Charged particles are widely used in the fields of defogging, haze removal and artificial rainfall. A novel transport strategy of charged particles based on the vortex rings is presented in this paper, to expand the effective action region and enhance the effect of charged particles. Transport distance and transport velocity (TV) of charged particles are the crucial two evaluation indexes. For the vortex rings generated by a piston-cylinder device, the transport velocity is closely related to Reynolds number and formation time. Based on the k-ω turbulence model, this paper verifies the relationship between vortex ring circulation, transport velocity and Formation Number in air by finite element methods, and studies the influence on the formation of vortex rings of an insulating bell mouth placed at the outlet of cylinder. The simulation results show that the Formation Number of vortex rings in the air is 4.0 ~ 5.0, and the growth rate of transport velocity of vortex ring slows down when the formation time is larger than Formation Number. The study also indicates that the bell mouth has little effect on the velocity of the vortex ring, when the bell mouth angle is greater than 45° and the length of generatrix is between 0.2 m and 1.0 m. Therefore, the research results can provide a reference for the design and optimization of a vortex ring generator for transporting charged particles to a certain target area.
The China Fusion Engineering Test Reactor (CFETR) device is a milestone in the roadmap for the utilizing of fusion energy in China, whose final goal of plasma current is up to 10.02 MA. As the key system to generate a high enough voltage (20 kV) required for gas breakdown and plasma initiation, the Switch Network Unit (SNU) should have the ability to transfer 80 kA direct current by inserting resistor (0.25 ) to the superconducting coil circuit in 12 milliseconds. SNU topologies applied in other fusion devices are mostly based on the utilization of oscillation zero-point circuit, or combination of mechanical switch and semiconductor switch and so on, which bring stricter requirements for the components in the circuit and raise the cost due to the series and parallel connection of multiple devices if used in 80 kA/ 20 kV application. Based on the combination of solid-state switch (SSS) and auxiliary capacitor, this paper proposes a novel hybrid switch scheme. The SSS consists of insulated gate bipolar transistors (IGBT) group and thyristors group connected in series. The combination of added auxiliary capacitor and SSS can significantly reduce the number of series-connected IGBTs. This paper introduces the operation principle, design methods and simulation analysis of proposed scheme in detail. Coinciding with the analysis, the simulation results of SNU demonstrates the feasibility and reliability of the proposed scheme, which suggests its promising applications in fast switches with tens of kilovolts and hundreds of kilo-amperes.INDEX TERMS CFETR, switch network unit, hybrid switch, auxiliary capacitor.
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