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  • 1. Aiba, N
    et al.
    Giroud, C
    Honda, M
    Delabie, E
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Saarelma, S
    Hillesheim, J
    Pamela, S
    Wiesen, S
    Maggi, C
    Urano, H
    Drewelow, P
    Leyland, M
    Moulton, D
    Menmuir, S
    Diamagnetic MHD Equations for Plasmas with Fast Flow and its Application to ELM Analysis in JT-60U and JET-ILW2016Inngår i: 26th IAEA Fusion Energy Conference, 17-22 October 2016, 2016Konferansepaper (Fagfellevurdert)
  • 2. Aiba, N.
    et al.
    Giroud, C.
    Honda, M.
    Delabie, E.
    Saarelma, S.
    Frassinetti, L
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lupelli, I.
    Casson, F. J.
    Pamela, S.
    Urano, H.
    Maggi, C. F.
    Numerical analysis of ELM stability with rotation and ion diamagnetic drift effects in JET2017Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, nr 12, artikkel-id 126001Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Stability to the type-I edge localized mode (ELM) in JET plasmas was investigated numerically by analyzing the stability to a peeling-ballooning mode with the effects of plasma rotation and ion diamagnetic drift. The numerical analysis was performed by solving the extended Frieman-Rotenberg equation with the MINERVA-DI code. To take into account these effects in the stability analysis self-consistently, the procedure of JET equilibrium reconstruction was updated to include the profiles of ion temperature and toroidal rotation, which are determined based on the measurement data in experiments. With the new procedure and MINERVA-DI, it was identified that the stability analysis including the rotation effect can explain the ELM trigger condition in JET with ITER like wall (JET-ILW), though the stability in JET with carbon wall (JET-C) is hardly affected by rotation. The key difference is that the rotation shear in JET-ILW plasmas analyzed in this study is larger than that in JET-C ones, the shear which enhances the dynamic pressure destabilizing a peeling-ballooning mode. In addition, the increase of the toroidal mode number of the unstable MHD mode determining the ELM trigger condition is also important when the plasma density is high in JET-ILW. Though such modes with high toroidal mode number are strongly stabilized by the ion diamagnetic drift effect, it was found that plasma rotation can sometimes overcome this stabilizing effect and destabilizes the peeling-ballooning modes in JET-ILW.

  • 3. Aiba, N
    et al.
    Giroud, C
    Honda, M
    Delabie, E
    Saarelma, S
    Lupelli, I
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Maggi, C
    Impact of rotation and ion diamagnetic drift on ELM stability in JET-ILW2016Inngår i: 33rd Annual meeting of Japan society of plasma science and nuclear fusion research JSPF, Nov 2016. Japan, 2016Konferansepaper (Annet vitenskapelig)
  • 4. Aiba, N.
    et al.
    Pamela, S.
    Honda, M.
    Urano, H.
    Giroud, C.
    Delabie, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Lupelli, I.
    Hayashi, N.
    Huijsmans, G.
    Analysis of ELM stability with extended MHD models in JET, JT-60U and future JT-60SA tokamak plasmas2018Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 60, nr 1, artikkel-id 014032Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The stability with respect to a peeling-ballooning mode (PBM) was investigated numerically with extended MHD simulation codes in JET, JT-60U and future JT-60SA plasmas. The MINERVA-DI code was used to analyze the linear stability, including the effects of rotation and ion diamagnetic drift (omega(*i)), in JET-ILW and JT-60SA plasmas, and the JOREK code was used to simulate nonlinear dynamics with rotation, viscosity and resistivity in JT-60U plasmas. It was validated quantitatively that the ELM trigger condition in JET-ILW plasmas can be reasonably explained by taking into account both the rotation and omega(*i) effects in the numerical analysis. When deuterium poloidal rotation is evaluated based on neoclassical theory, an increase in the effective charge of plasma destabilizes the PBM because of an acceleration of rotation and a decrease in omega(*i). The difference in the amount of ELM energy loss in JT-60U plasmas rotating in opposite directions was reproduced qualitatively with JOREK. By comparing the ELM affected areas with linear eigenfunctions, it was confirmed that the difference in the linear stability property, due not to the rotation direction but to the plasma density profile, is thought to be responsible for changing the ELM energy loss just after the ELM crash. A predictive study to determine the pedestal profiles in JT-60SA was performed by updating the EPED1 model to include the rotation and w*i effects in the PBM stability analysis. It was shown that the plasma rotation predicted with the neoclassical toroidal viscosity degrades the pedestal performance by about 10% by destabilizing the PBM, but the pressure pedestal height will be high enough to achieve the target parameters required for the ITER-like shape inductive scenario in JT-60SA.

  • 5. Airila, M. I.
    et al.
    Aho-Mantila, L.
    Brezinsek, S.
    Coad, J. P.
    Kirschner, A.
    Likonen, J.
    Matveev, D.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet. KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Strachan, J. D.
    Widdowson, A.
    Wiesen, S.
    ERO modelling of local deposition of injected C-13 tracer at the outer divertor of JET2009Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T138, s. 014021-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The 2004 tracer experiment of JET with the injection of (CH4)-C-13 into H-mode plasma at the outer divertor has been modelled with the Monte Carlo impurity transport code ERO. EDGE2D solutions for inter-ELM and ELM-peak phases were used as plasma backgrounds. Local two-dimensional (2D) deposition patterns at the vertical outer divertor target plate were obtained for comparison with post-mortem surface analyses. ERO also provides emission profiles for comparison with radially resolved spectroscopic measurements. Modelling indicates that enhanced re-erosion of deposited carbon layers is essential in explaining the amount of local deposition. Assuming negligible effective sticking of hydrocarbons, the measured local deposition of 20-34% is reproduced if re-erosion of deposits is enhanced by a factor of 2.5-7 compared to graphite erosion. If deposits are treated like the substrate, the modelled deposition is 55%. Deposition measurements at the shadowed area around injectors can be well explained by assuming negligible re-erosion but similar sticking behaviour there as on plasma-wetted surfaces.

  • 6. Airila, M. I.
    et al.
    Jarvinen, A.
    Groth, M.
    Belo, P.
    Wiesen, S.
    Brezinsek, S.
    Lawson, K.
    Borodin, D.
    Kirschner, A.
    Coad, J. P.
    Heinola, K.
    Likonen, J.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Preliminary Monte Carlo simulation of beryllium migration during JET ITER-like wall divertor operation2015Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 800-804Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Migration of beryllium into the divertor and deposition on tungsten in the final phase of the first ITER-like-wall campaign of JET are modelled with the 3D Monte Carlo impurity transport code ERO. The simulation covers the inner wall and the inner divertor. To generate the plasma background for Monte Carlo tracing of impurity particles, we use the EDGE2D/EIRENE code set. At the relevant regions of the wall, the estimated plasma conditions vary around T-e approximate to 5eV and n(e) 2 x 10(17) m(-3) (far-scrape-off layer; more than 10 cm away from the LCFS). We calculate impurity distributions in the plasma using the main chamber source as a free parameter in modelling and attempt to reproduce inter-ELM spectroscopic BeII line (527 nm) profiles at the divertor. The present model reproduces the level of emission close to the inner wall, but further work is needed to match also the measured emission peak values and ultimately link the modelled poloidal net deposition profiles of beryllium to post mortem data.

