•Ten Si probes were located on the outer side of the LHD first-wall surface in each 36° toroidal section.•During the 16th plasma campaign, mixed-material layers were deposited on the probes.•The ...mixed-material layers were examined by RBS/ERDA and cross-sectional TEM-EDX.
Processes occurring on the plasma-facing walls in the Large Helical Device (LHD) and in-vessel material migration were investigated using a technique of material deposition probes. Ten Si plates were located on the outer side of the first-wall surface in each 36° toroidal section (Nos. 1–10). Mixed-material layers deposited on the probes during the fiscal year 2012 plasma campaign contained carbon, boron, hydrogen, and metals from which the plasma-facing elements were made. Metallic impurities and hydrogen content in deposited layers were examined by Rutherford backscattering spectrometry (RBS) and elastic recoil detection analysis (ERDA), respectively. The cross-sectional observations of the deposited mixed-material layers were performed with the help of a scanning electron microscope equipped with an energy dispersive X-ray (EDX) spectrometer. The results of the combined RBS/ERDA analysis and TEM-EDX examination allow tracing the processes occurring on plasma-facing components during the plasma campaign.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The equiatomic high-entropy alloy (HEA) CoCrFeMnNi not only has excellent mechanical properties but also good irradiation resistance. However, the mechanical properties of some equiatomic ...medium-entropy alloys (MEAs) are superior to those of CoCrFeMnNi HEA. In this study, the irradiation resistance and changes in composition due to irradiation in CoCrNi and CoCrFeNi MEAs and CoCrFeMnNi HEA are investigated. Thin film samples of the MEAs and HEA and Ni used for comparison were irradiated with up to 1.7 × 1019 ions/m2 of 2.4 MeV Cu ions at 673 and 873 K. The average damage in the observed area was 1 displacement per atom (dpa). No voids were observed in any of the MEA and HEA samples even after irradiation at 873 K; however, large voids were formed in Ni irradiated at 873 K. This indicates that the irradiation resistance of CoCrNi and CoCrFeNi MEAs and CoCrFeMnNi HEA was better than that of Ni. In addition, the formation of stacking fault tetrahedra (SFTs), a type of vacancy cluster, at 873 K was much more pronounced in CoCrNi and CoCrFeNi MEAs than in CoCrFeMnNi HEA. Therefore, the irradiation resistance of CoCrNi and CoCrFeNi MEAs is lower than that of CoCrFeMnNi HEA. Moreover, significant Cr segregation occurred in the CoCrNi and CoCrFeNi MEA samples irradiated at 873 K. In contrast, no segregation occurred in CoCrFeMnNi HEA. First-principles calculation results show that the formation rate of Cr-dumbbells is higher in CoCrNi and CoCrFeNi MEAs than in CoCrFeMnNi HEA, and that Cr interstitials are more stable in the MEAs. Therefore, Cr segregation is more likely to occur in the MEAs. Element segregation may affect the irradiation resistance of the alloys.
•The irradiation resistance of CoCrNi, CoCrFeNi, and CoCrFeMnNi is higher than that of Ni.•Significant Cr segregation occurred in the CoCrNi and CoCrFeNi samples irradiated at 873 K. In contrast, no segregation occurred in CoCrFeMnNi.•First-principles calculation results show that the formation rate of Cr-dumbbells is higher in CoCrNi and CoCrFeNi than in CoCrFeMnNi, and that Cr interstitials are more stable in the CoCrNi and CoCrFeNi.•Cr segregation is more likely to occur in the CoCrNi and CoCrFeNi.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
A novel fabrication method for a divertor heat removal component with tungsten (W) armour and copper alloy heat sink was newly developed and named as the “Advanced Multi-Step Brazing (AMSB). The ...basic principle of multi-step brazing is to apply the “advanced brazing technique” repeatedly during the manufacturing process of the single divertor heat removal component. The advanced brazing technique was originally developed by our previous work for joining between oxide dispersion strengthened copper alloy (ODS-Cu) and W with BNi-6 (Ni–11%P) filler material. The applied ODS-Cu was GlidCop® (Cu-0.3wt%Al2O3). One of the possible examples of the AMSB fabrication process can be considered as follows. First, an appropriate cooling flow path channel is processed into a GlidCop® heat sink. Then, the flow path channel is sealed in a leak tightness condition with a lid made by GlidCop®. The