Sources of temperature variance in dispenser cathodes

Summary form only given. Typical temperature specifications for dispenser cathodes range from 950°Cb to 1100°Cb with 1 to 2 percent tolerance. With current techniques, tolerance and repeatability of measurements are impacted by variables in construction materials, material surface conditions, test equipment and arrangements, and temperature measurement when dispenser cathodes are vacuum thermal tested. Dispenser cathodes are constructed from various refractory metals and oxide materials which present certain unique properties and associated unique uncertainties. This paper discusses the manufacturing processes and materials contributing to these temperature variables, including emitter surface conditions, surface finish variability on the cathode body and heat shields, heater wire resistance, potting density, and temperature measurement error. The data includes sample sets of cathode test data demonstrating the cumulative effects of the variables, error factors, and specific parameters evaluated in the paper.