Scandate Cathode for High Power Long Life Electric Propulsion

NASA needs the cathode in ion thrusters, amplifiers for RF space communications, and terahertz sources and amplifiers. These tubes need very small cathodes with very high emission levels. The most pressing need is for space communications, primarily high-speed transmissions of video images from outer space. The frequencies most likely to use this cathode are 32 GHz and higher. This cathode must be miniaturized, an e beam specialty. But a larger cathode with low beam convergence in tubes below 32 GHz is also an option. In space applications, long life has been the overruling priority and cathode loading was secondary. But given the upsurge in high data rate applications, cathode loading is going up. e beam has worked with NASA Glenn and JPL to develop cathodes for these applications. Another NASA application is atmospheric research to excite molecular resonances in the 600 GHz to 1200 GHz region. JPL has been looking for sources and amplifiers such as reflex klystrons, BWOs (backward wave oscillators) or traveling wave tubes. The third NASA requirement is for ion thrusters. e beam received a contract from NASA Glenn to produce the RF source for the ion engine for the Jupiter Icy Moons Orbiter in 2004. Two approaches were taken: 1) use an RF source to excite the ions inside the ion chamber; 2) directly excite the ions with electrons produced by a hollow cathode. Both approaches require long life, and high cathode loading, such as proposed here.

The Department of Defense is also interested in ion thrusters, but its interest is confined to near-earth applications. Its primary interest is for linear beam amplifiers for communications and radars. It is also interested in terahertz sources and amplifiers. In the commercial sector, there are several requirements for highly loaded, long-life cathodes. For example, e-beam stimulated lasers could be used as backlights for high power projection displays. These could also be used to generate high intensity UV light for curing inks and sterilization. E-beam lithography systems for making 20-30 nanometer line width masks for the semiconductor industry are now cathode limited. These systems need electron beams in the 20-30 Amps/cm2 range. Some micro-focus x-ray inspection tools are also now current density limited. More »