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  • 1.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Bykov, Igor
    Zhou, Yushan
    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.
    contributors, JET
    Deep deuterium retention and Be/W mixingat tungsten coated surfaces in the JETdivertor2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896Artikkel i tidsskrift (Fagfellevurdert)
    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.

  • 2.
    Bhatti, Muhammad Khurram
    et al.
    Informat Technol Univ, Embedded Comp Lab, 346-B Ferozpur Rd, Lahore, Pakistan..
    Oz, Isil
    Izmir Inst Technol, Comp Engn Dept, Izmir, Turkey..
    Amin, Sarah
    Informat Technol Univ, Embedded Comp Lab, 346-B Ferozpur Rd, Lahore, Pakistan..
    Mushtaq, Maria
    Informat Technol Univ, Embedded Comp Lab, 346-B Ferozpur Rd, Lahore, Pakistan..
    Farooq, Umer
    Dhofar Univ, Dept Elect & Comp Engn, Salalah 211, Oman..
    Popov, Konstantin
    SICS, Isafjordsgatan 22, S-16429 Kista, Sweden..
    Brorsson, Mats
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik. , S-16429 Kista, Sweden..
    Locality-aware task scheduling for homogeneous parallel computing systems2018Inngår i: Computing, ISSN 0010-485X, E-ISSN 1436-5057, Vol. 100, nr 6, s. 557-595Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In systems with complex many-core cache hierarchy, exploiting data locality can significantly reduce execution time and energy consumption of parallel applications. Locality can be exploited at various hardware and software layers. For instance, by implementing private and shared caches in a multi-level fashion, recent hardware designs are already optimised for locality. However, this would all be useless if the software scheduling does not cast the execution in a manner that promotes locality available in the programs themselves. Since programs for parallel systems consist of tasks executed simultaneously, task scheduling becomes crucial for the performance in multi-level cache architectures. This paper presents a heuristic algorithm for homogeneous multi-core systems called locality-aware task scheduling (LeTS). The LeTS heuristic is a work-conserving algorithm that takes into account both locality and load balancing in order to reduce the execution time of target applications. The working principle of LeTS is based on two distinctive phases, namely; working task group formation phase (WTG-FP) and working task group ordering phase (WTG-OP). The WTG-FP forms groups of tasks in order to capture data reuse across tasks while the WTG-OP determines an optimal order of execution for task groups that minimizes the reuse distance of shared data between tasks. We have performed experiments using randomly generated task graphs by varying three major performance parameters, namely: (1) communication to computation ratio (CCR) between 0.1 and 1.0, (2) application size, i.e., task graphs comprising of 50-, 100-, and 300-tasks per graph, and (3) number of cores with 2-, 4-, 8-, and 16-cores execution scenarios. We have also performed experiments using selected real-world applications. The LeTS heuristic reduces overall execution time of applications by exploiting inter-task data locality. Results show that LeTS outperforms state-of-the-art algorithms in amortizing inter-task communication cost.

  • 3.
    Blanken, T. C.
    et al.
    Eindhoven Univ Technol, Control Syst Technol Grp, Dept Mech Engn, POB 513, NL-5600 MB Eindhoven, Netherlands.;Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fridström, Richard
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia-Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, T.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vignitchouk, Ladislas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Dori, V
    Univ Split, Fac Elect Engn Mech Engn & Naval Architecture, R Boskovica 32, Split 21000, Croatia..
    Real-time plasma state monitoring and supervisory control on TCV2019Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 2, artikkel-id 026017Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In ITER and DEMO, various control objectives related to plasma control must be simultaneously achieved by the plasma control system (PCS), in both normal operation as well as off-normal conditions. The PCS must act on off-normal events and deviations from the target scenario, since certain sequences (chains) of events can precede disruptions. It is important that these decisions are made while maintaining a coherent prioritization between the real-time control tasks to ensure high-performance operation. In this paper, a generic architecture for task-based integrated plasma control is proposed. The architecture is characterized by the separation of state estimation, event detection, decisions and task execution among different algorithms, with standardized signal interfaces. Central to the architecture are a plasma state monitor and supervisory controller. In the plasma state monitor, discrete events in the continuous-valued plasma state arc modeled using finite state machines. This provides a high-level representation of the plasma state. The supervisory controller coordinates the execution of multiple plasma control tasks by assigning task priorities, based on the finite states of the plasma and the pulse schedule. These algorithms were implemented on the TCV digital control system and integrated with actuator resource management and existing state estimation algorithms and controllers. The plasma state monitor on TCV can track a multitude of plasma events, related to plasma current, rotating and locked neoclassical tearing modes, and position displacements. In TCV experiments on simultaneous control of plasma pressure, safety factor profile and NTMs using electron cyclotron heating (ECI I) and current drive (ECCD), the supervisory controller assigns priorities to the relevant control tasks. The tasks are then executed by feedback controllers and actuator allocation management. This work forms a significant step forward in the ongoing integration of control capabilities in experiments on TCV, in support of tokamak reactor operation.

  • 4.
    Brunsell, Per R.
    et al.
    KTH, Tidigare Institutioner (före 2005), Alfvénlaboratoriet.
    Bergsåker, Henric
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Brzozowski, Jerzy
    Cecconello, Marco
    Drake, James R.
    Malmberg, Jenny-Ann
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS).
    Schnack, Dalton
    Mode Dynamics and Confinement in the Reversed-field Pinch2000Inngår i: 18th IAEA Fusion Energy Conference in Sorrento, Italy, 4-10 Oct. 2000. Paper IAEA-CN-77/EXP3/14, 2000Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Tearing mode dynamics and toroidal plasma flow in the RFP has been experimentally studied in the Extrap T2 device. A toroidally localised, stationary magnetic field perturbation, the ``slinky mode'' is formed in nearly all discharges. There is a tendency of increased phase alignment of different toroidal Fourier modes, resulting in higher localised mode amplitudes, with higher magnetic fluctuation level. The fluctuation level increases slightly with increasing plasma current and plasma density. The toroidal plasma flow velocity and the ion temperature has been measured with Doppler spectroscopy. Both the toroidal plasma velocity and the ion temperature clearly increase with I/N. Initial, preliminary experimental results obtained very recently after a complete change of the Extrap T2 front-end system (first wall, shell, TF coil), show that an operational window with mode rotation most likely exists in the rebuilt device, in contrast to the earlier case discussed above. A numerical code DEBSP has been developed to simulate the behaviour of RFP confinement in realistic geometry, including essential transport physics. Resulting scaling laws are presented and compared with results from Extrap T2 and other RFP experiments.

  • 5. Bílková, P.
    et al.
    Böhm, P.
    Komm, M.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Stefániková, Estera
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Peterka, M.
    Šos, M.
    Seidl, J.
    Grover, O.
    Havlíček, J.
    Mitošinková, K.
    Varju, J.
    Vondráček, P.
    Urban, J.
    Imríšek, M.
    Markovič, T.
    Weinzettl, V.
    Hron, M.
    Pánek, R.
    Relative shift in position of temperature and density pedestals at the COMPASS tokamak2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 6.
    Coad, J. P.
    et al.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Likonen, J.
    VTT Tech Res Ctr Finland, POB 1000, FIN-02044 Espoo, Finland..
    Bekris, N.
    Karlsruhe Inst Technol, D-76021 Karlsruhe, Germany..
    Brezinsek, S.
    Forschungszentrum Juelich, Inst Energieforsch Plasmaphys, D-52425 Julich, Germany..
    Matthew, G. F.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Mayer, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Widdowson, A. M.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Material migration and fuel retention studies during the JET carbon divertor campaigns2019Inngår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 138, s. 78-108Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The first divertor was installed in the JET machine between 1992 and 1994 and was operated with carbon tiles and then beryllium tiles in 1994-5. Post-mortem studies after these first experiments demonstrated that most of the impurities deposited in the divertor originate in the main chamber, and that asymmetric deposition patterns generally favouring the inner divertor region result from drift in the scrape-off layer. A new monolithic divertor structure was installed in 1996 which produced heavy deposition at shadowed areas in the inner divertor corner, which is where the majority of the tritium was trapped by co-deposition during the deuterium-tritium experiment in 1997. Different divertor geometries have been tested since such as the Gas-Box and High-Delta divertors; a principle objective has been to predict plasma behaviour, transport and tritium retention in ITER. Transport modelling experiments were carried out at the end of four campaigns by puffing C-13-labelled methane, and a range of diagnostics such as quartz-microbalance and rotating collectors have been installed to add time resolution to the post-mortem analyses. The study of material migration after D-D and D-T campaigns clearly revealed important consequences of fuel retention in the presence of carbon walls. They gave a strong impulse to make a fundamental change of wall materials. In 2010 the carbon divertor and wall tiles were removed and replaced with tiles with Be or W surfaces for the ITER-Like Wall Project.

  • 7. Di Siena, A.
    et al.
    Görler, T.
    Doerk, H.
    Bilato, R.
    Citrin, J.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Schneider, M.
    Poli, E.
    Impact of realistic fast ion distribution function in gyrokinetic GENE simulations2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Understanding the stabilising mechanism of fast particles on plasma turbulence is an essential task for a fusion reactor, where the energetic particles can constitute a significant fraction of the main ions. While the consideration of equivalent Maxwellian distributed fast ions in the simulations has greatly improved the agreement with experiments, fast ion electromagnetic stabilization seems to be somewhat over-estimated. Power balance is usually reached only with increased plasma gradients. However, it is well known that to rigorously model highly non thermalised particles, a non-Maxwellian background distribution function is needed. To this aim, a previous study on a particular JET plasma has been revised and analysed with the gyrokinetic code GENE. Fast particles have been modelled with a number of different analytic and numerical distributions. The latter have been imported from the modelling tools NEMO/SPOT and SELFO. 