  • 7. Airila, M. I.
    et al.
    Makkonen, T.
    Järvinen, A.
    Groth, M.
    Brezinsek, S.
    Coad, J. P.
    Jachmich, S.
    Kirschner, A.
    Likonen, J.
    Meigs, A.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Re-deposition dynamics of trace 13C in H-mode divertor conditions2013Inngår i: 40th EPS Conference on Plasma Physics, EPS 2013, 2013, s. 629-632Konferansepaper (Fagfellevurdert)
  • 8. Alegre, Daniel
    et al.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Gasior, Pawel
    Kubkowska, Monika
    Kowalska-Strzeciwilk, Ewa
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tabares, Francisco L.
    Study of correlation of deuterium content in a-C:D dust induced by laser irradiation from the co-deposited surface with the grain size and velocity2014Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T161, s. 014010-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the study described here, the laser ablation method was applied to clean thick (40-60 m) a-C: D co-deposits on the ALT-II limiter blade from the TEXTOR tokamak, and at the same time to characterize the ejected particles formed during ablation and measure the amount of fuel carried by them. Ablation was accomplished by similar to 3.5 ns, 0.5 J Nd: YAG laser pulses in either vacuum or an O-2 atmosphere at different pressures. Fast camera tracking of the process provided an estimate of the population and velocity of up to 100ms(-1) for larger dust particles. In the same experiment, the dust particles were caught using ultra-light Si aerogel collectors placed in front of the ablation target. SEM analysis of aerogel surfaces verified the speed estimate, providing the trapped particles' size distribution and particle yield during ablation. The D/C atomic concentration ratio was measured with the 3HE ion beam nuclear reaction analysis method in deposited layers before ablation and with a micro-ion beam in individual particles on aerogel collectors. This indicated that most of the D was thermally released during ablation, leaving no more than 5% of its original amount in the particles. The effect of ablation conditions on the acceleration of ejected particles, their population, composition and D content is the main subject of this paper.

  • 9. Alfier, A.
    et al.
    Pasqualotto, R.
    Spizzo, G.
    Canton, A.
    Fassina, A.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Electron temperature profiles in RFX-mod2008Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 50, nr 3, s. 035013-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Electron temperature profiles have been measured by the main Thomson scattering ( TS) diagnostic on the RFX-mod reversed field pinch experiment in Padova, Italy. The increased accuracy and spatial and temporal resolution permits one to measure in detail the improvements in T-e profiles, obtained with the active saddle coil system, which allows one to obtain core temperature 30% higher and scaling stronger with plasma current, steeper gradients in the core (+30%) and at the edge (+60%). 1D power balance calculations show that the active control of MHD modes largely reduces the values of electron heat diffusivity along the whole plasma radius, with similar to 50% reduction at the edge and similar to 30% in the core. The resulting electron energy confinement time is doubled. Further improvements occur during quasi-single helicity (QSH) states: the new TS allows one to study in detail the hot island that develops in the core. A characterization of the island electron thermal profile is presented, in terms of width, temperature increase, gradients and asymmetry; the effect on density profile is also discussed. A 2D transport code has been applied to calculate the heat diffusivity inside the magnetic island corresponding to the QSH state, also considering the correlation between temperature increase and pressure gradient with the chaos level around the island. Finally, electron energy confinement time during QSH states is compared with that in MH states.

  • 10. Allen, S. L.
    et al.
    Wampler, W. R.
    McLean, A. G.
    Whyte, D. G.
    West, W. P.
    Stangeby, P. C.
    Brooks, N. H.
    Rudakov, D. L.
    Phillips, V.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Matthews, G. F.
    Nagy, A.
    Ellis, R.
    Bozek, A. S.
    C-13 transport studies in L-mode divertor plasmas on DIII-D2005Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 337-39, nr 03-jan, s. 30-34Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    (CH4)-C-13 was injected with a toroidally-symmetric gas system into 22 identical lower-single-null L-mode discharges on DIII-D. The injection level was adjusted so that it did not significantly perturb the core or divertor plasmas, with a duration of similar to 3 s on each shot, for a total of similar to 300 T L of injected particles. The plasma shape remained very constant; the divertor strike points were controlled to similar to 1 cm at the divertor plate. At the beginning of the subsequent machine vent, 29 carbon tiles were removed for nuclear reaction analysis of C-13 content to determine regions of carbon deposition. It was found that only the tiles inboard of the inner strike point had appreciable 1 3 C above background. Visible spectroscopy measurements of the carbon injection and comparisons with modeling are consistent with carbon transport by means of scrape-off layer flow.

  • 11.
    Anderson, Taurug
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Iterative Learning Control model for a Resistive Wall Mode Active Controller2013Independent thesis Advanced level (degree of Master (Two Years)), 20 poäng / 30 hpOppgave
    Abstract [en]

    The EXTRAP T2R is a Reversed Field Pinch (RFP) device purposed to conduct magnetic confinement fusion research. Magnetic confinement works on the principle of isolating the hot plasma from the cool walls by locking in the plasma onto the magnetic field lines. Due to the generally unstable nature of plasma, the plasma column will shift off its centered position and encroach upon the cooling walls. To counteract this, a series of magnetic sensor coil are placed around the torus that serve as the input for another set of coils that will generate a magnetic field to force the plasma column back in place. This is a feedback mechanism that uses a Proportional-Integral-Derivative (PID) as the loop gain control mechanisms. While this was effective in stabilizing the system it was discovered that during the start up phase of the experiment there was a repeatable pattern of disturbance. As such it offers the opportunity to make use of a feedforward Iterative Learning Control (ILC) that could provide a much more precise stabilization and occlude the possibility of saturating the feedback coils. In this thesis an ILC system will be built upon the existing PID system, it will be modeled in MATLAB and SIMULINK then run to simulate and gauge its performance.

  • 12. Antoni, V.
    et al.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Spada, E.
    Spolaore, M.
    Vianello, N.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Cavazzana, R.
    Cecconello, Marco
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Martines, E.
    Serianni, G.
    Coherent structures and anomalous transport in reversed field pinch plasmas2006Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T122, s. 1-7Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The results leading to the identification of coherent structures emerging from the background turbulence in the edge region of the reversed field pinch experiments EXTRAP-T2R and RFX are reviewed. These structures have traits of vortices in velocity field and blobs in density, and the reconstruction of their spatial structure and of their time evolution is discussed focusing on the analysis tools applied. The role of these structures in the particle anomalous transport is addressed, showing that their collisions can contribute up to 50% the total particle losses. This process is shown to be responsible for bursts in particle flux and it is found to set a characteristic collision time, which is in agreement with the statistical properties of laminar times for particle flux bursts.

