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  • 1
    Electronic Resource
    Electronic Resource
    High power operation of first and second harmonic gyrotwystrons (1995)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 78 (1995), S. 550-559 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: We report the first experimental operation of overmoded first and second harmonic gyrotwystron amplifier configurations. Both devices utilize a single cavity which is driven near 9.87 GHz in the TE011 mode, heavily attenuated drift tubes, and long tapered output waveguide sections. A magnetron injection gun produces a 460 kV, 245 A beam with a maximum average perpendicular-to-parallel velocity ratio approximately equal to one. The axial magnetic field profile is sharply tapered in the output section. Peak powers above 21 MW are achieved in 1 μs pulses with an efficiency exceeding 22% and a large signal gain near 24 dB in the first harmonic tube. The second harmonic tube achieves nearly 12 MW of the peak power with an efficiency of 11% and a gain above 21 dB. First harmonic amplifier performance is limited principally by competition from a fundamental mode output waveguide interaction; the second harmonic tube is limited by both travelling wave output modes and by a down-taper oscillation. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.360639
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  • 2
    Electronic Resource
    Electronic Resource
    Amplification studies of a two-cavity second harmonic gyroklystron with a mixed-mode output cavity (1994)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 75 (1994), S. 4721-4730 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of a two-cavity second harmonic gyroklystron employing a short, mixed-mode output cavity with stepped radial transitions is described. The short cavity was employed to prevent low frequency spurious oscillations that can compete with the harmonic signal. The radial rf field profile in the cavity and the output radiation consisted of both the TE01 and TE02 circular waveguide modes. This device produced a peak output power of 20 MW at 19.782 GHz, with an efficiency of 23% and a gain of 26 dB. The nominal mode mixture of the radiated power during optimal operation was found to be about 60% TE02 and 40% TE01. Variations from this ratio are observed at lower powers and are attributed to shifts in the cavity rf field profiles. Systematic studies of amplifier performance as a function of beam parameters and magnetic field profile are described. The sensitivities of output power production to changes in operating parameters are compared to results from earlier harmonic and fundamental gyroklystrons. The present device is found to be more stable to parasitic oscillations and less sensitive to variations in beam current and output cavity magnetic field than previous harmonic gyroklystrons that employed longer, smoothly transitioned cavities. However, both the peak power and efficiency in the present device are lower than the 30 MW at 28% efficiency obtained with the final smooth-cavity tube. The tradeoffs between the two output cavity concepts will be discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.355926
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  • 3
    Electronic Resource
    Electronic Resource
    Experimental studies of stability and amplification in four overmoded, two-cavity gyroklystrons operating at 9.87 GHz (1991)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 70 (1991), S. 2423-2434 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The performance of four overmoded (TE011 circular), two-cavity gyroklystron amplifier tubes operating in X band is reported. A summary of the theoretical design procedure is presented, followed by a description of the experimental setup. The stability and amplification properties of the four gyroklystron tubes are subsequently described, each being modified in sequence to improve performance. The fourth tube produced 2.0–2.7 MW pulses at 9.87 GHz for 0.5–1.0 μs, and exhibited gains of 17–19 dB and efficiencies of 5%. The results were obtained using electron beams with voltages, currents, and computed beam alphas (v⊥/vz) of 407–425 kV, 115–135 A, and 0.8–1.0, respectively. The presence of instabilities in the gun downtaper and drift tube prevented operation at the design point (500 kV, 160 A, and alpha 1.5). The effects of varying input frequency, input power, and beam parameters (voltage, current, magnetic compression) on the amplifier operation are reported. Detailed descriptions of the instabilities observed in the gyroklystrons are presented, and the use of lossy dielectrics to suppress the instabilities is discussed. The amplifier experimental performance is compared with simulations. Improvement schemes are summarized and follow-up experiments are outlined.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.349394
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  • 4
    Electronic Resource
    Electronic Resource
    Theory of relativistic gyro-traveling wave devices (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3494-3510 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Using a Hamiltonian formalism, nonlinear, fully relativistic, multimode, multifrequency equations are derived which describe gyro-traveling wave devices. Nonuniform waveguides and nonlinearly tapered magnetic fields are incorporated into the analysis. The formalism is used to analyze the effect of velocity spread on Doppler upshifted operation. It is shown that with present technology, gyro-traveling wave devices cannot operate far from cutoff if high efficiency is desired. As an example, the analysis is applied to a 10 GHz, 430 kV, 240 A gyrotwistron operating at the fundamental cyclotron harmonic with a tapered wall radius and magnetic field. A realistic design that achieves over 30% efficiency is produced. The issue of stability of this device with respect to competition from parasitic modes is taken up in a companion paper [Phys. Plasmas 2, 3511 (1995)]. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871131
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  • 5
    Electronic Resource
    Electronic Resource
    Modeling and design of millimeter wave gyroklystrons : The 40th annual meeting of the division of plasma physics of the american physical society (1999)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 6 (1999), S. 2233-2240 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: A series of high power, high efficiency Ka-band and W-band gyroklystron experiments has been conducted recently at the Naval Research Laboratory (NRL). Stagger tuning of the cavities for bandwidth enhancement is commonly used in the conventional multicavity klystrons. The desired stagger tuning is usually achieved via mechanical tuning of the individual cavities. However, in the millimeter wave regime, particularly, in the case of the high average power operation, it is desirable to be able to achieve the required stagger tuning by design. The NRL gyroklystron experiments explored the tradeoffs between power, bandwidth, efficiency, and gain to study the effects of large stagger tuning in millimeter wave without resorting to mechanical tuning of the cavities. Both, Ka-band and W-band, experiments demonstrated a record power-bandwidth product. The success of the experiments was due in large part to a battery of improved large-signal, stability, and cold test codes employed in the modeling and design stage. Theoretical models that provide the basis for these design simulation tools and the design methodology will be presented. © 1999 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.873476
