DEGRADATION MECHANISM OF IMPREGNATED CATHODES

To better understand the degradation mechanism of impregnated cathodes , chemical compositions of impregnated cathodes after extended usage w ere analyzed using a newly devised integral method. The results indica te that cathode degradation is caused by a decrease in Pa supply rate. This decrease is caused by an inward drift of the reaction front as t he reaction between an impregnant and a tungsten substrate proceeds. I t is also confirmed that the Pa supply rate is controlled by the Knuds en flow of Pa atoms. To compare cathode lives economically, a new diod e tube has been designed with an anode that has a taper hole. The diod e tube allowed economical measurement of cathode performance (which is almost identical to that of a traveling wave tube (TWT)). The testing of diode tubes confirms that it is possible to estimate the lives of the cathodes with various compositions by the method based on Delta T- 90. The methodology has been applied to identify the cathode with the longest life from four impregnated cathodes employed in satellite appl ications.