  • 13. Arnoux, G.
    et al.
    Loenen, J.
    Bazylev, B.
    Corre, Y.
    Matthews, G. F.
    Balboa, I.
    Clever, M.
    Dejarnac, R.
    Devaux, S.
    Eich, T.
    Gauthier, E.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Horacek, J.
    Jachmich, S.
    Kinna, D.
    Marsen, S.
    Mertens, Ph.
    Pitts, R. A.
    Rack, M.
    Sergienko, G.
    Sieglin, B.
    Stamp, M.
    Thompson, V.
    Thermal analysis of an exposed tungsten edge in the JET divertor2015Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 415-419Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    In the recent melt experiments with the JET tungsten divertor, we observe that the heat flux impacting on a leading edge is 3-10 times lower than a geometrical projection would predict. The surface temperature, tungsten vaporisation rate and melt motion measured during these experiments is consistent with the simulations using the MEMOS code, only if one applies the heat flux reduction. This unexpected observation is the result of our efforts to demonstrate that the tungsten lamella was melted by ELM induced transient heat loads only. This paper describes in details the measurements and data analysis method that led us to this strong conclusion. The reason for the reduced heat flux are yet to be clearly established and we provide some ideas to explore. Explaining the physics of this heat flux reduction would allow to understand whether it can be extrapolated to ITER.

  • 14.
    Askari, Sadegh
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Evaluation of a New Resampling Scheme for f Monte Carlo Methods2011Independent thesis Advanced level (degree of Master (One Year)), 10 poäng / 15 hpOppgave
    Abstract [en]

    A new class of methods for reducing the number of particles in delta-f Monte Carlo simulations is presented. The reduction of particles is necessary when there is a continuous growth of the number of particles during the simulation. The method is based on resampling the particles distribution in local partitions of the phase-space. The resampling is accomplished by replacing particles with fewer numbers of new particles in each partition while ensuring that the moments of distribution are conserved. It’s demonstrated that the method well preserves the distribution function.

  • 15. Askinazi, L. G.
    et al.
    Khrebtov, S.
    Komarov, A. D.
    Komev, V. A.
    Krikunov, S. V.
    Krupnik, L. I.
    Lebedev, S. V.
    Rozhdestvensky, V. V.
    Tendler, Michael B.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tukachinsky, A. S.
    Vildjunas, M. I.
    Zhubr, N. A.
    GAM evolution in the H-mode discharge in the TUMAN-3M tokamak2011Inngår i: 38th EPS Conference on Plasma Physics 2011, EPS 2011 - Europhysics Conference Abstracts, 2011, s. 529-532Konferansepaper (Fagfellevurdert)
  • 16. Askinazi, L. G.
    et al.
    Kornev, V. A.
    Krikunov, S. V.
    Krupnik, L. I.
    Lebedev, S. V.
    Smirnov, A. I.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Tukachinsky, A. S.
    Vildjunas, M. I.
    Zhubr, N. A.
    Plasma potential evolution in various operational modes in the TUMAN-3M tokamak2007Inngår i: 34th EPS Conference on Plasma Physics 2007, EPS 2007 - Europhysics Conference Abstracts, 2007, nr 3, s. 2010-2013Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In a scenario with Counter-NBI it was found using HIBP that, due to the NBI effect (most probably, orbit loss with some heating and momentum impact), core plasma potential plasma gradually became more negative (for ∼200V). Strong positive perturbation of the core plasma potential was registered by the HIBP during the burst of peripheral MHDs with low m, n. If such a burst takes place in the H-mode (both ohmic and counter-NBI heated), the positive potential perturbation leads to H-mode termination. The most probable mechanism of the positive field build-up during MHD burst is though to be a loss of fast electrons along partly disturbed magnetic field lines near the island's separatrix [3,4]. This mechanism is similar to the ergodic divertor's action on the TEXTOR [6], where radial electric field modification by the electron loses was also discussed. A quantitative analysis of the subject may be found in [7]. Similar mechanism may be responsible for a positive perturbation of central plasma potential registered in the sawtooth crashes. The GAM with δφ/φ∼0.3 and δφ/φ≫δn/n∼0.05 where observed with HIBP in a core region of the TUMAN-3M r/a∼0.33 in the current ramp phase. Further studies are needed to reveal a possible connection between the GAM evolution and plasma confinement in the TUMAN-3M.

  • 17. Askinazi, L. G.
    et al.
    Kornev, V. A.
    Krikunov, S. V.
    Krupnik, L. I.
    Lebedev, S. V.
    Smirnov, A. I.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Tukachinsky, A. S.
    Vildjunas, M. I.
    Zhubr, N. A.
    Radial electric field evolution in various operational modes in the TUMAN-3M tokamak2008Inngår i: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 123, s. 012010-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Radial electric field evolution has been studied on the TUAMN-3M tokamak in different modes of operation: ohmic and NBI heating, L- and H-modes, with and without strong MHD activity. Peripheral radial electric field was measured using Langmuire probes, which were inserted up to 2cm inside LCFS, while core plasma potential evolution was measured using HIBP diagnostic. It was found, that in presence of strong MHD activity radial electric field in a vicinity of the island changed sign from negative to positive and could reach up to 4kV/m. Central plasma potential exhibited a positive perturbation of ∼700V during the MHD burst. This positive radial electric field might lead to H-mode termination, both in ohmic and NBI heating cases. Possible mechanism of the positive Er generation, namely the electron losses along ergodized magnetic field lines in the presence of MHD-island, is discussed. The same mechanism might be responsible for the positive potential spikes during a saw-tooth crash, also observed using HIBP. Another phenomenon observed using HIBP was quasi-coherent potential oscillations with the frequency close to one of the GAM. Possible location of these oscillations in the core region r/a ∼ 0.33 is discussed.

  • 18. Askinazi, L. G.
    et al.
    Vildjunas, M. I.
    Zhubr, N. A.
    Komarov, A. D.
    Kornev, V. A.
    Krikunov, S. V.
    Krupnik, L. I.
    Lebedev, S. V.
    Rozhdestvensky, V. V.
    Tendler, Michael
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Tukachinsky, A. S.
    Khrebtov, S. M.
    Evolution of geodesic acoustic mode in ohmic H-mode in TUMAN-3M tokamak2012Inngår i: Technical physics letters, ISSN 1063-7850, E-ISSN 1090-6533, Vol. 38, nr 3, s. 268-271Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The behavior of a geodesic acoustic mode (GAM) in the TUMAN-3M tokamak has been experimentally studied using the heavy-ion beam probing technique. Oscillations of the electric potential under the action of a GAM localized at the plasma periphery have been detected. The GAM was observed in the regime of low confinement (L-mode) with low plasma density (similar to 0.8 x 10(19) m(-3)) and disappeared upon the transition to a high confinement regime (H-mode). The possible role of GAM as a precursor of the improved confinement (LH-transition) is discussed.

  • 19. Asunta, O.
    et al.
    Coelho, R.
    Kalupin, D.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Franke, T.
    Predictions of neutral beam current drive in DEMO using BBNBI and ASCOT within the European Transport Simulator2015Inngår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferansepaper (Fagfellevurdert)
    Abstract [en]

    It was demonstrated that BBNBI and ASCOT are capable of flexible and sophisticated modelling of NBI as a part of an ETS simulation. The simulations showed that tilting the DEMO beam vertically results in a few per cent higher current drive than comparable horizontal tilts.

