Heaterless 300 A lanthanum hexaboride hollow cathode.

Area of Science:

• Spacecraft Propulsion
• Plasma Physics
• Materials Science

Background:

• Traditional hollow cathodes require external heaters for thermionic emission.
• Heaterless hollow cathodes using Paschen discharge were limited to <5 A due to arcing and inefficiency.
• A previous 50 A heaterless design utilized a tube-radiator configuration to overcome these limitations.

Purpose of the Study:

• To extend the novel tube-radiator heaterless hollow cathode technology to a 300 A capability.
• To address ignition challenges associated with high heating power requirements in larger cathodes.
• To demonstrate the scalability of this technology for high-current electric propulsion.

Main Methods:

• A 300 A cathode was designed using a 5-mm diameter tantalum tube-radiator.
• A 6-A, 5-minute ignition sequence was developed, requiring high heating power (≥300 W).
• Keeper current was increased to 10 A during the initial emission phase to achieve self-heating from the low-voltage keeper discharge.

Main Results:

• The tube-radiator configuration successfully eliminated arcing and inefficient heating.
• Ignition challenges were overcome by adjusting keeper current once the LaB₆ insert began emitting.
• The technology proved scalable to large cathodes, capable of tens of thousands of ignitions.

Conclusions:

• The tube-radiator heaterless hollow cathode technology is scalable to high currents (300 A) and numerous ignition cycles.
• This advancement offers a more robust and efficient solution for electric propulsion systems.
• The design shows promise for future high-power spacecraft propulsion applications.