Minimization of impedance fluctuations in cold-cathode pseudospark switches (PSS)

The pseudospark discharge is characterized as a low-pressure gas discharge located on the left branch of the Paschen curve. Based on this discharge, a family of fast gas discharge closing switches for pulsed-power applications have been developed at Erlangen for more than 10 years. Due to the similarity to thyratrons, however, without having a hot cathode, the pseudospark devices are often described in literature as cold-cathode thyratron. The main features of a pseudospark switch are a high current rise closed to 10¹² A/s, the ability to carry reverse currents up to 100% and a high lifetime. The cold cathode also reduces the required standby power one magnitude lower than in thyratrons. On the other hand, especially at low-peak currents, undesired phenomena appear by the physics of the cold cathode. Current quenching, chopping, and impedance fluctuations are problems which occur at currents in the range of a few kiloamperes. Especially, the impedance fluctuations cause pulse-to-pulse fluctuations of the energy transferred to the load which could influence, i.e., the output energy of a laser system. For reducing this described problem of impedance fluctuations the dependencies of the geometry and material are investigated. With use of tungsten compound electrodes, this behavior of a cold cathode could be reduced significantly. This material shows also an improved reignition behavior after current zero.