Shou-Xi Xu

Broadband Tunable Pre-Bunched Electron Cyclotron Maser for Terahertz Application

The relativistic electron cyclotron maser (ECM) has been successfully applied to generating high-power THz wave. In order to realize the additional advantages of broadband tuning and high efficiency interaction, this paper is devoted to exploring the THz pre-bunched ECM. Other than a conventional open-cavity tunable gyrotron consecutively switching between axial modes to realize frequency tuning, a pre-bunched ECM system operates on the backward traveling-wave resonance to achieve broadband smooth tuning. Especially, an interaction circuit of specified axial profile of beam-wave detuning frequency is built to achieve high efficiency. An optimized 0.1 THz pre-bunched ECM system using an electron beam of 30 kV voltage and 3 A current is predicted to generate broad bandwidth of 10 GHz and efficiency between 10% ~ 25%. The broadband tuning pre-bunched ECM is promising for a new generation of broadband and high-power THz source.

Theory and Experiment of a W-Band Tunable Gyrotron Oscillator

A gyrotron capable of both frequency and power tuning is a promising coherent millimeter-THz wave source. A self-consistent nonlinear theory is applied to investigate the electron cyclotron interaction between electron beam and wave modes of axial nonfixed profiles in an extended W-band TE01 mode cylindrical cavity. It is revealed that tuning the magnetic field strength can excite electron cyclotron resonances on forward wave, backward wave, and even simultaneous on both waves, which makes the system operate under distinctive states, namely the gyrotron backward wave oscillation state and the gyromonotron state. In this paper, a W-band prototype gyrotron oscillator based on an extended cylindrical waveguide cavity is built, and the experiment test indicates that the system starts oscillation in a relative wide range of the operation parameters. The measured frequency spectrum reveals the system iteratively switches between the lower order instability axial modes, and it operates under nonstationary oscillation states. The experimental measurement of highest output power ~8 kW is consistent with the theoretical predictions. An optimized gyrotron circuit with efficiency exceeding 20% and tunable bandwidth over 10 GHz is also presented. The free oscillation behaviors revealed in this paper provide interesting guidance for developing tunable gyrotrons in millimeter-THz wave range.

Numerical simulation of a W-band four-cavity gyroklystron amplifier

Using a self-consistent nonlinear code and particle-in-cell simulation, the beam-wave interaction of a W-band four-cavity gyroklystron amplifier has been analyzed. The gyroklystron amplifier operates in the fundamental harmonic TE01 circular electric mode. The dependence of the efficiency and gain on the input power and the electron velocity ratio are studied. The effect of the electron velocity spread on the bandwidth and the electronic efficiency is analyzed. The simulated results show that the designed stable gyroklystron amplifier can produce an output power of over 142 kW, 33.8% electronic efficiency, 37 dB gain, and a 3 dB bandwidth of 1 GHz for a 70 kV, 6 A electron beam.

Particle simulation of a ka-band gyrotron traveling wave amplifier

The design of a ka-band gyrotron traveling wave (gyro-TWT) amplifier is presented. The gyro-TWT amplifier with a severed structure operates in the fundamental harmonic TE01 circular electric mode. The beam-wave interaction is studied by using a particle-in-cell (PIC) code. The simulations predict that the amplifier can produce an output peak power of over 155 kW, 22% efficiency, 23 dB gain, and a 3 dB bandwidth of 2 GHz for a 70 kV, 10 A electron beam with an axial velocity spread Δvz/vz=5%.

Recent Results in the Development of a Ka-Band Second Harmonic Gyroklystron Amplifier

High-power coherent millimeter-wave sources have been extensively studied for many applications including high-resolution radars, millimeter-wave electronic counters measures, material processing, and high- energy particle accelerators. This paper presents some recent experiment results in the development of this gyroklystron at IECAS.

Study of a Quasi-Optical Mode Converter for W-band Gyrotron Oscillator

A quasi-optical mode converter for a W-band TE02 mode gyrotron is designed, fabricated, and tested. The system consists of a step-cut waveguide launcher (cut-in-half circular waveguide) and a doubly curved reflector (an elliptical reflector and a parabolic reflector). Based on the geometric optics principle and the vector diffraction theory, the mode converter is optimized and simulated by using numerical calculations. The simulation results show that the good Gaussian mode is converted from the circular waveguide TE02 mode, and the conversion efficiency is 77.9%. Experimental measurements are performed on a quasi-continuous wave gyrotron operating in the TE02 mode at W-band and show a good agreement with theoretical predictions.

P3-12: Study of a Vlasov mode converter for 94GHz whispering gallery mode gyrotron

A Vlasov mode converter for a 94 GHz whispering gallery mode gyrotron, consisting of a Vlasov-type helically-cut launcher and two curved-mirror reflectors, is proposed in this paper. Applying the geometric optics theory and the vector diffraction theory, a numerical simulation code of the quasi-optical converter system is programmed. Simulation results indicate that the TE12,2 whispering gallery mode inside the 94 GHz gyrotron is converted into a highly Gaussian-like beam at the output window.

Research progress of Ka band Gyro-TWTs in IECAS

A high power Gyrotron Traveling-Wave Amplifier(Gyro-TWT) operating in the low-loss TE01 mode has been designed and demonstrated. The gyro-TWT consists of a double-anode magnetron injection gun(MIG), TE01 mode interaction circuit, a 36mm diameter collector, and a three disk sappire output window. A double-anode magnetron injection gun is designed to operate at 70 kV and 10A using the EGUN trajectory code and particle in cell program MAGIC. The electron beam with v⊥/vz =1.0 has a predicated axial velocity spread of 3-5%. The TE01 mode interaction circuit is made up of a section of alternating metal and lossy ceramic (BeO+TiO2) followed by a unloaded, metal-walled output region. The lossy property of the periodically loaded ceramic relieves the worries of the potential Bragg resonance arising from the periodicity of the interaction circuit, bring high attenuation to the potential competing mode, and enhances the stability of a gyro-TWT. The nonlinear self-consistent simulation code evaluated the operating characteristics of the gyro-TWT amplifier. For an axial velocity spread of Δvz/vz=3%, The predicted peak power is 180kW with -3dB bandwidths1.75GHz.

A Ka-Band Second Harmonic Gyroklystron Amplifier

The design and experiment of a ka-band second harmonic gyroklytron amplifier are reported. The three-cavity 35-GHz second harmonic gyroklystron operates in the TE021 circular electric mode. Based on the numerical simulation, a three-cavity, second harmonic gyroklystron amplifier prototype has been fabricated. Experiments show a peak output power of 212 kW at 35 GHz with a 3-dB bandwidth of 155 MHz (0.44%) when utilizing a 58 kV, 23 A, v⊥/vP = 1.45 electron beam from a magnetron injection gun. The efficiency is approximately 16%, and the gain is about 24 dB.

The design of a Vlasov mode converter for 94GHz TE 02 mode gyrotron

A Vlasov mode converter for a TE02 mode gyrotron, consisting of a Vlasov stepped-cut launcher, an elliptical reflector and a parabolic reflector, is proposed in this paper. Applying the geometric optics approximation and the vector diffraction theory, a numerical simulation code of the quasi-optical converter system is programmed. Simulation results indicate that the TE02 mode inside the 94GHz gyrotron is converted into a highly Gaussianlike beam at the output window, the conversion efficiency is 78.35%.