A novel all-metal metamaterial slow wave structure (MSWS) which suits high-power microwave sources was proposed in our previous work. Recently, an experiment on the transmission characteristics of the MSWS was carried out. The experiment results show that the MSWS can transmit electromagnetic waves in the 1.40–1.60 GHz frequency band, while the same size circular waveguide TM₀₁ mode has a cutoff frequency of 2.4 GHz. The experiment proved that the MSWS has the advantage of miniaturization. Then, based on the transmission characteristic experiment, a novel L-band relativistic Cherenkov oscillator with miniaturization and high conversion efficiency is proposed. By introducing a new coupled output structure and adjusting the MSWS period at both ends of the output structure, the electromagnetic field is better matched between the MSWS and the output coupler, and the conversion efficiency is increased from the previous 29.2% to 55.8%, with an average output power of 460 MW. Through the analysis of the electric field distribution at the main frequency of the generated microwave, it is determined that the working mechanism of the device is the Cherenkov mechanism.

A Ku-band relativistic transit-time oscillator with a three-cavity extractor and a distance-tunable reflector was proposed in our previous work [Ling et al., Phys. Plasmas 24(1), 013103 (2017)]. Recently, a new experiment was carried out on this device with an intense relativistic electron beam generator that produces electron beams with a duration of 55 ns and voltage of 0.4–1 MV. In preliminary experiments, mode competition was found with three main frequencies of which the reasons are analyzed theoretically and experimentally. The results show that plasmas generated from the collector's surface are most likely to cause this problem. To solve this problem, the collector structure is extended axially. With an input voltage of 600 kV and a current of 11.7 kA, a microwave output power 1.9 GW with pulse width 26 ns and frequency 12.42 GHz is obtained under a 0.7 T guiding magnetic field. These experimental results effectively confirm the potential of high power capacity of this proposed Ku band transit-time oscillator.

This article addresses the challenge of achieving extended pulse widths in high-power microwave sources operating in long-pulse accelerators. Through modifications and improvements to the transit-time oscillator (TTO) structure, including a high- ${Q}$ modulation cavity, angled corners, a four-cavity extraction structure, and an internally extracted microwave output, the device’s pulsewidth was successfully increased from 42 to 68 ns. Experimental results confirmed the effectiveness of these enhancements, enabling the generation of a 1.03 GW microwave output at a frequency of 12.4 GHz. This study provides valuable experimental results for the development of high-power microwave sources and serves as a reference to advance research and applications in related fields.

This study is an experimental investigation aimed at addressing the limitation of pulsewidth in traditional Ku -band transit-time oscillator (TTO) devices within a long-pulse accelerator as highlighted in a previous study. By controlling the number of shots and analyzing the variations in breakdown phenomena within the device, we identified the junction between the extraction cavity and drift section as a susceptible area for breakdown discharges. Through an increase in the number of shots, we confirmed the validity of the “anode plasma impact” model. Building upon adjustments made to the internal structure of the drift section, we successfully optimized the output pulsewidth of the TTO device from 68 to 82 ns, effectively maximizing the energy efficiency of the pulse. This research holds significant implications for the design optimization of devices in long-pulse accelerators.

In order to achieve the objectives of compactness and miniaturization in high-power microwave systems, along with reducing system energy consumption, this paper presents a design of a compact coaxial distributed intense relativistic electron beam (IREB) focusing system based on the transit time oscillator. The design methodology integrates theoretical analysis with a 2.5-dimensional particle simulation method. The entire IREB focusing system is composed of three sets of distributed magnetic rings and front-end focusing structures. The layout of this magnetic system is optimized based on periodic permanent magnets, leading to the formation of a quasi-trapezoidal wave magnetic field configuration. This optimization reduces the required number of magnetic rings while ensuring the efficient transmission of the IREB. To prevent the breakdown of the loaded magnetic rings and to optimize the radial electric field in the diode region, an additional front-end focusing structure was added. Based on the aforementioned structural configuration, a 100% electron beam transmission rate was achieved within a 150 mm range.

In this paper, a novel high-efficiency L-band Metamaterial Relativistic Oscillator (MRO) with high input and output power under relatively low guiding magnetic field has been proposed. In order to increase the power level while decreasing the guiding magnetic field, through our theoretical and simulation investigations on previously designed metamaterial (MTM) structure, we found that the thickness of the ring and the length of the drift tube are the two key factors that can improve the power handling capacity of the MTM structure and field uniformity. Through transmission analysis and electron conductance calculation of the novel MRO based on the improved MTM structure, preliminary MRO design is done. Within CST particle simulation of the proposed MRO and after optimizations, we computationally got a pure 718 MW TE₁₀ output signal at 1.49 GHz using a pulsed electron beam with energy of 700 keV and current of 2 kA under 1 T guiding magnetic field, and the corresponding conversion efficiency is 51.3%. Relevant results of particle simulation verified the previous high frequency analysis. A comparison between our proposed MRO and the previous one reveals that while keeping the high efficiency and miniaturization merits of MRO, the power handling capacity has been increased and the novel MRO works more stable under low guiding magnetic field.