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  • 1
    Electronic Resource
    Electronic Resource
    Experimental verification of the smooth-approximation theory for a space-charge dominated beam in an axisymmetric periodic focusing channel (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 76 (1994), S. 3970-3974 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The predictions of the smooth-approximation theory for the effective radius of a space-charge dominated beam in a periodic solenoid focusing channel were checked experimentally over a wide range of focusing conditions. Electron beams with an energy of 5 keV and currents of 50 to 70 mA were transported through a 5-m-long periodic channel and beam radii were measured by an axially moveable phosphor screen and a charge-coupled device camera. The phase advance of betatron oscillation per period without space-charge, σ0, was varied from σ0=45° to σ0=90°. The tune depression due to space-charge, σ/σ0, was in the range of 0.2–0.3. The theoretical results for average beam radius R¯ over one period and the ratio R¯/Rmax were found to agree with the experimental data to better than 5% when a correction due to spherical aberration was taken into account.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.357369
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  • 2
    Electronic Resource
    Electronic Resource
    Beam diagnostics with localized space-charge waves (1994)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 65 (1994), S. 3444-3448 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: A new method for the diagnostics of charged particle beams by employing localized space-charge waves is presented. The propagation of space-charge waves in the form of localized perturbations can be measured easily and accurately in experiments. The results carry valuable information about many beam parameters such as the wave speed, the geometry factor g for the longitudinal space-charge field, the beam radius, the beam impedance under longitudinal perturbations, etc. The principle of this technique and an experimental example are given in this article.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144520
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  • 3
    Electronic Resource
    Electronic Resource
    Experiments on space-charge waves in electron beams propagating through a resistive-wall channel (1999)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 86 (1999), S. 1699-1709 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Localized longitudinal space-charge waves in a transport channel with a resistive wall are investigated experimentally. The space-charge waves with various pulse widths are generated in electron beams with energies of 3.0–8.5 keV and currents of 30–135 mA, and they are transported through a resistive channel with a resistance of 5–10 kΩ and a length of 1 m. The resistive channel, made of a glass tube with a resistive material coating, is surrounded by a long solenoid which provides the focusing for the beam. The localized space-charge waves are measured with current monitors and energy analyzers at the entrance and exit of the resistive channel, and the wave-amplitude growth and damping rates are determined. The measured results are compared with the theory in the long-wavelength range. For localized waves with short widths, where the long-wavelength approximation is not valid any more, dispersion and distributed capacitance effects on the growth/damping rates are discussed. In addition, preliminary results on the energy width measurements of space-charge waves are presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.370950
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  • 4
    Electronic Resource
    Electronic Resource
    Comparison of Zakharov simulation and open boundary Vlasov simulation of strong Langmuir turbulence (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 111-121 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Both Zakharov equations and Vlasov equations are solved numerically to study the strong Langmuir turbulence developed in a plasma driven by an external pump field oscillating at the plasma frequency. A steady state turbulence in Vlasov simulations is reached by using open boundary conditions under which hot particles generated by strong caviton fields are replaced by initial cold Maxwellian particles when they cross the boundaries of simulation domain. A similar steady turbulent state in Zakharov simulations is easily achieved by implementing a phenomenological damping model and using periodic boundary conditions. Simulation results of these two different models are compared and investigated. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871837
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  • 5
    Electronic Resource
    Electronic Resource
    Vlasov simulation of modulational instability and Langmuir collapse (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 1129-1139 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Vlasov simulations are developed to study the one-dimensional modulational instability and Langmuir collapse in a plasma driven by an external field. Both electrons and ions in the plasma are described by the Vlasov equations. The external driving field energy density is ∼10−3 times the initial electron thermal energy density. The plasma has a mass ratio of mi/me=1836, and a temperature ratio of Ti/Te=0.1 or 1.0, where mi, me, Ti, and Te are the ion mass, electron mass, ion temperature, and electron temperature. The modulational instability is saturated by the formation of Langmuir cavitons which later collapse and burn out due to the strong wave–particle interactions. The particle heating during a single Langmuir collapse is small under this weak driving field. The accelerated electron and ion jet-like streams in phase space as well as the nucleation of cavitons are observed during the evolution. Zakharov equations with the same parameters and similar initial conditions are also simulated, and the results are compared with those of the Vlasov simulations. The two models agree with each other quantitatively up to the first collapse following the saturation of exponential growth; dynamic differences appear after the first collapse. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871391
