Free Decay of Gas Temperature After Spark Extinction in a Gas Peaking Switch

Summary form only given. A peaking switch is used to sharpen the rise time on a pulse. Modern gas peaking switches typically operate at gas pressure in the range of 100 arm. and are pulse charged very quickly. Fast gaseous recovery after spark extinction is desired since gas peaking switches are often used in repetitive mode. A model of gaseous recovery in a gas peaking gap was developed. In consideration of the gas neutrality recovery usually occurring in the first few tens of microseconds, very short compared to the gas density recovery, the gaseous recovery was simplified to the gas density recovery that is dependent on the gas temperature decay. The gas temperature decay was numerically simulated with using software ANSYS. The length of spark channel was assumed 1 mm, typical for gas peaking switches. The initial radius of an extinguished spark channel was determined based on the spark theory of a homogenous channel proposed by Branginskii. The initial temperature of the channel was deduced by the Joule heating of the channel before extinction. It was found that the heat flows out from the channel mainly through the electrodes since the short channel was inserted in between two parallel plane electrodes that are relatively big in diameter. The gas temperature of a switch with copper electrodes decays much faster than that with stainless steel. As expected, hydrogen switches recover much faster than nitrogen switches.