| 1. |
- Coad, J. P., et al.
(författare)
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Overview of material re-deposition and fuel retention studies at JET with the Gas Box divertor
- 2006
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 46:2, s. 350-366
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Tidskriftsartikel (refereegranskat)abstract
- in the period 1998-2001 the JET tokamak was operated with the MkII Gas Box divertor. On two occasions during that period a number of limiter and divertor tiles were retrieved from the torus and then examined ex situ with surface sensitive techniques. Erosion and deposition patterns were determined in order to assess the material erosion, material migration and fuel inventory on plasma facing components. Tracer techniques, e.g. injection of C-13 labelled methane and tiles coated with a low-Z and high-Z marker layer, were used to enhance the volume of information on the material transport. The results show significant asymmetry in the distribution of fuel and plasma impurity species between the inner (net deposition area) and the outer (net erosion) divertor channels. No significant formation of highly hydrogenated carbon films has been found in the Gas Box structure. The important processes for material migration, and the influence of operation scenarios on the morphology of the deposits are discussed. Comparison is also made with results obtained following previous divertor campaigns.
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| 2. |
- Bergsåker, Henric, et al.
(författare)
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Nuclear reaction analysis with ion microbeam of cross sections of surface layers deposited in tokamak divertor
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 362:2-3, s. 215-221
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Tidskriftsartikel (refereegranskat)abstract
- Ion micro beam analysis has been applied to the investigation of plasma deposited layers covering the divertor tiles in the JET tokamak. Since the layers are about 100 μm thick they are too thick to be completely investigated by ordinary ion beam analysis. Cross sections of the layers were prepared by cutting and polishing. Elemental depth profiles were determined from the two dimensional images that could be derived by nuclear reaction analysis and resonant backscattering spectrometry, using ion beams focused to a few μm spot size. A combination of analysis methods are shown, which allow measurements of the concentration profiles of carbon, beryllium, deuterium, oxygen and stainless steel components at levels of a few percent, with an accuracy better than 10%.
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| 3. |
- Likonen, J., et al.
(författare)
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Beryllium accumulation at the inner divertor of JET
- 2005
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 337-39:03-jan, s. 60-64
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Tidskriftsartikel (refereegranskat)abstract
- MkIIGB divertor tiles exposed in JET for the 1998-2001 and 1999-2001 campaigns have been used to assess the amount of beryllium and carbon deposited at the inner divertor wall. Total amount of Be at the inner divertor tiles was determined and integrated toroidally. Results were compared with data obtained with optical spectroscopy and good agreement was obtained. The amount of deposited C was computed from the amount of deposited Be assuming that the Be/C ratio arriving in the divertor is the same as the Be/C ratio in the main chamber. On the basis of this analysis we would expect there to be similar to 0.4 kg of C deposited. This gives an average C deposition rate lower than during the MkIIA phase.
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| 4. |
- Likonen, J., et al.
(författare)
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Post-mortem measurements of fuel retention at JET with MKII-SRP divertor
- 2009
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 390-91, s. 631-634
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Tidskriftsartikel (refereegranskat)abstract
- The deuterium inventory at JET after 2001-2004 operational campaign has been determined using nuclear reaction analysis (NRA) and secondary ion mass spectrometry (SIMS). A full poloidal set of divertor tiles and a set of outer poloidal limiter (OPL) tiles were analysed providing an estimation for the total deuterium retention of about 66 g. Deuterium is trapped mainly at the inner divertor on horizontal target tile and at the inner divertor louvre area where similar to 60% of the trapped D is found. The long-term D retention is similar to 4% of the total D input.
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| 5. |
- Likonen, J., et al.
(författare)
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Structural investigation of re-deposited layers in JET
- 2008
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 377:3, s. 486-491
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Tidskriftsartikel (refereegranskat)abstract
- JET Mk-II Gas Box divertor tiles exposed in 1998-2001 have been analysed with various ion beam techniques, secondary ion mass spectrometry (SIMS) and Raman spectroscopy. Inner divertor wall tiles removed in 2001 were covered with a duplex film. The inner layer was very rich in metallic impurities, with Be/C - 1 and H-isotopes only present at low concentrations. The outer layer contained higher concentrations of D than normal for plasma-facing surfaces in JET (D/C - 0.4), and Be/C - 0.14. Raman and SIMS analyses show that the deposited films on inner divertor tiles are hydrogenated amorphous carbon with low sp' fractions. The deposits have polymeric structure and low density. Both Raman scattering and SIMS indicate that films on inner divertor wall Tiles 1 and 3, and on floor Tile 4 have some differences in the chemical structure of the deposited films
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| 6. |
- Likonen, J., et al.
(författare)
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Structural studies of deposited layers on JET MkII-SRP inner divertor tiles
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 363, s. 190-195
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Tidskriftsartikel (refereegranskat)abstract
- Deposited layers formed on JET inner divertor tiles during 1998-2004 and 2001-2004 campaigns have been investigated using secondary ion mass spectrometry (SIMS), Rutherford Backscattering (RBS) and optical microscopy. The thickness of the deposit decreases from the top of vertical tile 1 to the bottom and then increases on vertical tile 3 reaching similar to 60 mu m. There are even thicker deposits on the small sloping section of the floor tile 4 that can be accessed by the plasma at the inner divertor legs. Deposited films on divertor inner wall tiles are enriched in Be indicating chemical erosion of C and a multi-step transport of C to the shadowed area on floor tile 4. The films have generally a layered and globular structure in the areas with plasma contact.
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| 7. |
- Widdowson, A., et al.
(författare)
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Efficacy of photon cleaning of JET divertor tiles
- 2007
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 363, s. 341-345
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Tidskriftsartikel (refereegranskat)abstract
- Photon cleaning by means of a flash-lamp was used for in-situ detritiation of the inner wall tiles of the JET divertor in May 2004. Additional trials were also performed ex-situ in October 2004 on divertor base tiles. Early work confirmed that for pulse energies between 150 J and 300 J some deposited material was removed. To increase the amount of material removed during photon cleaning, further experiments with higher pulse energies (500 J) were performed and are reported here. Analysis of cross sections confirmed a removal rate of 0.04 mu m/pulse, removing similar to 80 mu m from 200 mu m thick deposits over a treatment area of 15 x 10(-4) m(2). During the photon cleaning tests at least 12% of the tritium inventory for the tile was removed. It was also shown that deuterium was desorbed from a depth similar to 7 mu m beyond the depth of material removed. Crown
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