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To meet the application needs for producing long-pulse electron beams and high-power microwaves, a pulse-forming network Marx generator with a pulse duration of 260 ns is presented in this paper. This generator is composed of 20 stages of pulse-forming network modules. Each module is formed with nine capacitors connected in parallel. The generator functions at 44 kV, which is lower than the rated voltage of the mica paper capacitor, to improve the lifetime. The impedance of the generator is designed to reach 45 Ω. To avoid the strong coupling between the adjacent stages, the physical layout of the generator adopts a zigzag design. The generator is housed in a gas pressurized vessel of 600 mm in diameter and 580 mm in length. Across a 50 Ω load, it can deliver quasi-rectangular pulses with a pulse duration of 260 ns and an amplitude of 500 kV for a single shot. The output pulse features a plateau duration of 160 ns and a leading edge of 45 ns. In burst mode, it can steadily output ten pulses of 450 kV at a repetition rate of 10 Hz on either a resistive load or a diode. [ABSTRACT FROM AUTHOR]

Triggered gas switches with trigger electrodes, such as three-electrode spark switches and trigatron type spark switches, have been widely used in repetitive operating Marx generators due to their large current flowing capability. However, the ablation of trigger electrodes during repetitive operation is inevitable, which reduces the working life of triggered gas switches. In this paper, we introduced an over-voltage triggering method for two-electrode spark switches by replacing one of the charging inductors of the Marx generator with a pulse generator. The experimental results showed that a high-voltage trigger pulse with an amplitude of 60 kV and a rising speed of 7.65 kV/100 ns was obtained from a single stackable module with a 12 V lithium battery pack as the energy source. Due to the absence of trigger electrodes, the triggering method is beneficial to extend the lifetime of switches and realize a maintenance-free repetitive operating Marx generator. [ABSTRACT FROM AUTHOR]

Coupled microspherical whispering gallery modes are highly sensitive to environmental and structural changes in the region of contact between two microcavities. Placing a sample between two microspheres changes the refractive index of their contact region, which can be useful for sensing applications. Here, we propose a solid-liquid two-phase resonator structure ("bi-sphere") based on a pair of coupled microspheres with a water droplet in the gap between them, and investigate its spectral characteristics by monitoring the transmission spectral signal during water evaporation. In addition, the feasibility of the proposed sensor device is demonstrated by a refractive index sensing experiment where the resultant mode splitting is linearly related to the refractive index in the range of 1.400–1.450. The proposed bi-sphere device could have important applications in the detection of substances. [ABSTRACT FROM AUTHOR]

In this paper, a Ka-band coaxial transit time oscillator (TTO) with internal extraction is proposed. Particle-in-cell simulation of this oscillator is performed to obtain results as follows: under the conditions of a diode voltage of 459 kV, current of 3.9 kA, and guiding magnetic field of 0.5 T, microwaves with an output power of 0.75 GW and a frequency of 31.4 GHz can be achieved with an efficiency of 42% and a saturation time of nearly 25 ns. Moreover, the asymmetric mode competition is suppressed in the preliminary experiments. The study of a Ka-band TTO aims to extend the working frequency of high power microwave sources to a higher level. Such a device has three merits. First, it implements high power and high efficiency. Second, the internal extraction of the microwave output decreases the over-mode ratio in the microwave extraction region. Third, the over-mode ratio of the internal extraction is smaller compared with the external extraction, which can effectively suppress asymmetric mode competition. [ABSTRACT FROM AUTHOR]