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  • 1
    Electronic Resource
    Electronic Resource
    Beam breakup growth and reduction experiments in long-pulse electron beam transport (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 1258-1266 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The results of an experimental program whose sole objective is to investigate the cumulative beam breakup instability (BBU) in electron beam accelerators are presented. The BBU growth rate scalings are examined with regard to beam current, focusing field, cavity Q, and propagation distance. A microwave cavity array was designed and fabricated to excite and measure the cumulative BBU resulting from beam interactions with the deflecting TM110 cavity mode. One phase of this experiment used high Q(≈1000) cavities with relatively large frequency spread (Δf/f0≈0.1%). The observed TM110 mode microwave growth between an upstream (second) and a downstream (tenth) cavity indicated BBU growth of 26 dB for an electron beam of kinetic energy of 750 keV, 45 A, and focused by a 1.1 kG solenoidal field. At beam currents of less than 100 A the experiments agreed well with a two-dimensional continuum theory; the agreement was worse at higher beam currents ((approximately-greater-than)100 A) due to beam loading. The second-phase experiments used lower Q(≈200) cavities with relatively low frequency spread (Δf/f0≈0.03%). Theory and experiment agreed well for beam currents up to 220 A. Distance scaling experiments were also performed by doubling the propagation length. Instability growth reduction experiments using the technique of external cavity coupling resulted in a factor of four decrease in energy in BBU growth when seven internal beam cavities were coupled by microwave cable to seven identical external dummy cavities. A theory invoking power sharing between the internal beam cavities and the external dummy cavities was used to explain the experimental reduction with excellent agreement using an equivalent circuit model.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.356429
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  • 2
    Electronic Resource
    Electronic Resource
    The beam breakup instability in quadrupole and solenoidal electron-beam transport systems (1992)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 71 (1992), S. 3091-3102 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Dispersion relations are derived to determine the growth rate, dominant wavelength, and group velocity of disturbances caused by the beam breakup instability. Considerations include weak and strong focusing, x-y coupling in solenoidal transport, the spacing of accelerator cavities, and periodically pulsed beams. Beam breakup growth is minimum when the cavity spacing equals an integral number of half-betatron wavelengths for quadrupole focusing, and an integral number of betatron wavelengths for solenoidal focusing. Minimum growth is also found for periodic pulses separated by an integral number of half-periods of the TM110 cavity mode. Expressions for beam breakup growth at the minima are obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.351000
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  • 3
    Electronic Resource
    Electronic Resource
    Electron-beam-induced acoustic-wave enhancement of gaseous combustion (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 782-791 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The combustion rate of premixed gases in a closed vessel was increased by injecting a high-current electron beam into the gas mixture within about 20 ms of spark ignition. This effect was observed with the fuels ethylene, methane, ethane, propane, and n-butane. Experimental results provide strong evidence that e-beam excitation of the fundamental longitudinal-acoustic mode of the cylindrical chamber is the mechanism of combustion enhancement. An observable combustion enhancement required that the amplitude of the fluid velocity oscillation in this acoustic mode be greater than or approximately equal to the flame propagation speed and was associated with a wrinkled or cellular flame structure with dimensions on the order of 1/2 cm. These results are in good agreement with values for the threshold acoustic velocity amplitude and dimension of cellular structure predicted for a periodically accelerated flame.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.343068
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  • 4
    Electronic Resource
    Electronic Resource
    Radial oscillations and the ion hose instability of an electron beam propagating in a periodic ion channel (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 634-640 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Recently, the propagation of an electron beam through an ion channel with periodically varying ion density has been proposed as a method of transporting or modulating an electron beam. A theoretical treatment indicates that, in the absence of an external magnetic field, cylindrically symmetric radial oscillations of the beam electrons are excited by the channel, with resonant excitation occurring when the wavelength of the ion density variation equals the betatron wavelength. An analysis of the ion focusing regime (IFR) ion hose instability indicates that the e-folding length of this instability increases when the variations of the electron density are increased. In the absence of an external magnetic field and damping, moderate electron density variations (caused, for example, by a periodic ion channel or the nonrigidity of the beam and channel) result in a wavelength and e-folding length on the order of the beam-averaged betatron wavelength.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866793
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  • 5
    Electronic Resource
    Electronic Resource
