Chun-Rong Qiu

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.

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.

Design of a coaxial Bragg resonator for a 250 GHz cyclotron autoresonance maser oscillator

This paper concerns the design of a new kind coaxial Bragg resonator for a cyclotron autoresonance maser oscillator, which operates in TE11 mode at a frequency of 250 GHz. Two different Bragg reflectors with sinusoidal ripples have been employed in the resonator to improve the mode selectivity. For the upstream reflector, both the outer wall and the inner rod are properly corrugated to suppress the generation of the spurious modes; whereas only the outer wall is corrugated for the downstream reflector to provide a narrow bandwidth, which is favorable to only one high-Q axial mode. Numerical calculation is carried out to demonstrate the peculiarities of the designed resonator.

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.

Proposal of the large orbit cyclotron autoresonance maser amplifier with an outer-slotted-coaxial structure

The linear kinetic theory and nonlinear self-consistent model for the outer-slotted-coaxial cyclotron autoresonance maser (CARM) amplifiers with axis-encircling beam are presented. Good agreement is found between the simulations and the kinetic theory in the linear regime. The choice of the electron beam current for suppressing the absolute instability is discussed. Using 700 kV, 100 A axis-encircling beam with the velocity pitch alpha= 0.8, the nonlinear self-consistent analysis of a TE51 CARM amplifier predicts a peak output power of 6.27 MW and peak efficiency of 8.96%, which verifies that the large orbit outer-slotted-coaxial structure CARM would be expected to operate in millimeter and sub-millimeter wave band with high power, ultrahigh gain and low operating magnetic field,.

Linear investigations of the Cyclotron Autoresonance Maser amplifiers with coaxial structure

In this paper, we present the linear investigation of the cyclotron autoresonance maser (CARM) amplifiers with coaxial structure. The linear kinetic theory and the nonlinear simulation are used together for the power growth prediction. It is shown that the power behaviors predicated by the kinetic theory in the linear regime of the interaction of operating mode TE28,16 with 90-kV, 50A, alpha = 0.85 electron beam agreed well with its nonlinear simulation. The difference of the power obtained by the linear theory and nonlinear simulation at the saturate interaction length 30 cm is less than 17%. The power growth profile agrees very well with these two approaches when the device operates in lower order modes, i.e., TE21 etc.