Thermionic emission investigation of materials for directly heated cathodes of electron tubes

Gellert, B.; Rohrbach, W.

doi:10.1117/12.174603

Cited by 7 publications

(5 citation statements)

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“…For the segmented cathode, pure tungsten was used instead because lanthanum migration in the lanthanated tungsten caused electrical shorting between the segmented parts of the electrode. Also, we note that the pure tungsten operation did not show notable differences compared to the lanthanated tungsten operation, suggesting that a surface coverage of lanthanum to provide a lower effective work function [50] was not achieved.…”

Section: Planar Thermionic Discharge Setupmentioning

confidence: 85%

“…The anode, disk holder and rod are made of molybdenum, and the guard-ring is 304 stainless steel. For the emitter, in the disk cathode experiment, lanthanated tungsten, which can have a work function around 2.5-2.7 eV depending on a lanthanum coverage [50,51] was used. For the segmented cathode, pure tungsten was used instead because lanthanum migration in the lanthanated tungsten caused electrical shorting between the segmented parts of the electrode.…”

Section: Planar Thermionic Discharge Setupmentioning

confidence: 99%

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Quantification of plasma enabled surface cooling by electron emission from high temperature materials

Bak,

Tropina,

Creel

et al. 2024

Plasma Sources Sci. Technol.

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In this work, the potential for hypersonic leading edge cooling by electron emission is demonstrated. To overcome space charge limitations the experiments are carried out in an argon discharge at 1 Torr. Cooling is observed with time-resolved measurements of the electron emission current and surface temperature, taking advantage of well controlled laser heating of the emitting surface and time accurate surface pyrometry. For the ignited mode of the plasma discharge, surface cooling by the electron emission is directly observed, leading to an estimated cooling rate of 1.6±0.2 MW/m2. Higher cooling rates with self sustained plasmas for space charge mitigation are expected using cesium transpiration. A two-dimensional model of heat transfer has been developed, which reproduces well the experimentally observed cooling dynamics. Parametric tests of emitter materials with various work functions show that for effective surface cooling by electron emission, the optimal work function must be less than 3.0 eV. This result indicates that electron cooling can be a promising thermal protection method for leading edges of hypersonic vehicles in flight.

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Section: Planar Thermionic Discharge Setupmentioning

confidence: 85%

Section: Planar Thermionic Discharge Setupmentioning

confidence: 99%

Quantification of plasma enabled surface cooling by electron emission from high temperature materials

Bak,

Tropina,

Creel

et al. 2024

Plasma Sources Sci. Technol.

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show abstract

“…If the reason for the high Cs consumption is eventually shown to be related to the tungsten evaporated from the filaments, using different filaments (e.g. thoriated tungsten [26]) or an RF driven source could solve this problem [27]. However Cs will always escape from the source via the apertures in the accelerator (mainly between pulses), and the rate of loss could be proportional to the temperature of the source walls.…”

Section: Discussionmentioning

confidence: 99%

Some lessons from long pulse operation of negative ion sources and accelerators

Hemsworth

Boilson²,

Esch

et al. 2006

Nucl. Fusion

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Operation of the neutral beam system of ITER for the entire ITER pulse is foreseen, with pulse lengths extending up to 1 h. Operation for such a pulse length is entirely new for neutral beam systems and the associated sub systems. This paper reviews some of the experience gained so far in the operation of the MANTIS test bed where long pulse operation of the ITER reference type of negative ion source is being studied. The three identified adverse effects of long pulse operation-reduced negative ion yield, reduced plasma grid temperature effect (see below) and increased caesium consumption-are still being studied, but some tentative explanations for each effect are given. In addition to the aforementioned effects, some operational difficulties associated with long pulses will be discussed, and some areas where caution will be needed in the future long pulse, high power operation of the ITER injectors are indicated.

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“…Three different ranges of emission can be distinguished which are discussed in more detail in [4]. This is best seen for the case of lanthanum.…”

Section: Cathodesmentioning

confidence: 97%

New developments in power grid electron tubes

Gellert¹,

Rohrbach²

1995

IEEE Trans. Dielect. Electr. Insul.

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The reduction of costs, the enhancement of lifetime of tubes and the search for environmentally friendly processes and materials gave the main impact for research and development efforts within the last years for power grid electron tubes. Physical and chemical effects are discussed that determine the performance of todays devices. New material compositions are reported for directly heated cathodes. Ways t o enhance the lifetime of emitting filaments are described. Important physical properties limiting the performance of grids in electron tubes are given. Due to the progress made in the fundamental understanding, the reliability and reproducibility of electron tubes could be improved considerably. Modern computer controlled manufacturing met hods ensure a high reproducibility of production, while continuous quality certification according to I S 0 9001 guarantees future high quality standards. Some typical applications of these tubes are given as an example.

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Thermionic emission investigation of materials for directly heated cathodes of electron tubes

Cited by 7 publications

References 0 publications

Quantification of plasma enabled surface cooling by electron emission from high temperature materials

Quantification of plasma enabled surface cooling by electron emission from high temperature materials

Some lessons from long pulse operation of negative ion sources and accelerators

New developments in power grid electron tubes

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