  • 8.
    Dumont, R. J.
    et al.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Mailloux, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Aslanyan, V
    MIT, PSFC, 175 Albany St, Cambridge, MA 02039 USA..
    Baruzzo, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Challis, C. D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Coffey, I
    Queens Univ, Dept Pure & Appl Phys, Belfast BT7 1NN, Antrim, North Ireland..
    Czarnecka, A.
    Inst Plasma Phys & Laser Microfus, Hery St 23, PL-00908 Warsaw, Poland..
    Delabie, E.
    Oak Ridge Natl Lab, Oak Ridge, TN USA..
    Eriksson, J.
    Uppsala Univ, Dept Phys & Astron, SE-75119 Uppsala, Sweden..
    Faustin, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Ferreira, J.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Fitzgerald, M.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Garcia, J.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Giacomelli, L.
    Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Giroud, C.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Hawkes, N.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Jacquet, Ph
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Joffrin, E.
    CEA, IRFM, F-13108 St Paul Les Durance, France..
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Keeling, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    King, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Kiptily, V
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Lomanowski, B.
    Aalto Univ, POB 14100, FIN-00076 Aalto, Finland..
    Lerche, E.
    Ass EUROFUS Belgian State, LPP ERM KMS, TEC Partner, Brussels, Belgium..
    Mantsinen, M.
    Barcelona Supercomp Ctr, Barcelona, Spain.;ICREA, Barcelona, Spain..
    Meneses, L.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Menmuir, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    McClements, K.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Moradi, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Nabais, F.
    Univ Lisbon, IST, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Nocente, M.
    Univ Milano Bicocca, Piazza Sci 3, I-20126 Milan, Italy..
    Patel, A.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Patten, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Puglia, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scannell, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Sharapov, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Solano, E. R.
    CIEMAT, Lab Nacl Fus, Madrid, Spain..
    Tsalas, M.
    FOM Inst DIFFER, NL-3430 BE Nieuwegein, Netherlands.;ITER Org, Route Vinon Sur Verdon, F-13067 St Paul Les Durance, France..
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Weisen, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scenario development for the observation of alpha-driven instabilities in JET DT plasmas2018Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 8, artikkel-id 082005Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In DT plasmas, toroidal Alfven eigenmodes (TAEs) can be made unstable by the alpha particles resulting from fusion reactions, and may induce a significant redistribution of fast ions. Recent experiments have been conducted in JET deuterium plasmas in order to prepare scenarios aimed at observing alpha-driven TAEs in a future JET DT campaign. Discharges at low density, large core temperatures associated with the presence of internal transport barriers and characterised by good energetic ion confinement have been performed. ICRH has been used in the hydrogen minority heating regime to probe the TAE stability. The consequent presence of MeV ions has resulted in the observation of TAEs in many instances. The impact of several key parameters on TAE stability could therefore be studied experimentally. Modeling taking into account NBI and ICRH fast ions shows good agreement with the measured neutron rates, and has allowed predictions for DT plasmas to be performed.

  • 9.
    Fazinic, Stjepko
    et al.
    Rudjer Boskovic Inst, Bijenicka 54, Zagreb 10000, Croatia..
    Tadic, Tonic
    Rudjer Boskovic Inst, Bijenicka 54, Zagreb 10000, Croatia..
    Vuksic, Marin
    Rudjer Boskovic Inst, Bijenicka 54, Zagreb 10000, Croatia..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fortuna-Zalesna, Elibieta
    Warsaw Univ Technol, Fac Mat Sci & Technol, Woloska 141, PL-02507 Warsaw, Poland..
    Widdowson, Anna
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Ion Microbeam Analyses of Dust Particles and Codeposits from JET with the ITER-Like Wall2018Inngår i: Analytical Chemistry, ISSN 0003-2700, E-ISSN 1520-6882, Vol. 90, nr 9, s. 5744-5752Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Generation of metal dust in the JET tokamak with the ITER-like wall (ILW) is a topic of vital interest to next-step fusion devices because of safety issues with plasma operation. Simultaneous Nuclear Reaction Analysis (NRA) and Particle Induced X-ray Emission (PIXE) with a focused four MeV He-3 microbeam was used to determine the composition of dust particles related to the JET operation with the ILW. The focus was on "Be-rich particles" collected from the deposition zone on the inner divertor tile. The particles found are composed of a mix of codeposited species up to 120 m in size with a thickness of 30-40 mu m, The main constituents are D from the fusion fuel, Be and W from the main plasma-facing components, and Ni and Cr from the Inconel grills of the antennas for auxiliary plasma heating. Elemental concentrations were estimated by iterative NRA-PIXE analysis. Two types of dust particles were found: (i) larger Be-rich particles with Be concentrations above 90 at% with a deuterium presence of up to 3.4 at% and containing Ni (1-3 at%), Cr (0.4-0.8 at%), W (0.2-0.9 at%), Fe (0.3-0.6 at%), and Cu and Ti in lower concentrations and (ii) small particles rich in Al and/or Si that were in some cases accompanied by other elements, such as Fe, Cu, or Ti or W and Mo.

  • 10. Field, A. R.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Maggi, C.
    Saarelma, S.
    Inter-ELM power losses and their dependence on pedestal parameters in JET C-And ITER-like wall H-mode plasmas2018Inngår i: 45th EPS Conference on Plasma Physics, EPS 2018, European Physical Society (EPS) , 2018, s. 1636-1639Konferansepaper (Fagfellevurdert)
  • 11.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Dunne, M. G.
    Sheikh, U.
    Orain, F.
    Bernert, M.
    Birkenmeier, G.
    Blanchard, P.
    Carralero, D.
    Cavedon, M.
    Coda, S.
    Fischer, R.
    Hoelzl, M.
    Laggner, F.
    McDermott, R. M.
    Meyer, H.
    Merle, A.
    Theiler, C.
    Verhaegh, K.
    Viezzer, E.
    Wolfrum, E.
    Role of the scrape-off layer in the type I ELM dynamics in AUG and TCV2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 12.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Saarelma, S.
    Imbeaux, F.
    Verdoolaege, G.
    Bilkova, P.
    Bohm, P.
    Fridström, R.
    Giovannozzi, E.
    Owsiak, M.
    Dunne, M.
    Labit, B.
    Scannell, R.
    Hillesheim, J. C.
    The EUROfusion JET-ILW pedestal database2018Inngår i: 45th EPS Conference on Plasma Physics, EPS 2018, European Physical Society (EPS) , 2018, s. 1056-1059Konferansepaper (Fagfellevurdert)
  • 13.
    Frassinetti, Lorenzo
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Vektoranalys2019 (oppl. 1)Bok (Fagfellevurdert)
    Abstract [sv]

    Läroböcker i vektoranalys är ofta kortfattade. Denna bok, som kan användas för såväl grundläggande som mer avancerade kurser, behandlar ämnet mer utförligt.

    Bokens pedagogiska idé skiljer sig markant från liknande böcker. Återkommande inslag är tydligt formulerade problem som fångar det centrala i vektoranalysen. Syftet med problemen är dels att väcka intresse för den teori och de metoder som behandlas, dels att stimulera till aktivt lärande. 

    Boken innehåller genomarbetade och lättillgängliga teoriavsnitt - som börjar med grundläggande vektoralgebra och slutar med kartesiska tensorer och en härledning av vektoranalysens huvudsats. Dessutom ingår ett stort antal konkreta exempel och många tillämpningar. Sist i varje kapitel finns en sammanfattning av den viktigaste teorin och övningsuppgifter med svar. Ledningar och fullständiga lösningar finns på Libers webbplats. Där finns även ett Appendix med tillämpningar.

  • 14.
    Garcia Carrasco, Alvaro
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Fortuna-Zalesna, E.
    Jachmich, S.
    Brix, M.
    Marot, L.
    Plasma impact on diagnostic mirrors in JET2017Inngår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 506-512Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Metallic mirrors will be essential components of all optical systems for plasma diagnosis in ITER. This contribution provides a comprehensive account on plasma impact on diagnostic mirrors in JET with the ITER-Like Wall. Specimens from the First Mirror Test and the lithium-beam diagnostic have been studied by spectrophotometry, ion beam analysis and electron microscopy. Test mirrors made of molybdenum were retrieved from the main chamber and the divertor after exposure to the 2013-2014 experimental campaign. In the main chamber, only mirrors located at the entrance of the carrier lost reflectivity (Be deposition), while those located deeper in the carrier were only slightly affected. The performance of mirrors in the JET divertor was strongly degraded by deposition of beryllium, tungsten and other species. Mirrors from the lithium-beam diagnostic have been studied for the first time. Gold coatings were severely damaged by intense arcing. As a consequence, material mixing of the gold layer with the stainless steel substrate occurred. Total reflectivity dropped from over 90% to less than 60%, i.e. to the level typical for stainless steel.

  • 15.
    Garcia Carrasco, Alvaro
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Schwarz-Selinger, T.
    Wauters, T.
    Douai, D.
    Bobkov, V.
    Cavazzana, R.
    Krieger, K.
    Lyssoivan, A.
    Moeller, S.
    Spolaore, M.
    Rohde, V.
    Rubel, M.
    Investigation of probe surfaces after ion cyclotron wall conditioning in ASDEX upgrade2017Inngår i: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, s. 733-735Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    For the first time, material analysis techniques have been applied to study the effect of ion cyclotron wall conditioning (ICWC) on probe surfaces in a metal-wall machine. ICWC is a technique envisaged to contribute to the removal of fuel and impurities from the first wall of ITER. The objective of this work was to assess impurity migration under ICWC operation. Tungsten probes were exposed in ASDEX Upgrade to discharges in helium. After wall conditioning, the probes were covered with a co-deposited layer containing D, B, C, N, O and relatively high amount of He. The concentration ratio He/C+B was 0.7. The formation of the co-deposited layer indicates that a fraction of the impurities desorbed from the wall under ICWC operation are transported by plasma and deposited away from their original location.

