| 1. |
- Abreu, P., et al.
(författare)
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Measurement of the gluon fragmentation function and a comparison of the scaling violation in gluon and quark jets
- 2000
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 13:4, s. 573-589
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Tidskriftsartikel (refereegranskat)abstract
- The fragmentation functions of quarks and gluons are measured in various three-jet topologies in Z decays from the full data set collected with the DELPHI detector at the Z resonance between 1992 and 995. The results at different values of transverse momentum-like scales are compared. A parameterization of the quark and gluon fragmentation functions at a fixed reference scale is given. The quark and gluon fragmentation functions show the predicted pattern of scaling violations. The scaling violation for quark jets as a function of a transverse momentum-like scale is in a good agreement with that observed in lower energy e+e- annihilation experiments. For gluon jets it appears to be significantly stronger. The scale dependences of the gluon and quark fragmentation functions agree with the prediction of the DGLAP evolution equations from which the colour factor ratio CA/CF is measured to be: CA/CF = 2.26 ± 0.09stat. ± 0.06sys. ± 0.12clus.,scale..
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| 2. |
- Abreu, P., et al.
(författare)
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Study of dimuon production in photon-photon collisions and measurement of QED photon structure functions at LEP
- 2001
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Ingår i: European Physical Journal C. - : Springer Science and Business Media LLC. - 1434-6044 .- 1434-6052. ; 19:1, s. 15-28
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Tidskriftsartikel (refereegranskat)abstract
- Muon pair production in the process e+e- → e+e- μ+μ- is studied using the data taken at LEP1 (√s ≃ mz) with the DELPHI detector during the years 1992-1995. The corresponding integrated luminosity is 138.5 pb-1. The QED predictions have been tested over the whole Q2 range accessible at LEP1 (from several GeV2/c4 to several hundred GeV2/c4) by comparing experimental distributions with distributions resulting from Monte Carlo simulations using various generators. Selected events are used to extract the leptonic photon structure function Fγ 2. Azimuthal correlations are used to obtain information on additional structure functions, Fγ A and Fγ B, which originate from interference terms of the scattering amplitudes. The measured ratios Fγ A/Fγ 2 and FγB/Fγ 2 are significantly different from zero and consistent with QED predictions.
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| 3. |
- Alcorn, J, et al.
(författare)
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Basic instrumentation for Hall A at Jefferson Lab
- 2004
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Ingår i: Nuclear Instruments & Methods in Physics Research. Section A: Accelerators, Spectrometers, Detectors, and Associated Equipment. - : Elsevier BV. - 0167-5087 .- 0168-9002. ; 522:3, s. 294-346
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Tidskriftsartikel (refereegranskat)abstract
- The instrumentation in Hall A at the Thomas Jefferson National Accelerator Facility was designed to study electro-and photo-induced reactions at very high luminosity and good momentum and angular resolution for at least one of the reaction products. The central components of Hall A are two identical high resolution spectrometers, which allow the vertical drift chambers in the focal plane to provide a momentum resolution of better than 2 x 10(-4). A variety of Cherenkov counters, scintillators and lead-glass calorimeters provide excellent particle identification. The facility has been operated successfully at a luminosity well in excess of 10(38) CM-2 s(-1). The research program is aimed at a variety of subjects, including nucleon structure functions, nucleon form factors and properties of the nuclear medium. (C) 2003 Elsevier B.V. All rights reserved.
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| 4. |
- Botchkarev, V A, et al.
(författare)
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Noggin is required for induction of the hair follicle growth phase in postnatal skin.
- 2001
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Ingår i: FASEB journal : official publication of the Federation of American Societies for Experimental Biology. - : Wiley. - 1530-6860. ; 15:12, s. 2205-14
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Tidskriftsartikel (refereegranskat)abstract
- During postnatal development, the hair follicle (HF) shows cyclic activity with periods of relative resting, active growth (anagen), and regression. We demonstrate that similar to the HF induction in embryonic skin, initiation of a new hair growth phase in postnatal skin requires neutralization of the inhibitory activity of bone morphogenetic protein 4 (BMP4) by the BMP antagonist noggin. In the resting HF, BMP4 mRNA predominates over noggin in the epithelium and mesenchyme, and the BMP receptor IA is prominently expressed in the follicular germ. Anagen development is accompanied by down-regulation of the BMP4 and increased noggin mRNA in the HF. Furthermore, administration of noggin protein induces new hair growth phase in postnatal telogen skin in vivo. In contrast, BMP4 induces selective arrest of anagen development in the non-tylotrich (secondary) HF. As a hair growth inducer, noggin increases Shh mRNA in the HF whereas BMP4 down-regulates Shh. This suggests that modulation of BMP4 signaling by noggin is essential for hair growth phase induction in postnatal skin and that the hair growth-inducing effect of noggin is mediated, at least in part, by Shh.