  • 20. Badziak, J.
    et al.
    Czarnecka, A.
    Gasior, P.
    Parys, P.
    Philipps, V.
    Rosinski, M.
    Rubel, Marek J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Wolowski, J.
    Application of ion diagnostics to control the laser-induced removal of surface layer of a carbon substrate2006Inngår i: Plasma 2005, 2006, Vol. 812, s. 295-298Konferansepaper (Fagfellevurdert)
    Abstract [en]

    Among other methods of detritiation of in-vessel tokamak components the application of lasers for removal of fuel trapped in co-deposited layers is under investigation. The paper presents preparation and tests of ion diagnostic methods for on-line measurement of the amount and characteristics of ablated carbon, hydrogen/deuterium and contaminant species from the graphite target (plate) of the main toroidal limiter of the TEXTOR tokamak. For removal of the surface layer from the graphite limiter plate Nd:YAG laser was used. Determination of the characteristics of laser-produced ions has been performed by means of ion collectors and an electrostatic ion-energy analyser. The main ion stream parameters were measured depending on the number of laser shots and the laser power density on the target surface. The properties of modified carbon sample surface were determined with the use of optical methods and compared with the results of the ion measurements.

  • 21. Bailescu, V.
    et al.
    Burcea, G.
    Balan, N.
    Dinuta, G.
    Serban, G.
    Lungu, C. P.
    Mustata, I.
    Lungu, A. M.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Coad, P.
    Pedrick, L.
    Handley, R.
    Inconel tiles coated with beryllium by thermal evaporation2008Inngår i: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, nr 3Konferansepaper (Fagfellevurdert)
  • 22. Baiocchi, B.
    et al.
    Calabrò, G.
    Lauro-Taroni, L.
    Mantica, P.
    Cardinali, A.
    Corrigan, G.
    Crisanti, F.
    Farina, D.
    Figini, L.
    Giruzzi, G.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Marinucci, M.
    Parail, V.
    Predictive modelling of H-mode and steady-state scenarios in FAST2010Inngår i: 37th EPS Conference on Plasma Physics 2010, EPS 2010: Volume 1, 2010, s. 293-296Konferansepaper (Fagfellevurdert)
  • 23. Baiocchi, B.
    et al.
    Mantica, P.
    Giroud, C.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Naulin, V.
    Salmi, A.
    Tala, T.
    Tsalas, M.
    Discriminating the role of rotation and its gradient in determining ion stiffness mitigation in JET2013Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 55, nr 2, s. 025010-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Starting from recent JET experimental results that show a significant reduction of ion stiffness in the plasma core region due to plasma rotation in the presence of low magnetic shear, an experiment was carried out at JET in order to separate the role of rotation and rotation gradient in mitigating the ion stiffness level. Enhanced toroidal field ripple (up to 1.5%) and external resonant magnetic fields are the two mechanisms used to try and decouple the rotation value from its gradient. In addition, shots with reversed toroidal field and plasma current, yielding counter-current neutral beam injection, were compared with standard co-injection cases. These tools also allowed varying the rotation independently of the injected power. Shots with high rotation gradient are found to maintain their low stiffness level even when the absolute value of the rotation was significantly reduced. Conversely, high but flat rotation yields much less peaked ion temperature profiles than a peaked rotation profile with lower values. This behaviour suggests the rotation gradient as the main player in reducing the ion stiffness level. In addition, it is found that inverting the rotation gradient sign does not suppress its effect on ion stiffness.

  • 24. Baron-Wiechec, A.
    et al.
    Fortuna-Zalesna, E.
    Grzonka, J.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Widdowson, A.
    Ayres, C.
    Coad, J. P.
    Hardie, C.
    Heinola, K.
    Matthews, G. F.
    First dust study in JET with the ITER-like wall: sampling, analysis and classification2015Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 55, nr 11, artikkel-id 113033Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Results of the first dust survey in JET with the ITER-Like Wall (JET-ILW) are presented. The sampling was performed using adhesive stickers from the divertor tiles where the greatest material deposition was detected after the first JET-ILW campaign in 2011-2012. The emphasis was especially on sampling and analysis of metal particles (Be and W) with the aim to determine the composition, size, surface topography and internal dust structure using a large set of methods: high-resolution scanning and transmission electron microscopy, focused ion beam, electron diffraction and also wavelength and energy dispersive x-ray spectroscopy. The most important was the identification of beryllium dust both in the form of flakes and droplets with dimensions in the micrometer range. Tungsten, molybdenum, inconel constituents were identified along with many impurity species. The particles are categorised and the origin of the various constituents discussed.

  • 25. Baron-Wiechec, A.
    et al.
    Widdowson, A.
    Alves, E.
    Ayres, C. F.
    Barradas, N. P.
    Brezinsek, S.
    Coad, J. P.
    Catarino, N.
    Heinola, K.
    Likonen, J.
    Matthews, G. F.
    Mayer, M.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    van Renterghem, W.
    Uytdenhouwen, I.
    Global erosion and deposition patterns in JET with the ITER-like wall2015Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 157-161Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    A set of Be and W tiles removed after the first ITER-like wall campaigns (JET-ILW) from 2011 to 2012 has been analysed. The results indicate that the primary erosion site is in the main chamber (Be) as in previous carbon campaigns (JET-C). In particular the limiters tiles near the mid-plane are eroded probably during the limiter phases of discharges. W is found at low concentrations on all plasma-facing surfaces of the vessel indicating deposition via plasma transport initially from the W divertor and from main chamber W-coated tiles; there are also traces of Mo (used as an interlayer for these coatings). Deposited films in the inner divertor have a layered structure, and every layer is dominated by Be with some W and O content.

  • 26. Batistoni, P.
    et al.
    Likonen, J.
    Bekris, N.
    Brezinsek, S.
    Coad, P.
    Horton, L.
    Matthews, G.
    Rubel, Marek
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sips, G.
    Syme, B.
    Widdowson, A.
    The JET technology program in support of ITER2014Inngår i: Fusion engineering and design, ISSN 0920-3796, E-ISSN 1873-7196, Vol. 89, nr 7-8, s. 896-900Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    This paper presents an overview of the current and planned technological activities at JET in support of ITER operation and safety. The scope is very broad and it ranges from analysis of components from the ITER-like Wall (ILW) to determine material erosion and deposition, dust generation and fuel retention to neutronics measurements and analyses. Preliminary results are given of the post-mortem analyses of samples exposed to JET plasmas during the first JET-ILW operation in 2011-2012, and retrieved during the following in-vessel intervention. JET is the only fusion machine capable of producing significant neutron yields, up to nearly 10(19) n/s (14.1 MeV) in DT operations. Recently, the technological potential of a new DT campaign at JET in support of ITER has been explored and the outcome of this assessment is presented. The expected 14 MeV neutron yield, the use of tritium, the preparation and implementation of safety measures will provide a unique occasion to gain experience in several ITER relevant technological areas. A number of projects and experiments to be conducted in conjunction with the DT operation have been identified and they are described in this paper.

  • 27.
    Bergkvist, Tommy
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Non-linear dynamics of Alfvén eigenmodes excited by fast ions in tokamaks2007Doktoravhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    The tokamak is so far the most promising magnetic configuration for achieving a net production of fusion energy. The D-T fusion reactions result in 3.5 MeV alpha-particles, which may destabilize Alfvén eigenmodes through wave-particle interaction. These instabilities redistribute the alpha-particles from the central region of the plasma towards the edge, where they are thermalized, and hence result in a reduced heating efficiency. The high-energy alpha-particles may even be thrown out of the plasma and may damage the wall.