  • 16.
    Garcia-Munoz, M.
    et al.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Sharapov, S. E.
    Culham Sci Ctr, Abingdon, Oxon, England..
    Van Zeeland, M. A.
    Gen Atom, San Diego, CA USA..
    Ascasibar, E.
    CIEMAT, Madrid, Spain..
    Cappa, A.
    CIEMAT, Madrid, Spain..
    Chen, L.
    Zhejiang Univ, IFTS, Hangzhou, Zhejiang, Peoples R China.;Zhejiang Univ, Dept Phys, Hangzhou, Zhejiang, Peoples R China.;Univ Calif Irvine, Dept Phys & Astron, Irvine, CA USA..
    Ferreira, J.
    IST, Lisbon, Portugal..
    Galdon-Quiroga, J.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Geiger, B.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Gonzalez-Martin, J.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Heidbrink, W. W.
    Univ Calif Irvine, Dept Phys & Astron, Irvine, CA USA..
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Lauber, Ph
    Max Planck Inst Plasma Phys, Garching, Germany..
    Mantsinen, M.
    Barcelona Supercomp Ctr, Barcelona, Spain.;ICREA, Pg Lluis Companys 23, Barcelona, Spain..
    Melnikov, A. , V
    Nabais, F.
    Univ Calif Irvine, Dept Phys & Astron, Irvine, CA USA..
    Rivero-Rodriguez, J. F.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Sanchis-Sanchez, L.
    Univ Seville, Dept Atom Mol & Nucl Phys, Seville, Spain..
    Schneider, P.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Stober, J.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Suttrop, W.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Todo, Y.
    Natl Inst Fus Sci, Toki, Gifu, Japan..
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zonca, F.
    Zhejiang Univ, IFTS, Hangzhou, Zhejiang, Peoples R China.;Zhejiang Univ, Dept Phys, Hangzhou, Zhejiang, Peoples R China.;ENEA, Fus & Nucl Safety Dept, CR Frascati, Rome, Italy..
    Meyer, H.
    Active control of Alfven eigenmodes in magnetically confined toroidal plasmas2019Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, nr 5, artikkel-id 054007Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alfven waves are electromagnetic perturbations inherent to magnetized plasmas that can be driven unstable by a free energy associated with gradients in the energetic particles' distribution function. The energetic particles with velocities comparable to the Alfven velocity may excite Alfven instabilities via resonant wave-particle energy and momentum exchange. Burning plasmas with large population of fusion born super-Alfvenic alpha particles in magnetically confined fusion devices are prone to excite weakly-damped Alfven eigenmodes (AEs) that, if allowed to grow unabated, can cause a degradation of fusion performance and loss of energetic ions through a secular radial transport. In order to control the fast-ion distribution and associated Alfvenic activity, the fusion community is currently searching for external actuators that can control AEs and energetic ions in the harsh environment of a fusion reactor. Most promising control techniques are based on (i) variable fast-ion sources to modify gradients in the energetic particles' distribution, (ii) localized electron cyclotron resonance heating to affect the fast-ion slowing-down distribution, (iii) localized electron cyclotron current drive to modify the equilibrium magnetic helicity and thus the AE existence criteria and damping mechanisms, and (iv) externally applied 3D perturbative fields to manipulate the fast-ion distribution and thus the wave drive. Advanced simulations help to identify the key physics mechanisms underlying the observed AE mitigation and suppression and thus to develop robust control techniques towards future burning plasmas.

  • 17.
    Hoelzl, M.
    et al.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Huijsmans, G. T. A.
    CEA, IRFM, St Paul Les Durance, France.;Eindhoven Univ Technol, Eindhoven, Netherlands..
    Orain, F.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Artola, F. J.
    Aix Marseille Univ, CNRS, Marseille 20, France..
    Pamela, S.
    Culham Sci Ctr, CCFE, Abingdon, Oxon, England..
    Becoulet, M.
    CEA, IRFM, St Paul Les Durance, France..
    van Vugt, D.
    Eindhoven Univ Technol, Eindhoven, Netherlands..
    Liu, F.
    CEA, IRFM, St Paul Les Durance, France.;Univ Cote dAzur, Lab JA Dieudonne, CNRS, UMR 7351,UNS, Nice 02, France..
    Futatani, S.
    Barcelona Supercomp Ctr, Barcelona, Spain..
    Lessig, A.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Wolfrum, E.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Mink, F.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Trier, E.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Dunne, M.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Viezzer, E.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Eich, T.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Vanovac, B.
    Dutch Inst Fundamental Energy Res, DIFFER, Eindhoven, Netherlands..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Guenter, S.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Lackner, K.
    Max Planck Inst Plasma Phys, Boltzmannstr 2, D-85748 Garching, Germany..
    Krebs, I.
    Princeton Plasma Phys Lab, POB 451, Princeton, NJ 08543 USA..
    Insights into type-I edge localized modes and edge localized mode control from JOREK non-linear magneto-hydrodynamic simulations2018Inngår i: Contributions to Plasma Physics, ISSN 0863-1042, E-ISSN 1521-3986, Vol. 58, nr 6-8, s. 518-528Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Edge localized modes (ELMs) are repetitive instabilities driven by the large pressure gradients and current densities in the edge of H-mode plasmas. Type-I ELMs lead to a fast collapse of the H-mode pedestal within several hundred microseconds to a few milliseconds. Localized transient heat fluxes to divertor targets are expected to exceed tolerable limits for ITER, requiring advanced insights into ELM physics and applicable mitigation methods. This paper describes how non-linear magneto-hydrodynamic (MHD) simulations can contribute to this effort. The JOREK code is introduced, which allows the study of large-scale plasma instabilities in tokamak X-point plasmas covering the main plasma, the scrape-off layer, and the divertor region with its finite element grid. We review key physics relevant for type-I ELMs and show to what extent JOREK simulations agree with experiments and help reveal the underlying mechanisms. Simulations and experimental findings are compared in many respects for type-I ELMs in ASDEX Upgrade. The role of plasma flows and non-linear mode coupling for the spatial and temporal structure of ELMs is emphasized, and the loss mechanisms are discussed. An overview of recent ELM-related research using JOREK is given, including ELM crashes, ELM-free regimes, ELM pacing by pellets and magnetic kicks, and mitigation or suppression by resonant magnetic perturbation coils (RMPs). Simulations of ELMs and ELM control methods agree in many respects with experimental observations from various tokamak experiments. On this basis, predictive simulations become more and more feasible. A brief outlook is given, showing the main priorities for further research in the field of ELM physics and further developments necessary.

  • 18. Horvath, L.
    et al.
    Maggi, C. F.
    Belonohy, E.
    Delabie, E. G.
    Flanagan, J.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Giroud, C.
    Keeling, D.
    King, D.
    Maslov, M.
    Matthews, G. F.
    Menmuir, S.
    Saarelma, S.
    Silburn, S. A.
    Sips, A. C. C.
    Weisen, H.
    Gibson, K. J.
    Pedestal structure and stability in H and D isotope experiments on JET-ILW2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 19. Huber, A.
    et al.
    Brezinsek, S.
    Kirschner, A.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Sergienko, G.
    Huber, V.
    Borodkina, I.
    Douai, D.
    Jachmich, S.
    Linsmeier, Ch.
    Lomanowski, B.
    Matthews, G.F
    Mertens, P.h
    Determination of tungsten sources in the JET-ILW divertor by spectroscopic imaging in the presence of a strong plasma continuum2019Inngår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 18, s. 118-124Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The identification of the sources of atomic tungsten and the measurement of their radiation distribution in front of all plasma-facing components has been performed in JET with the help of two digital cameras with the same two-dimensional view, equipped with interference filters of different bandwidths centred on the W I (400.88 nm) emission line. A new algorithm for the subtraction of the continuum radiation was successfully developed and is now used to evaluate the W erosion even in the inner divertor region where the strong recombination emission is dominating over the tungsten emission. Analysis of W sputtering and W redistribution in the divertor by video imaging spectroscopy with high spatial resolution for three different magnetic configurations was performed. A strong variation of the emission of the neutral tungsten in toroidal direction and corresponding W erosion has been observed. It correlates strongly with the wetted area with a maximal W erosion at the edge of the divertor tile.

