Acoustically enhanced multichannel spark gap switch

The inductance of a gas switch is reduced by causing it to operate in a multichannel mode. The reduced inductance is desirable to increase the switching speed. Normally, multichannel operation is achieved by careful alignment of the electrodes, use of special gas mixtures and by application of a trigger which is faster than the arc channel formation time.[1] Under normal circumstances multichannel formation is of a somewhat random and unpredictable nature. By establishing an acoustic standing wave along the electrodes the molecular number density is modulated at a precise number of positions corresponding to the nodes of the standing wave. By synchronizing the trigger with the density modulation very predictable multichannel performance and other advantages are obtained. The electrical breakdown of the gas is determined primarily by the ratio of the electric field (E) to the molecular number density (N), i.e. E/N. In conventional gaps the sites where the emission initiates on the cathode are established by the fact that the cathode surface has small irregularities resulting in local E field enhancement. The gas pressure is static so N is the same everywhere. The resulting local E/N enhancements induce the initiations at these sites. The discharge erodes the cathode surface and thus the number and location of these enhanced sites are random. An experimental rail gap was constructed with acoustic drivers at each end. The drivers were powered with a dual channel audio amplifier rated at 200 watts per channel up to 20 kHz. Experiments were conducted at ambient air density using both DC and pulse excitation of the gap electrodes. It was found that a driver excitation power of less than 10 watts per channel was sufficient to establish absolute control of the position of the arc channel. The position of the standing wave node was controlled by changing the drive frequency or the phase between the drive amplifier channels. By applying a continuous phase modulation between the drivers it is possible to cause a gliding of the arc channel along the electrodes and thus establish a more uniform erosion rate and thus a longer electrode life. The gliding arc channel also should improve the recovery time of the switch.