Beijing Vaccum Electronic Research Institute

This article utilizes the MATLAB visualization interface to derive the physical image of electron cyclotron motion in electromagnetic fields, explaining the formation process of large-orbit electron beams. Building upon this foundation, experimental research on the large-orbit electron gun was conducted. By observing the large-orbit electron trajectories on a fluorescent screen placed at the gun’s exit, the influence of cusp magnetic field configurations on the shape, radius, and velocity spread of the large-orbit electron beam was investigated. Based on theoretical analysis and experimental findings, the key factors for forming the large-orbit electron beam were identified. Finally, testing with a large-orbit electron beam traveling-wave tube verifies the theoretical and experimental results on large-orbit electron beams presented in this article.

A modified folded waveguide (MFWG) slow wave structure (SWS), where the beam-tunnel wall in the conventional folded waveguide (CFWG) is partially removed, has been proposed for THz traveling wave tubes (TWTs). Compared with the CFWG, MFWG provides a wider operating bandwidth, lower circuit loss, and stronger longitudinal electric field, indicating higher interaction efficiency with significant bandwidth. Meanwhile, MFWG has stronger heat dissipation performance indicating high duty cycle and even continuous wave capability. Given these aforementioned advantages, the analysis, design, fabrication, assembly, and hot test of the MFWG-SWS were carried out for a TWT at G-band. With beam parameters of 22.4 kV and 58 mA, this TWT produces a maximum of 62.5W, around 217 GHz, corresponding to a saturation gain of 40.2dB. The measured 50 W power bandwidth exceeds 3 GHz. More importantly, the tube can work up to 40% duty cycle. The above experiments indicate excellent performance of the MFWG for application in THz TWTs.

Gyrotron traveling wave amplifiers (Gyro-TWAs) based on axis-encircling electron beam can stably operate at the high-order harmonic state, greatly reducing the applied magnetic field, and even can be realized to work under the permanent magnet, which improves the flexibility and mobility of gyro-TWA. In this article, a Ka-band second harmonic gyro-TWA based on axis-encircling electron beam is theoretically designed. To effectively suppress self-excited oscillations and reduce the sensitivity to the electron velocity spread, a threefold (3F) helically corrugated waveguide (HCW) is adopted as the high-frequency interaction circuit. The beam–wave interaction in the designed gyro-TWA is simulated by using 3-D particle simulation software. The second harmonic cyclotron mode of a 75-keV, 7–9-A, axis encircling electron beam could be used to resonantly interact with a traveling TE<sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><roman>2</roman>,<roman>1</roman></sub>-like eigenwave in the 3FHCW to achieve a broadband amplification. The 3-D particle-in-cell simulations showed that the maximum output power can reach 160 kW with a -3-dB bandwidth of 4.0 GHz and a maximum gain of 28 dB (~10% beam velocity spread). In addition, the effect of electron beam deviating the axial center on the performance of a gyro-TWA is investigated.

Gyro-TWT is a kind of high power microwave tube, and the output window, as one of the important parts of the cyclotron, plays the role of isolating the vacuum from the external environment and outputting microwave power as much as possible. In this paper, a Ka-band sapphire periodic notched output window is designed according to half-wavelength theory. The high power metasurface output window is simulated and theoretically calculated, and the reflection and transmission coefficients of the window are analyzed to verify the design of the metasurface output window with good shape and energy under <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{TE}_{21}$</tex> operating mode.

This article presents a study on the utilization of annular beams in broadband helix traveling wave tubes (HTWTs). The research delves into the beam-wave interaction (BWI) performance of HTWTs under different hollow electron beam conditions. The theoretical analysis includes the use of gain parameter C and space charge parameter QC to evaluate the performance within the linear interaction region. Based on the analysis, a 4–20 GHz ultra-wideband traveling wave tube (TWT) based on a hollow beam scheme was designed using the software microwave tube simulator suite (MTSS). The design process involved optimizing the slow wave structure (SWS), the BWI performance, the electron gun, and the magnetic system. An output power greater than 109 W is achieved, and the small signal gain is better than 23 dB across the entire operating bandwidth. The particle-in-cell (PIC) solver in CST was used to verify the saturated gain of the designed TWT.

In this article, in order to improve the transmission capacity and power capacity of the gyrotron traveling-wave tube (gyro-TWT) RF window, the RF window for a large orbit gyro-TWT in TE21-mode at Ka-band is studied by two aspects from structure design and thermal analysis. The double disk window working for TE21-mode at Ka-band is designed by transmission cascade matrix through the method of field matching theory. The results of theory analysis, simulation, and experiment are consistent, achieving a frequency bandwidth of VSWR below 1.3 of 4 GHz for this window. Thermal analysis result shows that when the average power of gyro-TWT is 10 kW, the maximum central temperature of the window is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$54.186~^{\circ }$ </tex-math></inline-formula>C and the critical temperature difference is <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$29.581~^{\circ }$ </tex-math></inline-formula>C, and combined with the maximum of the critical temperature difference of sapphire concludes that the power capacity is 50 kW.

A 220 GHz wideband traveling wave tube (TWT) has been developed by Beijing Vacuum Electronics Research Institute (BVERI). The TWT is capable of achieving 20 W output power in a 22 GHz bandwidth and 10 W output power in a 36 GHz bandwidth. The maximum output power is 24.5 W @ 220 GHz, and -3 dB bandwidth reaches 34 GHz (15 % of f<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">c</inf>). The gain of the TWT is greater than 32.8 dB, and a two-stage deep depressed collector is employed to achieve the efficiency exceeding 7 %. The beam transmission ratio is 90 %, and the maximum stable duty cycle is 10 %.

The G-band pencil beam TWT amplifiers with high output power, high efficiency and significant bandwidth have been successfully developed in BVERI. The recent progress of TWTs is presented.

A compact, broadband 263 GHz TWT amplifier is incorporated into a high-field pulse EPR spectrometer system. The pulsed TWT amplifier, with 10 GHz 3-dB bandwidth, operates at 20.25 kV cathode voltage and provides 25.5 dB gain in saturation. A preliminary experiment has been carried out to examine the performance of the implementation. The wideband and moderate power TWT demonstrates a dramatic improvement on the signal intensity of the nano-second pulse sequence from 200 mW to more than 7 W over 5 GHz bandwidth.

This paper present a series of 170 GHz gyrotron development of Beijing Vacuum Electronics Research Industrial (BVERI). The performance of MW-class high power has been demonstrated at the 170 GHz frequency point by optimizing design scheme and manufacturing 3 versions of gyrotron since 2017. The ongoing improvements of longer operating pulse length and better radiation performance also be described in this paper.