Development of a Self Focused Spindt Cathode for Millimeter-Wave Traveling Wave Tubes

We report ongoing development of a high-current (100 mA), low-emittance (< 0.5 mm-mrad) Spindt-type field emitter cathode for electron beam generation in mm-wave radio frequency (RF) microwave devices. These efforts include device modeling, design, fabrication, and beam profile characterization of a self-focused emitter array. We developed a pepperpot emittance characterization tool to characterize the emittance properties. To date we have demonstrated emission in excess of 80 mA from these cathodes when operating in an unfocused mode. Issues of breakdown between the gate and focus electrode in our early devices have limited measurements on the transverse emittance to < 0.5 mm-mrad at a current of 0.1 mA at 10 keV.