Pulsed corona generation using a high-power semiconductor diode switch

High-power semiconductor opening switches are the most critical components in nanosecond pulsed power systems with inductive energy storage. For industrial applications, such as pulsed corona processing, a long lifetime, high repetition rate, high efficiency and high reliability are required. At the Ioffe Institute, an unconventional switching mechanism has been found, based on the very fast recovery process in a silicon p⁺p´nn⁺ diode. This paper describes the application of such a ´drift-step recovery diode´ for high-power pulsed corona plasma generation. The principle of the diode-based nanosecond pulse generator is discussed in detail. The generator is coupled to a wire-plate corona reactor via a transmission-line-transformer, which has the following advantages: (i) increase of the output voltage, (ii) impedance transformation to improve the matching with the reactor, (iii) protection of the switch against reflections and mismatches, (iv) limitation of the switch current during short-circuit or breakdowns, and (v) easy coupling with a DC-bias voltage. The developed circuit has been tested at both a matched resistive load and a wire-plate pulsed corona reactor. Various ways to improve the matching with the reactor have been evaluated. We found that superposition of the pulse on a DC-bias voltage gives the best result. For example: without DC-bias, more than 50% of the energy-per-pulse reflects back to the source. However, the reflected energy could be reduced to <15% when using a DC-bias voltage of 25 kV.