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  • 1
    Electronic Resource
    Electronic Resource
    Ballistic transport and solenoidal focusing of intense ion beams for inertial confinement fusion (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 72 (1992), S. 395-404 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 Resource
    URL: http://dx.doi.org/10.1063/1.351867
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  • 2
    Electronic Resource
    Electronic Resource
    Effect of time-of-flight bunching on efficiency of light-ion-beam inertial-confinement-fusion transport schemes (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4402-4414 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The Laboratory Microfusion Facility (LMF) has been proposed for the study of high-gain, high-yield inertial-confinement-fusion targets. The light-ion LMF approach uses a multimodular system with applied-B extraction diodes as ion sources. A number of ion-beam transport and focusing schemes are being considered to deliver the beams from the diodes to the target. These include ballistic transport with solenoidal lens focusing, z-discharge channel transport, and wire-guided transport. The energy transport efficiency ηt has been defined and calculated as a function of various system parameters so that point designs can be developed for each scheme. The analysis takes into account target requirements and realistic constraints on diode operation, beam transport, and packing. The effect on ηt of voltage ramping for time-of-flight beam bunching during transport is considered here. Although only 5 mrad microdivergence calculations are presented here, results for bunching factors of ≤3 show that transport efficiencies of (approximately-greater-than)50% can be obtained for all three systems within a range of system parameters which seem achievable (i.e., for diode microdivergence within 5–10 mrad, for diode radius within 10–15 cm, and for diode-ion-current density within 2–10 kA/cm2). In particular, the point design for the baseline LMF system using ballistic transport with solenoidal lens focusing and a bunching factor of 2 was calculated to have ηt=84%. Other factors affecting the overall system efficiency, but not included in the analysis, are also identified and estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355984
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  • 3
    Electronic Resource
    Electronic Resource
    A photoemission study of cluster growth and morphology on inert substrates (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 7333-7341 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Thin metal overlayer growth on solid xenon was characterized by means of synchrotron radiation photoemission spectroscopy. We employed a simple experimental arrangement in which a closed-cycle refrigerator and in situ evaporated metal films were used as substrate for Xe condensation. A "sandwich'' geometry, in which the overlayer metal was used as substrate for Xe condensation, simplified the isolation of metal and Xe emission features. The evolution of the Xe and metal photoemission intensity and the line shape of core and valence states, as a function of metal coverage, were used to estimate average particle size and nucleation site density. The coverage dependence of the Sm 4f binding energy, as well as a number of newly identified spectral fingerprints of particle coalescence, support the measured film morphology and particle size.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349752
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  • 4
    Electronic Resource
    Electronic Resource
    Wire-guided transport of intense ion beams (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 69 (1991), S. 639-655 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 a wire-guided transport system that uses the azimuthal magnetic field, produced by a current driven through a thin wire, to radially confine the ion beam. Ion orbits are studied to determine the injection efficiency (i.e., the fraction of the beam which is transported) under various conditions. Some ions hit the wire because of too small angular momentum at injection; others hit the wire or are lost to large radius during transport because of chaotic orbit behavior induced by a small number of return-current wires close to the beam envelope. For a multimodular scheme (10–30 beams), individual transport system are packed around the target at some standoff distance. The fraction of the beam which is lost in this field-free standoff region is also evaluated under various conditions. The standoff efficiency is then combined with the injection efficiency to give the dependence of the total transport efficiency, ηt, on diode, focusing, transport, and standoff parameters. It is found that ηt can be as large as about 60% for parameter values which appear to be achievable.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.347344
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  • 5
    Electronic Resource
    Electronic Resource
    Gas breakdown effects in the generation and transport of light ion beams for fusion (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 2113-2121 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The efficiency of delivering an ion beam to an inertial confinement fusion target depends on the ability to control the breakdown of both unintended (in the "vacuum'' diode region) and intended (in the transport region) gas. The desorption and breakdown of anode-surface contaminants in an ion diode complicates the generation of a pure, high-brightness ion beam. Beyond the accelerator, the gas in the reactor vessel must provide excellent charge neutralization and specified current neutralization to permit the beam transport and focusing to a 〈1 cm radius, spherical target. Two schemes, in which controlling gas breakdown is essential, are "ballistic'' and "self-pinched'' ion transport. Results are discussed from hybrid particle-fluid simulations of anode contaminant desorption and ion beam transport. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871663
