Hui-Bo Zhang

A Coaxial Bragg Reflector for Cyclotron Autoresonance Maser Oscillators

A coaxial Bragg reflector is suggested for the application in the cyclotron autoresonance masers (CARMs), where both the outer wall and inner rod are corrugated with weak axisymmetric-sinusoidal-ripple, and a concept design is presented. It is found that, compared to the cylindrical Bragg reflector, the coaxial Bragg reflector has larger dimensional size, narrower bandwidth, and larger eigenvalue intervals. These peculiarities are favorable to the mode selectivity, the ability of dissipating the ohmic heat on the wall, the oscillating startup of the operating mode, and machining manufacture, and therefore, this new kind of Bragg reflector can be developed into a coaxial resonator for the high-power CARMs

Self-consistent nonlinear investigation of an outer-slotted-coaxial waveguide gyroton traveling-wave amplifier

A nonlinear self-consistent simulation code is employed to investigate the behavior of the outer-slotted-coaxial waveguide gyrotron traveling-wave amplifier (gyro-TWA). The influences of the velocity pitch, frequency, and input power of the electron beam on efficiency, output power, and saturated gain are simulated and discussed in detail. It is predicted that this design with 95 GHz, TE/sub 3,1/ will yield a peak output power of 264.3 KW, a peak efficiency of 33.7%, and saturated gain of 44.2 dB.

Coaxial-waveguide gyrotron amplifier operating with high power and ultrahigh gain in Millimeter and submillimeter waves

A coaxial-waveguide gyrotron-traveling wave amplifier is proposed, which may be suitable for the operation in the spectrum of the short millimeter and submillimeter waves with good mode selectivity, high power, and ultrahigh gain. An example is presented in terms of the linear gyrokinetics and nonlinear simulations. Theoretical results show that tens of kilowatts with ultrahigh gain up to 67 dB might be achieved for the operation of the coaxial-waveguide mode TE/sub 28,16/ in the fundamental cyclotron harmonic at the frequency of 140 GHz. The power enhancement by a tapered magnetic field is discussed.

Nonlinear theory of a cyclotron autoresonance maser (CARM) amplifier with outer-slotted-coaxial waveguide

A self-consistent nonlinear theory for the outer-slotted-coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier is presented, which includes the characteristic equation of the wave, coupling equation of the wave with the relativistic electron beam and the simulation model. The influences of the magnetic field, the slot depth and width are investigated. The interesting characteristic of the device is that the mode competition can be efficiently suppressed by slotting the outer wall of the coaxial waveguide. A typical example is given by the theoretical design of a 137 GHz outer-slotted-coaxial-waveguide CARM amplifier by utilizing an electron beam with a voltage of 90 kV, current of 50 A, velocity pitch angle of 0.85 and a magnetic field of 43.0 kG. The nonlinear simulation predicts a power of 467.9 kW, an electronic efficiency of 10.4% and a saturated gain of 46.7 dB, if the electron beam has no velocity spread. However, the axial velocity spread deteriorates the device; for example, if the axial velocity spread is 2%, the peak power decreases to 332.4 kW with an efficiency of 7.4% and a saturated gain of 45.22 dB. Simulation shows that the efficiency of the outer-slotted-coaxial-waveguide CARM amplifier may be increased from 10.4% to 29.6% by tapering the magnetic field.

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 e = −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.

Eigenfrequency analysis of a coaxial cavity with large eccentricity

A numerical approach is presented to analyze the eigenfrequency of a coaxial cavity with large eccentricity. An example is given to a lower mode TE/sub 111/ to compare with the software HFSS, where the eccentricity is up to 70%. Generally, this approach has the following peculiarities: the CPU time needed is much less than that needed by the software HFSS and especially, the calculation can be easily extended to higher-order mode such as TE/sub 28,16,11/as well as to high-frequency domain of hundreds giga hertz, which the software HFSS hardly reaches.

Efficiency Enhancement of Coaxial-Cavity Electron Cyclotron Resonance Maser by Tapering Guide Magnetic Field

A coaxial-cavity cyclotron resonance maser (CRM) oscillator with tapered guide magnetic field is proposed. It is shown that the transmission quality can be improved by tapering the guide magnetic field. Simulation indicates that the efficiency of a millimeter-wave gyrotron oscillator may be reached up to 38.7% by optimizing the tapered magnetic field.

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

A new concept of gyro-devices in the form of a coaxial-waveguide cyclotron autoresonance maser (CARM) is proposed, which may be well suited for operation at both high power and ultrahigh gain in the millimeter wave and far infrared regions. Example is presented for a coaxial configuration - with outer and inner radii of 1.83 cm and 0.50 cm - designed to operate in the TE/sub 28,16/ 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 and the suppression of the degenerate mode as well as the absolute instability.

Output power of a coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier with an electron-beam misalignment taken into account

Nonlinear simulation shows that the misalignment between the electron-beam axis and the waveguide axis substantially decreases the output power of a coaxial-waveguide cyclotron autoresonance maser (CARM) amplifier. This investigation is of importance, because, in practice, there often exists the misalignment between the electron-beam axis and the waveguide (or cavity) axis, and it has been shown by experimental and theoretical studies that this kind of misalignment has substantial influence on the performance of both the cylindrical-cavity and coaxial-cavity gyrotron oscillators.

Nonlinear Analysis of Relativistic Motion of Electrons in Self-Amplified Spontaneous Emission Free-Electron Laser in Ultraviolet and X-Ray Spectral Regions

The free-electron laser (FEL) based on the self-amplified spontaneous emission (SASE) is an effective candidate of the coherent optical sources at wavelengths in ultraviolet and x-rays. It requires a relativistic electron beam with extremely high quality and extremely stable transmission. In this paper we analyze the dynamic behavior of the relativistic electron in that device by calculating the entropy-like quantity. Results show that if there is no adiabatic field of the wiggler, the electron beam may have great fluctuation in velocity space and diverge in configuration space.