    Undulation of a magnetized electron beam by a periodic ion channel (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3127-3129 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Electron-beam dynamics are calculated for an electron beam propagating parallel to a uniform magnetic field through a periodic ion density channel. Results show that resonant excitation of transverse electron oscillations occurs when the wavelength of the ion density variation equals the axial distance over which an electron cyclotron orbit occurs. This indicates that a periodic ion channel behaves as an electrostatic undulator with magnetoresonance. It is found that periodic ion densities of 1011–1012 cm−3 are required to achieve transverse electron velocities comparable to those of a typical magnetostatic undulator.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866969
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  • 6
    Electronic Resource
    Electronic Resource
    Transport and stability of long-pulse relativistic electron beams in UV laser-induced ion channels (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 430-434 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Results are presented for the first experiments in which long-pulse (0.4–1 μsec), relativistic (0.8 MV) electron beams have been transported in the ion focused regime (IFR) in ion channels formed in low pressure diethylaniline gas by means of KrF excimer laser-induced ionization. These experiments demonstrate that the most efficient (50%–80%) and longest pulse (0.6 μsec) e-beam transport is obtained with laser-induced channels over a very narrow gas pressure range (0.3–1.7 mTorr). Higher than optimal pressures cause excess e-beam-induced ionization and instability of the electron beam. At lower pressures, the laser-induced ion channel density is insufficient for initial e-beam guidance. Transverse oscillations of the electron beam have been measured at a frequency close to that predicted for the ion hose instability. The growth length and wavelength of the transverse oscillations are comparable to the betatron wavelength, further suggesting that these oscillations result from the ion hose instability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859157
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  • 7
    Electronic Resource
    Electronic Resource
    The influence of damping on the ion hose instability (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 2006-2008 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The ion hose instability in the ion-focused regime is analyzed using a rigid beam model with phenomenological damping terms. Values of the instability wavelength, e-folding length, and group velocity are calculated and compared with numerical results. The impulse response function for this model is also obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866648
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  • 8
    Electronic Resource
    Electronic Resource
    Holographic interferograms from laser fusion code simulations (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 1569-1575 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The simulation of interferograms for laser fusion-type targets is described. Three-dimensional ray-tracing postprocessors to the two-dimensional hydrodynamic codes lasnex and sage are used for this purpose. Simulated interferograms can then be directly compared with experimentally obtained interferograms, thus providing insight into various aspects of target physics, such as anisotropic thermal transport and details of the hydrodynamic flow. The method is illustrated for two specific KMS microdisk target shots diagnosed with double-exposure holographic interferometry.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860464
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  • 9
    Electronic Resource
    Electronic Resource
    Collision and interpenetration of plasmas created by laser-illuminated disks (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 979-988 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Supersonic, counterstreaming plasmas were produced by ablating plasma from the inside surfaces of two parallel disks made of aluminum and magnesium, respectively, with a 0.53 μm laser at an intensity of 1014 W/cm2 for 1.3 nsec. Diagnostics included holographic interferometry, a time-integrated x-ray pinhole camera and a gated x-ray crystal spectrograph with imaging slits. The plasmas interpenetrate for the first half of the laser pulse but stagnate once the electron density exceeds 5×1020 cm−3. Spectroscopic measurements suggest a coronal electron temperature of ∼800 eV and an ion temperature of ∼15 keV in the stagnated plasma. The observations are in good agreement with a two ion fluid model of interpenetrating plasmas in which the dominant slowing down process is ion–ion collisions.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860114
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  • 10
    Electronic Resource
    Electronic Resource
    Deflection of carbon dioxide laser and helium-neon laser beams in a long-pulse relativistic electron beam diode (1991)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 62 (1991), S. 1776-1782 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: Deflection of carbon dioxide and helium-neon laser beams has been used to measure plasma and neutral density gradients during the operating mode and after the shorting time of a long-pulse field-emission electron beam diode. Plasma density gradients of (1014–1015) cm−4 were observed throughout the diode during the final microsecond of the 2–3 μs electron beam pulse. The neutral density gradient was less than 1×1018 cm−4 during the electron beam pulse. Upon diode shorting, neutral density gradients increased to (1018–1019) cm−4 over ∼1 μs, and decayed over many microseconds. Plasma density gradients of ∼1015 cm−4 were also observed after shorting. These experiments demonstrate the value of carbon-dioxide laser and helium-neon laser deflection for diagnosing plasma and neutral particles in long-pulse electron beam diodes.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1142421
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