Third-harmonic Gyrotron Research Articles

Theoretical Investigations on a 1-THz Third-Harmonic Gyrotron

Theoretical Investigations on a 1-THz Third-Harmonic Gyrotron

High-Efficiency Excitation of a Third-Harmonic Gyrotron

High-harmonic gyrotrons are challenging to generate high interaction efficiency and simultaneously suppress the mode competition. Investigation in this paper reveals that a high- $Q$ cavity is potential to realize high efficiency in a 94-GHz third-harmonic TE02 mode gyrotron. Unfortunately, the high- $Q$ cavity exhibits severe mode competition from the lower harmonic modes. A start-up scenario of active parameter control is employed to suppress the mode competition. The third-harmonic TE02 mode gyrotron finally achieves the steady single-mode operation with efficiency up to 20%. The physical mechanism during the mode formation process is theoretically investigated according to frequency-domain and time-domain nonlinear theories. The theoretical investigation in this paper is of guidance for future developing high-harmonic gyrotrons, especially toward terahertz applications.

TE02模式95GHz三次谐波回旋管实验

TE₀₂模式95GHz三次谐波回旋管实验

Terahertz Gyrotrons at IAP RAS: Status and New Designs

Powerful gyrotrons with radiation frequencies in the range 0.33–0.65 THz were demonstrated at the IAP as early as in the 1970–1980s. This trend has recently been renewed in connection with a significant increase in interest in terahertz frequency range. In the course of new experiments, the radiation frequency of pulsed gyrotrons was increased up to 1.3 THz and 1 THz at the fundamental and third cyclotron harmonics, respectively. In addition, gyrotrons operated in CW regime with a frequency of 0.3 THz for technological applications (in collaboration with the University of Fukui, Japan) and 0.26 THz for the dynamic nuclear polarization at a high-field NMR were implemented. Designs of a pulsed fundamental-harmonic gyrotron with MW-level power at 0.3 THz and a CW kW-level third-harmonic gyrotron with a frequency of 0.4 THz are currently developed. Estimates show that modern techniques for the creation of strong magnetic fields now make it possible to realize gyrotrons with an operating frequency at least up to 1–1.5 THz. Such generators utilize a relatively low particle energy and can provide higher average power than the existing FELs.

Design of a Third-Harmonic Gyrotron Oscillator Using a Photonic Crystal Cavity

A photonic crystal cavity of the transverse electric (TE) mode is designed to support the third harmonic interaction with a 30 keV–0.7 A axis-encircling electron beam at the operating frequency of the Ka-band, where a magnetic field of 0.38 T is used. The lattice parameters of a square lattice of alumina rods are determined to fit the TE301-like mode in the photonic-band-gap spectral region, and the output signal of a fundamental waveguide mode is conveniently coupled to a conventional waveguide. A particle-in-cell code simulation predicts the single mode operation with the output power of concerning 2.9 kW, corresponding with an efficiency rating of 14%. This scheme can be extended to a n-th harmonic gyrotron using the rectangular cavity of a TEm01-like mode.

A 35-ghz low-voltage third-harmonic gyrotron with a permanent magnet system

A systematic theoretical and experimental study on a 35-GHz 45-kV third-harmonic gyrotron with a permanent magnet system is presented in this paper. A complex cavity with gradual transition and a diode magnetron injection gun (MIG) are employed in the gyrotron. A self-consistent field nonlinear theoretical investigation and numerical simulation for electron beam interaction with RF fields are given. The diode MIG is simulated numerically utilizing our code in detail. The permanent magnet system provided the maximum axial magnetic field of about 4.5 kG in the cavity region of the gyrotron. The Ka band third-harmonic complex cavity gyrotron with a permanent magnet system has been designed, constructed, and tested. A pulse output power of 147.3 kW was obtained at a beam voltage of 45 kV with beam current of 32.2 A, corresponding to an efficiency of 10.2%.

A NONLINEAR ANALYSIS ON 8mm BAND THIRD-HARMONIC COMPLEX CAVITY GYROTRON WITH GRADUAL TRANSITION

Starting from general transmission line equation with an electron beam, a self-consistent nonlinear simulation on third-harmonic complex cavity gyrotron with gradual transition is presented, in which some practical factors are taken into account. The interaction between the electron beam and- H511-H521 RF field for third-harmonic gyrotron is simulated. The influences of the thickness and the velocity spread and the velocity ratio of the electron beam and the fluctuation of the magnetic field on the multi-modes interaction with an electron beam are analyzed.

A NONLINEAR SIMULATION ON BEAM-WAVE INTERACTION FOR HIGH-HARMONIC COMPLEX CAVITY GYROTRON WITH RADUAL TRANSITION

Starting from the general transmission line equation with an electron beam, a se lf-consistent nonlinear analysis on complex cavity gyrotron with gradual transit ion is presented, in which the multiple modes interacting with an electron beam and the mode coupling are taken into account. The interaction between the electr on beam and H51-H52 RF field for third-harmonic gyrotron i s simulated numerically. The influences of multiple modes on the interaction are analyzed.

