| 1. |
- Alegre, Daniel, et al.
(författare)
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Study of correlation of deuterium content in a-C:D dust induced by laser irradiation from the co-deposited surface with the grain size and velocity
- 2014
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Ingår i: Physica Scripta. - : Institute of Physics (IOP). - 0031-8949 .- 1402-4896. ; T161, s. 014010-
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Tidskriftsartikel (refereegranskat)abstract
- In the study described here, the laser ablation method was applied to clean thick (40-60 m) a-C: D co-deposits on the ALT-II limiter blade from the TEXTOR tokamak, and at the same time to characterize the ejected particles formed during ablation and measure the amount of fuel carried by them. Ablation was accomplished by similar to 3.5 ns, 0.5 J Nd: YAG laser pulses in either vacuum or an O-2 atmosphere at different pressures. Fast camera tracking of the process provided an estimate of the population and velocity of up to 100ms(-1) for larger dust particles. In the same experiment, the dust particles were caught using ultra-light Si aerogel collectors placed in front of the ablation target. SEM analysis of aerogel surfaces verified the speed estimate, providing the trapped particles' size distribution and particle yield during ablation. The D/C atomic concentration ratio was measured with the 3HE ion beam nuclear reaction analysis method in deposited layers before ablation and with a micro-ion beam in individual particles on aerogel collectors. This indicated that most of the D was thermally released during ablation, leaving no more than 5% of its original amount in the particles. The effect of ablation conditions on the acceleration of ejected particles, their population, composition and D content is the main subject of this paper.
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| 2. |
- Bergsåker, Henric, et al.
(författare)
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First results from the Be-10 marker experiment in JET with ITER-like wall
- 2014
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Ingår i: Nuclear Fusion. - : IOP Publishing. - 0029-5515 .- 1741-4326. ; 54:8, s. 082004-
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Tidskriftsartikel (refereegranskat)abstract
- When the ITER-like wall was installed in JET, one of the 218 Be inner wall guard limiter tiles had been enriched with Be-10 as a bulk isotopic marker. During the shutdown in 2012-2013, a set of tiles were sampled nondestructively to collect material for accelerator mass spectroscopy measurements of Be-10 concentration. The letter shows how the marker experiment was set up, presents first results and compares them to preliminary predictions of marker redistribution, made with the ASCOT numerical code. Finally an outline is shown of what experimental data are likely to become available later and the possibilities for comparison with modelling using the WallDYN, ERO and ASCOT codes are discussed.
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| 3. |
- Bergsåker, Henric, et al.
(författare)
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Microanalysis of deposited layers in the divertor of JET following operations with carbon wall
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 438:Suppl., s. S668-S672
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Tidskriftsartikel (refereegranskat)abstract
- Elemental mapping of cross sections of deposited layers on inboard tiles in the JET divertor after exposure to plasma operations with carbon wall are presented. The study was made using microbeam ion beam analysis methods in combination with optical microscopy and SEM. The surfaces had been exposed to plasma through different periods of operation (1998-2007, 2007-2009 and 1998-2009). The texture and composition of the layers are non-uniform. The physical structures include columnar, lamellar and disordered globular appearances. The distribution of trapped deuterium was frequently found to be lamellar, with well-defined sub layers with higher deuterium concentration. However, 3D regions with dimensions of about 100 μm with enhanced deuterium content were also found, both at the layer surfaces and in the layer cross sections. The distributions of beryllium and Inconel components were lamellar but did not otherwise show large non-uniformity on the same scale length as the deuterium.
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| 4. |
- Bergsåker, Henric, et al.
