Cold cathode thyratron development for pulsed power applications

The paper presents an overview on the current status of the development of the so called pseudospark switches. The pseudospark itself 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. One main task is to replace switching devices like ignitrons or high-pressure spark gaps due to their mercury filling or their limited lifetime. They are also able to replace thyratrons in many applications. The main features of the pseudospark switches are a high current rise closed to 10¹² A/sec., the ability to carry reverse currents up to 100 per cent, low pulse jitter and a high lifetime. The cold cathode reduces also the required standby power one magnitude lower than in thyratrons. On the other hand one gets especially at low peak currents also undesired phenomena by the physics of the cold cathode. Current quenching, chopping and impedance fluctuations are problems which occur at currents less than 2-3kA. At very high peak currents above 20-30kA a transition to a metal vapor arc occurs which is correlated with high cathode erosion. Depending on the requirements of different pulse power applications solutions are discussed to solve or to reduce the above described problems of the cold cathode emission.