    To investigate the destabilization of Alfvén eigenmodes by high-energy ions, ion cyclotron resonance heating (ICRH) and neutral beam injection (NBI) are often used to create a high-energy tail on the distribution function. The ICRH does not only produce high-energy anisotropic tails, it also decorrelates the wave-particle interaction with the Alfvén eigenmodes. Without decorrelation of the wave-particle interaction an ion will undergo a superadiabatic oscillation in phase space and there will be no net transfer of energy to the mode. For the thermal ions the decorrelation from collisions dominates while for the high-energy ions the decorrelation from ICRH dominates. As the unstable modes grow up, the gradients in phase space, which drive the mode, are reduced, resulting in a weaker drive. The dynamics of the system becomes non-linear due to a continuous restoration of the gradients by D-T reactions and ICRH.

    In this thesis the non-linear dynamics of toroidal Alfvén eigenmodes (TAEs) during ICRH has been investigated using the SELFO code. The SELFO code, which calculates the distribution function during ICRH self-consistently using a Monte-Carlo metod, has been upgraded to include interactions with TAEs. The fast decay of the mode amplitude as the ICRH is switched off, which is seen in experiments, as well as the oscillation of the mode amplitude as the distribution function is repetetively built up by the ICRH and flattened by the TAE has been reproduced using numerical simulations. In the presence of several unstable modes the dynamics become more complicated. The redistribution of an alpha-particle slowing down distribution function as well as the reduced heating efficiency in the presence of several modes has also been investigated.

  • 28.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Holmström, Kerstin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. KTH, Skolan för elektro- och systemteknik (EES), Centra, Alfvénlaboratoriet.
    Effects of ICRH on the dynamics of fast particle excited alfven eigenmodes2007Inngår i: Radio Frequency Power in Plasmas, American Institute of Physics (AIP), 2007, Vol. 933, s. 455-458Konferansepaper (Fagfellevurdert)
    Abstract [en]

    ICRH is often used in experiments to simulate destabilization of Alfvén eigenmodes by thermonuclear α-particles. Whereas the slowing down distribution of α-particles is nearly isotropic, the ICRH creates an anisotropic distribution function with non-standard orbits. The ICRH does not only build up gradients in phase space, which destabilizes the AEs, but it also provides a strong phase decorrelation mechanism between ions and AEs. Renewal of the distribution function by thermonuclear reactions and losses of α-particles to the wall lead to a continuous drive of the AEs. Simulations of the non-linear dynamics of AEs and the impact they have on the heating profile due to particle redistribution are presented.

  • 29.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Holmström, Kerstin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Non-linear dynamics of Alfvén eigenmodes excited by thermonulcear alpha particles in the presence of ion cyclotron resonance heating2007Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 47, nr 9, s. 1131-1141Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Alfvén eigenmodes (AEs) excited by thermonuclear α-particles can degrade the heating efficiency by spatial redistribution of the resonant α-particles. Changes of the orbit invariants in phase space by collisions and interactions with other waves, such as magnetosonic waves during ion cyclotron resonance heating (ICRH), lead to changes in the phase between the α-particles and AEs, causing a decorrelation of the interactions and stronger redistribution of the α-particles. Cyclotron interactions increase the decorrelation of the AE interactions with the high-energy ions and hence a stronger radial redistribution of the high-energy α-particles by the AEs. Renewal of the distribution function by thermonuclear reactions and losses of α-particles to the wall lead to a continuous drive of the AEs and a radial redistribution of the α-particles. The condition for excitation of AEs is shown to depend on the heating scenario where heating at the low field side creates a significant population of high-energy non-standard orbits which drive the modes. The redistribution results in a reduction in the averaged α-particle energy and a degradation of the heating efficiency. The effect on the distribution function in the presence of several unstable modes is not additive and the particle redistribution is found to saturate with an increasing number of modes.

  • 30.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, T.
    Laxåback, Martin
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Non-linear study of fast particle excitation of global Alfvén eigenmodes during ICRH2005Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 45, s. 485-493Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    High-power ion–cyclotron resonance heating (ICRH) can produce centrally peaked fast ion distributions with wide non-standard drift orbits exciting Alfvén eigenmodes (AEs). The dynamics of the AE excitation depends not only on the anisotropy and the peaking of the fast ion distribution but also on the decorrelation of the AE interactions and the renewal of the fast ions resonant with the AE by ion–cyclotron interactions. A method of self-consistently including the evolution of the distribution function of fast ions during excitation of AEs and ICRH has been developed and implemented in the SELFO code. Numerical simulations of the AE dynamics and ICRH give a variation of the AE amplitude consistent with the experimentally observed splitting of the mode frequency. The experimentally observed fast damping of the mode as the ICRH is switched off is also evident in the simulations.

  • 31.
    Bergkvist, Tommy
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hellsten, Torbjörn
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Johnson, Thomas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Self-consistent study of fast particle redistribution by Alfvén eigenmodes during Ion cyclotron resonance heating2005Inngår i: Proceedings of the 9th IAEA Technical Meeting on Energetic Particles in Magnetic Confinement Systems, 2005, s. 14-20Konferansepaper (Fagfellevurdert)
  • 32.
    Bergsåker, B. Henric M.
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Zhou, Yushan
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EUROfusion Consortium, Culham Science Centre, JET, Abingdon, United Kingdom.
    Possnert, G.
    Likonen, J.
    Pettersson, J.
    Koivuranta, S.
    Widdowson, A. M.
    Deep deuterium retention and Be/W mixing at tungsten coated surfaces in the JET divertor2016Inngår i: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896, Vol. T167, artikkel-id 014061Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 33.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Egde profiles and limiter tests in Extrap T21999Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 266-269, s. 777-782Artikkel i tidsskrift (Fagfellevurdert)
  • 34.
    Bergsåker, Henric
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Hydrogen recycling in graphite at higher fluxes1999Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 266-269, s. 856-851Artikkel i tidsskrift (Fagfellevurdert)
  • 35.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Widdowson, A. M.
    Microstructure and inhomogeneous fuel trapping at divertor surfaces in the JET tokamak2014Inngår i: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 332, s. 266-270Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The plasma deposited layers at divertor surfaces in the JET tokamak with carbon wall have been studied post mortem, using micro ion beam analysis (mu-IBA) methods, optical microscopy and scanning electron microscopy (SEM). The layers were formed during plasma operations over different periods through 1998-2009. They frequently have a columnar structure. For mu-IBA a 3 MeV He-3 beam was used, focused to about 5-15 mu m size. Nuclear reaction analysis was used to measure D, Be and C. Elemental mapping was carried out both at the original surface and on polished layer cross sections. Trapped deuterium is predominantly found in remote areas on the horizontal bottom divertor tiles and in regions with locally enhanced deuterium concentration on the vertical tiles. Pockets with enhanced deuterium concentration are found in the carbon fibre composite (CFC) substrate. Areas with dimensions of about 100 mu m with enhanced deuterium concentration are also found inside the deposited layers. The inhomogeneous fuel trapping is tentatively explained with co-deposition in partly protected pits in the substrate and by incorporation of dust particles in the growing layers.

