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  • 1. Alegre, Daniel
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Gasior, Pawel
    Kubkowska, Monika
    Kowalska-Strzeciwilk, Ewa
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tabares, Francisco L.
    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 velocity2014In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T161, p. 014010-Article in journal (Refereed)
    Abstract [en]

    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.

  • 2.
    Bergsåker, B. Henric M.
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Zhou, Yushan
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Possnert, G.
    Likonen, J.
    Pettersson, J.
    Koivuranta, S.
    Widdowson, A. M.
    Deep deuterium retention and Be/W mixing at tungsten coated surfaces in the JET divertor2016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, article id 014061Article in journal (Refereed)
    Abstract [en]

    Surface samples from a full poloidal set of divertor tiles exposed in JET through operations 2010-2012 with ITER-like wall have been investigated using SEM, SIMS, ICP-AES analysis and micro beam nuclear reaction analysis (μ-NRA). Deposition of Be and retention of D is microscopically inhomogeneous. With careful overlaying of μ-NRA elemental maps with SEM images, it is possible to separate surface roughness effects from depth profiles at microscopically flat surface regions, without pits. With (3He, p) μ-NRA at 3-5 MeV beam energy the accessible depth for D analysis in W is about 9 μm, sufficient to access the W/Mo and Mo/W interfaces in the coatings and beyond, while for Be in W it is about 6 μm. In these conditions, at all plasma wetted surfaces, D was found throughout the whole accessible depth at concentrations in the range 0.2-0.7 at% in W. Deuterium was found to be preferentially trapped at the W/Mo and Mo/W interfaces. Comparison is made with SIMS profiling, which also shows significant D trapping at the W/Mo interface. Mixing of Be and W occurs mainly in deposited layers.

  • 3.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Widdowson, A. M.
    Microstructure and inhomogeneous fuel trapping at divertor surfaces in the JET tokamak2014In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 332, p. 266-270Article in journal (Refereed)
    Abstract [en]

    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.

  • 4.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    Zhou, Yushan
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Possnert, G
    Likonen, J
    Pettersson, J
    Koivuranta, S
    Widdowson, A.M.
    contributors, JET
    Deep deuterium retention and Be/W mixingat tungsten coated surfaces in the JETdivertor2016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896Article in journal (Refereed)
    Abstract [en]

    Surface samples from a full poloidal set of divertor tiles exposed in JET through operations2010–2012 with ITER-like wall have been investigated using SEM, SIMS, ICP-AES analysisand micro beam nuclear reaction analysis (μ-NRA). Deposition of Be and retention of D ismicroscopically inhomogeneous. With careful overlaying of μ-NRA elemental maps with SEMimages, it is possible to separate surface roughness effects from depth profiles at microscopicallyflat surface regions, without pits. With (3He, p) μ-NRA at 3–5 MeV beam energy the accessibledepth for D analysis in W is about 9 μm, sufficient to access the W/Mo and Mo/W interfaces inthe coatings and beyond, while for Be in W it is about 6 μm. In these conditions, at all plasmawetted surfaces, D was found throughout the whole accessible depth at concentrations in therange 0.2–0.7 at% in W. Deuterium was found to be preferentially trapped at the W/Mo andMo/W interfaces. Comparison is made with SIMS profiling, which also shows significant Dtrapping at the W/Mo interface. Mixing of Be and W occurs mainly in deposited layers.

  • 5.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Widdowson, A. M.
    Microanalysis of deposited layers in the divertor of JET following operations with carbon wall2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S668-S672Article in journal (Refereed)
    Abstract [en]

    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.

  • 6.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Heinola, K.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Miettunen, J.
    Widdowson, A.
    Riccardo, V.
    Nunes, I.
    Stamp, M.
    Brezinsek, S.
    Groth, M.
    Kurki-Suonio, T.
    Likonen, J.
    Coad, J. P.
    Borodin, D.
    Kirschner, A.
    Schmid, K.
    Krieger, K.
    First results from the Be-10 marker experiment in JET with ITER-like wall2014In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, no 8, p. 082004-Article in journal (Refereed)
    Abstract [en]

    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.

  • 7.
    Bergsåker, Henric
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Heinola, K.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Miettunen, J.
    Widdowson, C.
    Riccardo, V.
    Nunes, I.
    Stamp, M.
    et al.,
    First results from10Be marker experiment in JET with ITER-like wallManuscript (preprint) (Other academic)
  • 8.
    Bergsåker, Henrik
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Van Renterghem, W.
    Uytdenhouwen, I.
    Widdowson, A. M.
    Microscopically nonuniform deposition and deuterium retention in the divertor in JET with ITER-like wall2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 956-960Article in journal (Refereed)
    Abstract [en]

    The divertor surfaces in JET with ITER-like wall (ILW) have been studied using micro ion beam analysis (mu-IBA) methods and scanning electron microscopy (SEM). Deposited layers with beryllium as main constituent had been formed during plasma operations through 2011-2012. The deuterium trapping and impurity deposition were non-uniform, frequently enhanced within pits, cracks and valleys, regions reaching in size from 10 mu m to 200 mu m. The impurity deposition and fuel retention were correlated with the surface slope with respect to the direction of ion incidence. Typically more than 70% of the total measured areal density of trapped D was found in less than 30% of the surface area. This is of consequence for the interpretation of other surface analyses and in extrapolation from fuel retention in JET with ITER-like wall and rough divertor surfaces to ITER with smoother surfaces.

  • 9.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    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 surfaces2014Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    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.
  • 10.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsaker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Zhou, Y.
    Heinola, K.
    Pettersson, J.
    Conroy, S.
    Likonen, J.
    Petersson, Per
    Widdowson, A.
    Studies of Be migration in the JET tokamak using AMS with Be-10 marker2016In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 371, p. 370-375Article in journal (Refereed)
    Abstract [en]

    The JET tokamak is operated with beryllium limiter tiles in the main chamber and tungsten coated carbon fiber composite tiles and solid W tiles in the divertor. One important issue is how wall materials are migrating during plasma operation. To study beryllium redistribution in the main chamber and in the divertor, a Be-10 enriched limiter tile was installed prior to plasma operations in 2011-2012. Methods to take surface samples have been developed, an abrasive method for bulk Be tiles in the main chamber, which permits reuse of the tiles, and leaching with hot HCl to remove all Be deposited at W coated surfaces in the divertor. Quantitative analysis of the total amount of Be in cm(2) sized samples was made with inductively coupled plasma atomic emission spectroscopy (ICP-AES). The Be-10/Be-9 ratio in the samples was measured with accelerator mass spectrometry (AMS). The experimental setup and methods are described in detail, including sample preparation, measures to eliminate contributions in AMS from the B-10 isobar, possible activation due to plasma generated neutrons and effects of diffusive isotope mixing. For the first time marker concentrations are measured in the divertor deposits. They are in the range 0.4-1.2% of the source concentration, with moderate poloidal variation. (C) 2015 Elsevier B.V. All rights reserved.

  • 11.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ogata, Douglas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Collection of mobile dust in the T2R reversed field pinch2012In: Nukleonika, ISSN 0029-5922, E-ISSN 1508-5791, Vol. 57, no 1, p. 55-60Article in journal (Refereed)
    Abstract [en]

    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.

  • 12.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Likonen, Jari
    Possnert, G.
    Widdowson, C.
    Combined ion micro probe and SEM analysis of strongly non uniform deposits in fusion devices2015In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 342, p. 19-28Article in journal (Refereed)
    Abstract [en]

    Conventional ion beam analysis (IBA) of deposited layers from fusion devices may have insufficient accuracy due to strongly uneven appearance of the layers. Surface roughness and spatial variation of the matrix composition make interpretation of broad beam spectra complex and non obvious. We discuss complications of applied IBA arising for fusion-relevant surfaces and demonstrate how quantification can be improved by employing micro IBA methods. The analysis is bound to pre-defined regions on the sample surface and can be extended by employing beams of several types, scanning electron microscopy (SEM) and stereo SEM techniques.

  • 13.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Likonen, Jari
    Possnert, Göran
    Quantitative plasma-fuel and impurity profiling in thick plasma-deposited layers by means of micro ion beam analysis and SIMS2014In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 332, p. 280-285Article in journal (Refereed)
    Abstract [en]

    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.

  • 14.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Litnovsky, A.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Time resolved collection and characterization of dust particles moving in the TEXTOR scrape-off layer2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S681-S685Article in journal (Refereed)
    Abstract [en]

    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.

  • 15.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henrik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Possnert, G.
    Heinola, K.
    Miettunen, J.
    Groth, M.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Widdowson, A.
    Likonen, J.
    Materials migration in JET with ITER-like wall traced with a Be-10 isotopic marker2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 773-776Article in journal (Refereed)
    Abstract [en]

    The current configuration of JET with ITER-like Wall (ILW) is the best available proxy for the ITER first wall. Beryllium redistribution in JET-ILW can be used for estimates of its migration in ITER. To trace it, a localized isotopic Be marker has been implemented. A bulk Be-9 tile has been enriched with Be-10 up to atomic concentrations of 1.7 x 10(-9) and installed at the inner midplane of JET before the campaign. During the 2012 shutdown over 100 surface samples were taken non destructively from surfaces of two toroidally opposite limiter beams. The absolute areal densities of the marker were inferred from Be-15 atomic concentration in each sample, measured with Accelerator Mass Spectrometry with sensitivity <10(-14). The results of marker mapping are compared with predictions made with the ASCOT orbit following code.

  • 16.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hallén, A.
    Possnert, G.
    Investigation of tritium analysis methods for ion microbeam application2012In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 273, p. 250-253Article in journal (Refereed)
    Abstract [en]

    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.

  • 17.
    Bykov, Igor
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Banon, Jean-Philippe
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Brunsell, Per R.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Transport asymmetry and release mechanisms of metal dust in the reversed-field pinch configuration2014In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 56, no 3, p. 035014-Article in journal (Refereed)
    Abstract [en]

    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.

  • 18.
    Garzotti, L.
    et al.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England.;CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Stefániková, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics. CCFE Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zhou, Yushan
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zychor, I.
    Natl Ctr Nucl Res, PL-05400 Otwock, Poland..
    Scenario development for D-T operation at JET2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 7, article id 076037Article in journal (Refereed)
    Abstract [en]

    The JET exploitation plan foresees D-T operations in 2020 (DTE2). With respect to the first D-T campaign in 1997 (DTE1), when JET was equipped with a carbon wall, the experiments will be conducted in presence of a beryllium-tungsten ITER-like wall and will benefit from an extended and improved set of diagnostics and higher additional heating power (32 MW neutral beam injection + 8 MW ion cyclotron resonance heating). There are several challenges presented by operations with the new wall: a general deterioration of the pedestal confinement; the risk of heavy impurity accumulation in the core, which, if not controlled, can cause the radiative collapse of the discharge; the requirement to protect the divertor from excessive heat loads, which may damage it permanently. Therefore, an intense activity of scenario development has been undertaken at JET during the last three years to overcome these difficulties and prepare the plasmas needed to demonstrate stationary high fusion performance and clear alpha particle effects. The paper describes the status and main achievements of this scenario development activity, both from an operational and plasma physics point of view.

  • 19. Joffrin, E.
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Fridström, Richard
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Moon, Sunwoo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Stefániková, Estera
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zhou, Yushan
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Zychor, I
    et al.,
    Overview of the JET preparation for deuterium-tritium operation with the ITER like-wall2019In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, no 11, article id 112021Article in journal (Refereed)
    Abstract [en]

    For the past several years, the JET scientific programme (Pamela et al 2007 Fusion Eng. Des. 82 590) has been engaged in a multi-campaign effort, including experiments in D, H and T, leading up to 2020 and the first experiments with 50%/50% D-T mixtures since 1997 and the first ever D-T plasmas with the ITER mix of plasma-facing component materials. For this purpose, a concerted physics and technology programme was launched with a view to prepare the D-T campaign (DTE2). This paper addresses the key elements developed by the JET programme directly contributing to the D-T preparation. This intense preparation includes the review of the physics basis for the D-T operational scenarios, including the fusion power predictions through first principle and integrated modelling, and the impact of isotopes in the operation and physics of D-T plasmas (thermal and particle transport, high confinement mode (H-mode) access, Be and W erosion, fuel recovery, etc). This effort also requires improving several aspects of plasma operation for DTE2, such as real time control schemes, heat load control, disruption avoidance and a mitigation system (including the installation of a new shattered pellet injector), novel ion cyclotron resonance heating schemes (such as the three-ions scheme), new diagnostics (neutron camera and spectrometer, active Alfven eigenmode antennas, neutral gauges, radiation hard imaging systems...) and the calibration of the JET neutron diagnostics at 14 MeV for accurate fusion power measurement. The active preparation of JET for the 2020 D-T campaign provides an incomparable source of information and a basis for the future D-T operation of ITER, and it is also foreseen that a large number of key physics issues will be addressed in support of burning plasmas.

  • 20. Krat, S.
    et al.
    Gasparyan, Yu
    Pisarev, A.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Mayer, M.
    Saint Aubin, G. de
    Balden, M.
    Lungu, C. P.
    Widdowson, A.
    Erosion at the inner wall of JET during the discharge campaign 2011-2012 in comparison with previous campaigns2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 456, p. 106-110Article in journal (Refereed)
    Abstract [en]

    The erosion of Be and W marker layers was investigated using long-term samples during the first ITER-like wall discharge campaign 2011-2012. The markers were mounted in Be coated Inconel tiles between the inner wall guard limiters (IWGL). They were analyzed using Rutherford backscattering (RBS) before and after exposure. All samples showed strong erosion. The results were compared to the data for Be and W erosion rates for the 2005-2009 and the 2001-2004 campaigns, respectively, when JET was operated with a carbon wall. In 2005-2009 Be and C samples were used, and W samples were used in 2001-2004. The mean W erosion rates and the toroidal and poloidal distributions of the W erosion were the same for the 2001-2004 and the 2011-2012 campaigns. The mean erosion rate of Be during the 2011-2012 campaign was smaller by a factor of about two compared to the 2005-2009 campaign and showed a different poloidal distribution. The mean erosion rate of the inner JET ITER-like wall was about 4-5 times smaller than the mean erosion rate of the carbon wall.

  • 21. Krat, S.
    et al.
    Mayer, M.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lungu, C. P.
    de Saint Aubin, G.
    Widdowson, A.
    Carvalho, I. S.
    Erosion at the inner wall of JET during the discharge campaign 2013-20142017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 11, p. 20-24Article in journal (Refereed)
    Abstract [en]

    The erosion of Be and W marker layers was investigated using long-term samples containing marker layers during the second ITER-like wall discharge campaign 2013-2014 (ILW-2). The samples were mounted in Be coated Inconel tiles between the inner wall guard limiters (IWGL). They were analyzed using elastic backscattering (EBS) before and after exposure. All samples showed noticeable erosion. The results were compared to the data for Be and W erosion rates for the first 2011-2012 JET ITER-like wall (ILW-1) campaign, and to the data for C erosion during the 2005-2009 campaign when JET was operated with a carbon wall. The mean W erosion rates and the toroidal and poloidal distributions of the W erosion were nearly the same for the ILW-1 and ILW-2 campaigns. The mean erosion rate of Be during the ILW-2 campaign was smaller by a factor of about two compared to the ILW-1 campaign.

  • 22. Litnovsky, A.
    et al.
    Rudakov, D. L.
    Bozhenkov, S.
    Smirnov, R. D.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henrik
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ashikawa, N.
    De Temmerman, G.
    Xu, Y.
    Krasheninnikov, S. I.
    Biel, W.
    Brezinsek, S.
    Coenen, J. W.
    Kreter, A.
    Kantor, M.
    Lambertz, H. T.
    Philipps, V.
    Pospieszczyk, A.
    Samm, U.
    Sergienko, G.
    Schmitz, O.
    Stoschus, H.
    Dust investigations in TEXTOR: Impact of dust on plasma-wall interactions and on plasma performance2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S126-S132Article in journal (Refereed)
    Abstract [en]

    Dust will have severe impact on ITER performance since the accumulation of tritium in dust represents a safety issue, a possible reaction of dust with air and steam imposes an explosion hazard and the penetration of dust in core plasmas may degrade plasma performance by increasing radiative losses. Investigations were performed in TEXTOR where known amounts of pre-characterized carbon, diamond and tungsten dust were mobilized into plasmas using special dust holders. Mobilization of dust changed a balance between plasma-surface interactions processes, significantly increasing net deposition. Immediately after launch dust was dominating both core and edge plasma parameters. Remarkably, in about 100 ms after the launch, the effect of dust on edge and core plasma parameters was vanished: no increase of carbon and tungsten concentrations in the core plasmas was detected suggesting a prompt transport of dust to the nearby plasma-facing components without further residence in the plasma.

  • 23. Lituadon, Xavier
    et al.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Garcia-Carrasco, Alvaro
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Jonsson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Stefániková, Estera
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Tholerus, Emmi
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Vallejos Olivares, Pablo
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Weckmann, Armin
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Zhou, Yushan
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ström, Petter
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    et al.,
    Overview of the JET results in support to ITER2017In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 10, article id 102001Article in journal (Refereed)
    Abstract [en]

    The 2014–2016 JET results are reviewed in the light of their significance for optimising the ITER research plan for the active and non-active operation. More than 60 h of plasma operation with ITER first wall materials successfully took place since its installation in 2011. New multi-machine scaling of the type I-ELM divertor energy flux density to ITER is supported by first principle modelling. ITER relevant disruption experiments and first principle modelling are reported with a set of three disruption mitigation valves mimicking the ITER setup. Insights of the L–H power threshold in Deuterium and Hydrogen are given, stressing the importance of the magnetic configurations and the recent measurements of fine-scale structures in the edge radial electric. Dimensionless scans of the core and pedestal confinement provide new information to elucidate the importance of the first wall material on the fusion performance. H-mode plasmas at ITER triangularity (H  =  1 at β N ~ 1.8 and n/n GW ~ 0.6) have been sustained at 2 MA during 5 s. The ITER neutronics codes have been validated on high performance experiments. Prospects for the coming D–T campaign and 14 MeV neutron calibration strategy are reviewed.

  • 24. Mayer, M.
    et al.
    Krat, S.
    Van Renterghem, W.
    Baron-Wiechec, A.
    Brezinsek, S.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Coad, P.
    Gasparyan, Y.
    Heinola, K.
    Likonen, J.
    Pisarev, A.
    Ruset, C.
    De Saint-Aubin, G.
    Widdowson, A.
    Erosion and deposition in the JET divertor during the first ILW campaign2016In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, article id 014051Article in journal (Refereed)
    Abstract [en]

    Erosion and deposition were studied in the JET divertor during the first JET ITER-like wall campaign 2011 to 2012 using marker tiles. An almost complete poloidal section consisting of tiles 0, 1, 3, 4, 6, 7, 8 was studied. The data from divertor tile surfaces were completed by the analysis of samples from remote divertor areas and from the inner wall cladding. The total mass of material deposited in the divertor decreased by a factor of 4-9 compared to the deposition of carbon during all-carbon JET operation before 2010. Deposits in 2011 to 2012 consist mainly of beryllium with 5-20 at.% of carbon and oxygen, respectively, and small amounts of Ni, Cr, Fe and W. This decrease of material deposition in the divertor is accompanied by a decrease of total deuterium retention inside the JET vessel by a factor of 10 to 20. The detailed erosion/deposition pattern in the divertor with the ITER-like wall configuration shows rigorous changes compared to the pattern with the all-carbon JET configuration.

  • 25.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Shalpegin, A.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angell, M.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bardin, S.
    Brochard, F.
    Ripamonti, D.
    den Harder, N.
    De Temmerman, G.
    Elastic-plastic adhesive impacts of tungsten dust with metal surfaces in plasma environments2015In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, p. 877-880Article in journal (Refereed)
    Abstract [en]

    Dust-surface collisions impose size selectivity on the ability of dust grains to migrate in scrape-off layer and divertor plasmas and to adhere to plasma-facing components. Here, we report first experimental evidence of dust impact phenomena in plasma environments concerning low-speed collisions of tungsten dust with tungsten surfaces: re-bouncing, adhesion, sliding and rolling. The results comply with the predictions of the model of elastic-perfectly plastic adhesive spheres employed in the dust dynamics code MIGRAINe for sub- to several meters per second impacts of micrometer-range metal dust.

  • 26.
    Ratynskaia, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Litnovsky, A.
    den Harder, N.
    Lazzaro, E.
    Migration of tungsten dust in tokamaks: role of dust-wall collisions2013In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, no 12, p. 123002-Article in journal (Refereed)
    Abstract [en]

    The modelling of a controlled tungsten dust injection experiment in TEXTOR by the dust dynamics code MIGRAINe is reported. The code, in addition to the standard dust-plasma interaction processes, also encompasses major mechanical aspects of dust-surface collisions. The use of analytical expressions for the restitution coefficients as functions of the dust radius and impact velocity allows us to account for the sticking and rebound phenomena that define which parts of the dust size distribution can migrate efficiently. The experiment provided unambiguous evidence of long-distance dust migration; artificially introduced tungsten dust particles were collected 120 degrees toroidally away from the injection point, but also a selectivity in the permissible size of transported grains was observed. The main experimental results are reproduced by modelling.

  • 27.
    Ratynskaya, Svetlana
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    Riva, G.
    Ripamonti, D.
    Daminelli, G.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Masselin, Matthieu
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Reggiori, A.
    Grosso, G.
    Dust-surface collisions in adhesion regime for tokamak relevant materials2013In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, no Suppl., p. S796-S799Article in journal (Refereed)
    Abstract [en]

    Empirical studies of dust-surface collisions for metal and carbon projectiles impacting on metal targets in the velocity range from a few m/s to those in excess of 1 km/s have been carried out with the use of a modified pellet injection system. The selected projectile/target shapes, sizes and materials are mimicking the scenario of dust colliding with plasma facing components (PFCs) of a metal machine. The low velocities (10's m/s) reported here, characteristic for dust motion in tokamak scrape-off layer plasmas, are in the range of sticking phenomenon; the critical velocity and size for bouncing off are essential and timely inputs for the dust dynamics codes and statistical models aiming to predict dust transport and redepo-sition on PFCs.

  • 28. Shalpegin, A.
    et al.
    Brochard, F.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    Vignitchouk, Ladislas
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Bardin, S.
    Bystrov, K.
    Morgan, T.
    De Temmerman, G.
    Highly resolved measurements of dust motion in the sheath boundary of magnetized plasmas2015In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, no 11, article id 112001Article in journal (Refereed)
    Abstract [en]

    Dust trajectories have been recorded with an unprecedented, under fusion-relevant plasma conditions, spatial resolution of 9 mu m/pixel in Pilot-PSI. The optical setup allowed the use of fast cameras as a basic microscope. It is demonstrated that such a resolution is essential for the correct interpretation of experiments on several aspects of dust-surface interactions. Highly resolved tungsten dust dynamics measurements are presented from dedicated experiments on dust collisions with plasma facing components, motion in the vicinity of castellated samples and remobilization from planar samples.

  • 29. Shalpegin, A.
    et al.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Erofeev, I.
    Brochard, F.
    Litnovsky, A.
    Bozhenkov, S.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    den Harder, N.
    Sergienko, G.
    Fast camera observations of injected and intrinsic dust in TEXTOR2015In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, no 12, article id 125017Article in journal (Refereed)
    Abstract [en]

    Stereoscopic fast camera observations of pre-characterized carbon and tungsten dust injection in TEXTOR are reported, along with the modelling of tungsten particle trajectories with MIGRAINe. Particle tracking analysis of the video data showed significant differences in dust dynamics: while carbon flakes were prone to agglomeration and explosive destruction, spherical tungsten particles followed quasi-inertial trajectories. Although this inertial nature prevented any validation of the force models used in MIGRAINe, comparisons between the experimental and simulated lifetimes provide a direct evidence of dust temperature overestimation in dust dynamics codes. Furthermore, wide-view observations of the TEXTOR interior revealed the main production mechanism of intrinsic carbon dust, as well as the location of probable dust remobilization sites.

  • 30.
    Ström, Petter
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Rubel, Marek
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Frassinetti, Lorenzo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Garcia Carrasco, Alvaro
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Menmuir, Sheena
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tholerus, Simon
    Weckmann, Armin
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics. KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Tolias, Panagiotis
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Ratynskaia, Svetlana V.
    KTH, School of Electrical Engineering and Computer Science (EECS), Space and Plasma Physics.
    Rachlew, Elisabeth
    KTH, School of Engineering Sciences (SCI), Physics, Atomic and Molecular Physics.
    Vallejos, Pablo
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Johnson, T.
    Stefanikova, E.
    Zhou, Y.
    Zychor, I.
    et al.,
    Analysis of deposited layers with deuterium and impurity elements on samples from the divertor of JET with ITER-like wall2019In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, p. 202-213Article in journal (Refereed)
    Abstract [en]

    Inconel-600 blocks and stainless steel covers for quartz microbalance crystals from remote corners in the JET-ILW divertor were studied with time-of-flight elastic recoil detection analysis and nuclear reaction analysis to obtain information about the areal densities and depth profiles of elements present in deposited material layers. Surface morphology and the composition of dust particles were examined with scanning electron microscopy and energy-dispersive X-ray spectroscopy. The analyzed components were present in JET during three ITER-like wall campaigns between 2010 and 2017. Deposited layers had a stratified structure, primarily made up of beryllium, carbon and oxygen with varying atomic fractions of deuterium, up to more than 20%. The range of carbon transport from the ribs of the divertor carrier was limited to a few centimeters, and carbon/deuterium co-deposition was indicated on the Inconel blocks. High atomic fractions of deuterium were also found in almost carbon-free layers on the quartz microbalance covers. Layer thicknesses up to more than 1 micrometer were indicated, but typical values were on the order of a few hundred nanometers. Chromium, iron and nickel fractions were less than or around 1% at layer surfaces while increasing close to the layer-substrate interface. The tungsten fraction depended on the proximity of the plasma strike point to the divertor corners. Particles of tungsten, molybdenum and copper with sizes less than or around 1 micrometer were found. Nitrogen, argon and neon were present after plasma edge cooling and disruption mitigation. Oxygen-18 was found on component surfaces after injection, indicating in-vessel oxidation. Compensation of elastic recoil detection data for detection efficiency and ion-induced release of deuterium during the measurement gave quantitative agreement with nuclear reaction analysis, which strengthens the validity of the results.

  • 31.
    Tolias, Panagiotis
    et al.
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Ratynskaia, Svetlana
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    De Angeli, M.
    De Temmerman, G.
    Ripamonti, D.
    Riva, G.
    Bykov, Igor
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Shalpegin, A.
    Vignitchouk, Ladislas Tancrède Raymond
    KTH, School of Electrical Engineering (EES), Space and Plasma Physics.
    Brochard, F.
    Bystrov, K.
    Bardin, S.
    Litnovsky, A.
    Dust remobilization in fusion plasmas under steady state conditions2016In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 58, no 2, article id 025009Article in journal (Refereed)
    Abstract [en]

    The first combined experimental and theoretical studies of dust remobilization by plasma forces are reported. The main theoretical aspects of remobilization in fusion devices under steady state conditions are analyzed. In particular, the dominant role of adhesive forces is highlighted and generic remobilization conditions-direct lift-up, sliding, rolling-are formulated. A novel experimental technique is proposed, based on controlled adhesion of dust grains on tungsten samples combined with detailed mapping of the dust deposition profile prior and post plasma exposure. Proof-of-principle experiments in the TEXTOR tokamak and the EXTRAP-T2R reversed-field pinch are presented. The versatile environment of the linear device Pilot-PSI allowed for experiments with different magnetic field topologies and varying plasma conditions that were complemented with camera observations.

  • 32.
    Zhou, Yushan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Paneta, C.
    Possnert, G.
    Micro ion beam analysis for the erosion of beryllium marker tiles in a tokamak limiter2019In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 450, p. 200-204Article in journal (Refereed)
    Abstract [en]

    Beryllium limiter marker tiles were exposed to plasma in the Joint European Torus to diagnose the erosion of main chamber wall materials. A limiter marker tile consists of a beryllium coating layer (7–9 μm) on the top of bulk beryllium, with a nickel interlayer (2–3 μm) between them. The thickness variation of the beryllium coating layer, after exposure to plasma, could indicate the erosion measured by ion beam analysis with backscattering spectrometry. However, interpretations from broad beam backscattering spectra were limited by the non-uniform surface structures. Therefore, micro-ion beam analysis (μ-IBA) with 3 MeV proton beam for Elastic backscattering spectrometry (EBS) and PIXE was used to scan samples. The spot size was in the range of 3–10 μm. Scanned areas were analysed with scanning electron microscopy (SEM) as well. Combining results from μ-IBA and SEM, we obtained local spectra from carefully chosen areas on which the surface structures were relatively uniform. Local spectra suggested that the scanned area (≈600 μm × 1200 μm) contained regions with serious erosion with only 2–3 μm coating beryllium left, regions with intact marker tile, and droplets with 90% beryllium. The nonuniform erosion, droplets mainly formed by beryllium, and the possible mixture of beryllium and nickel were the major reasons that confused interpretation from broad beam EBS.

  • 33.
    Zhou, Yushan
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bergsåker, Henric
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Bykov, Igor
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Petersson, Per
    KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
    Possnert, G.
    Likonen, J.
    Pettersson, J.
    Koivuranta, S.
    Widdowson, A. M.
    Microanalysis of deposited layers in the inner divertor of JET with ITER-like wall2017In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 412-417Article in journal (Refereed)
    Abstract [en]

    In JET with ITER-like wall, beryllium eroded in the main chamber is transported to the divertor and deposited mainly at the horizontal surfaces of tiles 1 and 0 (high field gap closure, HFGC). These surfaces are tungsten coated carbon fibre composite (CFC). Surface sampleswere collected following the plasma operations in 2011-2012 and 2013-2014 respectively. The surfaces, as well as polished cross sections of the deposited layers at the surfaces have been studied with micro ion beam analysis methods (mu-IBA). Deposition of Beand other impurities, and retention of D is microscopically inhomogeneous. Impurities and trapped deuterium accumulate preferentially in cracks, pits and depressed regions, and at the sides of large pits in the substrate (e.g. arc tracks where the W coating has been removed). With careful overlaying of mu-NRA elemental maps with optical microscopy images, it is possible to separate surface roughness effects from depth profiles at microscopically flat surface regions.

1 - 33 of 33
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