| 1. |
- Sergienko, G., et al.
(författare)
-
Experience with bulk tungsten test-limiters under high heat loads : melting and melt layer propagation
- 2007
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T128, s. 81-86
-
Tidskriftsartikel (refereegranskat)abstract
- The paper provides an overview of processes and underlying physics governing tungsten melt erosion in the fusion plasma environment. Experiments with three different bulk tungsten test-limiters were performed in TEXTOR: (i) thermally insulated solid plate fixed on a graphite roof-like limiter heated up by the plasma to the melting point, (ii) macro-brush of the ITER-relevant castellated structure and (iii) lamellae structure developed for the JET divertor. The main objectives were to determine the metal surface damage, the formation of the melt layer and its motion in the magnetic field. PHEMOBRID-3D and MEMOS-1.5D numerical codes were used to simulate the experiment with the roof-like test-limiter. Both experiments and simulation showed that the melting of tungsten can lead to a large material redistribution due to thermo-electron emission currents without ejection of molten material to the plasma.
|
|
| 2. |
|
|
| 3. |
- Kreter, A., et al.
(författare)
-
Fuel retention in carbon materials under ITER-relevant mixed species plasma conditions
- 2009
-
Ingår i: Physica scripta. T. - : Institute of Physics Publishing (IOPP). - 0281-1847 .- 0031-8949 .- 1402-4896. ; T138, s. 014012-
-
Tidskriftsartikel (refereegranskat)abstract
- Samples of CFC NB41 and fine-grain graphite ATJ have been exposed to PISCES plasmas containing (i) pure deuterium, (ii) deuterium and beryllium, (iii) deuterium, beryllium and helium, and (iv) deuterium, beryllium and argon. Thermal desorption spectrometry (TDS) and nuclear reaction analysis (NRA) have been used to measure the amount and distribution of retained deuterium in the samples. For the case of pure deuterium plasma, parametric studies of deuterium retention in NB41 have been done with variations of the incident deuterium fluence (Phi = 1 x 10(25)-5 x 10(26) m(-2)), ion energy (E-i = 20-120 eV) and sample surface temperature (T-s = 370-820 K). It has been found, that for T-s = 470K the retention scales as Phi(0.35). For T-s = 820K the retention saturates at a level of similar to 10(21) Dm(-2). The retention increases with E-i and drops with higher T-s. At T-s = 720 K, the beryllium seeding results in a building of a protective beryllium carbide layer, which appears to prevent the in-bulk diffusion of deuterium, thus reducing the retention. Admixture of Ar and, in the case of low E-i, He leads to a significant reduction of the retention.
|
|
| 4. |
|
|
| 5. |
- Rubel, Marek J., et al.
(författare)
-
An overview of fuel retention and morphology in a castellated tungsten limiter
- 2008
-
Ingår i: Fusion engineering and design. - : Elsevier BV. - 0920-3796 .- 1873-7196. ; 83:7-9, s. 1049-1053
-
Tidskriftsartikel (refereegranskat)abstract
- A castellated tungsten test limiter composed of detachable segments was exposed to plasma discharges in the TEXTOR to kamak operated with graphite main limiters. Dismantling of the limiter enabled the analysis Of Surfaces located inside the castellation, The emphasis was on the determination of: (i) deposition and fuel retention; (ii) material mixing and new Compound formation on plasma-facing Surfaces and in the grooves of castellation. The investigation performed by means of accelerator-based ion beam analysis methods, microscopy and X-ray diffraction has brought several essential results: (i) deuterium retention oil plasma-facing Surfaces and in the castellation of metal PFC is strongly related to the co-deposition with carbon; (ii) both carbon and deuterium are detected only in narrow belts, a few millimetre broad, clown the gap with the decay length of around 1.2-1.8 mm; (iii) the presence of copper droplets and tungsten oxide (WO(2)) has been identified in the gaps. Different pathways leading to the oxide formation are considered.
|
|
| 6. |
- Fortuna, E., et al.
(författare)
-
Plasma-induced damage of tungsten coatings on graphite limiters
- 2007
-
Ingår i: Physica Scripta. - 0031-8949 .- 1402-4896. ; T128, s. 162-165
-
Tidskriftsartikel (refereegranskat)abstract
- Vaccum plasma sprayed tungsten coatings with an evaporated sandwich Re - W interlayer on graphite limiter blocks were studied after the experimental campaign in the TEXTOR tokamak. The coating morphology was modified by high-heat loads and co-deposition of species from the plasma. Co-deposits contained fuel species, carbon, boron and silicon. X-ray diffractometer phase analysis indicated the coexistence of metallic tungsten and its carbides (WC and W2C) and boride (W2B). In the Re - W layer the presence of carbon was detected in a several micrometres thick zone. In the overheated part of the limiter, the Re - W layer was transformed into a sigma phase.
|
|
| 7. |
- Psoda, M., et al.
(författare)
-
Material mixing on plasma-facing components : Compound formation
- 2009
-
Ingår i: Journal of Nuclear Materials. - : Elsevier. - 0022-3115 .- 1873-4820. ; 386-388, s. 740-743
-
Tidskriftsartikel (refereegranskat)abstract
- Two different tungsten limiters (castellated bulk metal block and W-coated graphite), subjected to high power loads in the TEXTOR tokamak, were examined in order to determine chemical composition of deposits inside the castellated grooves and on side surfaces of the coated limiter. Comprehensive analyses carried out by X-ray diffraction, ion beam analysis and other methods revealed: (i) the formation of tungsten oxide (WO2) inside the castellated grooves: (ii) the formation of tungsten carbides (WC main phase and traces of W2C) on side surfaces of the coated limiter. Elemental tungsten was found in deposits on side surfaces only in trace quantities thus indicating that tungsten eroded from the limiter top and transported to the scrape-off layer reacted with carbon. Based on thermodynamic data, the pathways leading to the formation of compounds are discussed.
|
|
