Design and field emission test of carbon nanotube pasted cathodes for traveling-wave tube applications

This paper presents results of computational and experimental studies of carbon nanotube (CNT) cathodes in gridded focusing guns intended for traveling-wave tube applications. With a curved CNT cathode, a cold beam emission of 11 mA was observed in a diode configuration. Two gridded focusing cathodes pasted with CNTs were then fabricated. When the applied cathode voltage was -0.86 kV, both grid and anode were at ground potential, and the cathode-to-grid distance was 200 mu m, the dc emission current from the first gridded CNT cathode was measured to be 4.2 mA. The triode field emission characteristics with two accelerating stages in pulse operation were also examined. With the cathode voltage at -4 kV, a cathode-grid potential difference of 1.38 kV, and a pulsewidth of 20 mu s, the measured pulsed current emission was 4.6 mA. The measured current was found to agree with MAGIC213 simulation results. Furthermore, by configuring a double-gridded focusing gun, a significant improvement in the beam focusing data collected through computer modeling was seen.