Improving discharge performance of space-charge limited hot cathodes via local neutral collisionality

Abstract

Abstract The effects of neutral gas inlet location to the performance of SCL hot cathodes is investigated. It is found that placing the neutral gas inlet very close (∼5 mm) to the hot cathode can significantly improve the emission characteristics via immersing the hot cathode in a volume of elevated neutral density. Such placement of the neutral gas inlet was found to make no observable effect on global plasma parameters when the discharge conditions are otherwise identical, facilitating the implementation of this measure onto existing plasma devices. Even with only a small part of the hot cathode is immersed in a volume of an elevated neutral density, the improvement of electron emission is found to be very significant. Thus, one can envision a design of a hot cathode assembly with an integrated neutral gas inlet to significantly improve its emission performance. The underlying mechanism of this improvement of hot cathode performance is the reduction of SCL effects, thus applicable to SCL hot cathodes regardless of heating configurations. This will be particularly useful in low pressure applications where a widened range of operable plasma parameters are often desirable.