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Recent hot test details and inspiring results of the W-band lossy-dielectric-loaded gyrotron traveling-wave tube (gyro-TWT) developed at the University Electronic Science and Technology of China (UESTC) are reported in this letter. Measurement of the gyro-TWT had achieved a pulse output power over 100 kW with a broad bandwidth of 8.5 GHz (92.0~100.5 GHz). For the first time as we know, the W-band gyro-TWT can stably operate with a 10% duty cycle and the average output power is over 10.3 kW in the frequency range. Excellent stability, pure spectrum and mode patterns are all verified in the hot test experiment. [ABSTRACT FROM AUTHOR]

Overall design and cold test of a G-band gyrotron traveling-wave tube (gyro-TWT) amplifier are presented. This gyro-TWT aims at achieving a goal of 10-kW pulse output power in the range of 210–220 GHz. It is operated in a circular TE01 mode at the fundamental cyclotron harmonics, which is driven by a 50-kV, 3-A gyrating electron beam. Low velocity spread diode-type magnetron injection gun (MIG), multichannel TE01 mode input coupler, broadband metasurface output window, and lossy material loaded beam–wave interaction circuit are simulated and partially measured. Particle-in-cell (PIC) simulation shows that the designed gyro-TWT can achieve a saturated output power over 10 kW in the range of 210–228 GHz with a beam velocity spread of 2.29%. [ABSTRACT FROM AUTHOR]

Effects of the output window reflection instability on the performance of our designed ${W}$ -band broadband gyrotron traveling wave tube (gyro-TWT) were studied by the simulation and hot test experiments. Strong oscillations and frequency self-modulation (FSM) in the after-cavity interaction (ACI) region were observed in the zero-driven state with a two-layer window and are verified with the beam-wave particle-in-cell simulation. Oscillations and FSM of 80–81.8 GHz and 91.03–94.68 GHz are, respectively, generated from the TE22 and TE02 modes in the ACI region due to the high window reflection level. By using the “sandwich” and meta-surface windows with low reflection and broad bandwidth, the parasitic ACI oscillations can be effectively suppressed. The maximum saturated output power is improved to 156.8 kW at 94 GHz and is zero-driven stable in our recent hot test experiments. [ABSTRACT FROM AUTHOR]

This article explores an extremely high beam–wave interaction (BWI) efficiency technology of sheet beam traveling wave tubes (SBTWTs). An all-period phase velocity tapering optimization method is proposed to improve BWI efficiency of slow wave structure (SWS). The effects of the special electron bunching state and synchronous phase velocity change on the improvement of BWI efficiency generated by this method are analyzed. To solve the computational burden caused by dozens of parameters, self-developed 1-D nonlinear BWI code is used to calculate the BWI. For the best optimization effect, particle swarm optimization (PSO) algorithm selected from a variety of algorithms is utilized to search for the global optimal solution. The PIC simulation verification results show that by the all-period optimization method, the 80-period staggered double vane (SDV) SWS achieves a stable output power of 18 kW with 31 kV voltage 0.9-A current sheet beam at 30 GHz. The BWI efficiency of all-period phase velocity tapering SWS has reached 64.5% at center frequency, the efficiency between 28 and 35 GHz exceeds 40%. [ABSTRACT FROM AUTHOR]

A periodic dielectric meta-surface output window was cold and hot tested to extend the operating bandwidth and suppress the parasitic oscillations for a W-band wideband TE01 mode gyrotron traveling wave tube (gyro-TWT) in this letter. The fabricated beryllium oxide meta-surface dielectric window demonstrates a relative bandwidth of 37.84% with the reflection below −20 dB in the range of 75–110 GHz. The influences of engineering factors and machining errors on the performance are investigated and analyzed. Thermal analysis shows the average power handling capability of the window is over 33 kW within a wide frequency range. Hot test results demonstrate that the meta-surface window is excellent for oscillation suppression and the power handling capability is predicted larger than 20 kW. [ABSTRACT FROM AUTHOR]