  • 20.
    Jepu, I
    et al.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Natl Inst Laser Plasma & Radiat Phys, Magurele 077125, Romania.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Matthews, G. F.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Widdowson, A.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik. EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.
    Fortuna-Zalesna, E.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Warsaw Univ Technol, PL-02507 Warsaw, Poland..
    Zdunek, J.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Natl Inst Laser Plasma & Radiat Phys, Magurele 077125, Romania..
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik. EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.
    Thompson, V
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Dinca, P.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Natl Inst Laser Plasma & Radiat Phys, Magurele 077125, Romania..
    Porosnicu, C.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Natl Inst Laser Plasma & Radiat Phys, Magurele 077125, Romania..
    Coad, P.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Heinola, K.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Univ Helsinki, POB 64, Helsinki 00560, Finland..
    Catarino, N.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Univ Lisbon, Inst Super Tecn, IPFN, Av Rovisco Pais, P-1049001 Lisbon, Portugal..
    Pompilian, O. G.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Natl Inst Laser Plasma & Radiat Phys, Magurele 077125, Romania..
    Lungu, C. P.
    EUROfus Consortium, Culham Sci Ctr, JET, Abingdon OX14 3DB, Oxon, England.;Natl Inst Laser Plasma & Radiat Phys, Magurele 077125, Romania..
    Beryllium melting and erosion on the upper dump plates in JET during three ITER-like wall campaigns2019Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 8, artikkel-id 086009Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Data on erosion and melting of beryllium upper limiter tiles, so-called dump plates (DP), are presented for all three campaigns in the JET tokamak with the ITER-like wall. High-resolution images of the upper wall of JET show clear signs of flash melting on the ridge of the roofshaped tiles. The melt layers move in the poloidal direction from the inboard to the outboard tile, ending on the last DP tile with an upward going waterfall-like melt structure. Melting was caused mainly by unmitigated plasma disruptions. During three ILW campaigns, around 15% of all 12376 plasma pulses were catalogued as disruptions. Thermocouple data from the upper dump plates tiles showed a reduction in energy delivered by disruptions with fewer extreme events in the third campaign, ILW-3, in comparison to ILW-1 and ILW-2. The total Be erosion assessed via precision weighing of tiles retrieved from JET during shutdowns indicated the increasing mass loss across campaigns of up to 0.6 g from a single tile. The mass of splashed melted Be on the upper walls was also estimated using the high-resolution images of wall components taken after each campaign. The results agree with the total material loss estimated by tile weighing (similar to 130 g). Morphological and structural analysis performed on Be melt layers revealed a multilayer structure of re-solidified material composed mainly of Be and BeO with some heavy metal impurities Ni, Fe, W. IBA analysis performed across the affected tile ridge in both poloidal and toroidal direction revealed a low D concentration, in the range 1-4 x 10(17) D atoms cm(-2).

  • 21. Kappatou, A.
    et al.
    Angioni, C.
    Sips, A. C. C.
    Lerche, E.
    Pütterich, T.
    Dunne, M.
    Neu, R.
    Giroud, C.
    Challis, C.
    Hobirk, J.
    Kim, H. -T
    Nunes, I.
    Tsalas, M.
    Cave-Ayland, K.
    Valcarcel, D. F.
    Menmuir, S.
    Lebschy, A.
    Viezzer, E.
    McDermott, R. M.
    Potzel, S.
    Ryter, F.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Delabie, E.
    Saarelma, S.
    Bernert, M.
    The effect of helium on plasma performance at ASDEX Upgrade and JET2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 22. Koslowski, H.R.
    et al.
    Bhattacharyya, S.R.
    Hansen, P.
    Linsmeier, Ch.
    Rasinski, M.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Temperature-dependent in-situ LEIS measurement of W surface enrichment by 250 eV D sputtering of EUROFER2018Inngår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 16, s. 181-190Artikkel i tidsskrift (Fagfellevurdert)
  • 23.
    Labit, B.
    et al.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Jonsson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Thorén, Emil
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Vallejos Olivares, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Dependence on plasma shape and plasma fueling for small edge-localized mode regimes in TCV and ASDEX Upgrade2019Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 8, artikkel-id 086020Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Within the EUROfusion MST1 work package, a series of experiments has been conducted on AUG and TCV devices to disentangle the role of plasma fueling and plasma shape for the onset of small ELM regimes. On both devices, small ELM regimes with high confinement are achieved if and only if two conditions are fulfilled at the same time. Firstly, the plasma density at the separatrix must be large enough (n(e,sep)/n(G) similar to 0.3), leading to a pressure profile flattening at the separatrix, which stabilizes type-I ELMs. Secondly, the magnetic configuration has to be close to a double null (DN), leading to a reduction of the magnetic shear in the extreme vicinity of the separatrix. As a consequence, its stabilizing effect on ballooning modes is weakened.

  • 24.
    Lindvall, Kristoffer
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    A time-spectral method for initial-value problems using a novel spatial subdomain scheme2018Inngår i: COGENT MATHEMATICS, ISSN 2331-1835, Vol. 5, nr 1, artikkel-id 1529280Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    We analyse a novel subdomain scheme for time-spectral solution of initial-value partial differential equations. In numerical modelling spectral methods are commonplace for spatially dependent systems, whereas finite difference schemes are typically applied for the temporal domain. The Generalized Weighted Residual Method (GWRM) is a fully spectral method that spectrally decomposes all specified domains, including the temporal domain, using multivariate Chebyshev polynomials. The Common Boundary-Condition method (CBC) here proposed is a spatial subdomain scheme for the GWRM. It solves the physical equations independently from the global connection of subdomains in order to reduce the total number of modes. Thus, it is a condensation procedure in the spatial domain that allows for a simultaneous global temporal solution. It is here evaluated against the finite difference methods of Crank-Nicolson and Lax-Wendroff for two example linear PDEs. The CBC-GWRM is also applied to the linearised ideal magnetohydrodynamic (MHD) equations for a screw pinch equilibrium. The growth rate of the most unstable mode was efficiently computed with an error <0.1%.

  • 25.
    Lindvall, Kristoffer
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Can the Time-Spectral Method GWRM Advance Fusion Transport Modelling?2017Inngår i: 59th Annual Meeting of the APS Division of Plasma Physics, 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Transport phenomena in fusion plasma pose a daunting task for both real-time experiments and numerical modelling. The transport is driven by micro-instabilities caused by a host of unstable modes, for example ion temperature gradient and trapped electron modes. These modes can be modelled using fluid or gyrokinetic equations. However, the equations are characterised by high degrees of freedom and high temporal and spatial numerical requirements. Thus, a time-spectral method GWRM has been developed in order to efficiently solve these multiple time scale equations. The GWRM assumes a multivariate Chebyshev expansion ansatz in time, space, and parameter domain. Advantages are that time constraining CFL criteria no longer apply and that the solution accurately averages over small time-scale dynamics. For benchmarking, a two-fluid 2D drift wave turbulence model has been solved in order to study toroidal ion temperature gradient growth rates and nonlinear behaviour.

  • 26.
    Lindvall, Kristoffer
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Spectral Representation of Time and Physical Parameters in Numerical Weather Prediction2018Inngår i: Understanding of Atmospheric Systems with Efficient Numerical Methods for Observation and Prediction, IntechOpen , 2018Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Numerical weather prediction (NWP) is a difficult task in chaotic dynamical regimes because of the strong sensitivity to initial conditions and physical parameters. As a result, high numerical accuracy is usually necessary. In this chapter, an accurate and efficient alternative to the traditional time stepping solution methods is presented; the time-spectral method. The generalized weighted residual method (GWRM) solves systems of nonlinear ODEs and PDEs using a spectral representation of time. Not being subject to CFL-like criteria, the GWRM typically employs time intervals two orders of magnitude larger than those of time-stepping methods. As an example, efficient solution of the chaotic Lorenz 1984 equations is demonstrated. The results indicate that the method has strong potential for NWP. Furthermore, employing spectral representations of physical parameters and initial values, families of solutions are obtained in a single computation. Thus, the GWRM is conveniently used for studies of system parameter dependency and initial condition error growth in NWP.

  • 27.
    Litnovsky, A.
    et al.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Voitsenya, V. S.
    NSC Kharkov Inst Phys & Technol, IPP, UA-61008 Kharkov, Ukraine..
    Reichle, R.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 Saint Paul Lez Durance, France..
    Walsh, M.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 Saint Paul Lez Durance, France..
    Razdobarin, A.
    Ioffe Physictech Inst, Polytech Skaya 26, St Petersburg 194021, Russia..
    Dmitriev, A.
    Ioffe Physictech Inst, Polytech Skaya 26, St Petersburg 194021, Russia..
    Babinov, N.
    Ioffe Physictech Inst, Polytech Skaya 26, St Petersburg 194021, Russia..
    Marot, L.
    Univ Basel, Klingelbergstr 82, CH-4056 Basel, Switzerland..
    Moser, L.
    Univ Basel, Klingelbergstr 82, CH-4056 Basel, Switzerland..
    Yan, R.
    Chinese Acad Sci, Inst Plasma Phys, Hefei 230031, Anhui, Peoples R China..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Widdowson, A.
    CCFE EURATOM Fus Assoc, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Moon, Sunwoo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Oh, S. G.
    Ajou Univ, Suwon 16499, South Korea..
    An, Y.
    Natl Fus Res Inst, Daejeon 34133, South Korea..
    Shigin, P.
    ITER Org, Route Vinon Sur Verdon,CS 90 046, F-13067 Saint Paul Lez Durance, France..
    Orlovskiy, I
    Natl Res Ctr Kurchatov Inst, Moscow 123098, Russia..
    Vukolov, K. Yu
    Natl Res Ctr Kurchatov Inst, Moscow 123098, Russia..
    Andreenko, E.
    Natl Res Ctr Kurchatov Inst, Moscow 123098, Russia..
    Krimmer, A.
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Kotov, V
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Mertens, Ph
    Forschungszentrum Julich, Inst Energie & Klimaforsch Plasmaphys, D-52425 Julich, Germany..
    Diagnostic mirrors for ITER: research in the frame of International Tokamak Physics Activity2019Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 59, nr 6, artikkel-id 066029Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Mirrors will be used as first plasma-viewing elements in optical and laser-based diagnostics in ITER. Deterioration of the mirror performance due to e.g. sputtering of the mirror surface by plasma particles or deposition of impurities will hamper the entire performance of the affected diagnostic and thus affect ITER operation. The Specialists Working Group on First Mirrors (FM SWG) in the Topical Group on Diagnostics of the International Tokamak Physics Activity (ITPA) plays an important role in finding solutions for diagnostic first mirrors. Sound progress in research and development of diagnostic mirrors in ITER was achieved since the last overview in 2009. Single crystal (SC) rhodium (Rh) mirrors became available. SC rhodium and molybdenum (Mo) mirrors survived in conditions corresponding to similar to 200 cleaning cycles with a negligible degradation of reflectivity. These results are important for a mirror cleaning system which is presently under development. The cleaning system is based on sputtering of contaminants by plasma. Repetitive cleaning was tested on several mirror materials. Experiments comprised contamination/cleaning cycles. The reflectivity SC Mo and Rh mirrors has changed insignificantly after 80 cycles. First in situ cleaning using radiofrequency (RF) plasma was conducted in EAST tokamak with a mock-up plate of ITER edge Thomson Scattering (ETS) with five inserted mirrors. Contaminants from the mirrors were removed. Physics of cleaning discharge was studied both experimentally and by modeling. Mirror contamination can also be mitigated by protecting diagnostic ducts. A deposition mitigation (DeMi) duct system was exposed in KSTAR. The real-time measurement of deposition in the diagnostic duct was pioneered during this experiment. Results evidenced the dominating effect of the wall conditioning and baking on contamination inside the duct. A baffled cassette with mirrors was exposed at the main wall of JET for 23,6 plasma hours. No significant degradation of reflectivity was measured on mirrors located in the ducts. Predictive modeling was further advanced. A model for the particle transport, deposition and erosion at the port-plug was used in selecting an optical layout of several ITER diagnostics. These achievements contributed to the focusing of the first mirror research thus accelerating the diagnostic development. Modeling requires more efforts. Remaining crucial issues will be in a focus of the future work of the FM SWG.

