SBIR-STTR Award

Vacuum Process Engineering Inc. in collaboration with the UC Davis millimeter wave research group proposes to develop a large scale production process for nanocomposite scandate tungsten powder for advanced high current density and long life thermionic cathodes that have been previously demonstrated by UC Davis to be superior to the commercially available state-of-the-art. The produced cathodes demonstrated over 100 A/cm^2 loading at 1050C and over 40 A/cm^2 current loading at 850C with lifetime of over 20,000 hours. The team will develop a process that could be scaled up to 300-500 kg per year and confirm the high quality of the produced powder by providing detailed powder evaluation data as well as cathode testing results in diode type and Pierce gun type test vehicles for pulsed and continuous wave operation. Finally, the team will provide cathode samples for independent evaluation in real devices by CPI, L-3 Electron Devices, Teledyne MEC, SLAC, and JPL as attested to by collaboration endorsement letters. Semicon Associates will provide necessary support for packaging development and delivery to the customers. Dr. Randall German will provide powder metallurgy consulting services to the team for development of reliable and consistent large scale powder manufacturing process.

Benefit:
The microwave industry will benefit immensely from availability of the nanocomposite scandate tungsten cathodes: the newly developed cathodes would extend the life of existing devices that are used in satellite communication tubes and in millimeter wave imaging systems (medical, security, and plasma fusion). These cathodes will also open opportunities for development of future high frequency devices bridging the terahertz gap with potential to be the next revolution in high data rate transmission. Expanding beyond the microwave tube industry, nanocomposite cathodes have potential to take over the electron beam lithography market providing higher quality and higher power beam without life degradation. Furthermore, the applications can be expanded to include electron beam welding and electron beam machining. Finally, nanocomposite cathodes have a potential to expand into the electric propulsion market by enhancing efficiency and expanding lifetime of the thrusters. Need for longer life cathodes in the electric thrusters has been established as a technical challenge by NASA and the nanocomposite scandate cathodes would allow NASA and other electric propulsion companies to overcome this challenge.

Keywords:
nanocomposite cathodes, nanocomposite cathodes, nanocomposite scandate tungsten powder, long-life thermionic cathodes, scandate cathodes, Powder metallurgy, high-current density cathodes

Vacuum Process Engineering, Inc. (VPE), in collaboration with the University of California, Davis (UC Davis), proposes to develop and quantitatively verify a large scale production process for scandate tungsten nanocomposite powder to be used in high current density and long life cathodes during the Phase II effort. The plan for implementation of the large scale production process at VPE with powder and pellet quality evaluation at UC Davis was developed during the Phase I effort of the program. The purpose of the Phase II Period of Performance is to bring the Phase I large scale production plan to fruition as a prototype manufacturing process of the nanocomposite scandate tungsten powder. This will entail facility layout, equipment installation and retrofitting as well as production of nanocomposite material. Batches of the nanocomposite powder produced at VPE facilities will be evaluated after each processing step; the collected data will be used to complete a feedback loop to adjust details of the fabrication parameters and our facility efficiency. These quality evaluation and emission demonstrations will be made at UC Davis as well as at our collaborator facilities.

Benefit:
Incorporating a nanocomposite scandate tungsten cathode operating at lower temperature and higher emission current density with improved emission uniformity into a high power microwave tube should significantly increase its efficiency, reliability, and its output power. The higher current density means a smaller diameter cathode can be used, thereby significantly reducing the amount of beam compression needed to get the current from the cathode into a beam drift tube, for example. The typical area compression ratios of factors of 100 can be reduced to factors of a few or perhaps no compression at all, depending on the application. Lower compression will mean that the beam will be more resistant to instability and will be more easily transported thereby enhancing tube performance. Operating a cathode at lower temperature would also significantly increase the lifetime of a microwave tube since cathodes tend to be the primary lifetime limiting factors in a vacuum tube.

Keywords:
nanopowder, Large Scale production, tungsten, Nanocomposite, dispenser cathodes, scandate, cathodes, thermionic cathodes