  • 36.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Emmoth, Birger
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Mikroelektronik och tillämpad fysik, MAP.
    Petersson, P.
    Possnert, Göran
    Coad, J. P.
    Likonen, J.
    Renvall, T.
    Nuclear reaction analysis with ion microbeam of cross sections of surface layers deposited in a tokamak divertor2007Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 362, nr 03-feb, s. 215-221Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Ion micro beam analysis has been applied to the investigation of plasma deposited layers covering the divertor tiles in the JET tokamak. Since the layers are about 100 mu m thick they are too thick to be completely investigated by ordinary ion beam analysis. Cross sections of the layers were prepared by cutting and polishing. Elemental depth profiles were determined from the two dimensional images that could be derived by nuclear reaction analysis and resonant backscattering spectrometry, using ion beams focused to a few mu m spot size. A combination of analysis methods are shown, which allow measurements of the concentration profiles of carbon, beryllium, deuterium, oxygen and stainless steel components at levels of a few percent, with an accuracy better than 10%.

  • 37.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Menmuir, Sheena
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Rachlew, Elisabeth
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Brunsell, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Drake, James R.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Metal impurity fluxes and plasma-surface interactions in EXTRAP T2R2008Inngår i: PROCEEDINGS OF THE 17TH INTERNATIONAL VACUUM CONGRESS/13TH INTERNATIONAL CONFERENCE ON SURFACE SCIENCE/INTERNATIONAL CONFERENCE ON NANOSCIENCE AND TECHNOLOGY, 2008, Vol. 100Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The EXTRAP T2R is a large aspect ratio Reversed Field Pinch device. The main focus of interest for the experiments is the active feedback control of resistive wall modes [1]. With feedback it has been possible to prolong plasma discharges in T2R from about 20 ms to nearly 100 ms. In a series of experiments in T2R, in H- and D- plasmas with and without feedback, quantitative spectroscopy and passive collector probes have been used to study the flux of metal impurities. Time resolved spectroscopic measurements of Cr and Mo lines showed large metal release towards discharge termination without feedback. Discharge integrated fluxes of Cr, Fe, Ni and Mo were also measured with collector probes at wall position. Reasonable quantitative agreement was found between the spectroscopic and collector probe measurements. The roles of sputtering, thermal evaporation and arcing in impurity production are evaluated based on the composition of the measured impurity flux.

  • 38.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Widdowson, A. M.
    Microanalysis of deposited layers in the divertor of JET following operations with carbon wall2013Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 438, nr Suppl., s. S668-S672Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Elemental mapping of cross sections of deposited layers on inboard tiles in the JET divertor after exposure to plasma operations with carbon wall are presented. The study was made using microbeam ion beam analysis methods in combination with optical microscopy and SEM. The surfaces had been exposed to plasma through different periods of operation (1998-2007, 2007-2009 and 1998-2009). The texture and composition of the layers are non-uniform. The physical structures include columnar, lamellar and disordered globular appearances. The distribution of trapped deuterium was frequently found to be lamellar, with well-defined sub layers with higher deuterium concentration. However, 3D regions with dimensions of about 100 μm with enhanced deuterium content were also found, both at the layer surfaces and in the layer cross sections. The distributions of beryllium and Inconel components were lamellar but did not otherwise show large non-uniformity on the same scale length as the deuterium.

  • 39.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Heinola, K.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Miettunen, J.
    Widdowson, A.
    Riccardo, V.
    Nunes, I.
    Stamp, M.
    Brezinsek, S.
    Groth, M.
    Kurki-Suonio, T.
    Likonen, J.
    Coad, J. P.
    Borodin, D.
    Kirschner, A.
    Schmid, K.
    Krieger, K.
    First results from the Be-10 marker experiment in JET with ITER-like wall2014Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 8, s. 082004-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    When the ITER-like wall was installed in JET, one of the 218 Be inner wall guard limiter tiles had been enriched with Be-10 as a bulk isotopic marker. During the shutdown in 2012-2013, a set of tiles were sampled nondestructively to collect material for accelerator mass spectroscopy measurements of Be-10 concentration. The letter shows how the marker experiment was set up, presents first results and compares them to preliminary predictions of marker redistribution, made with the ASCOT numerical code. Finally an outline is shown of what experimental data are likely to become available later and the possibilities for comparison with modelling using the WallDYN, ERO and ASCOT codes are discussed.

  • 40.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Heinola, K.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Miettunen, J.
    Widdowson, C.
    Riccardo, V.
    Nunes, I.
    Stamp, M.
    et al.,
    First results from10Be marker experiment in JET with ITER-like wallManuskript (preprint) (Annet vitenskapelig)
  • 41.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Ratynskaia, Svetlana
    KTH, Skolan för elektro- och systemteknik (EES), Rymd- och plasmafysik.
    Litnovsky, A.
    Ogata, Douglas
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Sahle, Wubeshet
    KTH, Skolan för informations- och kommunikationsteknik (ICT), Materialfysik, Funktionella material, FNM.
    Studies of mobile dust in scrape-off layer plasmas using silica aerogel collectors2011Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 415, nr 1, s. S1089-S1093Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Dust capture with ultralow density silica aerogel collectors is a new method, which allows time resolved in situ capture of dust particles in the scrape-off layers of fusion devices, without substantially damaging the particles. Particle composition and morphology, particle flux densities and particle velocity distributions can be determined through appropriate analysis of the aerogel surfaces after exposure. The method has been applied in comparative studies of intrinsic dust in the TEXTOR tokamak and in the Extrap T2R reversed field pinch. The analysis methods have been mainly optical microscopy and SEM. The method is shown to be applicable in both devices and the results are tentatively compared between the two plasma devices, which are very different in terms of edge plasma conditions, time scale, geometry and wall materials.

  • 42.
    Bergsåker, Henric
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Welander, Anders
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Measurements of hot electrons in the Extrap T1 reversed field pinch1998Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 40, s. 319-333Artikkel i tidsskrift (Fagfellevurdert)
  • 43.
    Bergsåker, Henrik
    et al.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bykov, Igor
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Petersson, Per
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Possnert, G.
    Likonen, J.
    Koivuranta, S.
    Coad, J. P.
    Van Renterghem, W.
    Uytdenhouwen, I.
    Widdowson, A. M.
    Microscopically nonuniform deposition and deuterium retention in the divertor in JET with ITER-like wall2015Inngår i: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 463, s. 956-960Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

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

  • 44. Berk, H. L.
    et al.
    Boswell, C. J.
    Borba, D.
    Figueiredo, A. C. A.
    Johnson, Thomas J.
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Nave, M. F. F.
    Pinches, S. D.
    Sharapov, S. E.
    Explanation of the JET n=0 chirping mode2006Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 46, nr 10, s. S888-S897Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Persistent rapid up and down frequency chirping modes with a toroidal mode number of zero (n = 0) are observed in the JET tokamak when energetic ions, in the range of several hundred keV, are created by high field side ion cyclotron resonance frequency heating. Fokker-Planck calculations demonstrate that the heating method enables the formation of an energetically inverted ion distribution which supplies the free energy for the ions to excite a mode related to the geodesic acoustic mode. The large frequency shifts of this mode are attributed to the formation of phase space structures whose frequencies, which are locked to an ion orbit bounce resonance frequency, are forced to continually shift so that energetic particle energy can be released to counterbalance the energy dissipation present in the background plasma.

