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  • 11
    Electronic Resource
    Electronic Resource
    Space charge instabilities in gyrotron beams (1994)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 1 (1994), S. 714-729 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Space charge instabilities in gyrotron electron beams are studied via both the solution of the linear dispersion equation and by nonlinear particle simulation. The linear analysis addresses the stabilizing effects of energy spread in the beam and the inhomogeneity of the external magnetic field. The nonlinear multifrequency simulation demonstrates that for a uniform magnetic field, the energy spread induced by many unstable waves will be larger than the corresponding spread induced by a single unstable wave. This emphasizes the need to design electron guns that are stable to this mode.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.870817
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  • 12
    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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  • 13
    Electronic Resource
    Electronic Resource
    Propagation of wiggler focused relativistic sheet electron beams (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 6-11 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A recent design concept for millimeter-wave free-electron lasers [J. Appl. Phys. 60, 521 (1986)] would require the stable propagation of a sheet electron beam through a narrow waveguide channel. Experimental results reported in this article support the feasibility of such a configuration by demonstrating the stable propagation of relativistic sheet electron beams through a narrow waveguide gap (3.2 mm) using focusing by a short-period electromagnet wiggler. 90% of the electron current in a 100-keV sheet electron beam was transmitted through a 5-cm-long channel with peak wiggler fields of 800 G. Almost 80% of a 400-keV beam was similarly confined with a 1600-G wiggler field. The data were consistent with single electron trajectory models, indicating that space-charge effects were minimal. No evidence of beam breakup or filamentation instabilities was observed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341221
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  • 14
    Electronic Resource
    Electronic Resource
    Spontaneous radiation of an electron beam in a free-electron laser with a quadrupole wiggler (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 60 (1986), S. 1584-1590 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A calculation is presented of spontaneous radiation emitted by an electron beam passing through a continuously rotating quadrupole magnetic undulator. It is shown that radiation spectrum emitted in forward direction of beam propagation has four peaks, corresponding to four betatron frequencies. Utilizing the Madey theorem, a stimulated emission is calculated and presented as gain versus frequency curves, for different values of the quadrupole magnetic field. A free-electron laser operating at two or three radiation frequencies with a quadrupole magnetic wiggler is suggested.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.337295
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  • 15
    Electronic Resource
    Electronic Resource
    Electron orbits in combined rotating quadrupole and dipole magnetic fields (1986)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 59 (1986), S. 2634-2637 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The single-particle trajectories of relativistic electrons in a magnetic field configuration which consist of a periodic wiggler field produced by a helical winding of two wires ("dipole'' magnetic field) superimposed on a helical winding of four wires (continuously rotating "quadrupole'' magnetic field) are studied. The orbit equations can be reduced to a system of linear, inhomogeneous differential equations for variables related to transverse velocities. These equations are solved exactly and the stability region for the electron orbits in wide range of the parameters is obtained.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336966
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  • 16
    Electronic Resource
    Electronic Resource
    Nonlinear analyses for optimized short-period-wiggler free-electron laser oscillators (1989)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 65 (1989), S. 1453-1459 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Procedures to determine the parameters of optimized (for maximum efficiency) experimental short-period-wiggler free-electron laser (FEL) oscillators are presented. The calculations are based on a normalized set of nonlinear equations which describe a one-dimensional FEL oscillator. Scaling formulas relating the normalized theoretical parameters to dimensional experimental quantities are obtained. The physics of such realistic effects as waveguide dispersion, wiggler field dependence on magnet gap, beam energy spread, and the frequency tunability of tapered wigglers are considered. Finally, specific examples for both tapered and untapered 300-GHz, 1.0-MW FEL oscillators are calculated and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.342958
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  • 17
    Electronic Resource
    Electronic Resource
    Experimental realization of millimeter-wave amplification by a sheet beam free electron laser (1994)
    Woodbury, NY : American Institute of Physics (AIP)
    Applied Physics Letters 64 (1994), S. 1439-1441 
    Details
    ISSN: 1077-3118
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report an observation of millimeter-wave (94 GHz) amplification in a sheet beam, short period, planar wiggler, free electron laser amplifier. The observed gain is about 5 dB for a 530 keV, 4 A beam through a 54 cm wiggler. Wave energy absorption was also observed when the beam energy is off-resonance. Experimental results are in good agreement with numerical simulation. This amplifier configuration has potential for producing equally high output power but at relatively low voltage compared with longer period free electron lasers.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.111909
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  • 18
    Electronic Resource
    Electronic Resource
    Self-focusing and Raman scattering of laser pulses in tenuous plasmas (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 1440-1452 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The propagation and self-focusing of short, intense laser pulses in a tenuous plasma is studied both analytically and numerically. Specifically, pulses of length of the order of a few plasma wavelengths and of intensity, which is large enough for relativistic self-focusing to occur, are considered. Such pulses are of interest in various laser plasma acceleration schemes. It is found that these pulses are likely to be strongly affected by Raman instabilities. Two different regimes of instability, corresponding to large and small scattering angles, are found to be important. Small-angle scattering is perhaps the most severe since it couples strongly with relativistic self-focusing, leading the pulses to acquire significant axial and transverse structure in a time of the order of the self-focusing time. Thus it will be difficult to propagate smooth self-focused pulses through tenuous plasmas for distances longer than the Rayleigh length, except for pulse duration of the order of the plasma period.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860884
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  • 19
    Electronic Resource
    Electronic Resource
    Nonlinear theory of stable, efficient operation of a gyrotron at cyclotron harmonics (1993)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 5 (1993), S. 4473-4485 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: One of the main obstacles in achieving stable, efficient operation at the cyclotron harmonics in a gyrotron is mode competition with parasitic modes at the fundamental frequency. In this article, the nonlinear dynamics of mode interactions in such a system are studied using a multifrequency, time-dependent model. The results of numerical simulations for a second harmonic gyrotron are presented by considering two starting scenarios: (a) fast voltage rise or an instant turn-on case, and (b) slow voltage rise case. For the first case, it is demonstrated that for a certain range of operating parameters, the presence of a parasitic mode at the fundamental can be helpful in the excitation of the second harmonic operating mode. In the second case, it is found that the unstable operating region increases with the value of the rise time constant of the electrode voltages. Stable, efficient gyrotron operation at the second harmonic is demonstrated using the numerical study.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.860562
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  • 20
    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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