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  • 6
    Electronic Resource
    Electronic Resource
    Longitudinal space-charge waves and instabilities in intense beams : The 39th annual meeting of division of plasma physics of APS (1998)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 5 (1998), S. 2064-2070 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Space-charge effects and collective behavior play an important role in the dynamics of intense beams for accelerator applications. One of the research issues is the longitudinal space-charge waves and instabilities in high current accelerators. At the University of Maryland, an experimental program has been conducted to systematically study space-charge waves and longitudinal instabilities in space-charge dominated electron beams. This includes the generation of localized space-charge waves in an active device; the propagation and end reflection of space-charge waves in a conducting transport channel; and the longitudinal instabilities in a resistive-wall channel. This paper reports and discuss our experimental results. © 1998 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.872878
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  • 7
    Electronic Resource
    Electronic Resource
    One-dimensional simulations of Langmuir collapse in a radiation-driven plasma (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 2531-2546 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Langmuir collapse in a radiation-driven plasma is simulated in one dimension using both the hybrid Vlasov model and the modified Zakharov model. In the hybrid model, the electrons are described by the Vlasov equation and the ions are described by the fluid equations. Two numerical runs with different parameters are performed: (a) a weakly driven case, and (b) a strongly driven case. The comparisons of the results between the two models for each case are carried out in detail. It is found that the dynamic behavior of the plasma can be changed dramatically by varying the external driving field. The electron temperature increases only ∼10% in the weakly driven case, while it increases ∼200% in the strongly driven case during a single Langmuir collapse. The two models agree with each other during the first collapse after the saturation of modulational instability. Dynamic differences appear after the first collapse, caused by the electron heating in the hybrid model, which is not accounted for in the standard isothermal Zakharov model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870581
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  • 8
    Electronic Resource
    Electronic Resource
    Space-charge solitary waves in charged particle beams in resistive-wall transport channels (1996)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 3 (1996), S. 669-672 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The properties of solitary waves in space-charge dominated charged particle beams are investigated theoretically. Similarly to linear space-charge waves, both slow and fast solitary waves can exist. In a dissipative environment, e.g. a resistive-wall channel, it is shown that the slow space-charge solitary waves grow in amplitude, while the fast space-charge solitary waves decay. However, the growth and decay rates differ from those of the linear waves. A possible experiment with an electron beam is proposed to demonstrate these phenomena. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871893
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  • 9
    Electronic Resource
    Electronic Resource
    Longitudinal instability of space-charge dominated beams in transport channels with complex wall impedances (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 2286-2294 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The longitudinal instability of space-charge dominated beams in transport channels with complex wall impedances is studied. The dispersion equation, derived from the one-dimensional Vlasov equation, characterizes the instability with all the relevant parameters including the space charge, the beam energy spread, the real and imaginary parts of the complex wall impedances. For a beam without energy spread, the growth rates of the instability in the different parameter ranges are discussed. The application of the theory to a resistive-wall channel and to a channel with induction gaps is presented. For a beam with energy spread, Lorentzian and Gaussian distributions are treated and the results presented illustrate the dependence of the stable regions on the beam perveance, the energy spread and the wall properties.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860763
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  • 10
    Electronic Resource
    Electronic Resource
    Y-Ba-Cu-O superconducting fibers and wires by spray pyrolysis on carbon fibers (1990)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 67 (1990), S. 2160-2162 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Superconducting YBa2 Cu3 O7−x fibers and wires have been prepared by spray pyrolysis of metal nitrate precursors on a commercial carbon fiber substrate, followed by heating in air and annealing in O2. The fibers were characterized by x-ray diffraction, scanning electron microscope, and Tc and Jc measurements. The fibers consisted of well-aligned crystals and no carbon, with a Tc (zero) of 82 K and a Jc of 2150 A/cm2 in zero field. Ag-doped fibers were fabricated by adding AgNO3 in the precursor solution, and the Jc value nearly doubled with the addition of 4 wt. % Ag.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.345554
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