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  • 6
    Electronic Resource
    Electronic Resource
    Stability analysis of relativistic gyro-traveling wave devices (1995)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Plasmas 2 (1995), S. 3511-3523 
    Details
    ISSN: 1089-7674
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The stability of parasitic modes in gyro-traveling wave tubes is studied, both with and without the operating mode present. Using a Hamiltonian formalism, linear equations are derived which describe the spatial evolution of parasitic modes in the absence of the operating mode. Complications such as a nonuniform waveguide and tapered magnetic field are taken into account. As an example, the linearized equations are applied to a 10 GHz, 430 kV, gyro-traveling wave tube to determine the start current in the absence of the operating mode. Included in the analysis is the effect of frequency-dependent reflection from the output window. A relatively low start current is found, well below the nominal operating current of 240 A. Multi-mode equations are then derived which can be used to analyze the suppression of parasitic modes by the operating mode. An algorithm is developed that allows efficient computation of the nonlinear start current in this regime. The algorithm is applied to the 10 GHz, 430 kV device mentioned above, and a stable configuration is found. © 1995 American Institute of Physics.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.871132
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  • 7
    Electronic Resource
    Electronic Resource
    Linear analysis of a free-electron laser coupled to betatron oscillations (1989)
    New York, NY : American Institute of Physics (AIP)
    Physics of Fluids 1 (1989), S. 2085-2098 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The dispersion relation is derived for the interaction of a sheet beam propagating between parallel plates in a planar wiggler magnetic field. Instead of the usual free electron laser (FEL) mode, one is considered in which the radiation field is perpendicular to the quiver velocity and couples either to betatron or plasma oscillations. In the cold beam limit, coupling to betatron oscillations leads to an absolute instability. This mode competes with the conventional FEL and can disrupt the beam unless suppressed. The effects of energy spread are investigated, and a critical energy spread is found that suppresses the instability. For ultrarelativistic beams, this energy spread is an exponentially decreasing function of the beam energy. For moderately relativistic high current beams, it is proportional to the square root of the beam current. In this regime, there is a limit to the current that can propagate stably in the FEL circuit. Coupling to plasma oscillations also leads to an instability. However, the instability associated with this mode can be made convective with a suitable choice of parameters, and thus is not particularly dangerous to the conventional FEL. It is, however, interesting because the dispersion relation is characteristic of a second harmonic FEL, even though the wiggler is planar.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.859073
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  • 8
    Electronic Resource
    Electronic Resource
    Linear theory of a sheet beam free electron laser (1988)
    [S.l.] : American Institute of Physics (AIP)
    Physics of Fluids 31 (1988), S. 3379-3386 
    Details
    ISSN: 1089-7666
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The linear theory of a free electron laser based on a sheet beam propagating in a narrow gap is developed. The three-dimensional structure of the radiation field is determined for an infinitely thin sheet beam. Included are the effects of diffraction and space charge. The possibility of diffractive suppression of unwanted modes is discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.866903
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  • 9
    Electronic Resource
    Electronic Resource
    Long coherence length interferometer (1993)
    [S.l.] : American Institute of Physics (AIP)
    Review of Scientific Instruments 64 (1993), S. 1779-1784 
    Details
    ISSN: 1089-7623
    Source: AIP Digital Archive
    Topics: Physics , Electrical Engineering, Measurement and Control Technology
    Notes: An interferometer has been developed which is capable of measuring the envelope of the coherence function of lasers whose mode lifetimes exceed 300 ns, corresponding to lengths over 100 m. The precision of this interferometer is determined to be 6.0%. The interferometer utilizes optical fibers for the purpose of optical delay. The minimum resolvable bandwidth of the interferometer is 64 kHz. This interferometer is capable of measuring not only the coherence function of a single laser, but also the mutual coherence function of coupled lasers. Its resolution is limited only by the total length of the interferometer and the losses in the optical fiber.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.1144010
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  • 10
    Electronic Resource
    Electronic Resource
    The design of a small-orbit/large-orbit gyroklystron experiment (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 61 (1987), S. 519-528 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Detailed here are the characteristics of the designs of a 500-kV, 45-A electron gun and two 10-GHz gyroklystron circuits. The electron gun produces a rotating beam by passing an annular, linearly streaming beam through a nonadiabatic magnetic transition followed by an adiabatic-compression region. It is demonstrated that the same gun can produce either a small-orbit beam suitable for interaction with a TEo01 cavity mode or a large-orbit beam suitable for interaction with a TEo31 cavity mode. A detailed comparison of the relevant circuit characteristics, including peak gain and efficiency, performance degradation with increasing velocity spread, and AM and PM sensitivities to voltage and current fluctuations, is made.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.338252
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