| 1. |
- 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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| 2. |
- Ohya, K., et al.
(författare)
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Modeling of erosion and deposition patterns on C-W and W-Ta twin limiters exposed to the TEXTOR edge plasmas
- 2004
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 329-33, s. 732-736
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Tidskriftsartikel (refereegranskat)abstract
- The erosion and deposition patterns on tungsten and tantalum test limiters exposed to the TEXTOR deuterium plasma containing a small amount of C impurity are simulated with the modified EDDY code. At the very top of the W and Ta limiters, there occurs neither erosion nor deposition, but the erosion proceeds slowly along the surface. When approaching the edge, the surface is covered by a thick C layer, which shows a very sharp boundary similar to the observation in surface measurements. In the erosion zone, the re-deposited carbon forms a W (Ta)-C mixed layer with small C concentration. Assumptions for chemical erosion yields of similar to0.01 for W and
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| 3. |
- Pospieszczyk, A., et al.
(författare)
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B4C-limiter experiments at TEXTOR
- 2003
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 313, s. 223-229
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Tidskriftsartikel (refereegranskat)abstract
- In the TEXTOR tokamak the five top and five bottom poloidal carbon limiter blocks have been replaced by inertially cooled copper blocks coated with a 170 mum VPS-B4C layer. Similar limiter blocks have been inserted through lock systems, extensively diagnosed in situ as well as ex situ. During the thermal load by the plasma, the surface temperature rose and decayed extremely fast which can be explained by a different thermal conductivity and heat capacity of the coating. For heat loads below 8 MW m(-2) no severe cracking or delamination of the B4C-coating were observed. Due to the insulating behaviour of the layer, distinct craters developed on both limiter types, which reached down to the copper surface and are assumed to be caused by electrical arcs. An oscillation of the evolution of the surface temperature has been observed under certain conditions, which is clearly correlated to the use of the coated test limiter. Particle fluxes as well as hydrogen inventory turned out to be very similar to those from a low-Z surface in a carbon surrounding. No significant impact of the plasma on the coating and vice versa was observed.
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| 4. |
- Pospieszczyk, A., et al.
(författare)
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Operation of TEXTOR-94 with tungsten poloidal main limiters
- 2001
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 290, s. 947-952
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Tidskriftsartikel (refereegranskat)abstract
- In TEXTOR-93, experiments have been performed with the upper and lower poloidal limiter blocks made of vapour sprayed (VSP) tungsten (about 0.5 mm) deposited on graphite with a rhenium interlayer. A series of discharge conditions have been performed (density scan, scan of the auxiliary heating power, radius scan). There has been found no restriction for operation at any density with auxiliary heating. For Ohmic conditions the same density with testlimiters could be reached. Under siliconized conditions no severe accumulation of tungsten in the plasma centre could be detected. The blocks could in general stand surface temperatures below 1700 K. Most of them survived also temperatures above 3000 K without exfoliation. However, some blocks showed severe damage by melting or exfoliation probably due to insufficient contact of the tungsten layer with the graphite.
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| 5. |
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| 6. |
- Tsegaye, T., et al.
(författare)
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Experimental demonstration of three mutually orthogonal polarization states of entangled photons
- 2000
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Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 85:24, s. 5013-5017
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Tidskriftsartikel (refereegranskat)abstract
- Linearly polarized classical light can be expressed in a vertical and a horizontal component. Geometrically rotating vertically polarized light by 90 degrees will convert it to the orthogonal horizontal polarization. We have experimentally generated a two-photon state of light which evolves into an orthogonal state upon geometrical rotation by 60 degrees. Rotating this state by an additional 60 degrees will yield a state which is mutually orthogonal to the first two states. Generalizing this procedure, one can generate N + 1 mutually orthogonal N-photon states that cyclicly evolve from one to another upon a geometric rotation by 180/(N + 1) degrees.
