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  • 1
    Electronic Resource
    Electronic Resource
    Net current generation and beam transport efficiency of grad-B-drift transported relativistic electron beams (2001)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 8 (2001), S. 4972-4981 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 Resource
    URL: http://dx.doi.org/10.1063/1.1405437
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  • 2
    Electronic Resource
    Electronic Resource
    Space-charge limited currents in coaxial diodes with electron backscatter (2001)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 90 (2001), S. 4951-4956 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 Resource
    URL: http://dx.doi.org/10.1063/1.1410891
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  • 3
    Electronic Resource
    Electronic Resource
    Very intense pulsed electron beam (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 569-576 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: An intense beam of pulsed electrons has been developed using the extended planar-anode diode to extract and focus the HERMES-III beam in a low-pressure gas cell without anode destruction. Measurements and a simulation model are compared and found in good agreement for focal lengths of ∼7–8 cm. They show that with this source a peak dose (peak dose rate) ∼200 J/g (8×1014 rad/s) in graphite can be generated with useful areas of 70 cm2. For the shorter focal length of ∼11 cm, the model predicts that a peak dose (peak dose rate) of 3800 J/g (1.5×1016 rad/s) can be generated over an area of 5 cm2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357114
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  • 4
    Electronic Resource
    Electronic Resource
    Dynamics of a 700-kA 19-MeV electron beam in a short gas cell (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 472-482 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The transport of the Hermes III annular, 19-MeV, 700-kA, 25-ns, electron beam of radius (approximately-less-than)26 cm and current density (approximately-greater-than)0.4 kA/cm2, through short gas cells filled with N2, is characterized as a function of injection parameters, cell length, and gas pressure. These measurements are compared with predictions of numerical and analytical models. The comparisons confirm the main features of the models and show that the early-time behavior of the beam and gas ionization determines the net current and associated magnetic fields for the entire pulse, particularly at low pressure. The net current is minimized for pressures near 3 Torr and is 4%–7% of the injected current at peak power. Owing to the radial distribution of the net current density, the mean beam trajectory is effectively ballistic at this pressure.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.350680
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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
    Very high-current propagation in the ion-focused to collision-dominated regime (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 404-420 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Measurements and analysis show that the 13 TW, Hermes-III [J. J. Ramirez et al., Digest of Technical Papers, 6th IEEE Pulsed Power Conference (Institute of Electrical and Electronic Engineers, New York, 1987), p. 294], pulsed, electron beam has two windows of stable transport in long drift cells filled with N2 gas terminated by a bremsstrahlung producing target: a low-pressure window (between ∼1 and ∼100 mTorr) that is dominated by propagation in the semicollisionless ion-focused regime (IFR), and a high-pressure window (between ∼1 and ∼100 Torr) that is dominated by propagation in the resistive collisional regime. In the transition region between the two windows, beam plasma–electron instabilities significantly disrupt propagation. Propagation in both regimes (the IFR at early time and the collisional at later time) is observed from ∼5 to ∼100 mTorr, which produces two distinct bremsstrahlung pulses from the single injected beam pulse. As the pressure increases, two-stream instabilities terminate IFR propagation and the associated bremsstrahlung pulse earlier and earlier in time. Above 5 mTorr, the instability is sufficiently quenched by gas collisions that propagation in the collisional regime back in the beam body occurs, leading to a second propagation and associated bremsstrahlung pulse. Above 200 mTorr, the gas breaks down too rapidly for a significant IFR pulse to form, and for higher pressures only a single pulse in the collisional regime is propagated. Reasonable stability in the collisional regime is not achieved until pressures exceed 1 Torr.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870842
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  • 8
    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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  • 9
    Electronic Resource
    Electronic Resource
    Tertiary fusion neutron diagnostic for density-radius product and stability of inertial confinement fusion (1988)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 59 (1988), S. 610-615 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: The fluence of high-energy (〉14 MeV) "secondary'' neutrons, produced in D–T reactions involving suprathermal fuel ions created by elastic scattering with 14-MeV "primary'' neutrons, yields information about the fuel density-radius product (ρR) and the hydrodynamic stability of inertial-confinement fusion (ICF) targets. The suprathermal ions, produced in proportion to the fuel ρR, create secondary neutrons with energies ≤30 MeV when fusing with a thermal ion. The ratio of secondary to primary neutrons determines the mean fuel ρR. Since secondary neutrons, which are mainly formed near the fuel tamper interface with energies 〉24 MeV, are radially directed, the detection of their angular distribution provides a unique measurement of the deviation from spherical geometry of the fuel ρR. Valid for fuel ρR〉0.1 g/cm2 and D–T yield above 1014, this diagnostic would be valuable in upcoming ICF experiments.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1139842
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  • 10
    Electronic Resource
    Electronic Resource
    Steady-state erosion of propagating ion beams (2002)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 9 (2002), S. 1053-1056 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: 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 Resource
    URL: http://dx.doi.org/10.1063/1.1452102
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