  • 45. Beurskens, M
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik. EURATOM-VR.
    Maggi, C
    Calabro, C
    Alper, B
    Bourdelle, C
    Angioni, C
    Brezinsek, S
    Buratti, P
    Challis, C
    Flanagan, J
    Giovannozzi, E
    Giroud, C
    Groth, M
    Hobirk, J
    Joffrin, E
    Leyland, M
    Lomas, P
    de la Luna, E
    Kampenaars, M
    Mantica, P
    Maslov, M
    Matthews, G
    Mayoral, M
    Neu, R
    Snyder, P
    Saarelma, P
    Osborne, T
    de Vries, P
    L-H power Threshold, Pedestal Stability and Confinement in JET with a Metallic Wall2012Inngår i: 24th IAEA Fusion Energy Conference, 8-13 October 2012, 2012, s. EX/P4-23-Konferansepaper (Fagfellevurdert)
    Abstract [en]

    After the change-over from the Carbon-Fibre Composite (CFC) wall to an ITER-like metallic wall (ILW) the baseline type I ELMy H-mode scenario has been re-established in JET with the new plasma-facing materials Be and W. A key finding for ITER is that the power required to enter H-mode has reduced with respect to that in JET with the CFC wall. In JET with the ILW the power threshold to enter H-mode (PL-H) is below the international L-H power threshold scaling P_Martin-08. The minimum threshold is P_L-H=1.8MW compared to P_Martin-08=4MW with a pedestal density of nped=2x10^19m^-3 in plasmas with I_p=2.0 MA, B_t=2.4T. However the threshold depends strongly on density; using slow ion cyclotron heating (ICRH) power ramps P_L-H varies from 1.8 to 4.5MW in a range of lower and upper plasma triangularity (delta_L=0.32-0.4, delta_U =0.19-0.38). Stationary Type I ELMy H-mode operation has been re-established at both low and high triangularity with I_p≤ 2.5MA, q_95=2.8-3.6 and H_98≤1. The achieved plasma collisionality is relatively high, in the range of 1< nu_eff<4 due to the required strong gas dosing. Stability analysis with the linear MHD stability code ELITE show that the pedestal is marginally unstable with respect to the Peeling Ballooning boundary. Due to the stabilising effect of the global pressure Beta_N on the pedestal stability, a strong coupling between core and edge confinement is expected. Indeed in an H-mode profile database comparison with 119 CFC- (0.1< nu_eff<1) and 40 ILW-H-modes a strong coupling of the core versus edge confinement is found, independent of wall material. In addition, the pedestal predictions using the EPED predictive pedestal code coincide with the measured pedestal height over a wide range of normalised pressure 1.5< Beta_N<3.5. Due to the strong core-edge coupling, beneficial effects of core profile peaking on confinement are weak in the database comparison. However, differences in the individual temperature and density profile peaking occur across the database. When collisionality is increased from nu_eff=0.1 to 4, the density peaking decreases from R/L_ne=4 to 0.5 but is compensated by an increase in temperature peaking from R/L_Te = 5-8, offering a challenge for micro turbulence-transport models.

  • 46. Beurskens, M. N. A.
    et al.
    Dunne, M. G.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bernert, M.
    Cavedon, M.
    Fischer, R.
    Järvinen, A.
    Kallenbach, A.
    Laggner, F. M.
    McDermott, R. M.
    Potzel, S.
    Schweinzer, J.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    The role of carbon and nitrogen on the H-mode confinement in ASDEX Upgrade with a metal wall2016Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 56, nr 5, artikkel-id 056014Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Carbon (CD4) and nitrogen (N2) have been seeded in ASDEX Upgrade (AUG) with a tungsten wall and have both led to a 20-30% confinement improvement. The reference plasma is a standard target plasma with I p /B T = 1 MA/2.5 T, total input power P tot ∼ 12 MW and normalized pressure of β N ∼ 1.8. Carbon and nitrogen are almost perfectly exchangeable for the core, pedestal and divertor plasma in this experiment where impurity concentrations of C and N of 2% are achieved and Z eff only mildly increases from ∼1.3 to ∼1.7. As the radiation potentials of C and N are similar and peak well below 100 eV, both impurities act as divertor radiators and radiate well outside the pedestal region. The outer divertor is purposely kept in an attached state when C and N are seeded to avoid confinement degradation by detachment. As reported in earlier publications for nitrogen, carbon is also seen to reduce the high field side high density (the so-called HFSHD) in the scrape off layer above the inner divertor strike point by about 50%. This is accompanied by a confinement improvement for both low (δ ∼ 0.25) and high (δ ∼ 0.4) triangularity configurations for both seeding gases, due to an increase of pedestal temperature and stiff core temperature profiles. The electron density profiles show no apparent change due to the seeding. As an orthogonal effect, increasing the triangularity leads to an additionally increased pedestal density, independent of the impurity seeding. This experiment further closes the gap in understanding the confinement differences observed in carbon and metal wall devices; the absence of carbon can be substituted by nitrogen which leads to a similar confinement benefit. So far, no definite physics explanation for the confinement enhancement has been obtained, but the experimental observations in this paper provide input for further model development.

  • 47. Beurskens, M. N. A.
    et al.
    Dunne, M. G.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Bernert, M.
    Cavedon, M.
    Fischer, R.
    Järvinen, A.
    Kallenbach, A.
    Laggner, F. M.
    McDermott, R. M.
    Tardini, G.
    Viezzer, E.
    Wolfrum, E.
    The role of carbon on the H-mode confinement in ASDEX Upgrade with a metal wall2015Inngår i: 42nd European Physical Society Conference on Plasma Physics, EPS 2015, European Physical Society (EPS) , 2015Konferansepaper (Fagfellevurdert)
  • 48. Beurskens, M. N. A.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Challis, C.
    Giroud, C.
    Saarelma, S.
    Alper, B.
    Angioni, C.
    Bilkova, P.
    Bourdelle, C.
    Brezinsek, S.
    Buratti, P.
    Calabro, G.
    Eich, T.
    Flanagan, J.
    Giovannozzi, E.
    Groth, M.
    Hobirk, J.
    Joffrin, E.
    Leyland, M. J.
    Lomas, P.
    de la Luna, E.
    Kempenaars, M.
    Maddison, G.
    Maggi, C.
    Mantica, P.
    Maslov, M.
    Matthews, G.
    Mayoral, M-L
    Neu, R.
    Nunes, I.
    Osborne, T.
    Rimini, F.
    Scannell, R.
    Solano, E. R.
    Snyder, P. B.
    Voitsekhovitch, I.
    de Vries, Peter
    Global and pedestal confinement in JET with a Be/W metallic wall2014Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 54, nr 4, s. 043001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Type I ELMy H-mode operation in JET with the ITER-like Be/W wall (JET-ILW) generally occurs at lower pedestal pressures compared to those with the full carbon wall (JET-C). The pedestal density is similar but the pedestal temperature where type I ELMs occur is reduced and below to the so-called critical type I-type III transition temperature reported in JET-C experiments. Furthermore, the confinement factor H-98(y,H- 2) in type I ELMy H-mode baseline plasmas is generally lower in JET-ILWcompared to JET-C at low power fractions Ploss/P-thr,(08)< 2 (where P-loss is (P-in-dW/dt), and P-thr,(08) the L-H power threshold from Martin et al 2008 (J. Phys. Conf. Ser. 123 012033)). Higher power fractions have thus far not been achieved in the baseline plasmas. At Ploss/P-thr,P- 08 > 2, the confinement in JET-ILW hybrid plasmas is similar to that in JET-C. A reduction in pedestal pressure is the main reason for the reduced confinement in JET-ILW baseline ELMy H-mode plasmas where typically H-98((y, 2)) = 0.8 is obtained, compared to H-98((y, 2)) = 1.0 in JET-C. In JET-ILW hybrid plasmas a similarly reduced pedestal pressure is compensated by an increased peaking of the core pressure profile resulting in H-98((y, 2)) <= 1.25. The pedestal stability has significantly changed in high triangularity baseline plasmas where the confinement loss is also most apparent. Applying the same stability analysis for JET-C and JET-ILW, the measured pedestal in JET-ILW is stable with respect to the calculated peeling-ballooning stability limit and the ELM collapse time has increased to 2ms from typically 200 mu s in JET-C. This indicates that changes in the pedestal stability may have contributed to the reduced pedestal confinement in JET-ILW plasmas. A comparison of EPED1 pedestal pressure prediction with JET-ILW experimental data in over 500 JET-C and JET-ILW baseline and hybrid plasmas shows a good agreement with 0.8 < (measured p(ped))/(predicted p(ped), EPED) < 1.2, but that the role of triangularity is generally weaker in the JET-ILW experimental data than in the model predictions.

