Dependence of surface coverage on pore geometry in dispenser cathodes

Free, B.; Gibson, Rupert

doi:10.1016/0169-4332(85)90187-4

Cited by 12 publications

(4 citation statements)

References 6 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The best result is achieved if pores have the shape of slit with size of units of micrometers. Similar results may be obtained if round pores of small diameter form chains simulating a slit [26].…”

Section: Resultssupporting

confidence: 78%

“…This means that in order to provide high emission uniformity for a DC the more important parameter is the average pore size and the uniformity of their distribution with respect to size. As has been shown in [26], active substance distribution over the DC surface, and this means the emission uniformity of the cathode, depends entirely on pore configuration. The best result is achieved if pores have the shape of slit with size of units of micrometers.…”

Section: Resultsmentioning

confidence: 79%

See 1 more Smart Citation

Effect of microstructure on the mechanism of emission for tungsten-barium dispenser cathodes

Get’man

Lushkin

Panichkina

et al. 2005

Powder Metall Met Ceram

View full text Add to dashboard Cite

The effect of tungsten powder fineness and microstructure parameters of the tungsten skeleton on the emission of dispenser cathodes (DC) in the stages of degassing and high-temperature activation are studied. Quantitative analysis of the cathode surface microstructure is investigated. It is established that the work function of the DC after high-temperature activation does not depend upon the size of tungsten powder particles in the test range of fineness (average particle size 1.4-20 μm) and porosity of the tungsten skeleton (22 and 35%). The time for reaching the maximum DC activity increases with an increase in particle size and skeleton porosity. The highest emission uniformity is exhibited by cathodes with a uniform microstructure prepared from tungsten powder with an average size of 1 and 4 μm. It is shown that the DC emission capacity is connected with the marked three-dimensional structure of BaO − CaO at the cathode surface, and also monatomic films (Ba − O and Ba) and excess oxygen at the surface of the tungsten phase.

show abstract

Section: Resultssupporting

confidence: 78%

Section: Resultsmentioning

confidence: 79%

Effect of microstructure on the mechanism of emission for tungsten-barium dispenser cathodes

Get’man

Lushkin

Panichkina

et al. 2005

Powder Metall Met Ceram

View full text Add to dashboard Cite

show abstract

“…For sufficient lateral distance of beamlets or micro-beams the total emission of the cathode can be obtained by summation. A first experimental confirmation was obtained by Free and Gibson in 1985 [7], and a qualitative theoretical confirmation among others by Li et al in 2005 [17].…”

Section: History and Derivation Of The Beamlet Effectmentioning

confidence: 64%

“…Hasker has shown, that for circular beamlets where the radius r of the emitting beam area is much smaller than the cathode to anode distance D in a close-spaced diode, the local beamlet current density j b ¼ ðD=rÞ 1=2 j Ch is much higher than expected from the Child-Langmuir equation for the current density j Ch but is still space charge limited [5,6]. This effect was nicely supported by measurements of Free and Gibson of the Ba diffusion length on the surface of controlled porosity dispenser cathodes [7]. In the following contribution, it is shown that the overall emission from localized small low work function patches can be predicted quantitatively from their IVESC 2023 Conference…”

Section: Introductionmentioning

confidence: 66%

Electron Emission Model of Ba Dispenser Scandate Cathodes Based on the Beamlet Effect

Gaertner,

Vancil

2024

e-J. Surf. Sci. Nanotechnol.

View full text Add to dashboard Cite

Currently Ba scandate cathodes exhibit the highest electron emission capability of all thermionic cathodes and are very promising for future applications. They are essentially based on Ba dispenser matrix cathodes modified with differently distributed additions of scandia. The high emission capability is due to a very low work function of 1.15 eV for different types of Ba scandate cathodes but is also accompanied by a low Richardson constant in the range from 2 to 8 A cm −2 K −2 , depending on the type, and is also an indication of incomplete surface coverage. High resolution characterization after activation and some operation time have shown that Sc is concentrated in small patches on the surface, which also contain Ba and O. Based on the beamlet effect first introduced by Hasker, it is shown by model calculations that the high emission and the corresponding Richardson constant of a given type can be quantitatively explained from the sum of beamlets or micro-beams originating from these fine patches, which are rather uniformly distributed over the impregnated cathode surface.

show abstract