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Multipactors are avalanches of secondary electrons occurred in high-power vacuum microwave devices. Accurate prediction of their occurrences is challenging, especially for devices with complex geometric cavities under complex excitations. In this article, a generalized statistical theory is derived for predicting multipactors occurred in arbitrary metallic cavities under arbitrary excitations. Its computation burden is independent on the number of electrons, enabling investigations for dynamic evolutions of multipactors even in the presence of huge amount of avalanching electrons. Exampled with coaxial, rectangular, and ridged rectangular waveguides and excited with sinusoidal, multicarrier, and wideband radar signals, dynamic electron populations and breakdown levels were computed. While the obtained results agree well with previously reported experiments and particle-in-cell simulations, these results also explain three special phenomena occurred during multipactors, verifying the validity and accuracy of the proposed solution.

This article presents a study of the multipactor effect in a double-sided dielectric-loaded parallel-plate waveguide. To this end, a 1-D electrostatic particle-in-cell model is established, which considers the radio frequency electric fields, space charge fields, and surface charge fields generated by the accumulated charge on the dielectric surface. The dynamic evolution of multipactor breakdown for different operating voltages and dielectric materials with different secondary electron yield (SEY) properties is investigated by numerical calculation. The results obtained show that multipactor does occur self-extinguishing phenomenon due to the presence of the surface charge fields under certain circumstances in the double-sided dielectric-loaded parallel-plate waveguide. Moreover, a comparative study of multipactor between metal, single-sided, and double-sided dielectric-loaded parallel-plate waveguides is carried out. The simulation results show that the self-extinguishing time of the multipactor in the double-sided dielectric-loaded model is less than that in the single-sided dielectric-loaded model. Finally, a multipactor susceptibility diagram for the SEY curve of different bottom dielectric materials in the parallel-plate waveguide is constructed. The results show that the single-sided dielectric-loaded microwave components are more beneficial to suppress the multipactor effect. The results reported in this study can be used to guide the design of space high-power microwave components.

In this work, a discharge device is designed to realize the generation of alternative current (ac) and direction current (dc) cold atmospheric plasma (CAP) jet in the same generator for studying the production mechanism of H2O2 induced by plasma in water. The interaction between the plasma jets and deionized water is decomposed into three pathways by using a special reactor system, including electrochemical pathway, gaseous dissolution pathway, and the integrated pathway. Two kinds of ac plasma jets are generated by adjusting the electrode structure of the plasma generator, meanwhile two kinds of dc plasma jets are generated by adjusting the polarity of the discharge electrodes. Stable plasma jets are generated in all four configurations. The aqueous H2O2 as well as its vital precursor hydroxyl radical (OH) produced by the plasma jets is detected. The results show that the producing pathway of aqueous H2O2 depends on the position where the OH recombination reaction takes place during the treatment, and does not depend on whether the plasma is excited by ac or dc electric power.

This article introduced a multipactor threshold criterion based on collision and emission currents, and the simulation results were compared using a traditional method. The impact of macroparticle weight on multipactor saturation was studied using electromagnetic particle-in-cell (EM-PIC) simulations of CST Particle Studio. It was found that the simulation results converged when the macroparticle weight was less than 106. A model calculating accumulated charge on the dielectric surface was proposed and validated against theoretical calculations. The dynamic evolution of multipactor in dielectric-loaded parallel-plate waveguide was analyzed, and predictions were validated against results from the existing model. Finally, the effect of surface charge fields and space charge effect on the multipactor mechanism was studied. The results showed that the multipactor could be suppressed when the ratio of the number of accumulated electrons on the dielectric surface to the saturation electron population was greater than 3.96.

In spite of recent rapid development of flexible electronics, voltage-tunable spintronic structures and devices on flexible substrates have been rarely studied. Here, voltage control of magnetic anisotropy (VCMA) is demonstrated via ionic gel (IG) gating on flexible polyimide substrates with a circuit operating voltage of 1.8 V. A reversible, nonvolatile VCMA switching of 114 Oe is achieved in Pt/Fe/Pt multilayer, where the spatial magnetic anisotropy distribution is determined quantitatively by electron spin resonance technique. This IG gating process is repeatable as the substrates are under different bending conditions. The voltage modulation of magnetic anisotropy through IG gating with excellent flexibility proposes potential applications in low-power wearable spintronic devices.