Experimental Investigations Into Pulse-Charged Spark Gap Recovery Times and Influencing Factors

The spark gap switch is the key element in any pulsed power system, which directly determines the pulse repetitive frequency of the system. The dielectric recovery data of the spark gap play a basic role, but they have not yet been adequately studied for repetitive pulse charge conditions. This paper describes some of the factors that affect the recovery of spark gap switch for pulse-charged operation. A two-pulse technique has been used, in which the first pulse is applied to the spark gap to overvolt the gap and initiate the breakdown and the second pulse is used to determine the recovery voltage of the gap. The effects of electrode size, pulse rise time, and conduction current on the spark gap recovery performance are presented. Experiments were performed by using a double-pulse generator capable of generating 40-kV pulses with a delay of 1 ms-1 s. Spark gap electrodes of 34-, 40-, and 68-mm diameters and a point type were used in the study. The effect of voltage rise rate was studied by changing the charging capacitor to 100, 500, and 1000 nF in the circuit. An intermediate plateau was observed in the spark gap recovery curves. In addition, an increase in the output impedance resulted in a decrease in the time taken for the recovery of the spark gap. Also, the switch recovery appears to be largely dependent on the electrode shape and size compared with the pulse rise time.

I. Introduction

Fast recovery switches are a never-ending demand in pulse power applications. In recent years, pulsed power technology has been used for industrial, medical, ion implantation, and welding applications. More industrial applications of pulse power technology were discussed in [1]. The general choice for these pulse power applications is a spark gap switch, because they are cheap and offer excellent switching capability, robustness, and simplicity in construction and operation [2]. These switches can be made to operate in fast rise time with nanosecond jitter time [3], [4]. However, the lifetime and pulse repetition frequency are the main limitations of the spark gap. Improvements in voltage recovery time are possible through employing gas flow techniques [5]–[8] that clear the remnants of the switching arc from the interelectrode region during the interpulse period. However, as the required pulse repetition frequency extends into the kilohertz regime, the gas flow requirements become expensive and tend to dictate the switch design.