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| 7. |
- Gustavsson, B., Sergienko, T., Rietveld, M.T., Honary, F., Steen, A., Brandstrom, B.U., Leyser, T.B., Aruliah, A.L., Aso, T., Ejiri, M. and Marple, S.
(författare)
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First Tomographic estimate of volume distribution of HF-pump enhanced airglow emission.
- 2001
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Ingår i: Journal of Geophysical Research. ; 106:A12, s. 29105-29123
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Tidskriftsartikel (refereegranskat)abstract
- This report presents the first estimates of the three-dimensional volume emission rate of enhanced O(D-1) 6300 Angstrom airglow caused by HF radio wave pumping in the ionosphere. Images of the excitation show how the initially speckled spatial structure o
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| 8. |
- Hirai, T., et al.
(författare)
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Performance and erosion of a tungsten brush limiter exposed at the TEXTOR tokamak
- 2003
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 313, s. 67-71
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Tidskriftsartikel (refereegranskat)abstract
- To examine the performance of a castellated structure under plasma loading, a hemispherical solid tungsten brush limiter was exposed to the plasma in the TEXTOR-94 tokamak. Due to the thermally isolated column of W segments, IR camera showed a non-uniform temperature distribution. The maximum incident power density was calculated to be about 35-40 MW/m(2). Concerning impurity generation, the structure did not show any particular effects. During plasma exposure, only some minor cracks developed in one of the columns, however, the crack propagation was interrupted by a groove. It can be concluded that the W brush limiter had comparable performance and superior mechanical behaviour compared to a solid W limiter. To study erosion and long-range transport of W atoms, a graphite limiter was exposed simultaneously with the brush limiter. As a result, the deposited W atoms via long-range transportation were estimated to be 10(15) cm(-2) shot(-1) at 46.5 cm from the plasma centre of TEXTOR.
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| 9. |
- Hirai, T., et al.
(författare)
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Testing of tungsten and tantalum limiters at the TEXTOR tokamak : Material performance and deuterium retention
- 2003
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Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T103, s. 59-62
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Tidskriftsartikel (refereegranskat)abstract
- Tungsten and tantaium were examined in the TEXTOR tokamak as test limiters in order to compare their performance under plasma operation and to recognise fuel recycling on endothermic (W) and exothermic (Ta) hydrogen absorbers. Differences have been noticed in the distribution and microstructure of co-deposits. in the fuel inventory in the bulk of metals and, in the deuterium release mechanism (ratio of molecules to atoms). As a result of poor thermal conductivity. the surface temperature of Ta during the power deposition was higher than that of W and it increased shot-by-shot because of the degradation of thermal properties due to surface modification. Results on thermal response, fuel recycling and inventory show that. as a candidate material for plasma facing components. tungsten is superior to tantalum.
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| 10. |
- Huber, A., et al.
(författare)
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In-situ measurement of trapped hydrogen by laser desorption in TEXTOR-94
- 2001
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Ingår i: Physica scripta. T. - 0281-1847. ; T94, s. 102-105
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Tidskriftsartikel (refereegranskat)abstract
- First measurements on laser induced desorption of deuterium incorporated in a boron layer formed by plasma chemical vapor deposition on tungsten and graphite limiter surfaces have been performed. A ruby laser (lambda = 694 nm) with maximum energy of 50 J and a pulse length of about 0.5 ms was used as a heat source. The desorbed deuterium was detected by mass spectroscopy and total pressure analysis in the residual gas. The amount of desorbed deuterium is about 10(17) D atoms cm(-2). The majority of the deuterium is released during the first laser pulse. The limiter heads were investigated post-mortem by means of ion beam analysis to determine the spatial distribution of boron and deuterium and to investigate the effect of the laser pulse on the release of deuterium and sublimation of boron in the laser spot. All the deuterium has been released by the laser pulse. The boron is sublimated partly from the graphite and removed nearly completely from the tungsten surface.
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