  • 28. Louche, F.
    et al.
    Wauters, T.
    Ragona, R.
    Moeller, S.
    Durodie, F.
    Litnovsky, A.
    Lyssoivan, A.
    Messiaen, A.
    Ongena, J.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brezinsek, S.
    Linsmeier, Ch.
    Van Schoor, M.
    Design of an ICRF system for plasma-wall interactions and RF plasma production studies on TOMAS2017Inngår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 123, s. 317-320Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ion cyclotron wall conditioning (ICWC) is being developed for ITER and W7-X as a baseline conditioning technique in which the ion cyclotron heating and current drive system will be employed to produce and sustain the currentless conditioning plasma. The TOMAS project (TOroidal MAgnetized System, operated at the FZ-juelich, Germany) proposes to explore several key aspects of ICWC. For this purpose we have designed an ICRF system made of a single strap antenna within a metallic box, connected to a feeding port and a pre-matching system. We discuss the design work of the antenna system with the help of the commercial electromagnetic software CST Microwave Studio (R). The simulation results for a given geometry provide input impedance matrices for the two-port system. These matrices are afterwards inserted into various circuit models to assess the accessibility of the required frequency range. The sensitivity of the matching system to uncertainties on plasma loading and capacitance values is notably addressed. With a choice of three variable capacitors we show that the system can cope with such uncertainties. We also demonstrate that the system can cope as well with the high reflected power levels during the short breakdown phase of the RF discharge, but at the cost of a significantly reduced coupled power.

  • 29.
    Marco, Aitor
    et al.
    IDOM, Adv Design & Anal Dept, Bilbao, Spain..
    Garrido, Aitor J.
    Univ Basque Country, UPV EHU, Inst Res & Dev Proc, ACG,IIDP,Automat Control & Syst Engn Dept, Bilbao, Spain..
    Coda, Stefano
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Garrido, Izaskun
    Univ Basque Country, UPV EHU, Inst Res & Dev Proc, ACG,IIDP,Automat Control & Syst Engn Dept, Bilbao, Spain..
    Ahn, J.
    Albanese, R.
    Alberti, S.
    Alessi, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Allan, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Anand, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Anastassiou, G.
    Natl Tech Univ Athens, Athens, Greece..
    Andrebe, Y.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Angioni, C.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Ariola, M.
    Univ Napoli Parthenope, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Bernert, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Beurskens, M.
    Max Planck Inst Plasma Phys, Teilinst Greifswald, D-17491 Greifswald, Germany..
    Bin, W.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Blanchard, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Blanken, T. C.
    Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Boedo, J. A.
    Univ Calif San Diego, Energy Res Ctr, La Jolla, CA 92093 USA..
    Bolzonella, T.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Bouquey, F.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Braunmueller, F. H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Bufferand, H.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Buratti, P.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Calabro, G.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Camenen, Y.
    Aix Marseille Univ, CNRS, PIIM, F-13013 Marseille, France..
    Carnevale, D.
    Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy..
    Carpanese, F.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Causa, F.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Cesario, R.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Chapman, I. T.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Chellai, O.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Choi, D.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Cianfarani, C.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Ciraolo, G.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Citrin, J.
    FOM Inst DIFFER Dutch Inst Fundamental Energy Res, Eindhoven, Netherlands..
    Costea, S.
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Crisanti, F.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Cruz, N.
    Univ Lisbon, Inst Super Tecn, Inst Plasmas & Fusao Nucl, Lisbon, Portugal..
    Czarnecka, A.
    Inst Plasma Phys & Laser Microfus, Hery 23, PL-01497 Warsaw, Poland..
    Decker, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    De Masi, G.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    De Tommasi, G.
    Univ Napoli Federico II, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Douai, D.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Dunne, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Duval, B. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Eich, T.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Elmore, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Esposito, B.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Faitsch, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Fasoli, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Fedorczak, N.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Felici, F.
    Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Fevrier, O.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Ficker, O.
    Inst Plasma Phys AS CR, Za Slovankou 1782-3, Prague 18200, Czech Republic..
    Fietz, S.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Fontana, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Furno, I.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Galeani, S.
    Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy..
    Gallo, A.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Galperti, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Garavaglia, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Garrido, I.
    Univ Basque Country, UPV EHU, Fac Engn, Paseo RafaelMoreno 3, Bilbao 48013, Spain..
    Geiger, B.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.;Max Planck Inst Plasma Phys, Teilinst Greifswald, D-17491 Greifswald, Germany..
    Giovannozzi, E.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Gobbin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Goodman, T. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Gorini, G.
    Univ Milano Bicocca, Dept Phys G Occhialini, Piazza Sci 3, I-20126 Milan, Italy..
    Gospodarczyk, M.
    Univ Roma Tor Vergata, Via Politecn 1, I-00133 Rome, Italy..
    Granucci, G.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Graves, J. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Guirlet, R.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Hakola, A.
    VTT Tech Res Ctr Finland Ltd, POB 1000, FI-02044 Espoo, Finland..
    Ham, C.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Harrison, J.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Hawke, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Hennequin, P.
    Ecole Polytech, CNRS, UMR7648, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Hnat, B.
    Univ Oxford, Rudolf Peierls Ctr Theoret Phys, Oxford, England.;Culham Ctr Fus Energy, Abingdon, Oxon, England..
    Hogeweij, D.
    FOM Inst DIFFER Dutch Inst Fundamental Energy Res, Eindhoven, Netherlands..
    Hogge, J. -Ph.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Honore, C.
    Ecole Polytech, CNRS, UMR7648, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Hopf, C.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Horacek, J.
    Inst Plasma Phys AS CR, Za Slovankou 1782-3, Prague 18200, Czech Republic..
    Huang, Z.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Igochine, V.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Innocente, P.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Schrittwieser, C. Ionita
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Isliker, H.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Jacquier, R.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Jardin, A.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Kamleitner, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Karpushov, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Keeling, D. L.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Kirneva, N.
    Kurchatov Inst, Natl Res Ctr, Inst Phys Tokamaks, Kurchatov Sq 1, Moscow 123182, Russia.;Natl Res Nucl Univ MEPhI, Moscow Engn Phys Inst, Kashirskoe Sh 31, Moscow 115409, Russia..
    Kong, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Koubiti, M.
    Aix Marseille Univ, CNRS, PIIM, F-13013 Marseille, France..
    Kovacic, J.
    Jozef Stefan Inst, Jamova 39, SI-1000 Ljubljana, Slovenia..
    Kramer-Flecken, A.
    Forschungszentrum Julich, Inst Energie & Klimaforsch, Plasmaphys, D-52425 Julich, Germany..
    Krawczyk, N.
    Inst Plasma Phys & Laser Microfus, Hery 23, PL-01497 Warsaw, Poland..
    Kudlacek, O.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany.;Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Labit, B.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Lazzaro, E.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Le, H. B.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Lipschultz, B.
    Univ York, York Plasma Inst, Dept Phys, York YO10 5DD, N Yorkshire, England..
    Llobet, X.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Lomanowski, B.
    Univ Durham, Dept Phys, Durham DH1 3LE, England..
    Loschiavo, V. P.
    Univ Napoli Federico II, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Lunt, T.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Maget, P.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Maljaars, E.
    Eindhoven Univ Technol, POB 513, NL-5600 MB Eindhoven, Netherlands..
    Malygin, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Maraschek, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Marini, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Martin, P.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Martin, Y.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Mastrostefano, S.
    Univ Napoli Parthenope, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Maurizio, R.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Mavridis, M.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Mazon, D.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    McAdams, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    McDermott, R.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Merle, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Meyer, H.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Militello, F.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Miron, I. G.
    Natl Inst Laser Plasma & Radiat Phys, POB MG-36, Bucharest, Romania..
    Cabrera, P. A. Molina
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Moret, J. -M
    Moro, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Moulton, D.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Naulin, V.
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Nespoli, F.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Nielsen, A. H.
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Nocente, M.
    Univ Milano Bicocca, Dept Phys G Occhialini, Piazza Sci 3, I-20126 Milan, Italy..
    Nouailletas, R.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Nowak, S.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Odstrcil, T.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Papp, G.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Paprok, R.
    Inst Plasma Phys AS CR, Za Slovankou 1782-3, Prague 18200, Czech Republic..
    Pau, A.
    Univ Cagliari, Dept Elect & Elect Engn, Piazza Armi, I-09123 Cagliari, Italy..
    Pautasso, G.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Ridolfini, V. Pericoli
    Univ Napoli Parthenope, Consorzio CREATE, Via Claudio 21, I-80125 Naples, Italy..
    Piovesan, P.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Piron, C.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Pisokas, T.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Porte, L.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Preynas, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Ramogida, G.
    ENEA CR Frascati, Unita Tecn Fus, Via E Fermi 45, I-00044 Rome, Italy..
    Rapson, C.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Rasmussen, J. Juul
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Reich, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Reimerdes, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Reux, C.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Ricci, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Rittich, D.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Riva, F.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Robinson, T.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Saarelma, S.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Saint-Laurent, F.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Sauter, O.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Scannell, R.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Schlatter, Ch.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Schneider, B.
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Schneider, P.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Schrittwieser, R.
    Univ Innsbruck, Inst Ionen & Angew Phys, Tech Str 25, A-6020 Innsbruck, Austria..
    Sciortino, F.
    MIT, Plasma Sci & Fusion Ctr, 77 Massachusetts Ave, Cambridge, MA 02139 USA..
    Sertoli, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Sheikh, U.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sieglin, B.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Silva, M.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sinha, J.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sozzi, C.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Spolaore, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Stange, T.
    Max Planck Inst Plasma Phys, Teilinst Greifswald, D-17491 Greifswald, Germany..
    Stoltzfus-Dueck, T.
    Princeton Univ, Princeton, NJ 08544 USA..
    Tamain, P.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Teplukhina, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Testa, D.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Theiler, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Thornton, A.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Tophoj, L.
    Tech Univ Denmark, Dept Phys, Bldg 309, DK-2800 Lyngby, Denmark..
    Tran, M. Q.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Tsironis, C.
    Natl Tech Univ Athens, Athens, Greece..
    Tsui, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.;Univ Calif San Diego, Energy Res Ctr, La Jolla, CA 92093 USA..
    Uccello, A.
    CNR, IFP, Via R Cozzi 53, I-20125 Milan, Italy..
    Vartanian, S.
    IRFM, CEA, F-13108 St Paul Les Durance, France..
    Verdoolaege, G.
    UG Ghent Univ, Dept Appl Phys, St Pietersnieuwstraat 41, B-9000 Ghent, Belgium..
    Verhaegh, K.
    Univ York, York Plasma Inst, Dept Phys, York YO10 5DD, N Yorkshire, England..
    Vermare, L.
    Ecole Polytech, CNRS, UMR7648, Lab Phys Plasmas, F-91128 Palaiseau, France..
    Vianello, N.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland.;Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    Vijvers, W. A. J.
    FOM Inst DIFFER Dutch Inst Fundamental Energy Res, Eindhoven, Netherlands..
    Vlahos, L.
    Aristotle Univ Thessaloniki, Thessaloniki, Greece..
    Vu, N. M. T.
    Inst Polytech Grenoble, Lab Concept & Integrat Syst, BP54, F-26902 Valence 09, France..
    Walkden, N.
    Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Wauters, T.
    Ecole Royale Mil, Koninklijke Mil Sch, Lab Plasma Phys, Renaissancelaan 30 Ave Renaissance, B-1000 Brussels, Belgium..
    Weisen, H.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Wischmeier, M.
    Max Planck Inst Plasma Phys, D-85748 Garching, Germany..
    Zestanakis, P.
    Natl Tech Univ Athens, Athens, Greece..
    Zuin, M.
    Consorzio RFX, Corso Stati Uniti 4, I-35127 Padua, Italy..
    A Variable Structure Control Scheme Proposal for the Tokamak a Configuration Variable2019Inngår i: Complexity, ISSN 1076-2787, E-ISSN 1099-0526, artikkel-id 2319560Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Fusion power is the most significant prospects in the long-term future of energy in the sense that it composes a potentially clean, cheap, and unlimited power source that would substitute the widespread traditional nonrenewable energies, reducing the geographical dependence on their sources as well as avoiding collateral environmental impacts. Although the nuclear fusion research started in the earlier part of 20th century and the fusion reactors have been developed since the 1950s, the fusion reaction processes achieved have not yet obtained net power, since the generated plasma requires more energy to achieve and remain in necessary particular pressure and temperature conditions than the produced profitable energy. For this purpose, the plasma has to be confined inside a vacuum vessel, as it is the case of the Tokamak reactor, which consists of a device that generates magnetic fields within a toroidal chamber, being one of the most promising solutions nowadays. However, the Tokamak reactors still have several issues such as the presence of plasma instabilities that provokes a decay of the fusion reaction and, consequently, a reduction in the pulse duration. In this sense, since long pulse reactions are the key to produce net power, the use of robust and fast controllers arises as a useful tool to deal with the unpredictability and the small time constant of the plasma behavior. In this context, this article focuses on the application of robust control laws to improve the controllability of the plasma current, a crucial parameter during the plasma heating and confinement processes. In particular, a variable structure control scheme based on sliding surfaces, namely, a sliding mode controller (SMC) is presented and applied to the plasma current control problem. In order to test the validity and goodness of the proposed controller, its behavior is compared to that of the traditional PID schemes applied in these systems, using the RZIp model for the Tokamak a Configuration Variable (TCV) reactor. The obtained results are very promising, leading to consider this controller as a strong candidate to enhance the performance of the PID-based controllers usually employed in this kind of systems.