leak tightness joint between GlidCop® (GlidCop®/GlidCop®) can be realized by application of the “advanced brazing technique.” Second, in order to facilitate the weldability to connect the other cooling pipe system, the sleeves made by stainless steel (SUS) are jointed on the interface edge of the flow path channel of the GlidCop® heat sink with a leak tightness condition by the “advanced brazing technique.” Finally, W armour is jointed on the GlidCop® heat sink also by the “advanced brazing technique.” In this study, the mechanical strength of the SUS/GlidCop® joint was confirmed by the three-point bending test. Then, AMSB divertor mock-up with leak tightness condition was successfully produced.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The tungsten nanostructure (W-fuzz) created in the linear divertor simulator (NAGDIS) was exposed to the Large Helical Device (LHD) divertor plasma for only 2 s (1 shot) to study exfoliation/erosion ...and microscopic modifications due to the high heat/particle loading under high magnetic field conditions. Very fine and randomly moved unipolar arc trails were clearly observed on about half of the W-fuzz area (6 × 10 mm
2
). The fuzzy surface was exfoliated by continuously moving arc spots even for the very short exposure time. This is the first observation of unipolar arcing and exfoliation of some areas of the W-fuzz structure itself in a large plasma confinement device with a high magnetic field. The typical width and depth of each arc trail were about 8 µm and 1 µm, respectively, and the arc spots moved randomly on the micrometre scale. The fractality of the arc trails was analysed using a box-counting method, and the fractal dimension (
D
) of the arc trails was estimated to be
D
≈ 1.922. This value indicated that the arc spots moved in Brownian motion, and were scarcely influenced by the magnetic field. One should note that such a large scale exfoliation due to unipolar arcing may enhance the surface erosion of the tungsten armour and act as a serious impurity source for fusion plasmas.
A dispersion-strengthened W alloy, W-La2O3, was developed by spark plasma sintering (SPS). The D2 retention and microstructural evolution under 5-keV He irradiation at high temperatures were ...investigated. Although the density of the W-La2O3 alloy was lower than that of commercially available W, the D2 retention did not change significantly. In addition, the D2 thermal desorption peak, which did not appear in commercial W, appeared at ∼700 K due to the dissociation from D to vacancy clusters. In W-La2O3, the formation of He bubbles was observed at 773 K, 973 K and 1173 K. As the irradiation temperature was increased, void swelling also increased. For the same temperature, the formation of He bubbles was easier for W-La2O3 than for commercial W. This is considered to be the cause of low density of W-La2O3. W-La2O3 had a higher density of vacancies before He irradiation. The suppression of vacancy aggregation induced by the dispersion of La2O3 as the second phase appeared only at a high irradiation doses.
•The density of the W-La2O3 was low, however the D2 retention did not change significantly.•In W-La2O3, the formation of He bubbles was observed at 773 K, 973 K and 1173 K.•At the low He irradiation dose, void swelling of W-La2O3 irradiated at 1193 K was higher than that of commercial W.•At the high He irradiation dose, void swelling of W-La2O3 irradiated at 1193 K was lower than that of commercial W.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
We have investigated modification of WNOx films (thickness of 20–80 nm) by D and H ions with the energy of ~1 keV, where D and H ions are retained within the film and compared with the results by ...medium-energy and high-energy (~1 MeV/u) ion irradiation. WNOx films are prepared on C-plane-cut-sapphire (C-Al2O3) substrate. The composition x is determined to be ~0.4 and the film thickness by Rutherford backscattering spectroscopy (RBS) of He+ ions. X-ray diffraction with Cu- Kα radiation (XRD) is employed to study structural modification. We find monotonic decrease of the XRD intensity with D and H ion fluence, and lattice expansion and compaction for low and high D fluence, respectively. D and H retention is measured by nuclear reaction analysis (NRA) using 15N and 3He ion beams, and elastic recoil detection (ERD). It is discussed whether effects of energy deposition by ions can be separated from inclusion effects of D and H.
