Scandate-added tungsten dispenser cathode fabrication for 220 GHz sheet beam traveling wave tube amplifier

Nanocomposite Sc₂O₃-added tungsten dispenser cathodes are being developed for a 220 GHz sheet beam TWT (SBTWT) and were tested in Cathode Life Test Vehicles (CLTV) with a Pierce gun configuration under CW mode. In CLTV #1, owing to a perveance issue (there is a 100 micron gap between the focus electrode and cathode emission surface), 10 A/cm² dc current density can be achieved at practical temperature of 1120°C_br for more than 2000 hours. In CLTV #2 with a reduced focus electrode gap (30 μm), 45 A/cm² dc current density has been obtained. A collector pulsed current density of 56 A/cm² at 960°C_br at 4 kV, and up to 104 A/cm² at 1040°C_br was obtained in the CLTV #3 gun with a cathode out of 70 microns beyond electron focus. This CLTV is under CW life testing with 40 A/cm² current density which is the design value for the 220 GHz SBTWT.