  • 30.
    Moon, Sunwoo
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fortuna-Zalesna, E.
    Widdowson, A.
    Jachmich, S.
    Litnovsky, A.
    Alves, E.
    Contributors, J E T
    First mirror test in JET for ITER: Complete overview after three ILW campaigns2019Inngår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 19, s. 59-66Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The First Mirror Test for ITER has been carried out in JET with mirrors exposed during: (i) the third ILW campaign (ILW-3, 2015–2016, 23.33 h plasma) and (ii) all three campaigns, i.e. ILW-1 to ILW-3: 2011–2016, 63,52 h in total. All mirrors from main chamber wall show no significant changes of the total reflectivity from the initial value and the diffuse reflectivity does not exceed 3% in the spectral range above 500 nm. The modified layer on surface has very small amount of impurities such as D, Be, C, N, O and Ni. All mirrors from the divertor (inner, outer, base under the bulk W tile) lost reflectivity by 20–80% due to the beryllium-rich deposition also containing D, C, N, O, Ni and W. In the inner divertor N reaches 5 × 10 17 cm −2 , W is up to 4.3 × 10 17 cm −2 , while the content of Ni is the greatest in the outer divertor: 3.8 × 10 17 cm −2 . Oxygen-18 used as the tracer in experiments at the end of ILW-3 has been detected at the level of 1.1 × 10 16 cm −2 . The thickness of deposited layer is in the range of 90 nm to 900 nm. The layer growth rate in the base (2.7 pm s − 1 ) and inner divertor is proportional to the exposure time when a single campaign and all three are compared. In a few cases, on mirrors located at the cassette mouth, flaking of deposits and erosion occurred.

  • 31.
    Otsuka, T.
    et al.
    Kindai Univ, 3-4-1 Kowakae, Higashiosaka, Osaka 5778502, Japan..
    Masuzaki, S.
    Natl Inst Fus Sci, 322-6 Oroshi Cho, Toki, Gifu 5095292, Japan..
    Ashikawa, N.
    Natl Inst Fus Sci, 322-6 Oroshi Cho, Toki, Gifu 5095292, Japan..
    Hatano, Y.
    Univ Toyama, Gofuku 3190, Toyama 9308555, Japan..
    Asakura, Y.
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Suzuki, Tatsuya
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Suzuki, Takumi
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Isobe, K.
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Hayashi, T.
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Tokitani, M.
    Natl Inst Fus Sci, 322-6 Oroshi Cho, Toki, Gifu 5095292, Japan..
    Oya, Y.
    Shizuoka Univ, Shizuoka 4228529, Japan..
    Hamaguchi, D.
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Kurotaki, H.
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Sakamoto, R.
    Natl Inst Fus Sci, 322-6 Oroshi Cho, Toki, Gifu 5095292, Japan..
    Tanigawa, Hiroyasu
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Nakamichi, M.
    Natl Inst Quantum, Aomori 0393212, Japan.;Natl Inst Radiol Sci & Technol, Aomori 0393212, Japan..
    Widdowson, A.
    Culham Sci Ctr, Culham Ctr Fus Energy, Abingdon OX14 3DB, Oxon, England..
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tritium retention characteristics in dust particles in JET with ITER-like wall2018Inngår i: Nuclear Materials and Energy, E-ISSN 2352-1791, Vol. 17, s. 279-283Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A tritium imaging plate technique (TIPT) in combination with an electron-probe microscopic analysis (EPMA) were applied to examine tritium (T) retention characteristics in individual dust particles collected in the Joint European Torus with the ITER-like Wall (JET-ILW) after the first campaign in 2011-2012. A lot of carbon pre-existing carbon deposits in the JET-C or released carbon particles from the remaining carbon-fiber components in the JET-ILW. Most of T was retained at the surface of and/or in the C-dominated dust particles. The retention in tungsten, beryllium and other metal-dominated dust particles is relatively lower by a factor of 10-100 in comparison with that in the Cdominated particles.