(författare)
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Microstructure and inhomogeneous fuel trapping at divertor surfaces in the JET tokamak
- 2014
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 332, s. 266-270
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Tidskriftsartikel (refereegranskat)abstract
- The plasma deposited layers at divertor surfaces in the JET tokamak with carbon wall have been studied post mortem, using micro ion beam analysis (mu-IBA) methods, optical microscopy and scanning electron microscopy (SEM). The layers were formed during plasma operations over different periods through 1998-2009. They frequently have a columnar structure. For mu-IBA a 3 MeV He-3 beam was used, focused to about 5-15 mu m size. Nuclear reaction analysis was used to measure D, Be and C. Elemental mapping was carried out both at the original surface and on polished layer cross sections. Trapped deuterium is predominantly found in remote areas on the horizontal bottom divertor tiles and in regions with locally enhanced deuterium concentration on the vertical tiles. Pockets with enhanced deuterium concentration are found in the carbon fibre composite (CFC) substrate. Areas with dimensions of about 100 mu m with enhanced deuterium concentration are also found inside the deposited layers. The inhomogeneous fuel trapping is tentatively explained with co-deposition in partly protected pits in the substrate and by incorporation of dust particles in the growing layers.
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| 5. |
- Bykov, Igor, et al.
(författare)
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Collection of mobile dust in the T2R reversed field pinch
- 2012
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Ingår i: Nukleonika. - 0029-5922 .- 1508-5791. ; 57:1, s. 55-60
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Tidskriftsartikel (refereegranskat)abstract
- Intensive plasma-wall interactions in fusion devices result in the impurity production and the formation of films of redeposited material, debris and dust. In present day devices, with short pulses, the mobile dust does not pose any serious operational problems, but it is a matter of serious concern for ITER and for later power producing devices with a high duty cycle. We report results of a dust collection experiment carried out at the T2R reversed field pinch device and related heavy impurity flux measurements. Dust and impurities were collected on passive Si surface probes and on ultralow density silica aerogel collectors. The advantage of the latter method is the possibility of nondestructive capture of the micron- and submicron-sized dust particles. The toroidal and radial deposition fluxes of dust particles and impurities are estimated and discussed in the light of the dominant forces acting on the dust.
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| 6. |
- Bykov, Igor, 1986-
(författare)
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Experimental studies of materials migration in magnetic confinement fusion devices : Novel methods for measurement of macro particle migration, transport of atomic impurities and characterization of exposed surfaces
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- During several decades of research and development in the field of Magnetically Confined Fusion (MCF) the preferred selection of materials for Plasma Facing Components (PFC) has changed repeatedly. Without doubt, endurance of the first wall will decide research availability and lifespan of the first International Thermonuclear Research Reactor (ITER). Materials erosion, redeposition and mixing in the reactor are the critical processes responsible for modification of materials properties under plasma impact. This thesis presents several diagnostic techniques and their applications for studies of materials transport in fusion devices. The measurements were made at the EXTRAP T2R Reversed Field Pinch operated in Alfvén laboratory at KTH (Sweden), the TEXTOR tokamak, recently shut down at Forschungszentrum Jülich (Germany) and in the JET tokamak at CCFE (UK). The main outcomes of the work are:Development and application of a method for non-destructive capture and characterization of fast dust particles moving in the edge plasma of fusion devices, as well as particles generated upon laser-assisted cleaning of plasma exposed surfaces. Advancement of conventional broad beam and micro ion beam techniques to include measurement of tritium in the surfaces exposed in future D-T experiments. Adaption of the micro ion beam method for precision mapping of non uniform elements concentrations on irregular surfaces. Implementation of an isotopic marker to study the large scale materials migration in a tokamak and development of a method for fast non destructive sampling of the marker on surfaces of PFCs.
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| 7. |
- Bykov, Igor, et al.
