In situ reflectivity of tungsten mirrors under helium plasma exposure

Sakaguchi, Wataru; Kajita, Shin; Ohno, Noriyasu; Takagi, Makoto

doi:10.1016/j.jnucmat.2009.01.276

Cited by 63 publications

(39 citation statements)

References 11 publications

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“…Those observations are consistent with the observed darkening and decreased reflectivity of tungsten surfaces after exposure to pure helium plasmas, which has been reported previously. 6,15,16 The current results demonstrate that the surface blackening occurs on a very short time scale for fluences higher than 10 25 m À2 s…”

Section: Resultsmentioning

confidence: 52%

Nanostructuring of molybdenum and tungsten surfaces by low-energy helium ions

Temmerman¹,

Bystrov²,

Zielinski³

et al. 2012

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

122

102

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Document VersionPublisher's PDF, also known as Version of Record (includes final page, issue and volume numbers)Please check the document version of this publication:• A submitted manuscript is the author's version of the article upon submission and before peer-review. There can be important differences between the submitted version and the official published version of record. People interested in the research are advised to contact the author for the final version of the publication, or visit the DOI to the publisher's website.• The final author version and the galley proof are versions of the publication after peer review.• The final published version features the final layout of the paper including the volume, issue and page numbers. Link to publication General rightsCopyright and moral rights for the publications made accessible in the public portal are retained by the authors and/or other copyright owners and it is a condition of accessing publications that users recognise and abide by the legal requirements associated with these rights.• Users may download and print one copy of any publication from the public portal for the purpose of private study or research.• You may not further distribute the material or use it for any profit-making activity or commercial gain • You may freely distribute the URL identifying the publication in the public portal ? Take down policyIf you believe that this document breaches copyright please contact us providing details, and we will remove access to the work immediately and investigate your claim. The formation of metallic nanostructures by exposure of molybdenum and tungsten surfaces to high fluxes of low energy helium ions is studied as a function of the ion energy, plasma exposure time, and surface temperature. Helium plasma exposure leads to the formation of nanoscopic filaments on the surface of both metals. The size of the helium-induced nanostructure increases with increasing surface temperature while the thickness of the modified layer increases with time.In addition, the growth rate of the nanostructured layer also depends on the surface temperature. The size of the nanostructure appears linked with the size of the near-surface voids induced by the low energy ions. The results presented here thus demonstrate that surface processing by low-energy helium ions provides an efficient route for the formation of porous metallic nanostructures.

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Section: Resultsmentioning

confidence: 52%

Nanostructuring of molybdenum and tungsten surfaces by low-energy helium ions

Temmerman¹,

Bystrov²,

Zielinski³

et al. 2012

Journal of Vacuum Science &Amp; Technology A: Vacuum, Surfaces, and Films

122

102

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“…Moreover, the incident helium ion energy was an important parameter to form the nanostructured tungsten. When the incident helium ion energy was above 30 eV, the fiberform nanostructure was formed at the surface temperature of 1800 K, although only the helium bubbles and holes were formed when the incident ion energy was 15 eV [6]. Additionally, it was reported that a nanostructured layer thickness of 5 µm was observed by irradiating helium plasma at the fluence of 1.1 × 10 27 m −2 [9].…”

Section: Introductionmentioning

confidence: 99%

“…This is because thermal vacancies could be dominating trap sites for helium atoms when material temperature is high [3]. When tungsten is used as a material in fusion devices, the nanostructure may cause serious problems because it could lead to the decrease of the optical reflectivity [6] and the thermal conductivity [7]. Moreover, the nanostructure formation enhances the tungsten impurity release from the material in response to the transient heat load accompanied by ELMs (Edge Localized Modes) and disruptions in future fusion…”

Section: Introductionmentioning

confidence: 99%

“…Therefore, it is necessary to investigate the formation condition and the formation mechanism of the fiberform nanostructure. In recent studies, it has been revealed that the high helium ion fluence (> 10 25 m −2 ) was necessary to cover the surface with the fiberform nanostructured tungsten [4,6,9]. Moreover, the incident helium ion energy was an important parameter to form the nanostructured tungsten.…”

Section: Introductionmentioning

confidence: 99%

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Formation Condition of Fiberform Nanostructured Tungsten by Helium Plasma Exposure

Sakaguchi

Kajita

Ohno

et al. 2010

Plasma and Fusion Research

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Tungsten samples were irradiated with high density helium plasma in the divertor plasma simulator NAGDIS to investigate the formation condition of the fiberform nanostructured tungsten. Experimental results indicated that the surface temperature threshold for the formation of nanostructure was approximately 1000 K when the incident ion energy was 50 eV. When the surface temperature was above 1000 K, the width of the nanostructure increased with the surface temperature. Three tungsten samples manufactured by different procedures (ultra fine grained tungsten, ITER-reference tungsten grade and powder metallurgy tungsten) were exposed to the helium plasma. The nanostructure was formed on all samples.

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“…This implantation process leads to concerns about a change of the optical properties after long-term hydrogenhelium plasma exposure. Over the past few years, the effect of irradiation with low-energy hydrogen and helium ions on the optical reflectivity of W mirrors has been investigated [4][5][6][7]; and the degree of the optical reflectivity degradation was demonstrated to depend on type of ions, irradiation temperature, ion energy, ion flux, as well as on the physical and mechanical properties of material itself.…”

Section: Introductionmentioning

confidence: 99%