Light triggered thyristor crowbar for klystron protection application

High power klystrons have to be protected in case of arcing or other failures. In most applications this is achieved by fast closing switches operating in parallel to the klystron path. These switches are known as crowbars. Most commonly used crowbar switches are sparkgaps, thyratrons and ignitrons. Recent progress in the development of high power semiconductors introduces the possibility to apply semiconductor closing switches as crowbars. The most promising approach is the application of the Light Triggered Thyristor (LTT). This especially is interesting for high power high voltage dc installations, like hvdc klystron power supplies with appropriate protection requirements. This paper describes a solution using series connected LTTs as a closing crowbar switch. Static and dynamic behaviour of the thyristors are introduced. The special requirements regarding the crowbar applications are pointed out. Results of a first prototype are presented to replace sparkgaps within an existing installation, where very high charge transfer capability has to be achieved.