Авіаційно-космічна техніка та технологія (Apr 2022)
Increased ignition efficiency vacuum-arc discharge in plasma sources
Abstract
The analysis of the existing vacuum-arc discharge ignition systems showed the following ways to improve their efficiency: development of new design solutions for both individual units and the entire ignition system as a whole; the use of composite materials to fill the discharge gaps of starting devices; creation of new circuit solutions for power supplies of starting discharges; the use of non-traditional methods of ignition of a vacuum-arc discharge - the transition of a glow discharge into an arc one; using laser radiation to ignite the arc. Criteria for evaluating the reliability and durability of vacuum-arc discharge initiation systems in technological plasma sources are proposed, based on which complex studies of contact-type arc excitation systems with spark surface breakdown and two-stage launch systems with an autonomous plasma injector. Based on the performed studies, designs of vacuum-arc plasma sources with contact-type systems have been developed that ensure their performance in a certain range of technological parameters; The design of the ignition system turned out to be the most effective, in which the ignition electrode and the auxiliary anode are made as a single structural element in the form of a cut cone-shaped spiral. These design features, firstly, do not prevent the condensation on the surface of the starting discharge gap of a part of the metal evaporated by the cathode spot (CS) of the arc during the operation of the device, and secondly, they greatly facilitate the output of the CS from the place of initiation to the working end of the cathode. Here, the magnetic field, under the action of the CS moves, created by the current of the starting discharge itself, flows along with the turns of the cone-shaped spiral. This ignition system does not require a separate power supply and can operate in an automatic mode from the arc power source. To implement a non-contact method of arc excitation using a plasma injector, various designs of it were studied, when the discharge gap was filled with different materials; it was found that the resource of starting injectors when filling the discharge gap with M-7 ceramics does not exceed 104 operations, with 22XC ceramics at the level of 105 operations, and when using a composite material (CM), it exceeds 106 operations at ignition energy of 5 J, an operating pulse frequency of 1 Hz and arc duration 2 s. The developed composite materials are distinguished by increasing resistance to electric discharges and low surface breakdown voltage (up to 100…200 V/mm). Such characteristics are provided by the features of the CM structure, which is a dielectric glassy matrix filled with finely dispersed conductive particles and semiconductor components. The theoretical and experimental dependence of the arc ignition probability on the ignition energy during the operation of the injector in the electric film explosion mode are compared, showing satisfactory agreement between the results.
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