Study of a 35-GHz third-harmonic low-voltage complex cavity gyrotron

A self consistent nonlinear theoretical model for a complex cavity gyrotron with abrupt transitions is presented in this paper. The model accounts for mode conversion in the transition region of the complex cavity through the general theory of modal expansion techniques. The interaction between the electron beam and TE/sub 61//TE/sub 62/ RF field in the step cavity for a third-harmonic gyrotron is simulated; many calculations are carried out under different electron beam parameters.

Large-signal operation of a third-harmonic slotted gyro-TWT amplifier

The large-signal characteristics are reported for a slotted third-harmonic gyrotron traveling-wave tube (gyro-TWT) amplifier. The slotted interaction circuit yields strong harmonic interaction for relatively low-energy axis-encircling electrons. The circuit was sliced to suppress competing modes by interrupting their wall currents. The experiment was conducted in the X-band as a scaled test of a 95-GHz amplifier design developed in collaboration with CPI/Varian. A gyroresonant RF accelerator was employed to produce the required axis-encircling electron beam. The two-stage slotted third-harmonic gyro-TWT with a beam current equal to 60% of the design value was stable and yielded an output power of 6 kW with 5% efficiency and 11-dB saturated gain over a bandwidth of 3%.

Nonlinear Analysis of A Slotted Third-Harmonic Gyro-TWT Amplifier

The distribution of RF field of the slotted cylindrincal waveguide is discussed and the self-consistent nonlinear theory of the beam-wave interaction is presented in this paper.The behavior of the 95-GHz slotted third-harmonic gyrotron traveling-wave amplifier (gyro-TWT) with a uniform section is simulated by a Runge-Kutta algorithm code for an axis-encircling electron beam with velocity spread. Some important relations in the process of the beam-wave interaction are abtained and analyzed.

Third-harmonic complex cavity gyrotron self-consistent nonlinear analysis

Starting from general transmission line equations with an electron beam source, a self-consistent nonlinear theoretical model for a complex cavity gyrotron with gradual transitions is presented in this paper. The model accounts for mode coupling in the transition region of the complex cavity. The interaction between the electron beam and H/sub 61/-H/sub 62/ RF field in the complex cavity for a third-harmonic gyrotron is simulated; many calculations are carried out under different cavity dimensions and electron beam parameters.

35-GHz 25-kW CW low-voltage third-harmonic gyrotron

A 50-kV third-harmonic gyrotron is shown to be capable of high efficiency. Operation at the third harmonic allows the required magnetic field for 35 GHz generation to be supplied by a 4.5-kG permanent magnet. Two gyrotrons employing sliced circuits for mode control have been evaluated with a large-signal nonself-consistent particle-tracing simulation code and found to be capable of producing 25 kW continuously. The preliminary design of a third-harmonic TE/sub 41/ gyrotron utilizing a magnetron injection electron gun is predicted to yield a device efficiency of 17%, which can potentially be increased to 46% with an ideal single-stage depressed collector, while an axis-encircling electron beam from a Cusp electron gun is predicted to drive a third-harmonic TE/sub 31/ gyrotron with a device efficiency of 23%, which can theoretically be increased to 45% through the use of an ideal depressed collector.

Slotted third-harmonic gyro-TWT amplifier experiment

The first operation of a slotted third-harmonic gyrotron traveling-wave amplifier is reported. The low-magnetic-field moderate-voltage gyrotron amplifier's 62-keV 2.5-A /spl upsi//sub /spl perp////spl upsi//sub /spl par//=1.2 axis-encircling electron beam was supplied by a gyroresonant RF accelerator. The 10-GHz 1.3-kG single-section slotted third-harmonic amplifier is stable and yielded 12.5 dB of small signal gain with a bandwidth of 2.5%. The experiment was performed as a scaled proof-of-principle test of the 95-GHz multisection slotted amplifier under development at CPI (formerly Varian).

Observation of harmonic gyro-backward-wave oscillation in a 100 GHz CARM oscillator experiment

Abstract A cyclotron autoresonance maser (CARM) oscillator experiment is reported, using a 600 keV 200 A electron beam and a whispering-gallery-mode rippled-wall Bragg cavity. This device was designed to produce tens of megawatts of radiation at 100 GHz from a CARM interaction, but instead produced only moderate powers (tens of kilowatts) in fundamental gyrotron modes near 35 GHZ, in third-harmonic gyro-BWO modes and possibly third-harmonic gyrotron modes, at frequencies near the expected CARM frequency, with no discernable CARM radiation. The lack of observable CARM radiation is attributed to excessive ripple on the voltage waveform and to mode competition. Calculations of the spectrum and growth rate of the backward-wave oscillations are consistent with the experimental observation.