Scandate cathode for TWT

Because of its low work function, a scandate cathode can have a high emission current density at a low operating temperature. However, this cathode has got limited application because of its lack of emission uniformity and poor stability in operation. By modifying both the fabrication of the tungsten sponge and the cathode structure, the emission uniformity and the emission current density of these cathodes have been improved at well-chosen operating temperatures. If the variation of the heater power is kept within 5%, then the corresponding change of cathode temperature will be less than 25–30 8C, and the fluctuation in the emission current will be less than 2% in the application of traveling wave tubes (TWTs) in our company.