  • 32. Oya, Y.
    et al.
    Masuzaki, S.
    Tokitani, M.
    Azuma, K.
    Oyaidzu, M.
    Isobe, K.
    Asakura, N.
    Widdowson, A. M.
    Heinola, K.
    Jachmich, S.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Contributors, JET
    Correlation of surface chemical states with hydrogen isotope retention in divertor tiles of JET with ITER-Like Wall2018Inngår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 132, s. 24-28Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    To understand the fuel retention mechanism correlation of surface chemical states and hydrogen isotope retention behavior determined by XPS (X-ray photoelectron spectroscopy) and TDS (Thermal desorption spectroscopy), respectively, for JET ITER-Like Wall samples from operational period 2011–2012 were investigated. It was found that the deposition layer was formed on the upper part of the inner vertical divertor area. At the inner plasma strike point region, the original surface materials, W or Mo, were found, indicating to an erosion-dominated region, but deposition of impurities was also found. Higher heat load would induce the formation of metal carbide. At the outer horizontal divertor tile, mixed material layer was formed with iron as an impurity. TDS showed the H and D desorption behavior and the major D desorption temperature for the upper part of the inner vertical tile was located at 370 °C and 530 °C. At the strike point region, the D desorption temperature was clearly shifted toward higher release temperatures, indicating the stabilization of D trapping by higher heat load.

  • 33. Pinches, S. D.
    et al.
    Abadie, L.
    Appel, L. C.
    Artaud, J. -F
    Castro, R.
    Van Dellen, L. T. H.
    Van Eester, D.
    Hollocombe, J.
    Hosokawa, M.
    Imbeaux, F.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Khayrutdinov, R. R.
    Kim, S. H.
    Konovalov, S. V.
    Lerche, E.
    Lukash, V. E.
    Lupelli, I.
    Makushok, Y.
    Medvedev, S.
    Muir, D.
    Polevoi, A.
    Sauter, O.
    Schneider, M.
    Urban, J.
    Implementation of plasma simulators and plasma reconstruction workflows in ITER’s Integrated Modelling & Analysis Suite (IMAS)2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
    Abstract [en]

    IMAS has been installed within the majority of the ITER Members and is being used to support ITPA activities including code benchmarking and validation. Sophisticated workflows, such as Plasma Simulators and those describing H&CD systems, have been adapted to IMAS and applied to ITER scenarios. The framework is considered sufficiently flexible to handle all foreseen approaches to the integrated (probabilistic) determination of measurement parameters (and their errors). The inclusion of UDA within the IMAS data Access Layer has allowed the fetching of IDSs directly from experimental databases and the demonstration of the first plasma reconstruction chain. An interactive Live Display in which signals are selected through a web interface has also been demonstrated. 

  • 34. Pokol, G. I.
    et al.
    Aradi, M.
    Erdos, B.
    Papp, G.
    Hadar, A.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Coster, D.
    Kalupin, D.
    Strand, P.
    Ferreira, J.
    Development of the runaway electron modelling capabilities of the European transport simulator2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 35.
    Rubel, Marek
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Fusion Neutrons: Tritium Breeding and Impact on Wall Materials and Components of Diagnostic Systems2019Inngår i: Journal of fusion energy, ISSN 0164-0313, E-ISSN 1572-9591, Vol. 38, nr 3-4, s. 315-329Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A concise overview is given on the impact of fusion neutrons on various classes of materials applied in reactor technology: plasma-facing, structural and functional tested for tritium production and for diagnostic systems. Tritium breeding in the reactor blanket, fuel cycle and separation of hydrogen isotopes are described together with issues related to primary (tritium) and induced radioactivity. Neutron-induced damage and degradation of material properties are addressed. Material testing under neutron fluxes and safety issues associated with handling components in the radioactive environment are described. A comprehensive list of references to monographs and research papers is included to help navigation in literature.

  • 36.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Free Will of an Ontologically Open MindManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    Combining elements from algorithmic information theory and quantum mechanics, it has earlier been argued that consciousness is epistemically and ontologically emergent. Accordingly, consciousness is irreducible to neural low-level states, in spite of assuming causality and supervenience on these states. The mind-body problem is thus found to be unsolvable. In this paper the implications on free will is studied. In the perspective of a modified definition of free will, enabling scientific decidability, the ontological character of interactions of the cortical neural network is discussed. Identifying conscious processes as ontologically open, it is asserted that conscious states are indeterminable in principle. We argue that this leads to freedom of the will.

  • 37.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    On the Solvability of the Mind-Body ProblemManuskript (preprint) (Annet vitenskapelig)
    Abstract [en]

    The mind-body problem is analyzed in a physicalist perspective. By combining the concepts of emergence and algorithmic information theory in a thought experiment employing a basic nonlinear process, it is shown that epistemically strongly emergent properties may develop in a physical system. Turning to the significantly more complex neural network of the brain it is subsequently argued that consciousness is epistemically emergent. Thus reductionist understanding of consciousness appears not possible; the mind-body problem does not have a reductionist solution. The ontologically emergent character of consciousness is then identified from a combinatorial analysis relating to universal limits set by quantum mechanics, implying that consciousness is fundamentally irreducible to low-level phenomena.

  • 38.
    Scheffel, Jan
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    On the Solvability of the Mind–Body Problem2019Inngår i: Axiomathes, ISSN 1122-1151, E-ISSN 1572-8390Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The mind–body problem is analyzed in a physicalist perspective. By combining the concepts of emergence and algorithmic information theory in a thought experiment, employing a basic nonlinear process, it is shown that epistemologically emergent properties may develop in a physical system. Turning to the signi cantly more com- plex neural network of the brain it is subsequently argued that consciousness is epis- temologically emergent. Thus reductionist understanding of consciousness appears not possible; the mind–body problem does not have a reductionist solution. The ontologically emergent character of consciousness is then identi ed from a com- binatorial analysis relating to universal limits set by quantum mechanics, implying that consciousness is fundamentally irreducible to low-level phenomena.

  • 39.
    Scheffel, Jan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Lindvall, Kristoffer
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Optimizing Time-Spectral Solution of Initial-Value Problems2018Inngår i: American Journal of Computational Mathematics, ISSN 2161-1203, E-ISSN 2161-1211, Vol. 8, nr 1, s. 7-26, artikkel-id 82900Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Time-spectral solution of ordinary and partial differential equations is often regarded as an inefficient approach. The associated extension of the time domain, as compared to finite difference methods, is believed to result in uncomfortably many numerical operations and high memory requirements. It is shown in this work that performance is substantially enhanced by the introduction of algorithms for temporal and spatial subdomains in combination with sparse matrix methods. The accuracy and efficiency of the recently developed time spectral, generalized weighted residual method (GWRM) are compared to that of the explicit Lax-Wendroff and implicit Crank-Nicolson methods. Three initial-value PDEs are employed as model problems; the 1D Burger equation, a forced 1D wave equation and a coupled system of 14 linearized ideal magnetohydrodynamic (MHD) equations. It is found that the GWRM is more efficient than the time-stepping methods at high accuracies. The advantageous scalings Nt**1.0*Ns**1.43 and Nt**0.0*Ns**1.08 were obtained for CPU time and memory requirements, respectively, with Nt and Ns denoting the number of temporal and spatial subdomains. For time-averaged solution of the two-time-scales forced wave equation, GWRM performance exceeds that of the finite difference methods by an order of magnitude both in terms of CPU time and memory requirement. Favorable subdomain scaling is demonstrated for the MHD equations, indicating a potential for efficient solution of advanced initial-value problems in, for example, fluid mechanics and MHD. 

  • 40.
    Scheffel, Jan
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Lindvall, Kristoffer
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    SIR—An efficient solver for systems of equations2018Inngår i: Software Quality Professional, ISSN 1522-0540, Vol. 7, s. 59-62Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The Semi-Implicit Root solver (SIR) is an iterative method for globally convergent solution of systems of nonlinear equations. We here present MATLAB and MAPLE codes for SIR, that can be easily implemented in any application where linear or nonlinear systems of equations need be solved efficiently. The codes employ recently developed efficient sparse matrix algorithms and improved numerical differentiation. SIR convergence is quasi-monotonous and approaches second order in the proximity of the real roots. Global convergence is usually superior to that of Newton's method, being a special case of the method. Furthermore the algorithm cannot land on local minima, as may be the case for Newton's method with line search. 

  • 41.
    Sheikh, U. A.
    et al.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Dunne, M.
    Max Planck Inst Plasma Phys, Garching, Germany..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Blanchard, P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Duval, B. P.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Labit, B.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Merle, A.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Sauter, O.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Theiler, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Tsui, C.
    Ecole Polytech Fed Lausanne, SPC, CH-1015 Lausanne, Switzerland..
    Pedestal structure and energy confinement studies on TCV2019Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 61, nr 1, artikkel-id 014002Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High external gas injection rates are foreseen for future devices to reduce divertor heat loads and this can influence pedestal stability. Fusion yield has been estimated to vary as strongly as T-e,ped(2) so an understanding of the underlying pedestal physics in the presence of additional fuelling and seeding is required. To address this, a database scanning plasma triangularity, fuelling and nitrogen seeding rates in neutral beam (NBH) heated ELM-y H-mode plasmas was constructed on TCV. Low nitrogen seeding was observed to increase pedestal top pressure but all other gas injection rates led to a decrease. Lower triangularity discharges were found to be less sensitive to variations in gas injection rates. No clear trend was measured between plasma top P-e and stored energy which is attributed to the non-stiffness of core plasma pressure profiles. Peeling ballooning stability analysis put these discharges close to the ideal MHD stability boundary. A constant for D in the relation pedestal width w = D root beta(Ped)(theta), was not found. Experimentally inferred values of D were used in EPED1 simulations and gave good agreement for pedestal width. Pedestal height agreed well for high triangularity but was overestimated for low triangularity. IPED simulations showed that relative shifts in pedestal position were contributing significantly to the pedestal height and were able to reproduce the measured profiles more accurately.