(författare)
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Investigation of tritium analysis methods for ion microbeam application
- 2012
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 273, s. 250-253
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Tidskriftsartikel (refereegranskat)abstract
- The trapping and retention of tritium in deposited layers on plasma-facing components is a critical issue for the international tokamak experimental reactor (ITER) and for future power producing tokamak fusion reactors. Cross sections of deposited layers at surfaces in the JET tokamak divertor are being investigated using ion microbeam analysis. To include tritium analysis with high spatial resolution, a number of plausible ion beam techniques have been investigated. Calibration samples with 150 nm tritiated titanium films were used. Absolute concentrations were determined with classical ERD using 2.5-3.5 MeV C-12(+). Cross sections for non-Rutherford ERD and for the T(C-12,p)C-14 and T(C-12,alpha)B-11 nuclear reactions were measured for different angles in the energy range 2.5-15 MeV. Background spectra were collected from pure carbon, beryllium and deuterium enriched samples and the sensitivity for microbeam NRA measurements of the tritium concentration in thick targets with predominantly Be-C-D matrix was estimated.
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| 8. |
- Bykov, Igor, et al.
(författare)
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Quantitative plasma-fuel and impurity profiling in thick plasma-deposited layers by means of micro ion beam analysis and SIMS
- 2014
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Ingår i: Nuclear Instruments and Methods in Physics Research Section B. - : Elsevier BV. - 0168-583X .- 1872-9584. ; 332, s. 280-285
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Tidskriftsartikel (refereegranskat)abstract
- The operation of the Joint European Torus (JET) with full-carbon wall during the last decades has proven the importance of material re-deposition processes in remote areas of the tokamak. The thickness of the deposits in shadowed areas can reach 1 mm. The main constituent is carbon, with little inclusion of Inconel components. Atomic fractions Be/C and D/C can locally reach 1. Three methods were used to study thick deposits on JET divertor surfaces: (i) NRA analysis with a 15 mu m wide, 3 MeV He-3 ion microbeam on a polished cross section of the layer to determine the concentration distribution of D, Be and C and the distribution of Ni by particle induced X-ray emission; (ii) elastic proton scattering (EPS) from the top of the layers with a broad proton beam at 3.5 and 4.6 MeV. These methods were absolutely calibrated using thick elemental targets. (iii) Depth profiling of D, Be and Ni was done with secondary ion mass spectrometry (SIMS), sputtering the layers from the surface. The three methods are complementary. The thickest layers are accessible only by microbeam mapping of the cross sections, albeit with limited spatial resolution. The SIMS has the best depth resolution, but is difficult for absolute quantification and is limited in accessible depth. The probed depth with proton backscattering is limited to about 30 mu m. The combination of all three methods provided a coherent picture of the layer composition. It was possible to correlate the SIMS profiling results to quantitative data obtained by the microbeam method.
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| 9. |
- Bykov, Igor, et al.
(författare)
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Time resolved collection and characterization of dust particles moving in the TEXTOR scrape-off layer
- 2013
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Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 438:Suppl., s. S681-S685
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Tidskriftsartikel (refereegranskat)abstract
- Moving dust has been collected in the SOL of TEXTOR in a time-resolved way with silica aerogel collectors [1-3]. The collectors were exposed to the toroidal particle flux in NBI heated discharges during the startup and flat top phase. Intrinsic dust was collected in several discharges. Other discharges were accompanied with injection of known amounts of pre-characterized dust (W, C flakes and C microspheres) from a position toroidally 120° away from the collector. Particle flux, composition and dust size distribution have been determined with SEM and EDX. Calibration allowed particle velocity estimates to be made. Upper limits for the deuterium content of individual dust grains have been determined by NRA.
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| 10. |
- Bykov, Igor, et al.
(författare)
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Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration
- 2014
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Ingår i: Plasma Physics and Controlled Fusion. - : IOP Publishing. - 0741-3335 .- 1361-6587. ; 56:3, s. 035014-
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Tidskriftsartikel (refereegranskat)abstract
- Experimental data on dust resident in the EXTRAP T2R reversed-field pinch are reported. Mobile dust grains are captured in situ by silicon collectors, whereas immobile grains are sampled post mortem from the wall by adhesive tape. The simulation of collection asymmetries by the MIGRAINe dust dynamics code in combination with the experimental results is employed to deduce some characteristics of the mechanism of intrinsic dust release. All evidence suggests that re-mobilization is dominant with respect to dust production.
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