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  • 1
    Electronic Resource
    Electronic Resource
    Periodic magnetic focusing of sheet electron beamsf| (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 1714-1720 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Sheet electron beams focused by periodically cusped magnetic (PCM) fields are stable against low-frequency velocity-shear instabilities (such as the diocotron mode). This is in contrast to the more familiar unstable behavior in uniform solenoidal magnetic fields. A period-averaged analytic model shows that a PCM-focused beam is stabilized by ponderomotive forces for short PCM periods. Numerical particle simulations for a semi-infinite sheet beam verify this prediction and also indicate diocotron stability for long PCM periods is less constraining than providing for space-charge confinement and trajectory stability in the PCM focusing system. In this article the issue of beam matching and side focusing for sheet beams of finite width is also discussed. A review of past and present theoretical and experimental investigations of sheet-beam transport is presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870675
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  • 2
    Electronic Resource
    Electronic Resource
    Theory of relativistic backward wave oscillators operating near cutoff (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 730-740 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A numerical model for analyzing backward-wave oscillators (BWOs) operating near the upper edge of the transmission band is presented. The model is used to calculate starting currents for two finite length devices, an X-band BWO (f=8.4 GHz) and a J-band BWO (f=5.5 GHz). The operating frequency and efficiency predicted by the nonlinear numerical simulations are compared with experimental data for each device.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870818
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    Paper (German National Licenses)
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  • 3
    Electronic Resource
    Electronic Resource
    Adjustable resonant cavity for measuring the complex permittivity of dielectric materials (2000)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 71 (2000), S. 3207-3209 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An adjustable resonance cavity was developed to measure the complex permittivity of dielectric materials. The cavity has an inner diameter of 16.400 cm and an inner height of 2.54 cm. The aluminum stationary wall holder was positioned about 10.8 cm above the top of the cavity. It was fixed into place by three 1.27-cm-diam linear shafts. By suspending from the wall holder, the movable wall moved vertically by sliding on 1.27 cm bore-closed ball bushings. By turning a 1 in.-12 nut, the movable wall could be positioned so that the cavity height equaled the height of the sample. Therefore, this enables the measurement of the permittivity of samples with heights between 0.88 and 1.91 cm and radius between 1.27 and 3.18 cm. The complex permittivity of the sample was calculated based upon the sample dimensions, central frequency of TMono modes, and Q factor of the resonance curve using an exact solution. The complex permittivity was measured at the three lowest modes, where the frequency span is 1–4 GHz. © 2000 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1304865
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  • 4
    Electronic Resource
    Electronic Resource
    A dielectric mixing law for porous ceramics based on fractal boundaries (1996)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 80 (1996), S. 3992-4000 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The effect of porosity on the complex dielectric permittivity of microwave sintered zinc oxide at room temperature and 2.45 GHz is reported. The predictions of conventional Maxwell–Garnet theory and the effective medium approximation are in poor agreement with the experimental results. Various methods are employed to investigate the system in an effort to come up with new mixing laws, including combinations of these two analytic theories and finite difference electromagnetic simulations of representative microstructures. A model that assumes the existence of dielectrically inactive, fractal-geometry boundaries between ceramic grains provides an excellent description of the results with no free parameters. It gives physical insight into the experimentally observed mixing law. © 1996 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.363357
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    Paper (German National Licenses)
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  • 5
    Electronic Resource
    Electronic Resource
    Observation of a resonant enhancement of microwave radiation from a gas-filled backward wave oscillator (1988)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 53 (1988), S. 559-561 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: High-power microwave radiation at 8 GHz from a gas-filled backward wave oscillator driven by an intense relativistic electron beam has been measured. It has been observed that an order of magnitude resonant increase in microwave output power occurs at a particular pressure of the background gas. This resonance has also been observed to be strongly dependent on the value of applied axial magnetic field. Possible explanations for the observed results are discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.99856
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  • 6
    Electronic Resource
    Electronic Resource
    Novel method for determining the electromagnetic dispersion relation of periodic slow wave structures (1990)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 57 (1990), S. 1304-1306 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A novel method for calculating the dispersion relation of electromagnetic modes in an arbitrary periodic slow wave structure is reported. In this method it is sufficient to know the frequencies corresponding to three special wave number values, with other points calculated using an approximate analytical expression. This technique was successfully applied to determine the dispersion relation of the TM01 mode in a sinusoidally corrugated slow wave structure. This structure is commonly used in relativistic high-power backward wave oscillators and traveling-wave tubes, and is expected to have many additional applications.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.103466
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  • 7
    Electronic Resource
    Electronic Resource
    Wiggler focused relativistic sheet beam propagation in a planar free-electron laser configuration (1989)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 55 (1989), S. 2069-2071 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation of a relativistic sheet electron beam through a spatially periodic magnetic field (wiggler) has been studied experimentally. The wiggler serves two purposes; it provides beam focusing as well as the magnetostatic pump for the free-electron laser (FEL) interaction. Experiments conducted to study sheet beam generation and propagation in a short-period (1 cm) planar wiggler are presented. A 500 keV, 7 A sheet electron beam was propagated through a 3.2 mm waveguide with negligible losses due to intercepted current. In addition, the first observation of wiggler-induced radiation was obtained from the sheet beam FEL in a short-period wiggler oscillator configuration.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.102108
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  • 8
    Electronic Resource
    Electronic Resource
    Relativistic plasma microwave electronics: Studies of high-power plasma-filled backward-wave oscillators (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2286-2292 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The area of relativistic plasma microwave electronics has only recently generated renewed interest. New experimental data are presented demonstrating that the presence of a low-density background plasma in a relativistic backward-wave oscillator leads to several beneficial effects, including (a) enhanced interaction efficiency (40%), (b) operation at very low and possibly zero guiding magnetic field, (c) tunability by controlling the plasma density, (d) high degree of spectral coherency, and (e) operation well above the vacuum limiting current.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860198
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  • 9
    Electronic Resource
    Electronic Resource
    Relativistic backward-wave oscillators operating near cyclotron resonance (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1625-1638 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microwave sources based on backward-wave oscillators (BWO's) driven by relativistic electron beams are capable of producing high-power coherent radiation in the cm and mm wavelength region. When the axial magnetic field used in these devices to confine the electron beam satisfies the condition of cyclotron resonance there is a significant modification in the behavior of BWO due to beam coupling to cyclotron modes. In this paper a time-dependent, self-consistent theory of BWO's is developed, taking into account a possible cyclotron interaction. The analysis of the system near the cyclotron resonance yields the power drop due to the cyclotron absorption effect observed in many BWO experiments. In addition, the theory predicts that there exists a region of magnetic field strength, where an increase in power and efficiency is possible. Depending on the value of the magnetic field and beam coupling to cyclotron mode various regimes of BWO operation are possible, including stable single-frequency oscillations, self-modulation, and a succession of microwave bursts.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860902
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  • 10
    Electronic Resource
    Electronic Resource
    Relativistic backward-wave oscillators: Theory and experiment (1992)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 4 (1992), S. 2293-2299 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Microwave sources based on backward-wave oscillators driven by relativistic electron beams are capable of producing high-power coherent radiation in cm and mm wavelength regime. Although there have been a number of experiments reported over the last decade on this topic, there are only a few publications providing a theoretical description of these devices. Thus, there is a need for theoretical models which can be compared in detail with the experimental data. This work is devoted to fill this need and applied to the University of Maryland backward-wave oscillator experiment. It is shown that the theoretical predictions for the threshold current to start the oscillations, the frequency characteristics, and the efficiency of the device compared favorably with the experimental data.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860199
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