  • 42. Sheikh, U. A.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Blanchard, P.
    Dunne, M.
    Duval, B. P.
    Merle, A.
    Meyer, H.
    Theiler, C.
    Verhaegh, K.
    H-Mode pedestal studies with seeding and fuelling on TCV2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 43. Sipilä, S.
    et al.
    Varje, J.
    Johnson, Thomas
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Kurki-Suonio, T.
    Galdón Quiroga, J.
    González Martín, J.
    Monte Carlo ion cyclotron heating and fast ion loss detector simulations in ASDEX Upgrade2018Inngår i: 45th EPS Conference on Plasma Physics, EPS 2018, European Physical Society (EPS) , 2018, s. 773-776Konferansepaper (Fagfellevurdert)
  • 44.
    Stefániková, Estera
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Nunes, I.
    Rimini, F.
    Garzotti, L.
    Lerche, E.
    Lomas, P.
    Saarelma, S.
    Loarte, A.
    Drewelow, P.
    Kruezi, U.
    Lomanowski, B.
    De La Luna, E.
    Meneses, L.
    Peterka, M.
    Viola, B.
    Giroud, C.
    Maggi, C.
    Pedestal structure in high current scenarios in JET-ILW and JET-C2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 45. Stefániková, Estera
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Nunes, I.
    Rimini, F.
    Garzotti, L.
    Lerche, E.
    Lomas, P.
    Saarelma, S.
    Loarte, A.
    Drewelow, P.
    Kruezi, U.
    Lomanowski, B.
    De La Luna, E.
    Meneses, L.
    Peterka, M.
    Viola, B.
    Giroud, C.
    Maggi, C.
    Pedestal structure in high current scenarios in JET-ILW and JET-C2017Inngår i: 44th EPS Conference on Plasma Physics, EPS 2017, European Physical Society (EPS) , 2017Konferansepaper (Fagfellevurdert)
  • 46.
    Stefániková, Estera
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik. EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik. EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England..
    Saarelma, S.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Loarte, A.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;ITER Org, Route Vinon Sur Verdon, F-13067 St Paul Les Durance, France..
    Nunes, I.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Inst Plasmas & Fusao Nucl, IST, Lisbon, Portugal..
    Garzotti, L.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Lomas, P.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Rimini, F.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Drewelow, P.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Max Planck Inst Plasma Phys, Garching, Germany..
    Kruezi, U.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Lomanowski, B.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Ctr Adv Instrumentat, Dept Phys, Durham DH1 3LE, England..
    de la Luna, E.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Lab Nacl Fus CIEMAT, Madrid, Spain..
    Meneses, L.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Inst Plasmas & Fusao Nucl, IST, Lisbon, Portugal..
    Peterka, M.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Inst Plasma Phys AS CR, Prague, Czech Republic.;Charles Univ Prague, Fac Math & Phys, Prague, Czech Republic..
    Viola, B.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;CR Frascati, ENEA, Via E Fermi 45, Rome, Italy..
    Giroud, C.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Maggi, C.
    EUROfus Consortium, JET, Culham Sci Ctr, Abingdon OX14 3DB, Oxon, England.;Culham Sci Ctr, CCFE, Abingdon OX14 3DB, Oxon, England..
    Effect of the relative shift between the electron density and temperature pedestal position on the pedestal stability in JET-ILW and comparison with JET-C2018Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 58, nr 5, artikkel-id 056010Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The electron temperature and density pedestals tend to vary in their relative radial positions, as observed in DIII-D (Beurskens et al 2011 Phys. Plasmas 18 056120) and ASDEX Upgrade (Dunne et al 2017 Plasma Phys. Control. Fusion 59 14017). This so-called relative shift has an impact on the pedestal magnetohydrodynamic (MHD) stability and hence on the pedestal height (Osborne et al 2015 Nucl. Fusion 55 063018). The present work studies the effect of the relative shift on pedestal stability of JET ITER-like wall (JET-ILW) baseline low triangularity (d) unseeded plasmas, and similar JET-C discharges. As shown in this paper, the increase of the pedestal relative shift is correlated with the reduction of the normalized pressure gradient, therefore playing a strong role in pedestal stability. Furthermore, JET-ILW tends to have a larger relative shift compared to JET carbon wall (JET-C), suggesting a possible role of the plasma facing materials in affecting the density profile location. Experimental results are then compared with stability analysis performed in terms of the peeling-ballooning model and with pedestal predictive model EUROPED (Saarelma et al 2017 Plasma Phys. Control. Fusion). Stability analysis is consistent with the experimental findings, showing an improvement of the pedestal stability, when the relative shift is reduced. This has been ascribed mainly to the increase of the edge bootstrap current, and to minor effects related to the increase of the pedestal pressure gradient and narrowing of the pedestal pressure width. Pedestal predictive model EUROPED shows a qualitative agreement with experiment, especially for low values of the relative shift.

  • 47.
    Ström, Petter
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Material characterization for magnetically confined fusion: Surface analysis and method development2019Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The dream of abundant clean energy has brought scientists and laypeople alike to ponder the possibilities of nuclear fusion since it was established as the energy source of the stars in 1939. Starting from the mid the 20th century, significant effort has been put into overcoming the technological challenges related to the construction of a power plant, but initial optimism has faded somewhat due to a notable absence of practical outcomes. Nevertheless, the research continues and progress is made slowly but surely.

    The present work deals with a small part of the fusion puzzle, namely the materials to be used in the first wall surrounding a magnetically confined plasma. Carbon, which has historically been considered as the most viable element for this role, has been ruled out due to issues with plasma-induced erosion, hydrocarbon formation and a buildup of thick deposited material layers on wall components. The latter two lead to an unacceptable accumulation of radioactive tritium, both in the deposited layers and in dust particles. A metal wall, which would alleviate these particular problems but increase the severity of others, is therefore envisioned for a future demonstration reactor.

    Three contributions to the overall research effort are made though this thesis. First, an increased understanding of plasma-induced erosion of so-called reduced activation ferritic-martensitic steels and preferential sputtering of light material components is provided. High-resolution ion beam analysis and microscopy methods are used to examine samples of such a steel after exposure to plasma under controlled circumstances. Model films consisting of a mixture of iron and tungsten deposited on silicon substrates are also studied as they constitute simpler systems where the effects of interest may be simulated. The knowledge obtained is necessary for an assessment of the possibility to use reduced activation steel as a plasma-facing material in specific regions of a reactor wall.

    The second contribution consists of reports on the composition of deposited material layers on wall components retrieved from the plasma confinement experiments JET and TEXTOR. These provide limited conclusions on the range and rate of material erosion, transport and deposition in two cases.

    Finally, a detection system for the ion beam technique elastic recoil detection analysis has been assembled, tested and put into operation. In addition to improving the quality of analyses performed on fusion-related materials, the system has become an established tool available for users of the 5 MV electrostatic pelletron accelerator at Uppsala University’s Tandem Laboratory.

  • 48.
    Ström, Petter
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Arredondo Parra, R.
    Oberkofler, M.
    Schwarz-Selinger, T.
    Primetzhofer, D.
    Sputtering of polished EUROFER97 steel: Surface structure modification and enrichment with tungsten and tantalum2018Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 508, s. 139-146Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Surface structure modification and enrichment with tungsten and tantalum were measured for polished EUROFER97 samples after exposure to a deuterium ion beam. Time-of-flight medium energy ion scattering and time-of-flight elastic recoil detection analysis were implemented for measuring atomic composition profiles. Atomic force microscopy and optical microscopy were used to investigate surface morphology. The deuterium particle fluence was varied between 1021 D/m2 and 1024 D/m2, projectile energy was 200 eV/D and exposure temperatures up to 1050 K were applied. The average fraction of tungsten plus tantalum to total metal content in the 2 nm closest to the sample surface was increased from an initial 0.0046 to 0.12 for the sample exposed to the highest fluence at room temperature. The enrichment was accompanied by an increase in surface roughness of one order of magnitude and grain dependent erosion of the material. The appearance of protrusions with heights up to approximately 40 nm after ion beam exposure at room temperature was observed on individual grains. Samples exposed to 1023 D/m2 at temperatures of 900 K and 1050 K displayed recrystallization and cracking while changes to the total surface fraction of tungsten and tantalum were limited to less than a factor of two compared to the sample exposed to the same fluence at room temperature.

  • 49.
    Ström, Petter
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hamberg, Mathias
    Surface oxide and roughness on test samples for the Ultra High Vacuum section of the European XFEL2018Inngår i: Vacuum, ISSN 0042-207X, E-ISSN 1879-2715, Vol. 149, s. 83-86Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The European X-ray Free Electron Laser has recently started with operation for users. An approximately 3 m long ultra high vacuum laser heater section is implemented to overcome possible electron bunch instabilities. We describe the process of determining the oxide layer thickness and surface roughness on test samples of the internal surface material in the laser heater vacuum chambers using elastic recoil detection analysis and optical surface profiling. The results are compared to specified values and show that surface roughness on the samples is larger than the requested maximum, with RMS deviations from a mean plane of up to 1.76 μm for 0.60 × 0.45 square millimeter scans. The maximum oxide layer thickness is 5.5 nm on non-electropolished surfaces assuming cuprous oxide with density 6.0 g per cubic centimeter and 4.0 nm on electropolished surfaces.

  • 50.
    Ström, Petter
    et al.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Rubel, Marek
    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.
    Frassinetti, Lorenzo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Garcia Carrasco, Alvaro
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tholerus, Simon
    Weckmann, Armin
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik. KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    Tolias, Panagiotis
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Ratynskaia, Svetlana V.
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Rymd- och plasmafysik.
    Rachlew, Elisabeth
    KTH, Tidigare Institutioner (före 2005), Fysik. KTH, Skolan för teknikvetenskap (SCI), Fysik, Atom- och molekylfysik.
    Vallejos, Pablo
    KTH, Skolan för elektroteknik och datavetenskap (EECS), Fusionsplasmafysik.
    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 wall2019Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 516, s. 202-213Artikkel i tidsskrift (Fagfellevurdert)
    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.

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