| 1. |
- Rubel, Marek J., et al.
(författare)
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Thick co-deposits and dust in controlled fusion devices with carbon walls : Fuel inventory and growth rate of co-deposited layers
- 2003
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T103, s. 20-24
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Tidskriftsartikel (refereegranskat)abstract
- Recent results regarding the formation of co-deposits, fuel accumulation and overall material transport at the TEXTOR tokamak are described. Two categories of brittle flaking co-deposits were identified: (i) smooth stratified layers of a thickness of up to 50 mum and a fuel content of up to 16 at.%. (ii) granular and columnar structures reaching 1 mm in thickness and containing around 0.5 at.% of fuel species. They were formed on the blades of the toroidal belt pump limiter (similar to 15000 s of plasma operation) and on the neutraliser plates of this limiter (similar to 90000 s), respectively. A comparison is made to the fuel inventory measured in other controlled fusion devices with carbon walls.
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| 2. |
- Huber, A., et al.
(författare)
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Comparison of impurity production, recycling and power deposition on carbon and tungsten limiters in TEXTOR-94
- 2001
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 290, s. 276-280
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Tidskriftsartikel (refereegranskat)abstract
- Impurity production, hydrogen recycling and power deposition on carbon and tungsten limiters have been investigated in TEXTOR-94 using a C-W twin test limiter. Considerable differences have been observed on W and C surfaces, which can be explained by the different particle and energy reflection coefficients of hydrogen on these surfaces. The measurements show in addition that the majority of the carbon release is from recycled carbon and that only a small part (below 10%) is due to net-erosion from the bulk carbon material. The heat deposition on C and W sides differs under the same plasma conditions significantly and is typically about 30% larger on the cal bon surface. The behaviour of the impurity production: recycling and power deposition for various discharge conditions is presented.
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| 3. |
- Mayer, M., et al.
(författare)
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Hydrogen inventories in nuclear fusion devices
- 2001
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 290, s. 381-388
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Tidskriftsartikel (refereegranskat)abstract
- Hydrogen retention in tokamaks is due to implantation into plasma-facing materials and trapping in deposited layers. In the limiter tokamak TEXTOR-94 hydrogen-rich deposited layers with thicknesses up to 1 mm are observed on recessed parts of the limiters, areas perpendicular to the magnetic field in the scrape-off layer (SOL), neutralizer plates of the pumped limiter and inside the pumping ducts. In the divertor tokamak JET the main deposition is observed in the divertor, additional deposits are observed in the main chamber on the sides of the guard limiters. Codeposition of carbon ions with hydrogen is the major mechanism of layer growth at areas with direct plasma contact. At remote areas without direct plasma contact, sticking of neutral hydrocarbon radicals seems to play an important role for hydrogen trapping.
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| 4. |
- Ohya, K., et al.
(författare)
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Simulation study of carbon and tungsten deposition on W/C twin test limiter in TEXTOR-94
- 2000
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 283, s. 1182-1186
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the impurity release and surface modification on a W/C twin test limiter, made of a half of W and the other half of C, exposed to the edge plasma of TEXTOR-94, simulation calculations of ion-surface interaction are conducted by a Monte Carlo code. According to the calculations, experimentally observed spatial distributions of WI and CII line intensities around the W side of the limiter can be explained by physical sputtering of W, reflection of bombarding C ions and physical sputtering of implanted C. The CII line emission, resulting from thermal C atoms, around the C side of the limiter is suppressed by deposition of W, and the reflection of C ions from W deposited on C causes the CII intensity to decay more slowly than that from C without the deposition. Bombardment with deuterium edge plasmas, containing impurity W, produces a thick W layer on the C side of the limiter, whereas C implanted in the W side is strongly sputtered due to impact of most constituent D ions.
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| 5. |
- Rubel, Marek J., et al.
(författare)
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Graphite-tungsten twin limiters in studies of material mixing processes on high heat flux components
- 2000
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 283, s. 1089-1093
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Tidskriftsartikel (refereegranskat)abstract
- Graphite-tungsten twin limiters have been used at the TEXTOR tokamak for testing of high-Z metals as plasma facing materials and, in particular, for studies of the local and global transport of tungsten. The emphasis was on the change in surface morphology of limiters: the formation and properties of multicomponent co-deposits and the trapping characteristics of fuel on carbon and high-Z substrates exposed to the plasma under various operation conditions, i.e., heating scenarios, configuration of limiters, etc. Vast quantities of tungsten have been found to be locally transported to the adjacent graphite surfaces. Ion beam analysis also indicated strong intermixing of carbon, tungsten and boron on the hottest parts of the limiters. The results are discussed in terms of various mechanisms involving the transport of tungsten-containing species, possibilities of oxide production and formation of mixed (W-C-B) compounds.
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| 6. |
- Rubel, M., et al.