  • 49. Beurskens, M. N. A.
    et al.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Challis, C.
    Osborne, T.
    Snyder, P. B.
    Alper, B.
    Angioni, C.
    Bourdelle, C.
    Buratti, P.
    Crisanti, F.
    Giovannozzi, E.
    Giroud, C.
    Groebner, R.
    Hobirk, J.
    Jenkins, I.
    Joffrin, E.
    Leyland, M. J.
    Lomas, P.
    Mantica, P.
    McDonald, D.
    Nunes, I.
    Rimini, F.
    Saarelma, S.
    Voitsekhovitch, I.
    De Vries, P.
    Zarzoso, D.
    Comparison of hybrid and baseline ELMy H-mode confinement in JET with the carbon wall2013Inngår i: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 53, nr 1, s. 013001-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The confinement in JET baseline type I ELMy H-mode plasmas is compared to that in so-called hybrid H-modes in a database study of 112 plasmas in JET with the carbon fibre composite (CFC) wall. The baseline plasmas typically have βN ∼ 1.5-2, H98 ∼ 1, whereas the hybrid plasmas have βN ∼ 2.5-3, H98 &lt; 1.5. The database study contains both low- (δ ∼ 0.2-0.25) and high-triangularity (δ ∼ 0.4) hybrid and baseline H-mode plasmas from the last JET operational campaigns in the CFC wall from the period 2008-2009. Based on a detailed confinement study of the global as well as the pedestal and core confinement, there is no evidence that the hybrid and baseline plasmas form separate confinement groups; it emerges that the transition between the two scenarios is of a gradual kind rather than demonstrating a bifurcation in the confinement. The elevated confinement enhancement factor H98 in the hybrid plasmas may possibly be explained by the density dependence in the τ98 scaling as n0.41 and the fact that the hybrid plasmas operate at low plasma density compared to the baseline ELMy H-mode plasmas. A separate regression on the confinement data in this study shows a reduction in the density dependence as n0.09±0.08. Furthermore, inclusion of the plasma toroidal rotation in the confinement regression provides a scaling with the toroidal Alfvén Mach number as and again a reduced density dependence as n0.15±0.08. The differences in pedestal confinement can be explained on the basis of linear MHD stability through a coupling of the total and pedestal poloidal pressure and the pedestal performance can be improved through plasma shaping as well as high β operation. This has been confirmed in a comparison with the EPED1 predictive pedestal code which shows a good agreement between the predicted and measured pedestal pressure within 20-30% for a wide range of βN ∼ 1.5-3.5. The core profiles show a strong degree of pressure profile consistency. No beneficial effect of core density peaking on confinement could be identified for the majority of the plasmas presented here as the density peaking is compensated by a temperature de-peaking resulting in no or only a weak variation in the pressure peaking. The core confinement could only be optimized in case the ions and electrons are decoupled, in which case the ion temperature profile peaking can be enhanced, which benefits confinement. In this study, the latter has only been achieved in the low-triangularity hybrid plasmas, and can be attributed to low-density operation. Plasma rotation has been found to reduce core profile stiffness, and can explain an increase in profile peaking at small radius ρtor = 0.3.

  • 50. Beurskens, M. N. A.
    et al.
    Osborne, T. H.
    Horton, L. D.
    Frassinetti, Lorenzo
    KTH, Skolan för elektro- och systemteknik (EES), Fusionsplasmafysik.
    Groebner, R.
    Leonard, A.
    Lomas, P.
    Nunes, I.
    Saarelma, S.
    Snyder, P. B.
    Balboa, I.
    Bray, B.
    Crombe, K.
    Flanagan, J.
    Giroud, C.
    Giovannozzi, E.
    Kempenaars, M.
    Kohen, N.
    Loarte, A.
    Lonnroth, J.
    de la Luna, E.
    Maddison, G.
    Maggi, C.
    McDonald, D.
    McKee, G.
    Pasqualotto, R.
    Saibene, G.
    Sartori, R.
    Solano, E.
    Suttrop, W.
    Wolfrum, E.
    Walsh, M.
    Yan, Z.
    Zabeo, L.
    Zarzoso, D.
    Pedestal width and ELM size identity studies in JET and DIII-D; implications for ITER2009Inngår i: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 51, nr 12, s. 124051-Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    The dependence of the H-mode edge transport barrier width on normalized ion gyroradius (rho* = rho/a) in discharges with type I ELMs was examined in experiments combining data for the JET and DIII-D tokamaks. The plasma configuration as well as the local normalized pressure (beta), collisionality (nu*), Mach number and the ratio of ion and electron temperature at the pedestal top were kept constant, while rho* was varied by a factor of four. The width of the steep gradient region of the electron temperature (T-e) and density (n(e)) pedestals normalized to machine size showed no or only a weak trend with rho*. A rho(1/2) or rho(1) dependence of the pedestal width, given by some theoretical predictions, is not supported by the current experiments. This is encouraging for the pedestal scaling towards ITER as it operates at lower rho* than existing devices. Some differences in pedestal structure and ELM behaviour were, however, found between the devices; in the DIII-D discharges, the n(e) and T-e pedestal were aligned at high rho* but the ne pedestal shifted outwards in radius relative to T-e as rho* decreases, while on JET the profiles remained aligned while rho* was scanned by a factor of two. The energy loss at an ELM normalized to the pedestal energy increased from 10% to 40% as rho* increased by a factor of two in the DIII-D discharges but no such variation was observed in the case of JET. The measured pedestal pressures and widths were found to be consistent with the predictions from modelling based on peeling-ballooning stability theory, and are used to make projections towards ITER

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