Conceptual design of a high-voltage compact bushing for application to future N-NBI systems of fusion reactors

Simonin, A.; Esch, H.; Doceul, L.; Christin, L.; Faïsse, F.; Villecroze, F.

doi:10.1016/j.fusengdes.2012.04.025

Cited by 26 publications

(20 citation statements)

References 23 publications

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“…Indeed, one of the heating strategies of a magnetically confined plasma in tokamaks uses high energy hydrogen or deuterium atoms accelerated by the electrostatic field of a high voltage system, the performance of which is severely limited by damaging electron currents induced by field emission. [2][3][4] The intensity of such a field emission current can be reduced by raising the pressure in the vacuum system, typically from high or ultrahigh vacuum to pressures of the order of 10 À4 À 10 À2 Pa. [5][6][7][8][9] This effect has been known for quite some time 10,11 and has been investigated recently in detail for tungsten carbide and tungsten cathodes. [12][13][14] These changes in field emission intensity with ambient pressure are related to modifications of the cathode surface state at some unknown scale, which may be the micrometer size scale or an even smaller one.…”

Section: Introductionmentioning

confidence: 99%

Static electric field enhancement in nanoscale structures

Lepetit

Lemoine

Márquez-Mijares

2016

Journal of Applied Physics

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We study the effect of local atomic-and nano-scale protrusions on field emission and, in particular, on the local field enhancement which plays a key role as known from the Fowler-Nordheim model of electronic emission. We study atomic size defects which consist of right angle steps forming an infinite length staircase on a tungsten surface. This structure is embedded in a 1 GV/m ambient electrostatic field. We perform calculations based upon density functional theory in order to characterize the total and induced electronic densities as well as the local electrostatic fields taking into account the detailed atomic structure of the metal. We show how the results must be processed to become comparable with those of a simple homogeneous tungsten sheet electrostatic model. We also describe an innovative procedure to extrapolate our results to nanoscale defects of larger sizes, which relies on the microscopic findings to guide, tune, and improve the homogeneous metal model, thus gaining predictive power. Furthermore, we evidence analytical power laws for the field enhancement characterization. The main physics-wise outcome of this analysis is that limited field enhancement is to be expected from atomic-and nano-scale defects. Published by AIP Publishing.

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Section: Introductionmentioning

confidence: 99%

Static electric field enhancement in nanoscale structures

Lepetit

Lemoine

Márquez-Mijares

2016

Journal of Applied Physics

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“…The new bushing [4] is a compact sealed unit and as such it can be conditioned against high-voltage breakdowns on an installation with a low capacitance and consequently low stored-energy breakdowns. This conditioning can be performed to voltages in excess of the intended operating voltage on a future neutral beam system.…”

Section: Discussionmentioning

confidence: 99%

“…In the context of the "High Voltage holding In Vacuum" (HVIV) project, IRFM intend to manufacture and test a novel type of high-voltage bushing [4]. This bushing will be more compact than the one to be used in the ITER HNB injector.…”

Section: Introductionmentioning

confidence: 99%

“…The new bushing concentrates the electric fields in its interior, allowing the field in the vacuum vessel to be low. In this way it is intended to reduce the dark current (an electronic current that flows between polarized electrodes in vacuum [4,5]) in the vacuum vessel, while the bushing itself can make use of low-pressure gas and surface treatments to suppress the dark current internally. In order to make an informed choice about a suitable material to use, high stored-energy tests have been performed on electrodes made of Stainless Steel, Titanium, Molybdenum and Copper.…”

Section: Introductionmentioning

confidence: 99%

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High stored-energy breakdown tests on electrodes made of stainless steel, copper, titanium and molybdenum

Esch

Simonin

Grand

2015

AIP Conference Proceedings

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“…To reach such high energies, the negative ions D − are accelerated in a multigrid direct current (dc) system under vacuum [1][2][3]. A possible limitation of the system could come from the unpredictable breakdown events between grid electrodes or inside the high voltage vacuum feedthrough system called "bushing" [1].…”

Section: Introductionmentioning

confidence: 99%

Dynamics of microparticles in vacuum breakdown: Cranberg’s scenario updated by numerical modeling

Seznec

Dessante

Jäger

et al. 2017

Phys. Rev. Accel. Beams

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Microparticles (MP) and thermofield emission in vacuum are mainly caused by the roughness present at the surface of electrodes holding a high voltage. They can act as a trigger for breakdown, especially under high vacuum. This theoretical study discusses the interactions between one MP and the thermofield emission electron current as well as the consequences on the MP's transit. Starting from Cranberg's assumptions, new phenomena have been taken into account such as MP charge variation due to the secondary electron emission induced by energetic electron bombardment. Hence, the present model can be solved only numerically. Four scenarios have been identified based on the results, depending on the electron emission current from the cathode roughness (tip) and the size of the MP released at the anode, namely (i) one way; (ii) back and forth; (iii) oscillation; and (iv) vaporization. A crash study of the MP on the cathode shows that the electron emission can decrease if the MP covers the thermoemissive tip, i.e., if the MP is larger than the tip size-a phenomenon often called "conditioning"-and helping to increase the voltage holding in vacuum without breakdown.

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Conceptual design of a high-voltage compact bushing for application to future N-NBI systems of fusion reactors

Cited by 26 publications

References 23 publications

Static electric field enhancement in nanoscale structures

Static electric field enhancement in nanoscale structures

High stored-energy breakdown tests on electrodes made of stainless steel, copper, titanium and molybdenum

Dynamics of microparticles in vacuum breakdown: Cranberg’s scenario updated by numerical modeling

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