•Lattice expansion and compaction of WNOx film have been observed for low and high fluence of D and H ion irradiation.•Lattice disordering at low fluence of D and H ions can be explained by doping effect.•After H ion irradiation for WNOx, H’s distribute within the depth of 20 nm, in agreement with the simulation.•Considerable H exists in as deposited WNOx and D(H) saturation-density by D(H) ion irradiation is comparable with W density.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Deuterium (D) retention is compared between various reduced-activation ferritic/martensitic steels, including CLF-1, Eurofer, F82H, and Rusfer, exposed to pure D plasma (ion flux ∼1.5-2 × 1021 ...m−2s−1, fluence, φD, ∼1 × 1025 m−2, sample temperature ∼373 K, and incident ion energy ∼100 eV). It is found that there is a large difference (up to ∼30x) in the D retention between CLF-1 and F82H even with the same plasma exposure condition and similar nominal composition. The φD dependence of the D retention exhibits a peculiar, counterintuitive feature: the D retention decreases with an increase in φD from 2 × 1023 m−2 to 1 × 1025 m−2. Surface analyses reveal that a Cr-rich surface layer is formed during outgassing at 773 K for 1 h before plasma exposure, and that there exists a clear correlation between the D retention and the Cr content in the surface layer.
Achievement of reactor relevant plasma condition in Helical type magnetic devices and exploration in its related plasma physics and fusion engineering are the aim of the Large Helical Device (LHD) ...project. In the recent experiments on LHD, we have achieved ion-temperature of 8.1 keV at 1 × 10
19
m
−3
by the optimization of wall conditioning using long pulse discharge by Ion Cyclotron Heating (ICH). The electron temperature of 10 keV at 1.6 × 10
19
m
−3
was also achieved by the optimization of Electron Cyclotron Heating (ECH). For further improvement in plasma performance, the upgrade of the Large Helical Device (LHD), including the deuterium experiment, is planned. In this paper, the recent achievements on LHD and the upgrade of LHD are described.
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BFBNIB, GIS, IJS, KISLJ, NUK, PNG, UL, UM, UPUK
In our previous work, the joint between oxide dispersion strengthened copper alloy (ODS-Cu), GlidCop® (Cu–0.3 wt%Al2O3) and tungsten (W) demonstrated superior fracture strength (∼200 MPa). This joint ...was fabricated by the direct brazing method between W and ODS-Cu using BNi-6 (Ni–11%P) filler material without any intermediate layer. This method was named as the improved or the advanced brazing technique. In the present study, deformation and fracture behavior of the joint after the three-point bending test was investigated. At first, it was found that the crack initiation points were dominantly in the W bulk, although it was not clear that the crack initiated from grain boundary or not. Secondly, the crack propagation proceeded mostly in the W bulk but tended to deflect towards the bonding layer. These results interpret the strength of the bonding interface is superior and the present bonding technique is applicable for severe environments such as a high heat flux divertor component on the fusion reactor. Based on the above physical and technological understanding, we successfully fabricated the large scale divertor mock-up which has twenty-eight plates of W with each size of 20 × 20 × 5 mm3.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The joint of the oxide dispersion strengthened copper alloy, ODS-Cu (ODS-Cu/ODS-Cu), was prepared. The applied ODS-Cu was GlidCop® (Cu-0.3 wt%Al2O3). The joint procedures were based on the brazing ...technique between GlidCop® and tungsten (W) with BNi-6 (Ni-11%P) filler material. This method was performed without compressive load and without any intermediate layer, and was named the advanced brazing technique. In this study, first, the joint GlidCop®/GlidCop® was prepared without any compressive load. The joint was subjected to the three-point bending test, the Vickers hardness test, microstructure observation and the leak tightness test. The yield strength of the joint was approximately one-half of that of the GlidCop® bulk. In addition, the joint was not leak tightness against fluids. Next, the joint was prepared with compressive load of ˜0.54 MPa which was applied in the direction perpendicular to the joint interface. The yield strength of the joint was almost as high as that of the GlidCop® bulk. Furthermore, the joint achieved leak tightness against fluids. The special feature of this joint method is that a limited volume of the GlidCop® surfaces near the bonding interface are melted during the bonding heat treatment phase at 960 °C due to the eutectic reaction of the Cu-P system. Then, after finalizing the solidification, a tight bonding layer are created without any cavities and cracks. This phenomenon seems to resemble a micro scale welding. The present brazing technique can promise fabrication of a high heat flux component with a complex shaped fluid flow path system with leak tightness.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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