M.D. Vorobyev, O.Y. Maslennikov, D.N. Yudaev, E.D. Orlova, L.A. Solovyeva

One of the most important elements responsible for long non-failure operation of electrovacuum devices is thermionic cathode, which provides a necessary beam current. New models of cathodes based on constantly improved technologies are applied so as to increase the duration of work. There is a necessity of an objective estimation of their quality with the purpose of rejections and influence on technological processes. The present work shows the results of estimation quality of cathodes due to the traditional methods - measurements of current-voltage and heating characteristics in pulse regime with shot pulse time (a few micro seconds) and big pulse ratio (more than 1000). It is shown that fuller information about cathodes can be found during the electrofluctuation diagnostics - measurements of the noise created by cathodes in the low frequency range (10 - 100000 Hz). The object of studying was dispenser cathodes with W sponge, covered with the thin layer of Os, and placed into the experimental electrovacuum devices with diode system. The value of work function at working temperature defined by results of impulse probing was in the known limits for cathodes of this kind. The measurements of cathode noise were made with minimum current loadings using digital methods and preliminary analog filtration of noise signal. It is established that all experimental spectral characteristics contain three noise components: flicker, shot and "relaxation" (a component of "relaxed" type). During the research the main interest has been concentrated on two components: flicker and "relaxation", which are connected with the processes on the cathode emitting surface. This conclusion was made on the basis of authors - experiments in attempts of quality estimation of semiconductor materials and structures and confirmed by other authors in literature. The informative noise parameters were found from results analysis of noise measurements. These parameters allow to detect the structure inhomogeneity of the emitting surface, which does not influence on the emission characteristics on the first stages of cathode work, but forecasts fast approach of degradation refusals during the long operation. Among such parameters there is the degree of a deviation from square law dependence of noise level on cathode current. The analysis of "relaxation" components and simultaneous use of the noise model on the basis of surface diffusion mechanism allowed to estimate the characteristic dimension of emitting parts on the cathode surface.