Calcium Aluminate Electride Hollow Cathode Material and Design

Artist's concept of a solar electric propulsion system

Available for Licensing
TRL: 5


Lauren Rand
John D Williams

Reference No: 13-094
Licensing Manager

Steve Foster

At a Glance

Researchers at Colorado State University have developed an improved hollow cathode design based on a cutting edge electride material, calcium aluminate (C12A7). Although C12A7 was not discovered at CSU,  current researchers have developed a simplified, one-step synthesis approach that results in a more conductive C12A7 material. Moreover, the group has designed hollow cathodes using C12Athat take advantage of the unique properties of this exciting material.



Space propulsion presents many challenges, including both thermal and environmental (vacuum) based challenges to operate efficiently and move objects outside of the Earth’s atmosphere.  Typically, hollow cathodes are the primary electron source in space propulsion applications as they are capable of producing an electron stream, which in turn produces energy that can be used. Moreover, these hollow cathodes have increased robustness and a longer lifetime as compared to any other energy producing solutions.  However, current state-of-the-art cathodes must be heated to over 1200ºC to operate, which is costly in both power and time required to start producing energy. Other applications of this technology include many ground-based devices such as gaseous lasers and plasma processing sources.


Whereas current hollow cathodes must be heated to over 1200 ºC to begin operation, the CSU cathodes are capable of starting at room temperature without the a heater. This technology has been shown to be both stable and reproducible in a diode configuration at low flow rates at temperatures as low as 590 ºC without evidence of degradation. Calculations predict equivalent levels of current emission as LaB6 or CeB6 hollow cathode inserts, at a much lower temperature.


Furthermore, the heaterless start-up mechanism of the C12A7 electride hollow cathode allows for the almost instant operation of the cathode, which is a desirable trait from a tactical point of view, and the lack of a heater simplifies the system. Additionally, the robust nature of C12A7 electride is an improvement over current state-of-the-art thermionic emitters, which are highly sensitive to oxygen contamination and must undergo a lengthy conditioning procedure prior to operation.

  • Simplified synthesis of calcium aluminate (C12A7)
  • Proven enhanced performance as a cathode
  • Customized hollow cathode design results in stable device, low operation temperature, and heaterless start
  • Heaterless start simplifies design and allows the device to provide power instantly
  • Suitable for any device requiring an electron beam (, gaseous lasers, plasma processing)
  • Space propulsion
  • Gaseous lasers
  • Plasma processing