In this article, the design and experimental verification of a 200-kW Q-band gyrotron traveling wave tube (gyro-TWT) amplifier are presented. A low-velocity spread magnetic injection electron gun (MIG), a new type of multichannel TE01 mode input coupler, and a broadband double-disk output window are adopted in the design to improve the performance of the gyro-TWT. At the same time, the lossy ceramic ring-loaded high-frequency interaction circuit is constructed to provide the required loss for stable operation, and the potential oscillations are effectively suppressed. Saturated peak power of 208 kW and 12.5-kW average output power are measured at 47 GHz by hot test, corresponding to a saturated gain of 50.2 dB, an efficiency of 29.4%, and a −3-dB bandwidth of 5.5 GHz. [ABSTRACT FROM AUTHOR]

This article presents the development of a dual-state Ku-band gyrotron traveling-wave tube (gyro-TWT) dual-state curved-profile magnetic injection gun (MIG) generating high-quality electron beams, in which the pitch factor is up to 1.2 and 1.35 for the pulse wave (PW) state and the continuous wave (CW) state, separately. A multiobjective genetic algorithm (MOGA) is applied in the profile optimization. Meanwhile, the parametric sensitivity is also discussed in detail. A periodic dielectric-loaded interaction circuit is adopted to suppress oscillations. Furthermore, thermal analyses of the interaction circuit under different duty cycles are also elaborated. The interaction circuit is analyzed in accordance with the proposed nonlinear self-consistent theory and particle-in-cell (PIC) codes. The results of hot experiments show that the dual-state tube obtains the output power of 150/30 kW corresponding to a saturated gain of 40/41 dB and the maximum efficiency of 25%/21% within the bandwidth of 2.0/1.1 GHz for the PW/CW state, respectively. [ABSTRACT FROM AUTHOR]

This paper presents the development of highly efficient gyrotron traveling-wave tube (gyro-TWT) with a nonuniform dielectric-loaded interaction circuit. The high-quality electron beam has been generated by curved-profile magnetron injection gun (MIG). With regard to the profile optimization, simulated annealing algorithm (SAA) and genetic algorithm (GA) are applied. An electron beam with a pitch factor of 1.6 and low-axial velocity spread of 0.9182% have been obtained. The parametric sensitivity is discussed in detail. A nonuniform dielectric-loaded circuit has been employed to suppress both global oscillations and local oscillations. Different thicknesses of dielectric materials have been manufactured and measured, demonstrating the circuit loss of oscillation modes that are enough for stable operation. The interaction circuit is analyzed under the guidance of nonlinear self-consistent theory and particle-in-cell (PIC) codes. The tube achieves a saturated peak output power of 36.24 kW at 93 GHz, corresponding to a saturated gain of 54 dB and a maximum efficiency of 45.3% within a 3-dB saturated bandwidth of 5 GHz. [ABSTRACT FROM AUTHOR]

In this paper, a lossy dielectric-loaded high-gain $X$ -band gyrotron traveling-wave tube (gyro-TWT) which operates at the fundamental circular TE11 mode is designed and analyzed. The designed gyro-TWT has the features of high-gain and megawatt level output power. Lossy dielectric is applied to suppress spurious oscillations and to improve the stability of the gyro-TWT. In addition, the interaction behavior of the electron beam is investigated. In the condition of 4.5 W input power, a peak RF output power of 2.14 MW with a gain of 56.7 dB at 8.4 GHz is predicted, corresponding to the electron beam-wave interaction efficiency of 35.6% at 150 kV, 40 A. The research also obtains stable output power over 1.5 MW in the range of 8–8.4 GHz with 2-W input power and output power over 1.2 MW with 150-W input power in the range of 8.6–9 GHz. [ABSTRACT FROM AUTHOR]

