A Thermionic Cathode with Functionalized Carbon Nanotubes as Emitters

A thermionic cathode based on barium strontium oxide coated CNTs is presented. The cathode resembles a conventional oxide cathode structurally. It has a coiled tungsten filament as base structure, but uses barium oxide coated CNTs as emitters instead of the widely used barium strontium calcium oxide powder mixture in conventional oxide cathodes. Plasma enhanced chemical vapor deposition was used to grow CNTs onto the coiled tungsten filament; and magnetron sputtering was used to deposit the barium strontium oxide coating onto the CNT surface; both are highly versatile and adaptable techniques. With the combination of a low work function surface and a large field effect induced by the CNTs, the oxide coated CNT emitters help produce a strong thermionic emission from the cathode.  The thermionic emission current density of 2.9 A/cm² was obtained  at 1395 K and 2.5 V/mm, which is three times of that from a conventional oxide cathode. The cathode was also tested in low pressure argon gas discharge to assess its adaptability and performance in a real plasma environment. The cathode fall of the cathode was found to be much lower than that of a conventional oxide cathode, indicating that it is highly efficient in emitting electrons.