Ab initio study of the effects of thin CsI coatings on the work function of graphite cathodes

Abstract

Cesium-iodide (CsI)-coated graphite cathodes are promising electron sources for high power microwave generators, but the mechanism driving the improved emission is not well understood. Therefore, an ab initio modeling investigation on the effects of thin CsI coatings on graphite has been carried out. It is demonstrated that the CsI coatings reduce the work function of the system significantly through a mechanism of induced dipoles. The results suggest that work function modification is a major contribution to the improved emission seen when CsI coatings are applied to C.

Plasma physics and related challenges of millimeter-wave-to-terahertz and high power microwave generation

“…Using ab initio computational models, it has recently been shown that very thin, partial monolayer films of CsI reduce the work function of graphite by over a factor of 3, thereby reducing the turn-on electric field by nearly an order of magnitude. 103 One of the persistent hopes for FEA cathodes has been the desire to exploit demonstrated high-current-density emission capabilities 89 for generating microwave or THz-regime radiation with higher efficiency and/or higher power. Recent analytic and computational studies help to explain the reason why after more than a decade that this objective still remains elusive.…”

Design of a simple annular electron beam source and its operating characteristics in single and repetitive shot modes

“…However, one should also consider the effect of electron transverse or thermal energy, sometimes characterized by beam emittance. 20 It is also possible that low turn-on electric field and high emission uniformity tend to be closely tied. 25 In the present experiments, the beam emittance will contribute mainly to the width of the annular beam.…”

“…12 Particularly, carbon fiber is considered to be one of the best materials for manufacturing explosive emission cathodes as a result of its ability to generate highly uniform plasma across large area. 20,21 Therefore, this type of cathodes is presently an appropriate choice for generating high-current electron beams. 8 However, the physical mechanisms governing the electron emission ͑field or explosive emission, or flashover plasma͒ from carbon fiber cathodes are still questionable.…”

Propagation of individual plasma spots on cathode surface by high-current discharge process

“…For high-current vacuum discharge, several recent cathodes have emerged as providing high current density emission from cathodes with mechanically and thermally robust construction. These cathodes include carbon fiber cathodes, carbon velvet cathodes with or without CsI coating, and graphite cathodes [4][5][6][7][8]. Since the quite large fields are required for delivering enough energy to electrons to enable their escape of the binding forces into the vacuum, researcher often employ cathodes consisting of long slender structures with a large aspect ratio, of which carbon nanotube cathodes are the most extreme [9].…”