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| 5. |
- Gayou, O, et al.
(författare)
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Measurement of G(Ep)/G(Mp) in (e)over-right-arrowp -> e(p)over-right-arrow to Q(2)=5.6 GeV2
- 2002
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Ingår i: Physical Review Letters. - 1079-7114. ; 88:9
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Tidskriftsartikel (refereegranskat)abstract
- The ratio of the electric and magnetic form factors of the proton G(Ep)/G(Mp), which is an image of its charge and magnetization distributions, was measured at the Thomas Jefferson National Accelerator Facility (JLab) using the recoil polarization technique. The ratio of the form factors is directly proportional to the ratio of the transverse to longitudinal components of the polarization of the recoil proton in the elastic (e) over right arrowp --> e (p) over right arrow reaction. The new data presented span the range 3.5 < Q(2) < 5.6 GeV2 and are well described by a linear Q(2) fit. Also, the ratio rootQ(2) F-2p/F-1p reaches a constant value above Q(2) = 2 GeV2.
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| 6. |
- 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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| 7. |
- Schulte, EC, et al.
(författare)
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High energy angular distribution measurements of the exclusive deuteron photodisintegration reaction
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - : American Physical Society. - 0556-2813 .- 1089-490X. ; 66:4
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Tidskriftsartikel (refereegranskat)abstract
- The first complete measurements of the angular distributions of the two-body deuteron photodisintegration differential cross section at photon energies above 1.6 GeV were performed at the Thomas Jefferson National Accelerator Facility. The results show a persistent forward-backward asymmetry up to E-gamma=2.4 GeV, the highest-energy measured in this experiment. The Hard Rescattering and the Quark-Gluon string models are in fair agreement with the results.
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| 8. |
- Wijesooriya, K, et al.
(författare)
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Polarization measurements in high-energy deuteron photodisintegration
- 2001
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Ingår i: Physical Review Letters. - : American Physical Society. - 0031-9007 .- 1079-7114. ; 86:14, s. 2975-2979
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the recoil proton polarization for the d(γ⃗,p⃗)n reaction at θc.m. = 90° for photon energies up to 2.4 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. The induced polarization py vanishes above 1 GeV, contrary to meson-baryon model expectations, in which resonances lead to large polarizations. However, the polarization transfer Cx does not vanish above 1 GeV, inconsistent with hadron helicity conservation. Thus, we show that the scaling behavior observed in the d(γ,p)ncross sections is not a result of perturbative QCD. These data should provide important tests of new nonperturbative calculations in the intermediate energy regime.
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| 9. |
- Wijesooriya, K, et al.
(författare)
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Polarization measurements in neutral pion photoproduction
- 2002
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Ingår i: Physical Review C (Nuclear Physics). - 0556-2813. ; 66:3
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Tidskriftsartikel (refereegranskat)abstract
- We present measurements of the recoil proton polarization for the H-1((γ) over right arrow,(p) over right arrow)pi(0) reaction for theta(c.m.)(pi) = 60degrees-135degrees and for photon energies up to 4.1 GeV. These are the first data in this reaction for polarization transfer with circularly polarized photons. Various theoretical models are compared with the results. No evidence for hadron helicity conservation is observed. Models that employ factorization are not favored. It appears from the strong angular dependence of the induced polarization at photon energies of 2.5 and 3.1 GeV that a relatively high spin resonance or background amplitude might exist in this energy region.
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| 10. |
- Botchkarev, Vladimir A, et al.
(författare)
-
Modulation of BMP signaling by noggin is required for induction of the secondary (nontylotrich) hair follicles.
