Development of Impulse Arc Discharge in a Spark
Ignited Vacuum Diode

Abstract

In a number of technology fields (devices for lighting fast processes with Xray impulses, neutron logging equipment), the heavy current electronic devices of which must comply with certain key requirements such as lack of incandescent circuits, compact sizes, wide range of switched currents, and stability to external impacts, compact vacuum switches are used, which are sometimes called in the literature as vacuum diodes. The insulating vacuum gap in such devices is closed by injecting a plasma bunch into it. As is well known, the plasma propagation velocity under such conditions depends of the electric field direction in the switched gap. The simplest apparatus among electric discharge switching devices, which therefore can be made with the most compact sizes, is the one in which breakdown is initiated, followed by spark discharge over the dielectric surface, as a result of which plasma from the dielectric surface is injected into the vacuum gap. It is shown that conducting medium is generated in rarefied gas through photoionization, and the breakdown current over the dielectric surface is produced by the flow of electrons emitted from the cathode spot. The transition of discharge to the arc stage in the switched vacuum gap is preceded by escape of electrons from the plasma jet produced on the cathode, emission of ions, and ambipolar drift of plasma to the anode.