Coaxial-waveguide Cyclotron Autoresonance Maser Research Articles

Mode competition in a large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier

Physics issues of mode competition in a large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier are investigated. It is shown that the use of a coaxial waveguide brings about two peculiarities: possible enhancement of the transverse dimensional size and the rarefied spectrum and that the applications of a large-orbit electron beam and CARM mechanism can efficiently exclude the parasitic effect of the cyclotron harmonics and spurious oscillations of undesired modes. The dispersion diagram and numerical simulation demonstrate that mode competition and spurious gyrotron-like or CARM-like oscillations can be suppressed when a large-orbit coaxial-waveguide CARM amplifier operates in a higher-order mode.

Nonlinear analysis of a large-orbit coaxial-waveguide cyclotron autoresonance maser amplifier

Nonlinear simulations are presented to analyze the influences of the electron beam and the magnetic field parameters on the output power of a large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier. It is found that the guiding-center spread of the relativistic electrons has negligible impact on the output power due to the small field change felt by the large-orbit electrons. The electron-beam velocity spread and energy spread substantially decrease the output power, because these spreads directly affect the beam-wave interaction through the Doppler term and the relativistic cyclotron frequency term in the cyclotron resonance condition. However, this adverse effect may be offset by properly tapering the operating magnetic field. The output power is sensitive to both the slope and the amplitude of the tapered magnetic field. Nonlinear simulation demonstrates the feasibility that a large-orbit coaxial-waveguide CARM amplifier can be expected to provide output power with several megawatts, ultrahigh gain, and good bandwidth in the millimeter and submillimeter wavelength ranges.

Linear Study of a Large-orbit Coaxial-waveguide Cyclotron Autoresonance Maser Amplifier

A linear theory based on Maxwell-Vlasov equations and the Laplace transform is presented to describe the large-orbit coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier. A 35-GHz, TE5,1-mode large-orbit coaxial-waveguide CARM amplifier is specifically analyzed. Good agreement between the linear theory and the nonlinear simulations is found in the exponentially growing region of the wave. Results show that the operating magnetic field and the electron-beam energy and average radius substantially affect the power, and especially, a small beam current may be unsuitable to a large-orbit CARM amplifier operation.

Nonlinear characteristics of a coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier

A detailed model of nonlinear self-consistent simulation for a coaxial-waveguide cyclotron autoresonance maser amplifier is presented to analyse the nonlinear characteristics of the device. Mode spectrums in cylindrical-waveguide and coaxial-waveguide are analysed. The effects of the electron-beam velocity spread and the misalignment between the electron-beam axis and the waveguide axis on the characteristics of the device are investigated and found to be detrimental to the power and efficiency. Specific simulations show that the output power and the efficiency drop from 493.4 kW and 10.97% to 382.33 kW and 8.5% when the axial velocity spread is 1% and decrease to 3.33% efficiency at 0.1 cm misalignment. However, the use of a tapering guide magnetic field with a slope ε = −0.001 cm−1 and the starting position z = 25 cm may enhance the power and efficiency to 1.84 MW and 40.82%, respectively.

Influences of the initial parameters on the performance of a coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier

Nonlinear simulations demonstrate the possibility for a coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier to operate at a frequency of 140 GHz emitting hundreds of watts with an ultrahigh gain of 68 dB. Careful design of the operating magnetic field is of importance to the power of the device, although the other initial parameters such as electron-beam radius and voltage also affect the power. Like a cylindrical-waveguide CARM, a coaxial-waveguide CARM amplifier is sensitive to the velocity spread of the electron beam.

Linear and nonlinear investigation of a coaxial-waveguide cyclotron autoresonance maser amplifier

A different concept of gyrodevices in the form of a coaxial-waveguide cyclotron autoresonance maser (CARM) is proposed. Embodying the salient features of large cross-sectional area, low guiding magnetic field, and good mode selectivity as compared to the gyrotron and to the conventional CARM, the proposed device is well suited for operation at both high power and ultrahigh gain in the millimeter wave and far infrared regions. Gyrokinetic analysis and nonlinear simulation are given in detail for a coaxial configuration—with outer and inner radii of 1.83 and 0.50 cm—designed to operate in the TE28,16 mode at 335 GHz, yielding a gain of 64 dB on using a 90 keV and 50 A electron beam confined by a 9.35 T magnetic field. Nonlinear simulation demonstrates the possibility of power enhancement via a tapered magnetic field. The competition of the degenerate mode and the excitation of the absolute instability are discussed.

Nonlinear Investigation of a Coaxial-Waveguide Cyclotron Autoresonance Maser Amplifier

A nonlinear approach is presented to simulate the coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier. Simulation shows an interesting result that the efficiency of a coaxial-waveguide CARM amplifier may be increased from 7.5% to 33.9% by tapering the magnetic field.