- 2002
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Ingår i: The Journal of investigative dermatology. - : Elsevier BV. - 0022-202X. ; 118:1, s. 3-10
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Tidskriftsartikel (refereegranskat)abstract
- Increasing evidence suggests that morphogenesis of the distinct developmental structures derived from the same organ-committed epithelium is controlled by differential mechanisms. As was recently shown in mice with mutations in the downless (dL) gene, induction of primary or tylotrich hair follicles is strikingly dependent of signaling through the Tnf receptor homologue, Edar. Here, we show that dorsal skin of murine embryos with constitutive deletion of the BMP2/4 antagonist noggin, after transplantation into SCID mice, is characterized by the lack of induction of secondary hair follicles, and by the arrest of primary hair follicle development prior to hair shaft formation. The loss of noggin activity was associated with failure to express genes that specify hair follicle cell fates in the epidermis (Lef-1, beta-catenin, Shh) and dermal papilla (p75 kDa neurotrophin receptor, alkaline phosphatase). This suggests that regulation of BMP2/4 signaling by noggin is essential for the induction of secondary hair follicles, as well as for advanced stages of development in primary hair follicles.
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| 11. |
- Cieslik, D., et al.
(författare)
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Connectivity calculus
- 2003
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Ingår i: Applied Mathematical Letters. ; 16, s. 395-399
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Tidskriftsartikel (refereegranskat)
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| 12. |
- 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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| 13. |
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| 14. |
- 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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| 15. |
- 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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| 16. |
- Huber, KT, et al.
(författare)
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Replacing cliques by stars in quasi-median graphs
- 2004
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Ingår i: Discrete Applied Mathematics. ; 143:1-3, s. 194-203
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Tidskriftsartikel (refereegranskat)abstract
- For a multi-set Sigma of splits (bipartitions) of a finite set X, we introduce the multi-split graph G(Sigma). This graph is a natural extension of the Buneman graph. Indeed, it is shown that several results pertaining to the Buneman graph extend to the multi-split graph. In addition, in case Sigma is derived from a set R of partitions of X by taking parts together with their complements, we show that the extremal instances where R is either strongly compatible or strongly incompatible are equivalent to G(Sigma) being either a tree or a Cartesian product of star trees, respectively.
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| 17. |
- Huber, KT, et al.
(författare)
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The tight span of an antipodal metric space: Part II - Geometrical properties
- 2004
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Ingår i: Discrete & Computational Geometry. - 0179-5376. ; 31:4, s. 567-586
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Tidskriftsartikel (refereegranskat)abstract
- Suppose that X is a finite set and let R-x denote the set of functions that map X to R. Given a metric d on X, the tight span of (X, d) is the polyhedral complex T (X, d) that consists of the bounded faces of the polyhedronP(X, d) := {f is an element of R-x : f(x) + f (y) greater than or equal to d(x, y)}.In a previous paper we commenced a study of properties of T(X, d) when d is antipodal, that is, there exists an involution sigma : X --> X: x --> (x) over bar so that d(x, y) + d(y,(x) over bar) = d(x, (x) over bar) holds for all x, y c X. Here we continue our study, considering geometrical properties of the tight span of an antipodal metric space that arise from a metric with which the tight span comes naturally equipped. In particular, we introduce the concept of cell-decomposability for a metric and prove that the tight span of such a metric is the union of cells, each of which is isometric and polytope isomorphic to the tight span of some antipodal metric. In addition, we classify the antipodal cell-decomposable metrics and give a description of the polytopal structure of the tight span of such a metric.
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| 18. |
- 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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| 19. |
- Ohya, K., et al.
(författare)
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Simulation calculations of mutual contamination between tungsten and carbon and its impact on plasma surface interactions
- 2001
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Ingår i: Journal of Nuclear Materials. - 0022-3115 .- 1873-4820. ; 290, s. 303-307
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Tidskriftsartikel (refereegranskat)abstract
- Mutual contamination between C and W, resulting from the simultaneous use of these materials as plasma facing components, is simulated by means of a computer simulation code, Erosion and Deposition based on Dynamic model (EDDY). W deposition on C rapidly increases the reflection coefficient for D and C impurity. In comparison between the calculation and a C-W twin test limiter experiment in TEXTOR-94, C release from the C side of the limiter is dominated by reflection of C impurity from the W deposits, in addition to physical sputtering of C; chemical erosion is strongly suppressed. Due to the dynamic effect which makes C-W mixed layer, C deposition on W gradually changes the reflection coefficient and sputter yields. Formation of a sharp boundary between erosion and C deposition zones on the W side of the limiter is well reproduced by simulation. Local redeposition patterns of C and W on the limiter surface are also calculated.
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| 20. |
- 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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| 21. |
- 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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| 22. |
- 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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| 23. |
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| 24. |
- 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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| 25. |
- 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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