Evaluation of dispenser cathodes for use in gaseous environments

A design model and method for use of dispenser cathodes in a hydrogen environment have been developed. The test cathodes were evaluated in the ITT-ETD Type 8264 diode test vehicles used to simulate the grid/cathode space of a conventional hydrogen thyratron. The authors describe the development of the cathode design procedure, the test apparatus and procedure, and the test results. The problems encountered when implementing dispenser cathodes in a gaseous environment have been experimentally verified and resolved. Ion bombardment of the cathode surface leads to high device power losses and low emission. Utilization of vertical emission surfaces will result in a decrease in the adverse effects of ion bombardment on the cathode surface. The grooved cathode design was found to decrease power losses by reducing the current rise time and on-state voltage drop. Use of impregnated tungsten cathodes, as opposed to oxide coated cathodes, has led to improved switch lifetimes