropore flow. We explored solute transport in aggregated soils under intermittent leaching in three ways: theoretically, by laboratory experiments on columns of porous ceramic spheres as analogues of aggregates, and by simulation. Solute movement during displacement is described by the mobile-immobile convection-dispersion equation. During the rest period flow ceases, and solute redistributes within the aggregates by diffusion, the key variable being the effective diffusion coefficient, De of the solute in the aggregates, and longitudinally by diffusion within macropores (though this was ignored in the simulation). We estimated De for our porous spheres from observations of solute outflow into finite volumes of stirred distilled water. The theory was validated against experiments on saturated columns for different aggregate-size distributions, flow velocities, and displacement and rest periods, with most parameters estimated independently. Experiments and simulations showed that water savings of 25% were possible under our laboratory conditions, increasing as aggregate size, flow velocity and duration of rest period increased. The potential of intermittent leaching in the field is considered.Type of Medium: Electronic ResourceURL: -
17Articles: DFG German National LicensesStaff View
ISSN: 1365-2389Source: Blackwell Publishing Journal Backfiles 1879-2005Topics: GeosciencesAgriculture, Forestry, Horticulture, Fishery, Domestic Science, NutritionType of Medium: Electronic ResourceURL: -
18Articles: DFG German National LicensesStaff View
ISSN: 1365-2389Source: Blackwell Publishing Journal Backfiles 1879-2005Topics: GeosciencesAgriculture, Forestry, Horticulture, Fishery, Domestic Science, NutritionType of Medium: Electronic ResourceURL: -
19Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The depth profile of the chemical composition in InxGa1−xAs single quantum wells (SQWs), epitaxially grown onto a GaAs[001] substrate and covered by a GaAs cap layer, has been determined by use of grazing incidence diffraction (GID). This method allows the scattering signal from the SQW to be enhanced and the scattering depth to be tailored. The coherently illuminated area is large, due to the small incident angle αi; this makes GID a unique technique for investigating buried thin layers over a lateral length scale of several microns. In the case of very thin SQWs the measurements could be described assuming a Gaussian-like distribution of the In content with depth. The broad In profile seen using this method is in contrast with the sharp monolayer signal achieved by photoluminescence measurements. This can be explained by the assumption of a terracelike In distribution and the very different lateral integration length of both experiments. For thicker SQWs we could verify that at least one of the two interfaces is not sharp but shows a gradient in the chemical composition. © 1997 American Institute of Physics.Type of Medium: Electronic ResourceURL: -
20Articles: DFG German National LicensesStaff View
ISSN: 1089-7550Source: AIP Digital ArchiveTopics: PhysicsNotes: The space-charge limiting current for an intense, magnetized, relativistic electron beam injected into a grounded metallic pipe is investigated with a 2(1/2)-dimensional particle-in-cell code. Comparisons between the simulation results, the well known Bogdankevich-Rukhadze limiting current, and more recent theoretical estimates of the limiting current are presented. Transmitted currents (approximately-greater-than)15% above those predicted by the Bogdankevich–Rukhadze and other limiting current estimates are observed. However, good agreement between the simulation results and the analytic estimates of Uhm [Phys. Fluids B 5, 1919 (1993)] and Fessenden [Lawrence Livermore Lab. Rep. No. UCID-16527 (1974)] is found. For an injected current above the limiting value, a virtual cathode is formed which alters the transmitted current density profile of the beam. A theoretical estimate of the magnitude of the transmitted current under this condition is compared with simulation results. The predicted transmitted current is found to be valid only for injected currents slightly above the limiting current. In addition, the transition between vacuum and ion-focused-regime transport, with and without an applied axial magnetic field is simulated. For ion-focus-regime densities (np ∼ nb), the effect of the virtual cathode in limiting the beam transmission is greatly diminished as expected. © 1995 American Institute of Physics.Type of Medium: Electronic ResourceURL: