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  • 801. Widdowson, A.
    et al.
    Brezinsek, S.
    Coad, J. P.
    Hole, D. E.
    Likonen, J.
    Philipps, V.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Stamp, M. F.
    An overview of erosion-deposition studies for the JET Mk II high delta divertor2009Ingår i: Physica scripta. T, ISSN 0281-1847, Vol. T138, s. 014005-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Post-mortem analyses of tiles removed from the JET MkII HD divertor in 2007 are presented. The results indicate an increase in deposition at the outer plasma-shadowed region of the divertor, not seen prior to 2004 and indicate a shift away from the asymmetric picture of net deposition at the inner divertor compared with no overall deposition or erosion at the outer divertor. Surface analysis of the inner and outer vertical divertor tiles is largely the same as observed previously; however, a notable increase in Be composition on the inner and outer floor tiles is observed. An attempt has been made to correlate these data with campaign-averaged plasma configurations and spectroscopy results. While some changes in deposition/erosion characteristics can be explained, further detailed analysis of diagnostics and especially of time-resolved data, such as from rotating collector and quartz microbalance diagnostics, is required.

  • 802. Widdowson, A.
    et al.
    Coad, J. P.
    Alves, E.
    Baron-Wiechec, A.
    Barradas, N. P.
    Brezinsek, S.
    Catarino, N.
    Corregidor, V.
    Heinola, K.
    Koivuranta, S.
    Krat, S.
    Lahtinen, A.
    Likonen, J.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfus Consortium JET, England.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfus Consortium JET, England.
    Overview of fuel inventory in JET with the ITER-like wall2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 8, artikel-id 086045Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Post mortem analyses of JET ITER-Like-Wall tiles and passive diagnostics have been completed after each of the first two campaigns (ILW-1 and ILW-2). They show that the global fuel inventory is still dominated by co-deposition; hence plasma parameters and sputtering processes affecting material migration influence the distribution of retained fuel. In particular, differences between results from the two campaigns may be attributed to a greater proportion of pulses run with strike points in the divertor corners, and having about 300 discharges in hydrogen at the end of ILW-2. Recessed and remote areas can contribute to fuel retention due to the larger areas involved, e.g. recessed main chamber walls, gaps in castellated Be main chamber tiles and material migration to remote divertor areas. The fuel retention and material migration due to the bulk W Tile 5 during ILW-1 are presented. Overall these tiles account for only a small percentage of the global accountancy for ILW-1.

  • 803. Widdowson, A.
    et al.
    Coad, J. P.
    Alves, E.
    Baron-Wiechec, A.
    Barradas, N. P.
    Catarino, N.
    Corregidor, V.
    Heinola, K.
    Krat, S.
    Likonen, J.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    KTH.
    Impurity re-distribution in the corner regions of the JET divertor2017Ingår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T170, artikel-id 014060Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The International Thermonuclear Experimental Reactor (ITER) will use a mixture of deuterium (D) and tritium (T) as the fuel to generate power. Since T is both radioactive and expensive the Joint European Torus (JET) has been at the forefront of research to discover how much T is used and where it may be retained within the main reaction chamber. Until the year 2010 the JET plasma facing components were constructed of carbon fibre composites. During the JET carbon (C) phases impurities accumulated at the corners of the divertor located towards the bottom of the chamber in regions shadowed from the plasma where they are very difficult to reach and remove. This build-up of C and the associated H-isotope (including T) retention were of particular concern for future fusion reactors therefore, in 2010 JET changed the wall protection to (mainly) Be and the divertor to tungsten (W)-the JET ITER-like wall (ILW)-the choice of materials for ITER. This paper reveals that with the JET ILW impurities are still accumulating in the shadowed regions, with Be being the majority element, though the overall quantities are very much reduced from those in the C phases. Material will be transported into the shadowed regions principally when the plasma strike points are on the corner tiles, but particles typically have about a 75% probability of reflection from line-of sight surfaces, and multiple reflection/scattering results in deposition over all surfaces.

  • 804. Widdowson, A.
    et al.
    Coad, J. P.
    Bekris, N.
    Counsell, G.
    Forrest, M. J.
    Gibson, K. J.
    Hole, D.
    Likonen, J.
    Parsons, W.
    Renvall, T.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Efficacy of photon cleaning of JET divertor tiles2007Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 363, s. 341-345Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    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

  • 805.
    Widdowson, A.
    et al.
    EURATOM/CCFE Fusion Association, Culham Science Centre, UK.
    Coad, J. P.
    EURATOM/CCFE Fusion Association, Culham Science Centre, UK.
    de Temmerman, G.
    FOM Insititute for Plasma Physics Rijnhuizen, The Netherlands.
    Farcage, D.
    CEA Saclay, DEN/DANS/DPC/SCP/LILM, Farnce.
    Hole, D.
    Dept. of Engineering and Design, University of Sussex, UK.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Leontyev, A.
    CEA Saclay, DEN/DANS/DPC/SCP/LILM, Farnce.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Semerok, A.
    CEA Saclay, DEN/DANS/DPC/SCP/LILM, Farnce.
    Schmidt, A.
    IEF-Plasmaphysik, Forschungszentrum fülich, Association EURATOM-FZJ, Germany.
    Thro, P.-Y.
    CEA Saclay, DEN/DANS/DPC/SCP/LILM, Farnce.
    Removal of beryllium-containing films deposited in JET from mirror surfaces by laser cleaning2011Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, ISSN 0022-3115, Vol. 415, nr 1, s. S1199-S1202Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A set of stainless steel (SS) and molybdenum mirror samples located in the divertor and at the outer mid-plane of the vessel were exposed in JET from 2005 to 2007. A selection of these mirror samples with well adhered deposits (i.e. not flaking) of up to a few hundred nanometers in thickness and with Be/C ratios ranging from 0 to similar to 1 have been cleaned using a laser system developed at CEA, Saclay. Following laser cleaning the recovered reflectivity was generally better in the infrared than the visible spectrum, with recovery of up to 90% of the initial reflectivity being obtained at 1600 nm for both Mo and SS mirrors falling as low as 20-30% of initial reflectivity at a wavelength of 400 nm for some SS mirrors, rising to similar to 80% for Mo mirrors. Some deposit remained on the mirrors after the cleaning trials.

  • 806. Wienhold, P.
    et al.
    Litnovsky, A.
    Philipps, V.
    Schweer, B.
    Sergienko, G.
    Oelhafen, P.
    Ley, M.
    De Temmerman, G.
    Schneider, W.
    Hildebrandt, D.
    Laux, M.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Emmoth, Birger
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och Informationsteknik, IMIT.
    Exposure of metal mirrors in the scrape-off layer of TEXTOR2005Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 337-39, nr 03-jan, s. 1116-1120Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Large molybdenum mirrors have been exposed in the SOL of TEXTOR in order to simulate conditions relevant for ITER optical components. Distortions of the reflectivity - increase as well as decrease - are found in the erosion and deposition dominated areas, respectively. The changes are most pronounced in the near UV and level off in the IR and can partly be attributed to observed surface changes. A novel periscope system was installed and mirrors exposed in a pilot experiment to simulate the transmission of light to distant sensors in ITER.

  • 807. Wiesen, S
    et al.
    Brezinsek, M
    Wischmeier, M
    de la Luna, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Groth, M
    Järvinen, A
    Losada, U
    Martin, A
    Impact of the JET ITER-Like Wall on H-Mode Plasma Fueling2016Ingår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferensbidrag (Refereegranskat)
  • 808.
    Wiesen, S.
    et al.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Brezinsek, S.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Bonnin, X.
    ITER Org, Route Vinon Sur Verdon,CS90 046, F-13067 St Paul Les Durance, France..
    Delabie, E.
    Oak Ridge Natl Lab, POB 2009, Oak Ridge, TN 37831 USA..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Groth, M.
    Aalto Univ, Espoo, Finland..
    Guillemaut, C.
    Univ Lisbon, Inst Plasmas & Fusao Nucl, IST, P-1049001 Lisbon, Portugal..
    Harrison, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Harting, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Henderson, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Huber, A.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Kruezi, U.
    ITER Org, Route Vinon Sur Verdon,CS90 046, F-13067 St Paul Les Durance, France..
    Pitts, R. A.
    ITER Org, Route Vinon Sur Verdon,CS90 046, F-13067 St Paul Les Durance, France..
    Wischmeier, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    On the role of finite grid extent in SOLPS-ITER edge plasma simulations for JET H-mode discharges with metallic wall2018Ingår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 17, s. 174-181Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The impact of the finite grid size in SOLPS-ITER edge plasma simulations is assessed for JET H-mode discharges with a metal wall. For a semi-horizontal divertor configuration it is shown that the separatrix density is at least 30% higher when a narrow scrape-off layer (SOL) grid width is chosen in SOLPS-ITER compared to the case for which the SOL grid width is maximised. The density increase is caused by kinetic neutrals being not confined inside the divertor region because of the reduced extent of the plasma grid. In this case, an enhanced level of reflections of energetic neutrals at the low-field side (LFS) metal divertor wall is observed. This leads to a shift of the ionisation source further upstream which must be accounted for as a numerical artefact. An overestimate in the cooling at the divertor entrance is observed in this case, identified by a reduced heat flux decay parameters lambda(div)(q). Otherwise and further upstream the mid-plane heat decay length lambda(q) parameter is not affected by any change in divertor dissipation. This confirms the assumptions made for the ITER divertor design studies, i.e. that lambda(q) upstream is essentially set by the assumptions for the ratio radial to parallel heat conductivity. It is also shown that even for attached conditions the decay length relations lambda(ne)>lambda(Te)>lambda(q) hold in the near-SOL upstream. Thus for interpretative edge plasma simulations one must take the (experimental) value of lambda(ne) into account, rather than lambda(q), as the former actually defines the required minimum upstream SOL grid extent.

  • 809. Wiesen, S.
    et al.
    Brezinsek, S.
    Wischmeier, M.
    De La Luna, E.
    Groth, M.
    Jaervinen, A. E.
    De La Cal, E.
    Losada, U.
    De Aguilera, A. M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. Association VR.
    Gao, Y.
    Guillemaut, C.
    Harting, D.
    Meigs, A.
    Schmid, K.
    Sergienko, G.
    Impact of the JET ITER-like wall on H-mode plasma fueling2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 6, artikel-id 066024Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    JET ITER-like wall (ILW) experiments show that the edge density evolution is strongly linked with the poloidal distribution of the ionization source. The fueling profile in the JET-ILW is more delocalized as compared to JET-C (JET with carbon-based plasma-facing components PFCs). Compared to JET-C the H-mode pedestal fueling cycle is dynamically influenced by a combination of plasma-wall interaction features, in particular: (1) edge-localized modes (ELMs) induced energetic particles are kinetically reflected on W divertor PFCs leading to distributed refueling away from the divertor depending on the divertor plasma configuration, (2) delayed molecular re-emission and outgassing of particles being trapped in W PFCs (bulk-W at the high field side and W-coated CFCs at the low field side) with different fuel content and (3) outgassing from Be co-deposits located on top of the high-field side baffle region shortly after the ELM. In view of the results of a set of well diagnosed series of JET-ILW type-I ELMy H-mode discharges with good statistics, the aforementioned effects are discussed in view of H-mode pedestal fueling capacity. The ongoing modelling activities with the focus on coupled core-edge plasma simulations and plasma-wall interaction are described and discussed also in view of possible code improvements required.

  • 810. Wilson, H. R.
    et al.
    Bowman, C.
    Cowley, S. C.
    Cziegler, I.
    Dickinson, D.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Gibson, K.
    Ham, C.
    Horvath, L.
    Kirk, A.
    Lipschultz, B.
    Lunniss, A. E. L.
    Maggi, C. F.
    Roach, C. M.
    Saarelma, S.
    Snyder, P. B.
    Thornton, A.
    Wynn, A.
    Inter-ELM pedestal evolution in low triangularity JET-ILW discharges2017Ingår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    Studies of the pedestal stability in low triangularity, d=0.2, JET ITER-Like Wall discharges are presented, following the evolution between ELMs. The pressure gradient tracks the ideal MHD ballooning threshold, only lagging behind it when the threshold rises rapidly as the plasma penetrates the second stability region. This is consistent with a role for the kinetic ballooning mode in the pedestal structure. When the plasma has second stability access, e.g. for low gas puff discharges, the peeling-ballooning mode is marginally stable at ELM onset. In cases where there is no second stability access the discharges are some way short of the peeling-ballooning threshold, so this alone cannot be the trigger for the ELM. A low amplitude sinusoidal oscillation in the Be-II emission is observed that correlates well with the ELMs, and has an associated high frequency magnetic field fluctuation, ~100-250kHz, with modulated amplitude. This might be associated with a new filamentary equilibrium state. 

  • 811. Wisse, M.
    et al.
    Marot, L.
    Widdowson, A.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Ivanova, Darya
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Doerner, R. P.
    Baldwin, M. J.
    Likonen, J.
    Alves, E.
    Hakola, A.
    Koivuranta, S.
    Steiner, R.
    Meyer, E.
    Laser-assisted cleaning of beryllium-containing mirror samples from JET and PISCES-B2014Ingår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 89, nr 2, s. 122-130Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A set of seven polycrystalline mirror samples retrieved from the JET tokamak has been cleaned in vacuum using a pulsed laser system. The surfaces of samples exposed to plasma during 2008-2009 campaigns as part of the second phase of a comprehensive first mirror test contained a mixture of carbon, beryllium and tritium. For this reason, the samples were treated in a vacuum chamber constructed specially for this purpose. In some cases mirrors show an increase of the specular reflectivity after cleaning, though beryllium and carbon deposits were not fully removed. Additionally, three samples coated in PISCES-B with a 110-120 nm beryllium layer were subjected to laser cleaning tests as well.

  • 812.
    Yadikin, Dimitry
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Paccagnella, R.
    Advanced feedback control methods in EXTRAP T2R2006Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 13, nr 7, s. 072109-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Previous experiments in the EXTRAP T2R reversed field pinch device have shown the possibility of suppression of multiple resistive wall modes (RWM). A feedback system has been installed in EXTRAP T2R having 100% coverage of the toroidal surface by the active coil array. Predictions based on theory and the previous experimental results show that the number of active coils should be sufficient for independent stabilization of all unstable RWMs in the EXTRAP T2R. Experiments using different feedback schemes are performed, comparing the intelligent shell, the fake rotating shell, and the mode control with complex feedback gains. Stabilization of all unstable RWMs throughout the discharge duration of t(d)approximate to 10 tau(w) is seen using the intelligent shell feedback scheme. Mode rotation and the control of selected Fourier harmonics is obtained simultaneously using the mode control scheme with complex gains. Different sensor signals are studied. A feedback system with toroidal magnetic field sensors could have an advantage of lower feedback gain needed for the RWM suppression compared to the system with radial magnetic field sensors. In this study, RWM suppression is demonstrated, using also the toroidal field component as a sensor signal in the feedback system.

  • 813.
    Yadikin, Dmitriy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Drake, James Robert
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Intelligent shell feedback control of resistive wall modes in EXTRAP T2R2005Ingår i: 32nd EPS Conference on Plasma Physics 2005, EPS 2005, Held with the 8th International Workshop on Fast Ignition of Fusion Targets: Europhysics Conference Abstracts, 2005, s. 1602-1605Konferensbidrag (Refereegranskat)
  • 814. Yadykin, D.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Delabie, E.
    Chapman, I. T.
    Gerasimov, S.
    Kempenaars, M.
    Rimini, F. G.
    Studies of the non-axisymmetric plasma boundary displacement in JET in presence of externally applied magnetic field2015Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 57, nr 10, artikel-id 104003Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Non-axisymmetric plasma boundary displacement is caused by the application of the external magnetic field with low toroidal mode number. Such displacement affects edge stability, power load on the first wall and could affect efficiency of the ICRH coupling in ITER. Studies of the displacement are presented for JET tokamak focusing on the interaction between error field correction coils (EFCCs) and shape control system. First results are shown on the direct measurement of the plasma boundary displacement at different toroidal locations. Both qualitative and quantitative studies of the plasma boundary displacement caused by interaction between EFCCs and shape control system are performed for different toroidal phases of the external field. Axisymmetric plasma boundary displacement caused by the EFCC/shape control system interaction is seen for certain phase values of the external field. The value of axisymmetric plasma boundary displacement caused by interaction can be comparable to the non-axisymmetric plasma boundary displacement value produced by EFCCs.

  • 815. Yadykin, D.
    et al.
    Gryaznevich, M.
    Frasinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gerasimov, S.
    Effect of the external helical fields on the plasma boundary shape in JET2014Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 1, s. 013016-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Externally applied helical magnetic fields are now often used on tokamaks for various purposes. This paper presents results of studies of the effect of the external fields, produced by the error field correction coils (EFCCs) on JET, on the plasma boundary shape. Significant 3D distortions, predicted in the previous studies, have been confirmed using upgraded magnetic diagnostics and high-resolution Thomson scattering diagnostics. A simple method of estimating the edge distortion using magnetic diagnostics calibrated on the kinetic measurements is proposed and demonstrated.

  • 816. Yambe, Kiyoyuki
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hirano, Yoichi
    Yagi, Yasuyuki
    Koguchi, Haruisa
    Sakakita, Hajime
    Frequency Dependence of Fast Magnetic Fluctuations in TPE-RX plasma2008Ingår i: Journal of Plasma and Fusion Research, ISSN 0918-7928, Vol. 3, s. 060-Artikel i tidskrift (Refereegranskat)
  • 817. Yambe, Myoyuki
    et al.
    Kiyama, Satoru
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hirano, Yoichi
    Yagi, Yasuyuki
    Koguchi, Haruhisa
    Sakakita, Hajime
    Measurement of fast magnetic fluctuations in edge region of TPE-RX reversed-field pinch plasma2007Ingår i: Japanese Journal of Applied Physics, ISSN 0021-4922, E-ISSN 1347-4065, Vol. 46, nr 10A, s. 6831-6833Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fast magnetic fluctuation (0) levels are measured using a newly developed complex edge probe (CEP) in the edge region of TPE-RX reversed-field pinch plasma. The CEP is installed inside a vacuum vessel and is sensitive to fast delta B. The delta B levels measured using the CEP are compared with those measured using an extensive magnetic measurement system (MMS), which is located outside the vacuum vessel and has little sensitivity to fast delta B. The delta B levels before and after the appearance of the locked mode (LM) are compared in both the CEP and MMS signals. It was found that the rapid increase in the delta B signal level obtained using the MMS just after the appearance of LM is mainly caused by the slowing of plasma rotation.

  • 818. Yavorskij, V.
    et al.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. Culham Science Centre, United Kingdom .
    Goloborod'ko, V.
    Brix, M.
    Challis, C.
    Gerasimov, S.
    Kiptily, V.
    Korotkov, A.
    Parail, V.
    Reznik, S.
    Santala, M.
    Schoepf, K.
    Sharapov, S. E.
    Surrey, E.
    De Vries, P.
    TF ripple effects on the NBI deuteron confinement in JET2007Ingår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 2, s. 876-879Konferensbidrag (Refereegranskat)
    Abstract [en]

    Ripple induced reduction of the fluxes of deuterium neutrals in the 5-40 keV energy range from the plasma mid-plane was observed in recent JET experiments. The maximum observed reduction of D0 fluxes due to ripple is approximately 50 % and occurs at energies above 30 keV. In positive shear plasmas without ICRH ripple reduction of D0 fluxes vanishes at energies below 10 keV. However, in the case of plasmas with low or reversed shear core, increased D0 fluxes were observed for energies below 10-20 keV in the presence of additional ripple and ICRH heating. Interpretive modeling of the deuterium neutral emission that accounts for the superbanana ripple diffusion of NBI ions is in reasonable agreement with measurements at least for the scenarios without ICRH. Note that ripples may essentially effect the fast ion confinement in ITER where TF ripple magnitude at the outer separatrix is expected to be δ ∼ 0.5%.

  • 819. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sharapov, S. E.
    Testa, D. S.
    Kurbet, I. I.
    Suprathermal deuterium ions produced by nuclear elastic scattering of ICRH driven He-3 ions in JET plasmas2007Ingår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 49, nr 11, s. 1747-1766Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Measurements of the suprathermal tail of the energy distribution function of deuterium ions, in plasmas containing MeV energy ICRH driven minority He-3 ions and majority deuterium ions, revealed that the suprathermal tail ion density exceeded by nearly an order of magnitude that expected due to nuclear elastic scattering (NES) of He-3 projectile ions on deuterium target ions. The experiments were performed on the Joint European Torus (JET), measurements of the line-of-sight integrated energy distribution functions of He-3 and suprathermal deuterium ions were made using a high energy neutral particle analyzer. The NES or 'knock-on' deuterium ion energy distribution function was simulated using the FPP-3D Fokker-Plank code (Zaitsev et al 2002 Nucl. Fusion 42 1340) which solves the 3D trajectory averaged kinetic equations in JET tokamak geometry while taking into account NES of He-3 ions on the deuterium ions. The required input energy distribution function of ICRH driven He-3 ions was simulated using the SELFO code (Hedin et al 2002 Nucl. Fusion 42 527). The comparison between measurement and simulation in the He-3 ICRH experiments is contrasted with an analogous previous comparison between measurements and simulation of JET plasmas in which 3.5MeV DT fusion alpha-particles were the projectile ions, where measurement and simulation roughly agreed. Possible explanations for the observed excess knock-on deuterium tail in the experiments with He-3 minority

  • 820. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Kiptily, V. G.
    Sharapov, S. E.
    Simulations to elucidate suprathermal deuterium ion tail observed in He3 minority ICRF heated JET plasmas2008Ingår i: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, nr 1, s. 501-504Konferensbidrag (Refereegranskat)
  • 821. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas Joe
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Sharapov, S. E.
    Testa, D. S.
    Kurbet, I. I.
    Simulation of deuteron tails produced by close collisions with ICRH Accelerated He3 ions in JET2006Ingår i: EPS Conf. Plasma Phys., EPS, 2006, s. 412-415Konferensbidrag (Refereegranskat)
  • 822. Zarzoso, D.
    et al.
    Beurskens, M. N. A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Eich, T.
    Joffrin, E.
    Loarte, A.
    Maddison, G.
    Rimini, F. G.
    Saibene, G.
    Solano, E. R.
    Thomsen, H.
    ELM size analysis in JET advanced tokamak and hybrid scenarios2010Ingår i: 37th EPS Conference on Plasma Physics 2010, EPS 2010: Volume 2, 2010, s. 922-925Konferensbidrag (Refereegranskat)
  • 823. Zarzoso, D.
    et al.
    Beurskens, M. N. A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Joffrin, E.
    Rimini, F. G.
    Solano, E. R.
    ELM size analysis in JET hybrid plasmas2011Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 51, nr 11, s. 112001-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Experimental results are presented in this paper, characterizing the behaviour of type I ELMs for a JET database of standard ELMy H-mode and hybrid plasmas. Whereas the collisionality scaling published in [ 1] has been reproduced for the new baseline discharges, no clear correlation can be established from the analysis of hybrid scenarios. The ELM losses normalized to the pedestal stored energy for high triangularity hybrid plasmas seem to be significantly larger than the energies for baseline plasmas at similar values of collisionality. For low triangularity hybrid plasmas, the ELM losses are of the same order as those obtained in baseline scenarios. The important scatter of the results seems to be due to the sensitivity of hybrid plasmas to gas fuelling. Analysis of the ITER-like wall compatibility of hybrid discharges is also reported.

  • 824. Zarzoso, D.
    et al.
    Beurskens, M.N.A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Joffrin, E.
    ELM size scaling in JET advanced tokamak scenarios2010Konferensbidrag (Refereegranskat)
  • 825. Zhao, M. L.
    et al.
    Chen, Y. P.
    Guo, H. Y.
    Ye, M. Y.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Li, G. Q.
    Luo, Z. P.
    Modeling of divertor geometry effects in China fusion engineering testing reactor by SOLPS/B2-Eirene2014Ingår i: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 21, nr 5, s. 052503-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The China Fusion Engineering Testing Reactor (CFETR) is currently under design. The SOLPS/B2-Eirene code package is utilized for the design and optimization of the divertor geometry for CFETR. Detailed modeling is carried out for an ITER-like divertor configuration and one with relatively open inner divertor structure, to assess, in particular, peak power loading on the divertor target, which is a key issue for the operation of a next-step fusion machine, such as ITER and CFETR. As expected, the divertor peak heat flux greatly exceeds the maximum steady-state heat load of 10MW/m(2), which is a limit dictated by engineering, for both divertor configurations with a wide range of edge plasma conditions. Ar puffing is effective at reducing divertor peak heat fluxes below 10MW/m(2) even at relatively low densities for both cases, favoring the divertor configuration with more open inner divertor structure.

  • 826.
    Zhou, Yushan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Impact of Surface Structures onDeposition and Erosion in a Tokamak2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [sv]

    Fusion är en potentiellt obegränsad och miljövänlig energikälla för det mänskliga samhället i framtiden. Det återstår emellertid vissa problem att lösa. Bland dem är deposition och erosion vid ytor som är i kontakt med plasmat kritiska. Deposition av bränsle och föroreningar ger potentiellt långsiktig ackumulation av bränsle (tritium) som kan ge upphov till säkerhetsproblem och försämra bränsleekonomin. Erosion av vakuumkärlets väggar i in fusionsanläggning alstrar förorenar plasmat och kan begränsa livstiden för väggkomponenter. Arbetet i denna avhandling fokuserar på deposition och erosion på ytor i JET-ILW-projektet, som består av volfram (eller volframbelagd kolfiberkomposit) i divertor och beryllium i limiter.

    För depositionsfrågorna användes mikroanalys för att observera hur deuterium och beryllium fördelas över ytorna efter plasmaexponering. Yttopografi erhölls från SEM, optisk mikroskopi och konfokal laserskanmikroskopi. Distributionskartor från IBA jämfördes med yttopografin. För att förklara experimentella resultat användes modellering av jontrajektorior, dels på verklig experimentell topografi, dels på förenklade modellytor. Micro IBA-resultat visar att deuterium och beryllium ansamlas i mikroskopiskt nedsänkta områden, t.ex. gropar och sprickor. Modelleringen visar att joners gyratation delvis kan förklara denna ojämna fördelning av deuterium och beryllium.

    För erosionsproblemet gjordes mätningar på markerplattor, konstruerade för att observera materialosion i JET. En ny metod införs för att erhålla erosionsdata, genom att kombinera mikro IBA och SEM-bild. Denna metod kan skilja på inflytande på IBA-resultat från skrovlighet, vilket är annars är ett problem IBA för på skrovlig yta. På samma sätt används mikroanalys för att förbättra tolkningen av analyser av deuterium som trängt in i en skiktad struktur.

  • 827.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Paneta, C.
    Possnert, G.
    Micro ion beam analysis for the erosion of beryllium marker tiles in a tokamak limiter2019Ingår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 450, s. 200-204Artikel i tidskrift (Refereegranskat)
    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.

  • 828.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Possnert, G.
    Likonen, J.
    Pettersson, J.
    Koivuranta, S.
    Widdowson, A. M.
    Microanalysis of deposited layers in the inner divertor of JET with ITER-like wall2017Ingår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 412-417Artikel i tidskrift (Refereegranskat)
    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.

  • 829.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Modelling of effect from rough surface on deuterium and beryllium deposition on divertor targetManuskript (preprint) (Övrigt vetenskapligt)
  • 830.
    Zhou, Yushan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Possnert, G
    Likonen, J
    contributors, JET
    The effect of gyration on the deposition of beryllium and deuterium at rough surface on thedivertor tiles with ITER-like-wall in JET2019Ingår i: Nuclear Materials and Energy, E-ISSN 2352-1791Artikel i tidskrift (Refereegranskat)
  • 831. Zuin, M.
    et al.
    Dal Bello, S.
    Marrelli, L.
    Puiatti, M. E.
    Agostinetti, P.
    Agostini, M.
    Antoni, V.
    Auriemma, F.
    Barbisan, M.
    Barbui, T.
    Baruzzo, M.
    Belli, F.
    Bettini, P.
    Bigi, M.
    Bilel, R.
    Boldrin, M.
    Bolzonella, T.
    Bonfiglio, D.
    Brombin, M.
    Buffa, A.
    Bustreo, C.
    Canton, A.
    Cappello, S.
    Carraro, L.
    Cavazzana, R.
    Cester, D.
    Chacon, L.
    Chitarin, G.
    Cooper, W. A.
    Cordaro, L.
    Palma, M. Dalla
    Deambrosis, S.
    Delogu, R.
    De Lorenzi, A.
    De Masi, G.
    Dong, J. Q.
    Escande, D. F.
    Fassina, A.
    Felici, F.
    Ferro, A.
    Finotti, C.
    Franz, P.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gaio, E.
    Ghezzi, F.
    Giudicotti, L.
    Gnesotto, F.
    Gobbin, M.
    Gonzalez, W. A.
    Grando, L.
    Guo, S. C.
    Hanson, J. D.
    Hirshman, S. P.
    Innocente, P.
    Jackson, J. L.
    Kiyama, S.
    Komm, M.
    Kudlacek, O.
    Laguardia, L.
    Li, C.
    Liu, B.
    Liu, S. F.
    Liu, Y. Q.
    Lopez-Bruna, D.
    Lorenzini, R.
    Luce, T. C.
    Luchetta, A.
    Maistrello, A.
    Manduchi, G.
    Mansfield, D. K.
    Marchiori, G.
    Marconato, N.
    Marcuzzi, D.
    Martin, P.
    Martines, E.
    Martini, S.
    Mazzitelli, G.
    McCormack, O.
    Miorin, E.
    Momo, B.
    Moresco, M.
    Narushima, Y.
    Okabayashi, M.
    Paccagnella, R.
    Patel, N.
    Pavei, M.
    Peruzzo, S.
    Pilan, N.
    Pigatto, L.
    Piovan, R.
    Piovesan, P.
    Piron, C.
    Piron, L.
    Predebon, I.
    Pucella, G.
    Rea, C.
    Recchia, M.
    Rizzolo, A.
    Rostagni, G.
    Ruset, C.
    Sajo-Bohus, L.
    Sakakita, H.
    Sanchez, R.
    Sarff, J. S.
    Sattin, F.
    Scarin, P.
    Schmitz, O.
    Schneider, W.
    Siragusa, M.
    Sonato, P.
    Spada, E.
    Spagnolo, S.
    Spolaore, M.
    Spong, D. A.
    Spizzo, G.
    Stevanato, L.
    Suzuki, Y.
    Taliercio, C.
    Terranova, D.
    Tudisco, O.
    Urso, G.
    Valente, M.
    Valisa, M.
    Vallar, M.
    Veranda, M.
    Vianello, N.
    Villone, F.
    Vincenzi, P.
    Visona, N.
    White, R. B.
    Xanthopoulos, P.
    Xu, X. Y.
    Yanovskiy, V.
    Zamengo, A.
    Zanca, P.
    Zaniol, B.
    Zanotto, L.
    Zhang, Y.
    Zilli, E.
    Overview of the RFX-mod fusion science activity2017Ingår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 10, artikel-id 102012Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports the main recent results of the RFX-mod fusion science activity. The RFX-mod device is characterized by a unique flexibility in terms of accessible magnetic configurations. Axisymmetric and helically shaped reversed-field pinch equilibria have been studied, along with tokamak plasmas in a wide range of q(a) regimes (spanning from 4 down to 1.2 values). The full range of magnetic configurations in between the two, the so-called ultra-low q ones, has been explored, with the aim of studying specific physical issues common to all equilibria, such as, for example, the density limit phenomenon. The powerful RFX-mod feedback control system has been exploited for MHD control, which allowed us to extend the range of experimental parameters, as well as to induce specific magnetic perturbations for the study of 3D effects. In particular, transport, edge and isotope effects in 3D equilibria have been investigated, along with runaway mitigations through induced magnetic perturbations. The first transitions to an improved confinement scenario in circular and D-shaped tokamak plasmas have been obtained thanks to an active modification of the edge electric field through a polarized electrode. The experiments are supported by intense modeling with 3D MHD, gyrokinetic, guiding center and transport codes. Proposed modifications to the RFX-mod device, which will enable further contributions to the solution of key issues in the roadmap to ITER and DEMO, are also briefly presented.

  • 832.
    Åkermark, Torbjörn
    et al.
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik.
    Emmoth, Birger
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Laser annealing in combination with mass spectroscopy, a technique to study deuterium on tokamak carbon samples, a tool for detritiation2006Ingår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 359, nr 3, s. 220-226Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this study, a method is presented based on mass spectroscopy to measure the a real density of deuterium on a graphite surface exposed to tokamak discharges. The studied sample was cut from a bumper limiter exposed in the TEXTOR tokamak and annealed by a 1 J Excimer laser (KrF). The energy used was 400 mJ cm(-2), which is below the threshold for ablation. 1 J cm(-2). The release of HD and D, was measured by a mass spectroscopy set-up and no other species released from the sample were detected in this experiment. The amount of D released from the sample after 20 laser pulses was measured to 7 x 10(16) D atoms per cm(-2) (for this particular sample) and most of the hydrogen at the surface was released in the first pulse, as checked by nuclear reaction analysis (NRA) techniques, which gave changes of the amount of deuterium before and after laser annealing. The sensitivity in this experiment was 5 x 10(14) atoms per cm(-2) for HD and 5 x 10(13) atoms per cm(-2) for D-2.

  • 833.
    Štefániková, E.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lomas, P.
    Nunes, I.
    Baruzzo, M.
    Rimini, F.
    Saarelma, S.
    Wiesen, S.
    Peterka, M.
    Confinement and pedestal structure in high performance scenarios in JET-ILW and comparison with JET-C2015Ingår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferensbidrag (Refereegranskat)
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