Search

Axis coincidence consideration is necessary in the design of gyrotron solenoids; besides, radial field component strongly affects the performance of gyrodevices owing to the transverse particle–wave interaction mechanism in it, especially for high-frequency operation. In this article, the theory of multiple eccentric coils is derived. It is capable of calculating the off-axis field inside the solenoid with specified displacement and tilt. Numerical calculations are validated by 3-D electromagnetic simulation methods. Based on the measured magnet field, the displacement and tilt of a three-coil magnet system are successfully predicted with a global optimization algorithm, and then, the magnet system is well calibrated using a pair of flanges. [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]

A diode magnetron injection gun (MIG) has been designed and analyzed for G-band gyro-traveling wave tube (Gyro-TWT). A novel curved surface emitter is proposed to enhance the beam quality. An electron beam with velocity ratio of 1.20 and transverse velocity spread of 2.11% is obtained. The beam transportation stability with geometry misalignment is also analyzed, and the assembly accuracy should be controlled under 0.1 mm. The stray electron is intercepted by the capture structure to avoid the bombardment to the interaction circuit. Then the cathode is fabricated, and the temperature distribution is measured. The experimental result matches well with the simulation. The electron beam quality considering expansion, surface roughness, and thermal emission is estimated, and the total transverse velocity spread is about 2.63%. [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]

In order to enhance the power capacity of gyro-traveling wave tube (Gyro-TWT), a novel multisectorial-tunnel circuit is presented in this article. The multisectorial tunnel could extend the transverse dimension of RF circuit for higher power electron beam transportation. The azimuthal drifting and transportation distortion performance for rotated electron beam are analyzed. A multibeam magnetron injection gun (MIG) is designed. The electron beam with pitch factor of 1.09 and axial velocity spread of 3.5% is obtained. And the designed cathode was fabricated and temperature distribution was measured. It provides a possible method to enhance the power capacity of Gyro-TWT. [ABSTRACT FROM AUTHOR]