Switching in High Vacuum Enviroment

An analysis is made of the properties and problems of Maximum current interrupting ability and photos of contacts contacts, switching, and holding off high and low voltages, high which are interrupting up to 18,000 a are shown. and low currents ac, dc, and RF in a high vacuum environment with some relation to outer space problems. Characteristics of contacts from above atmospheric pressure down to less than 10
^-9
mm of mercury of pressure are listed in detail. Sparkover and spacing vs pressure (or vacuum) level, "cold" field emission currents vs spacing and voltage are graphed up to 200 kv. Change in vacuum levels vs time and arcing for sealed enclosures is listed showing average change from 10
^-9
to 10
^-5
mmHg taking 20 to 50 years under static conditions. Arc voltages in the order of twenty to one hundred volts for 1 to 18,000 a interruptions are shown. Switching recovery voltages and transient over-voltages from switching in vacuum are shown to be compatible with normal switching requirements, but awareness should be made of transient generating circuitry and mechanisms. A detailed analysis is shown in photographs of tungsten contacts after interrupting various high and low currents ac and dc. Examination shows that most high vacuum contact surface pitting, welding or projections are created by the "make" of current and the "break" or interruption of current results in only slight relatively smooth erosion or build up. In all cases with tungsten, the metal transfer is from the negative to the positive electrode, the same direction as electron flow.