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

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 (~5mm) 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.

Instability enhanced thermalization of bi-Maxwellian EEDF in multi-dipole confined hot cathode discharge: an experimental observation

“…The rods are inserted into cathode holders, leaving approximately 0.5 cm of length exposed on each end. A straightforward approach to markedly enhance the emission characteristics of an spacecharge limited (SCL) LaB 6 cathode involves positioning the gas inlet in close proximity to the cathode, with the closest distance being approximately 5 mm [23]. This method allows for the local elevation of neutral pressure near the inlet, resulting in a substantial reduction of the SCL effect.…”

Recent development of LIF diagnostics in ASIPP

“…At a discharge current currently limited to 0.6 A restricted by chamber heating issues, plasmas with densities ranging from 10 8 to 10 10 cm −3 and electron temperatures in the range of 1-5 eV can be produced at an operating pressure range spanning from 10 −2 Pa to 10 −1 Pa [50]. With recent advances in hot cathode discharge techniques [51] and improved vacuum chamber cooling, higher discharge currents and therefore higher plasma densities can be readily achieved.…”