Gyrotron traveling-wave tubes (gyro-TWTs) have been proved to be an attractive power source in many applications such as high-resolution radars, high-power communication systems, and electronic warfare systems. The main output indexes such as peak and average output power, interaction efficiency, and bandwidth are important for these devices. In addition, a great deal of reliability requirements such as nonstop stable operating time, operation lifetime, and environmental adaptability should be met. In this paper, detailed developing processes of gyro-TWTs in high average power operations are presented, including theoretical analyses, multiphysics simulations of key components, fabrication, and construction of the automatic hot test platform. Finally, the measured results of a Ka-band gyro-TWT for industrial applications are presented. The amplifier exhibits an excellent performance of 100-h nonstop stable operation, a 1-dB fraction bandwidth of 8%, an efficiency of more than 20%, and a peak power and an average power of more 150 and 10 kW, respectively. [ABSTRACT FROM AUTHOR]

Based on the previous double-staggered grating waveguide slow-wave structures (SWSs), an improved design is presented in this paper. The linear profile of the beam tunnel is replaced by a curved shape on its broad side. The high-frequency characteristics and beam–wave interaction are presented before and after the alteration. A novel approach in loading the attenuator with high attenuation is proposed to ensure a stable beam–wave interaction for the improved SWS. From our calculations, the improved SWS possesses a larger average interaction impedance with a rate of about 13.1%. Particle-in-cell simulation predicts that the saturated output power, the corresponding gain, and the electronic efficiency are all significantly improved, with an increase of more than 1-kW output power and 3-dB gain over the operating frequency range, and the maximum efficiency increases from 19.4% to 22.2%. The operating bandwidth is almost unaffected, remaining in a frequency range from 38 to 46 GHz. [ABSTRACT FROM AUTHOR]

A methodology to generate a circular TE13 mode for the operation of high-order mode (HOM) gyrotron-traveling-wave tubes is presented in this paper. A rectangular TE10 mode is efficiently converted into a circular TE13 mode using Y-type power dividers. Symmetric curved lossy dielectrics and dielectric rings are, respectively, positioned to suppress the potential coupling TE32 and TE71 modes according to their electric and magnetic field distribution properties. An HOM converter without dielectrics loaded was designed, constructed, and cold tested. Back-to-back transmission measurements exhibit good agreement with the results of computer simulations. [ABSTRACT FROM AUTHOR]

Wider bandwidth property of traveling-wave tubes (TWTs) is continuously pursued to satisfy the increased data rates and multiple channels in modern communications. In this paper, the coalesced-mode operation instead of the general single-mode operation for the double staggered grating waveguide (DSGW) slow-wave structure (SWS) is proposed to achieve an ultrawideband property of the TWTs driven by sheet electron beam. Analytical results of the high-frequency properties for the SWS, including the dispersion characteristics, interaction impedance, and transmission property, demonstrate that the coalesced-mode operation for the DSGW is possible. A novel loading approach of the attenuator with good performance, and meanwhile, a compact configuration is proposed to suppress the potential oscillations, thus leading to a steady beam–wave interaction for the coalesced-mode operation. To verify the concept of coalesced-mode operation, particle-in-cell simulation is performed. Simulation results demonstrate that the optimized RF circuit indeed can steadily operate in coalesced mode and produce over 5-kW saturated output power ( $\sim 10$ % efficiency) in a very broad frequency ranging from 37 to 52 GHz, corresponding to a relative bandwidth of 33.7%. [ABSTRACT FROM AUTHOR]

Design techniques and experimental results are presented on a Ku-band TE11 mode gyro-traveling wave tube. The hot test of this amplifier gives more than 153-kW output power, 2.3-GHz bandwidth (14%), 41-dB saturated gain, and 20% efficiency driven by a 63 kV, 12-A electron beam with a pitch angle (vtvz) of 1.2, and velocity spread of 5%. A linear polarized TE11 mode input coupler is used to introduce the input power. The stability of the amplifier from oscillation, including both the operating TE11 mode and the backward wave TE21 mode, has been investigated with linear codes, nonlinear self-consistent theory, and 3-D PIC CHIPIC simulation. To suppress the potential gyro-backward wave oscillator interactions, the high frequency circuit is loaded with lossy ceramic rings. The lossy structure is optimized by nonlinear theory and 3-D PIC simulation. A low velocity spread magnetron injection gun is designed with a new structure. [ABSTRACT FROM AUTHOR]