We offer several innovations in the joining of various elements in hollow cathodes and the surrounding structures. These replace the more expensive, less compact, brazing technology and mechanical capture currently used. The proposed techniques include welding 1) molybdenum to molybdenum; 2) molybdenum and molybdenum alloys to porous tungsten; 3) molybdenum to stainless steel; 4) molybdenum to kovar; 5) a new potted tungsten heater to cathodes and supports; and 6) alternative materials such as niobium and hafnium. All of these weld processes allow automated production.
E beam has over 30 years’ experience developing new, innovative cathode structures. It is the leader in cathode miniaturization. Precision laser and resistance welding is essential for these structures. E beam is the only company that can reliably weld impregnated cathodes to base metals.
The secret to successful welding of disparate refractories is the choice of interface materials and the allowance for mismatches in the coefficient of thermal expansion. We routinely employ TIG, resistance, and laser welding in cathode production, and have done ebeam welding.
In addition to conventional hollow cathodes, we plan to apply the new joining techniques to scandate hollow cathodes, hollow reservoir cathodes, and planar micro-thruster cathodes. The proposed innovations will improve and lower the cost of conventional hollow cathodes. A planar 0.050-inch diameter planar scandate cathode using heater power of only half a watt is able to produce over one ampere of discharge current.
The innovations apply to NASA’s Hall and ion thrusters that employ conventional impregnated cathodes. These cathodes will be more compact, use less power, be more manufacturable and reliable. For long-range space missions, hollow reservoir cathodes provide longer life than impregnated cathodes. The improvements here will improve the reliability of reservoir cathodes. NASA has several initiatives involving micro-thrusters. The weld technology proposed is critical for very small planar scandate cathodes capable of up to 4A of discharge.
The innovations proposed here would apply to hollow cathodes, including reservoir cathodes used in orbit-raising of heavy communications satellites. They also apply to micro-thrusters for SmallSats and CubeSats, where much commercial work is occurring.