Characterisation of thermionic emission current with a laser-heated system

Andrade, Hugo Dominguez; Croot, Alex; Wan, Gary; Smith, James A.; Fox, Neil A.

doi:10.1063/1.5088150

Cited by 6 publications

(6 citation statements)

References 26 publications

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“…In future work, we aim to further reduce the contacting area between the sample and the quartz and introduce a cold cathode into a fully sealed commercial grade vacuum device. Surface treatment of the molybdenum will be used to maximise the thermionic emission [5].…”

Section: Discussionmentioning

confidence: 99%

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Solar thermal characterization of micropatterned high temperature selective surfaces

et al. 2020

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This paper presents measured optical absorptivity, emissivity and maximum solar-heated temperatures for micro-patterned molybdenum. The molybdenum samples were fabricated using laser micromachining and characterised using an integrating sphere and an infrared microscope. In-air solar simulator-heated temperature results for the molybdenum samples with different microstructures are presented and COMSOL modelling is then used to predict in-vacuum maximum temperatures. A vacuum chamber was developed to reduce the convection heat loss with a mount designed to minimise conduction loss and a maximum measured temperature of 413 ℃ was obtained.

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Section: Discussionmentioning

confidence: 99%

“…Much work has been done developing such surfaces, but they tend to be for lower temperatures < 300 ℃ [3,4]. For thermionic emission [5,23] temperatures > 500 ℃ are required and this paper explores approaches to achieve such high temperature selective surfaces.…”

Section: Introductionmentioning

confidence: 99%

Solar thermal characterization of micropatterned high temperature selective surfaces

et al. 2020

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“…To eliminate the space charge between the sample and collector and to saturate the thermionic emission current, a positive bias of 25 V was applied to the collector. A more detailed description of the thermionic testing setup, including temperature and current measurements, can be found elsewhere …”

Section: Methodsmentioning

confidence: 99%

“…A more detailed description of the thermionic testing setup, including temperature and current measurements, can be found elsewhere. 30 Total hydrogen desorption experiments were performed by heating the diamond from 573 to 1193 K at a constant rate of 1 K/s followed by a cooling down to 573 K at the same rate following a triangular wave profile. The heating and cooling rate was controlled by a closedloop feedback (PID control).…”

Section: ■ Experimental Detailsmentioning

confidence: 99%

Correlating Thermionic Emission with Specific Surface Reconstructions in a <100> Hydrogenated Single-Crystal Diamond

Andrade

Anaya

Croot

et al. 2020

ACS Appl. Mater. Interfaces

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Thermionic emission relies on the low work function and negative electron affinity of the, often functionalized, surface of the emitting material. However, there is little understanding of the interplay between thermionic emission and temperature-driven dynamic surface transformation processes as these are not represented on the traditional Richardson–Dushman equation for thermionic emission. Here, we show a new model for thermionic emission that can reproduce the effect of dynamic surface changes on the electron emission and correlate the components of the thermionic emission with specific surface reconstruction phases on the surface of the emitter. We use hydrogenated <100> single-crystal and polycrystalline diamonds as thermionic emitters to validate our model, which shows excellent agreement with the experimental data and could be applicable to other emitting materials. Furthermore, we find that tailoring the coverage of specific structures of the C(100)-(2 × 1):H surface reconstruction could increase the thermionic emission of diamond by several orders of magnitude.

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“…3 ) that directly applies beam to the sample, enabling rapid and controllable heating. The laser used (Synrad Inc, Firestar V40 series) was a continuous wave CO 2 laser ( λ = 10.6 μm) with linear polarisation and an output power of 40 W. System optical losses are estimated to be 25% thus the maximum power applied to the laser-incident sample face was approximately 30 W. More details about this system can be found elsewhere [35] .…”

Section: Heat Treatmentmentioning

confidence: 99%

The effects of fusion reactor thermal transients on the microstructure of Eurofer-97 steel

Kumar

Hargreaves

Bharj

et al. 2021

Journal of Nuclear Materials

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Plasma-wall interactions in a commercial-scale fusion power station may exert high transient thermal loads on plasma-facing surfaces, repeatedly subjecting underlying structural materials to high temperatures for short durations. Specimens of the reduced activation ferritic-martensitic steel Eurofer-97 were continuously aged at constant temperature in the range of 550 °C to 950 °C for up to 168 hours in a furnace to investigate the microstructural effects of short-term high temperature exposure. A CO 2 laser was also used to repeatedly heat another specimen from 400 °C to 850 °C a total of 1,480 times over a period of 41 hours to explore transient heating effects. Microstructural changes were studied via scanning electron and focused ion beam microscopy and include (i) the coarsening of Cr-rich secondary phase precipitates when continuously heated above 750 °C, (ii) an increase in average grain size above 800 °C and (iii) the evolution of a new lath martensite microstructure above 850 °C. Conversely, transient heating via a laser was found to result in the decomposition of the as-received lath martensite structure into ferrite and Cr-rich carbide precipitates, accompanied by a significant increase in average grain size from 0.1-2 μm to 5-40 μm. Experimental analysis was supported by thermodynamic simulation of the equilibrium phase behaviour of Eurofer-97 in MatCalc and thermal finite element modelling of plasma-wall interaction heating on the water-cooled lithium-lead tritium breeding blanket concept in Comsol Multiphysics. Simulated thermal transients were found to significantly alter the microstructure of Eurofer-97 and the implications of this are discussed.

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Characterisation of thermionic emission current with a laser-heated system

Cited by 6 publications

References 26 publications

Solar thermal characterization of micropatterned high temperature selective surfaces

Solar thermal characterization of micropatterned high temperature selective surfaces

Correlating Thermionic Emission with Specific Surface Reconstructions in a <100> Hydrogenated Single-Crystal Diamond

The effects of fusion reactor thermal transients on the microstructure of Eurofer-97 steel

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