Use of the work function distribution for cathode characterization

Due to a work function distribution which is not uniform over the cathode surface an abrupt transition is replaced by a smooth continuous variation that links the space charge curve to the temperature limited curve. From the standard deviation of the work function distribution one can deduce a quality factor of the cathode and the trend of its probable evolution. Evolution of σ calculated from aged cathodes can be plotted versus time. This leads to a quality estimate and survey of cathode evolution. The higher the σ the more exhausted the cathode is. This type of analysis has been used on cathodes during reactivation after the surface was argon sputter cleaned. It is then possible to follow the coverage evolution by correlating the results with Auger analysis.