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  • 6
    Electronic Resource
    Electronic Resource
    Interaction of intense MeV light-ion beams with low-pressure gasesf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1700-1707 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 Resource
    URL: http://dx.doi.org/10.1063/1.870673
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  • 7
    Electronic Resource
    Electronic Resource
    Simulation of charged-particle beam transport in a gas using a hybrid particle-fluid plasma model (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 764-773 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The simulation of charged-particle beam transport in a ∼1 Torr gas requires accurate plasma-electron modeling. A simple resistive model, which assumes local energy deposition and a thermal plasma-electron distribution, is inadequate. A hybrid model has been implemented into the particle-in-cell simulation code, iprop (The iprop Three-Dimensional Beam Propagation Code, AMRC-R-966, available from D. Welch, Mission Research Corporation, 1720 Randolph Road SE, Albuquerque, NM 87106, September 1987), in which plasma electrons are divided into high-energy macroparticle and thermal-fluid components. This model, which includes "knock-on'' bound-electron collision and runaway sources for high-energy electrons, is then used in the simulation of relativistic electron-beam and ion-beam experiments. Results are found to be in agreement with HERMES III [Performance of the HERMES III Gamma Ray Simulator, in Digest of Technical Papers, 7th IEEE Pulsed Power Conference, Monterey, CA, 11 June 1989 (Institute of Electrical and Electronic Engineers, New York, 1989), pp. 26–31] and GAMBLE II [Phys. Rev. Lett. 70, 2573 (1993)] experimental observables.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870768
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  • 8
    Electronic Resource
    Electronic Resource
    Implications of high-energy photons and electrons on target preheat at the Sandia "Z" facility : 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. 566-568 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: High-energy photons and electrons on the Sandia National Laboratories "Z" accelerator, a z-pinch device, will deposit energy into a capsule and fuel; this may create a potential preheat problem for inertial confinement infusion (ICF). In this article we discuss heating of the capsule and fuel by high-energy photons and electrons. The fuel is heated to 〈2 eV, in a time-integrated sense, on Z by these particles. Because peak implosion occurs at the peak in the soft x-ray emission on Z, the heating at times of interest is reduced roughly an order of magnitude to ∼0.2 eV for times of interest and fuel preheat from this mechanism is concluded to be small. These estimates are generated from time-integrated bremsstrahlung measurements. The uncertainty in the heating is high because the electron spectrum is not known directly, but inferred. In addition, the influence of photons and electrons at energies between 5 and 60 keV is not known. Given the uncertainties at this point, we do not know the impact on the feasibility of internal dynamic hohlraums for a z-pinch-driven ICF implosion. We discuss these issues and suggest directions for further study. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1149445
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  • 9
    Electronic Resource
    Electronic Resource
    Effect of strain relaxation on forward bias dark currents in GaAs/InGaAs multiquantum well p–i–n diodes (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 5815-5820 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of the dislocation line density produced by the relaxation of strain in GaAs/InxGa1−xAs multiquantum wells where x=0.155–0.23 has been studied. There is a strong correlation between the dark line density, observed by cathodoluminescence, before processing of the wafers into photodiode devices, and the subsequent low forward bias (〈1.5 V) dark current densities of the devices. A comparison is made of the correlation between the reverse bias current density and dark line density and it is found that, in this range of strain, the forward bias current density varies more. Two growth methods, molecular beam epitaxy and metal organic vapor phase epitaxy, have been used to produce the wafers and no difference between the growth methods has been found in dark line or current density variations with strain. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363574
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  • 10
    Electronic Resource
    Electronic Resource
    Search for a proximity effect induced gap in gold/high Tc junctions (1991)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 58 (1991), S. 1332-1334 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We have used high-resolution photoemission spectroscopy to search for a proximity effect induced superconducting gap in gold overlayers on c-axis single crystals of Bi2Sr2CaCu2O8 and a-axis thin films of YBa2Cu3O7. These two junction types give us a representative sampling of very well characterized near-ideal interfaces (gold/c-axis Bi2Sr2CaCu2O8) and junctions in which the geometry more strongly favors the existence of the proximity effect but the interfacial quality may not be as ideal (gold/a-axis YBa2Cu3O7). In neither of these junction types did we observe any evidence for a proximity effect induced gap, and we place an upper limit of approximately 5 meV on its existence in the junctions that we have studied.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.104301
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