Office of Technology Transfer – University of Michigan

Gas-Fed Hollow Cathode Keeper

Technology #3289

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Alec D. Gallimore
Managed By
Richard Greeley
Senior Licensing Specialist, Engineering 734-936-2093
Patent Protection
US Patent Pending


Ion thrusters are high-efficiency, high-specific impulse, advanced-electric space propulsion systems that are being proposed for ambitious deep-space missions that can require thruster operational lifetimes measured in years. One of the primary components of an ion thruster is the discharge cathode assembly (DCA). The DCA can include a hollow cathode with a surrounding keeper and is responsible for initiating and sustaining ion thruster operation. Unfortunately, wear-test and extended-life test results of a 30-cm ion thruster show that a molybdenum (Mo) keeper DCA can last only 3 years due to ion bombardment erosion. Therefore, contemporary Mo keeper DCAs utilized in ion thrusters are incapable of satisfying the 7-14 year mission requirement.


Researchers at the University of Michigan have developed a gas-fed hollow cathode keeper, which can reduce ion bombardment erosion by expelling gas through the keeper faceplate. The expelled gas effectively creates a high-pressure “shield” around the keeper such that bombarding ions suffer energy-reducing collisions before impacting the keeper. As the bombarding ion energy is reduced enough, the erosion is eliminated since sputtering is a threshold phenomenon. By protecting the discharge cathode from this erosion damage, which involves minimal changes to the established, space-rated designs, the cathode lifetimes may be extended to fulfill the critical 7 - 14 year timeframe to allow operation for long-duration missions.

Applications and Advantages


  • Ion thruster
  • Other plasma applications including Hall-nl-thruster systems and non-electric propulsion-nl-applications
  • Semiconductor industry to maintain pristine-nl-plasma environment


  • Erosion-resistant cathode keeper
  • Minimal changes to the established, space–nl-rated designs, requires no new components