Liu Ying-hui

Development of high-power gyrotrons with gradually tapered cavity

In high power gyrotrons, the parasitic modes coupled with the operating mode cannot be avoided in the beam-wave interaction. These parasitic modes will decrease the efficiency of the gyrotrons. The purity of the operating mode affected by different tapers should be carefully studied. The steady-state self-consistent nonlinear theory for gyrotron with gradually tapered cavity is developed in this paper. A steady-state calculation code including “cold cavity” and “hot cavity” is designed. By comparison, a time-domain model analysis of gyrotron operation is also studied by particle-in-cell (PIC). It is found that the tapers of gyrotron have different influences on the modes coupling between the operating mode and the parasitic modes. During the study, an example of 94 GHz gyrotron with pure operating mode TE03 has been designed. The purity of the operating mode in the optimized cavity is up to −77 dB, and in output waveguide of the cavity is up to −76 dB. At the same time, the beam-wave interaction in the de...

A Study on 94 GHz Low-Voltage, Low-Current Gyrotron

A theoretical and experimental study on a 94 GHz low-voltage, low-current gyrotron is presented in this paper. In order to obtain stable radiation and make great use of the equipment in the lab, the TE6,2 mode is selected as the operating mode of the desired gyrotron. The efficiency of the electron beam interaction with RF fields under different conditions has been calculated by a code, which is based on the self-consistent nonlinear theory for gyrotrons. The gyrotron is equipped with a single-stage depressed collector and a quasi-optical mode converter. Then, a gyrotron with optimized parameters has been designed, constructed, and tested. An output power of 23 kW is obtained at an accelerating beam voltage of 31.5 kV, a beam current of 1.8 A, and a collector depression voltage of 7.4 kV, corresponding to an overall efficiency of 53%.

Study of the Effect of the Electron Beam Parameters on a 0.4 THz Second Harmonic Gyrotron

The performance of the electromagnetic wave with power of over 100 kW at 0.4 THz is very attractive in plasma diagnostics; the 0.4 THz second harmonic gyrotron is strict with the quality of the electron beam. The quality model of the electron beam is built in practical engineering in this paper. Based on the self-consistent nonlinear beam-wave interaction theory for gyrotrons, the relationship among the quality of the electron beam, the performance of the terahertz gyrotron from the aspects of the orbital-to-axial velocity ratio, the guiding center radius, the spread of the velocity, and the thickness of the electron beam of the designed gyrotron is studied. The results show that the gyrotron is insensitive to the voltage and current of the electron beam in a wide range, and sensitive to the orbital-to-axial velocity ratio and the guiding center radius of the electron beam. The efficiency decreases when the electron beam spread is deepening, and the deepening has a little improvement when both guiding center and velocity spreads are involved in the beam-wave interaction.

Multimode calculations of frequency tunable gyrotrons for dynamic nuclear polarization applications

Summary form only given. Recently, gyrotron-based spectrometers suitable for nuclear magnetic resonance (NMR) studies have been constructed to study dynamic nuclear polarization which can result in significant enhancement of the NMR signal. In the present paper multimode calculations of a low-power (above 10W) high-frequency (200 GHz -300 GHz) gyrotron for NMR spectroscopy applications have been performed. The co- rotating TE-7,2 mode has been chosen to be the main operating cavity mode. Five neighbor modes (TE7,2; TE-4,3; TE4,3; TE-2,4; TE2,4) whose coupling factors are above 30% of the main mode and most probably can be excited in the cavity are included into the calculation using the FZK SELFT code packet designed for time dependent and self-consistent multimode calculations. The frequency fine tuning was obtained via the excitation of a sequence of longitudinal modes of TE-7,2,q by varying the beam voltage from 15 kV upward and the magnetic field from 9.6 T to 9.77 T. The results show that the main mode TE-7,2 is quite stable against the possible transverse mode competitors within this magnetic field range and a continuous frequency tuning range more than 800 MHz (263.43 GHz - 264.28 GHz) has been achieved with a velocity ratio of 1.3, the beam radius and current being 1.33 mm and 100 mA respectively.

A quasi-self-consistent field theory and simulation for gyroklystrons with abrupt transition

A systematic theoretical study of gyroklystrons with a series of abrupt transitions along the axial has been done already. A quasi-self-consistent field nonlinear theoretical investigation and a result of numerical simulation of electron beam interacting with RF field in a gyroklystron are presented in this paper. Parameters of Ka band gyroklystrons were calculated for designs using this theory and they provide useful information for experiments and further study.

Analysis of RF Field in Open Cavity by Mode-Matching Technique

Open cavity with abrupt changes is generally used in the gyro-oscillators and amplifiers. On the basis of mode-matching technique we present the high frequencies structure analyses code for gyrotron. The code provides a method for computing the resonant frequency and Q value in an open cavity. We present the theory and an example which demonstrates the operation and the possible usage of the code.

Numerical study of a gradually tapered cavity in a 170 GHz gyrotron

How to improve the efficiency of the gyrotron is always the focus of attention in studying gyrotron. There are many way to enhance the efficiency of the gyrotron, which are mainly concentrated in two aspects, one is designing the gyrotron with a depressed collector, the another is by changing the cavity structure to improve efficiency. In the paper, we adopt a new cavity structure which can better inhibit mode competition and get higher coupling efficiency. the gyrotron with the new cavity has been optimized and simulated. An output power more than 1.5 MW is obtained at the accelerating beam voltage of 80 kV, the beam current of 45 A, the transverse-to-axial velocity ratio of 1.3, corresponding to the overall efficiency of 47.2%.

Numerical study of a 170-GHz, gradient-cavity gyrotron

Summary form only given. How to improve the efficiency of the gyrotron is always the focus of attention in studying gyrotron. There are many way to enhance the efficiency of the gyrotron, which are mainly concentrated in two aspects, one is designing the gyrotron with a depressed collector, the another is by changing the cavity structure to improve efficiency. In the paper, we adopt a new cavity structure which can better inhibit mode competition and get higher coupling efficiency, the gyrotron with the new cavity has been optimized and simulated. An output power more than 1.5 MW is obtained at the accelerating beam voltage of 80 kV, the beam current of 45 A, the transverse-to-axial velocity ratio of 1.3, corresponding to the overall efficiency of 47.2%.In order to further verify the new design of tube, the hot cavity should be simulated adequately. Through numerical simulation, we finally determine the working parameters as follows: The accelerating beam voltage of 80 kV, the beam pitch ratio of 1.3, the beam current of 45 A, the efficiency of 47.12%, the power of above 1.5 MW.

Simulation of the structure for W-band gyroklystron amplifiers

Based on the mode-matching technique and simulation software CST, this paper analyzes and simulates the input cavity of gyroklystron amplifier, and gets the structure model of TE01 mode W-band gyroklystron input cavity. Then it contrasts the influence of the size of coupling slots to the coupling frequency and Q-value.

Study and design of a single-anode magnetron injection gun for W band gyrotron

Cyclotron electron beam provided by magnetron injection gun has a direct impact on the performance of the whole gyro-devices. Based on the initial study and computer simulations, A 10 A single-anode electron gun has been studied and designed according to the requirements of the gyrotron. Calculations have been performed to optimize the electrode shape and the beam parameters. The electron beam with a beam pitch ratio of 1.5 and a low velocity spread of 4% are obtained.