(författare)
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Silicon fluxes in the scrape-off layer plasma during silicon-assisted operation of TEXTOR
- 1995
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 220-222, s. 536-540
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Tidskriftsartikel (refereegranskat)abstract
- Surface collector probes were applied at TEXTOR for the investigation of silicon fluxes in the scrape-off layer during the first silicon-assisted (silane puffing, siliconization) operation of a tokamak. Probe exposures were made in order to measure the evolution of Si fluxes and the influence of silicon on the behaviour of other impurity fluxes like boron, oxygen and metals. Studies were performed under different conditions: heating mode, plasma density and gas filling. Comparative exposures were made before introduction of Si into the machine as well as immediately and long time after the siliconization. The exposed graphite samples were examined by surface analysis techniques, including Auger electron and Rutherford backscattering spectroscopies, nuclear reaction analysis and ultra-high resolution microscopies. The most important findings are concerned with: (i) the relation between silicon to carbon and silicon to oxygen in the deposits; (ii) the change in radial profiles of Si, B and D fluxes during consecutive stages of the silicon-assisted operation, and the retention of deuterium in the Si containing codeposited layers. The influence of plasma density on the fluxes is considered and gettering of oxygen by silicon is also addressed. Comparison is also made to the results of VUV spectroscopy signals of silicon and oxygen impurities in the plasma.
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| 7. |
- Tanabe, T., et al.
(författare)
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Application of tungsten for plasma limiters in TEXTOR
- 2000
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 283, s. 1128-1133
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Tidskriftsartikel (refereegranskat)abstract
- Three different types of W limiters were exposed in the TEXTOR plasma and the response of the plasma and materials performance of the limiters were investigated. 1. A W bulk limiter operated with preheating above 800 K withstood a plasma heat load of about similar to 20 MW/m(2) for a few seconds with some slight surface melting during the highest heat load shot. However, it was severely damaged when operated at around 500 K. 2. A C/W twin test limiter, half made of bulk W and the other half of graphite (EK-98) gave very useful information on how low- and high-Z materials behave under conditions of simultaneous utilization as PFM such as cross-contamination and the influence of a large mass difference on hydrogen reflection and deposition. 3. Two sets of main poloidal W limiters made of vacuum vapor sprayed (VPS)-W deposited on graphite (IG-430U) with a Re interlayer could absorb about 60% of the total convection heat and the ohmic plasma with a density as high as 5 x 10(13) cm(-3) was sustained. Most of the VPS-W coated limiters tolerated a heal load of similar to 20 MW/m(2). This series of W limiters experiments in TEXTOR has shown that W is applicable as a PFM, if its central accumulation is avoided by NBI and/or ICRH heating. Nevertheless, some concerns still remain, including difficulty of plasma startup, W behavior in higher temperature plasmas, and materials' selection.
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| 8. |
- Tanabe, T., et al.
(författare)
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Material mixing on W/C twin limiter in TEXTOR-94
- 2000
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Ingår i: Fusion engineering and design. - 0920-3796 .- 1873-7196. ; 49, s. 355-362
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Tidskriftsartikel (refereegranskat)abstract
- In order to investigate the effect of mutual contamination between tungsten (W) and carbon
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| 9. |
- von Seggern, J., et al.
(författare)
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Erosion and deposition effects on the vessel wall of TEXTOR-94
- 2001
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 290, s. 341-345
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Tidskriftsartikel (refereegranskat)abstract
- Two different sets of long term samples (LTS) were exposed in TEXTOR-94 at the liner with boronized and siliconized wall conditions. Measured erosion/deposition rates of the coating constituents were compared with sputtering rates calculated for pure elements. D-0-fluxes at the LTS locations were determined by the B2-EIRENE code. Over the whole liner, erosion of initial coatings by D-0 is observed. Boron erodes at a rate of 8.4 x 10(13) B cm(-2) s(-1),while silicon erodes at a rate of 5.6 x 10(13) Si cm(-2) s(-1), a factor of 1.5 lower than that of boron. With boronized walls, carbon atoms initially present in the a-C/B:D layers are eroded at a rate of 7.6 x 10(12) C cm(-2) s(-1), at the same time 1.7 x 10(12) (Fe + Cr + Ni) cm(-2) s(-1) are deposited. Compared to boronized conditions where carbon erodes, deposition of carbon (1.7 x 10(13) cm(-2) s(-1)) and of metals (3.8 x 10(12) cm(-2) s(-1) occurred during the Si campaign. Due to long time exposure at high wall temperature (350 degreesC), hydrogenic isotopes desorb; (D + H)/(B + C) and (D + H)/(Si + C) ratios degrade from originally similar to0.4 to similar to0.2.
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| 10. |
- Wienhold, P., et al.
(författare)
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Short and long range transport of materials eroded from wall components in fusion devices
- 2003
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 313, s. 311-320
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Tidskriftsartikel (refereegranskat)abstract
- Carbon sources and the sinks have been quantified in TEXTOR and are discussed in terms of short and long range transport. The major source (22 g/h) is the graphite belt limiter, but part (10 g/h) of the carbon is directly re-deposited after short range transport. Long range transport causes flake formation on obstacles and neutralisers, but little and deuterium rich (D/C approximate to 0.7) deposition in remote areas. The rest is leaving via the pumps in gaseous form. This behaviour is different from that in JET where large amounts of deuterium rich deposits were found in the louvers. Tungsten is favoured for the ITER divertors because of its low sputtering yield for hydrogen, but melting and erosion by carbon may be an additional concern. The short range transport of tungsten has been investigated in a well defined experiment and quantitatively re-constructed by means of the ERO-TEXTOR code. Code validation is necessary in order to increase the confidence and the applicability to JET and ITER.
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