Long-term erosion of plasma-facing materials with different surface roughness in ASDEX Upgrade

Hakola, A.; Karhunen, J.; Koivuranta, S.; Likonen, J.; Balden, M.; Herrmann, A.; Mayer, M.; Müller, Hans; Neu, R.; Rohde, V.; Sugiyama, K.

doi:10.1088/0031-8949/2014/t159/014027

Cited by 17 publications

(14 citation statements)

References 9 publications

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“…The strongest deposition is measured on the pre-damaged samples with a large effective surface area while on the smooth bulk W and Mo samples deposition outside the PFR is almost non-existent. This is in line with the conclusions made in [17,18] on rough surfaces favouring accumulation of material in shadowed valleys behind protruding surface peaks. For tungsten, however, the deposition peak in the PFR is almost independent of the surface roughness but relatively rough marker samples and smooth bulk Mo samples indicate net deposition being comparable (FIG.…”

Section: P6-349supporting

confidence: 91%

Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

et al. 2017

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Plasma-wall interaction was studied in the full-W ASDEX Upgrade during its dedicated helium campaign. Relatively clean plasmas with a He content of >80% could be obtained by applying ICWC discharges upon changeover from D to He. Surface analyses of W samples, however, indicated co-deposited layers with significant amounts of He and D being locally formed albeit globally D was released from the plasma-facing components. When exposing W samples to ELMy H-mode helium plasmas in the outer strike-point region of the divertor, no net erosion was observed but the surfaces had been covered with co-deposited layers. The layers were the thickest in the private flux region and extended throughout the OSP region in the case of rough and modified surfaces. Also, no clear signs of nanostructure growth or destruction could be seen The growth of such layers may impact the operation of future fusion reactors. Retention of He, for its part, remained small and uniform throughout the strike-point region.

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Section: P6-349supporting

confidence: 91%

Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

et al. 2017

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“…The effect of surface roughness on the longterm erosion patterns of tungsten coatings was investigated in the outer strike-point region of ASDEX Upgrade during the 2010/11 campaign. A total of ∼6000 s of plasma operation was analyzed [268]. When the surface roughness was R 1.5 a = μm, the net erosion rate was 0.03 nm s −1 .…”

Section: Erosion-migration-depositionmentioning

confidence: 99%

Material testing facilities and programs for plasma-facing component testing

et al. 2017

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Component development for operation in a large-scale fusion device requires thorough testing and qualification for the intended operational conditions. In particular environments are necessary which are comparable to the real operation conditions, allowing at the same time for in situ/in vacuo diagnostics and flexible operation, even beyond design limits during the testing. Various electron and neutral particle devices provide the capabilities for high heat load tests, suited for material samples and components from lab-scale dimensions up to full-size parts, containing toxic materials like beryllium, and being activated by neutron irradiation. To simulate the conditions specific to a fusion plasma both at the first wall and in the divertor of fusion devices, linear plasma devices allow for a test of erosion and hydrogen isotope recycling behavior under well-defined and controlled conditions. Finally, the complex conditions in a fusion device (including the effects caused by magnetic fields) are exploited for component and material tests by exposing test mock-ups or material samples to a fusion plasma by manipulator systems. They allow for easy exchange of test pieces in a tokamak or stellarator device, without opening the vessel. Such a chain of test devices and qualification procedures is required for the development of plasma-facing components which then can be successfully operated in future fusion power devices. The various available as well as newly planned devices and test stands, together with their specific capabilities, are presented in this manuscript. Results from experimental programs on test facilities illustrate their significance for the qualification of plasma-facing materials and components. An extended set of references provides access to the current status of material and component testing capabilities in the international fusion programs.

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“…Based on the above results, the lower mass loss of PoMa-W f /W samples compared with the theoretical value can be referred to the re-deposition effect due to high surface roughness of the matrix. As sketched in figure 6, when the surface roughness is high, the particles being sputtered away can be re-trapped by the surface bumps with much higher probability, as it has been reported in [38,39]. Additionally, according to the less mass loss of PoMa-W f /W, together with the SEM observation, the loose matrix structure does not cause the shedding of W particles under plasma erosion.…”

Section: Plasma Erosionmentioning

confidence: 61%

Demonstrating tungsten fiber-reinforced porous-matrix tungsten composites for future fusion application

et al. 2022

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Tungsten fiber reinforced tungsten (Wf/W) has been developed to improve the fracture toughness of W materials, as demonstrated in previous studies (Nucl. Fusion 59(8) (2019) 086034 & Mater. Sci. Eng. A 817 (2021) 141361). In the present study, we focus on the performance of the developed Wf/W materials under fusion-relevant test conditions and further demonstrate their use as plasma facing materials in future fusion reactor. Specifically, one set of Wf/W samples were exposed to Ne plasma to investigate the erosion resistance against plasma sputtering, in comparison to the reference ITER-grade W sample. In addition, deuterium (D) retention in the plasma-exposed Wf/W samples was studied via thermal desorption spectroscopy. Furthermore, laser thermal shock tests were performed on Wf/W to simulate the transient heat load condition and to investigate the material performance under extreme heat flux. With increasing porosity, Wf/W exhibits lower mass loss (net erosion) after Ne plasma exposure. Though porous, Wf/W composites show unexpectedly a comparable D retention to the reference bulk W, which is attributed to the openness of the pores in the matrix. Thermal shock testing results indicate similar cracking threshold (0.38 GW/m2, 1 ms) as compared with that of ITER-grade W materials. However, due to the lower thermal conductivity of porous matrix Wf/W, under extremely high loading condition (1.6 GW/m2, 2 ms) surface melting was observed. The present work demonstrates great potential of the porous matrix Wf/W for future fusion application.

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Long-term erosion of plasma-facing materials with different surface roughness in ASDEX Upgrade

Cited by 17 publications

References 9 publications

Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

Plasma-wall interaction studies in the full-W ASDEX upgrade during helium plasma discharges

Material testing facilities and programs for plasma-facing component testing

Demonstrating tungsten fiber-reinforced porous-matrix tungsten composites for future fusion application

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