A novel method of hybrid plasma injection driven by the pulsed discharge of a metal-polytetrafluoroethylene-stacked capillary in high-pressure SF.

A reliable and repeatable triggering technology for a megavolt gap switch with a low working coefficient η is an urgent need and a research focus. In this study, a novel method of hybrid plasma injection (HPI) driven by pulsed discharge inside a capillary was first proposed. The HPI actuator adopted a metal-polytetrafluoroethylene (PTFE)-stacked capillary, in which severe ablation could generate a hybrid plasma containing gas and metal vapor ionized component ejected outward from the nozzle. The HPI actuator could perform repeatedly with an extremely strong plasma injection and triggering ability and, thus, provided a solution for megavolt ultrafast bypass switches (UFBPSs). The evolution and the trigger properties of the HPI actuator were investigated, and the influence of the stacked material (Al, Zn, and Sn) and its proportion (3/15, 7/15, and 10/15) was studied, followed by the performance degradation in multi-shot. It was found that stacking chemically active and low-ionization-energy aluminum in a proportion of 7/15 strongly enhanced the HPI, with an initial velocity of 1200 m/s and a maximum height of 7.5 cm in 0.5 MPa SF. In repeated operations, the HPI actuator performance degraded obviously due to capillary expansion and deformation, and the lifetime was tens of magnitude. Finally, the optimized HPI actuator was used to trigger a 7 cm-0.5 MPa SF gap, with a breakdown voltage of ∼1.5 MV. When a 100 kV DC voltage was applied (η < 7%), the gap was successfully and continuously triggered for 27 shots with the trigger delay ranging from 301 to 670 µs, indicating that the HPI actuator could effectively and repeatedly trigger megavolt-magnitude SF gaps at a very low η and was a good solution for megavolt UFBPSs.