Bao-Liang Hao

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.

Conformal Cross-Flow Axis-Encircling Electron Beam for Driving THz Harmonic Gyrotron

In a magnetic cusp gun, the canonical-angular-momentum (CAM) spread of the initially emitted electrons is crucial in generating substantial beam velocity spread. A new method called electron beam flow-feature compensation is proposed to build an axis-encircling electron beam with zero velocity spread by optimizing the cross-flow trajectories to compensate for the initial CAM spread. This method provides an effective solution to the velocity-spread problem in terahertz gyrotrons and increases the emission current to a level that is several times higher than the level that can be obtained using current technology.

13.6: Development of 40W 26.5–40GHz helix-TWT with 37% overall efficiency

A new 26.5–40GHz helix-TWT with high efficiency has been developed at the Institute of Electronic, Chinese Academy of Sciences, China. The main methods include the optimization of slow wave structure and large signal simulation, and a special 5-stage multistage depressed collector to increase power recovery. The test results show that this device has an average power of 40W, a gain of more than 38dB, an overall efficiency of more than 37%.

P2-36: Simulation of crossmodulation and intermodulation products of helix TWT using a new 2.5D multifrequency large signal code

A 2.5D multifrequency large signal beam-wave reaction code of TWT based on the field theory is developed for crossmodulation and intermodulation products, in which space charge fields are obtained through solving discrete Helmholtz equations with the help of Particle-in-cell method. Two-tone experiment and simulation of L band space helix-TWT shown that a good agreement in CM and IM products.

Development of Ka-band space and high power helix TWTs at IECAS

Development of Ka-band TWTs at Institute of Electronics, Chinese Academy of Sciences (IECAS) are reported, include 50W space TWT and 200W high power helix TWT. The space TWT has 50% efficiency, good linearity, while TWTA (TWT+EPC) has 45% efficiency. The high power prototype TWTs have 250W CW output power with 2GHz bandwidth, 150W output power over 30-40GHz.

2D FE code for the simulation and design of TWT electron guns

A two-dimensional finite-element (FE) code TGSD for the simulation and design of axially symmetric electron guns of TWTs is reported. TGSD is a 2D steady-state trajectory code, which takes into account the space-charge effect and external magnetic field. A friendly interface is provided to simulate, test and design the electron gun. The theoretical models are discussed and the results of a dual anode gun are presented.

Development of two Ka-band high efficiency helix-TWTs at IECAS

Two new Ka-band traveling wave tubes (TWTs), included a narrow band 40W with 50% efficiency and a 26.5–40GHz 100W with 30% efficiency, has been designed and tested at the Institute of Electronic, Chinese Academy of Sciences (IECAS).

Theoretical analysis of conductivity and dielectric attenuations in millimeter-wave helical SWS

Conductivity and dielectric attenuation in millimeter-wave helical slow-wave structure (SWS) have been analyzed by a stratified dielectric helix tape and a 3D electromagnetic model. An analysis of a Ka helical SWS shows that the conductivity loss of helix and dielectric attenuation of supported rods are greater than conductivity loss of envelope, the dielectric attenuation is linear with ceramic loss tangent and should not be neglected in millimeter wave band.