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  • 151. Tala, T.
    et al.
    Lin, Y.
    Mantica, P.
    Nave, M. F. F.
    Sun, Y.
    Versloot, T. W.
    de Vries, P. C.
    Angioni, C.
    Asunta, O.
    Corrigan, G.
    Giroud, C.
    Ferreira, J.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Koslowski, H. R.
    Lerche, E.
    Liang, Y.
    Lönnroth, J.
    Naulin, V.
    Peeters, A. G.
    Rice, J. E.
    Salmi, A.
    Solomon, W.
    Strintzi, D.
    Tardini, G.
    Tsalas, M.
    van Eester, D.
    Weiland, J.
    Weisen, H.
    Zastrow, K.-D.
    Experimental Progress in Rotation Physics towards the Capability to Predict the Toroidal Rotation Profile2010Conference paper (Other academic)
  • 152. Tardocchi, M.
    et al.
    Gorini, G.
    Andersson-Sunden, E. A.
    Conroy, S.
    Ericsson, G.
    Johnson, M. Gatu
    Giacomelli, L.
    Hellesen, C.
    Hjalmarsson, A.
    Kallne, J.
    Ronchi, E.
    Sjostrand, H.
    Weiszflog, M.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Lamalle, P. U.
    Modeling of neutron emission spectroscopy in JET discharges with fast tritons from (T)D ion cyclotron heating2006In: Review of Scientific Instruments, ISSN 0034-6748, E-ISSN 1089-7623, Vol. 77, no 12Article in journal (Refereed)
    Abstract [en]

    The measurement of fast ion populations is one of the diagnostic capabilities provided by neutron emission spectroscopy (NES). NES measurements were carried out during JET trace tritium campaign with the magnetic proton recoil neutron spectrometer. A favorable plasma scenario is (T)D where the resulting 14 MeV neutron yield is dominated by suprathermal emission from energetic tritons accelerated by radio frequency at their fundamental cyclotron frequency. Information on the triton distribution function has been derived from NES data with a simple model based on two components referred to as bulk (B) and high energy (HE). The HE component is based on strongly anisotropic tritium distribution that can be used for routine best-fit analysis to provide tail temperature values (T-HE). This article addresses to what extent the T-HE values are model dependent by comparing the model above with a two-temperature (bi-) Maxwellian model featuring parallel and perpendicular temperatures. The bi-Maxwellian model is strongly anisotropic and frequently used for radio frequency theory.

  • 153.
    Tholerus, Emmi
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    A bump-on-tail model for Alfvén eigenmodes in toroidal plasmas2015Conference paper (Other academic)
    Abstract [en]

    Presented is a numerical model for solving the nonlinear dynamics of Alfvén eigenmodes and energetic ions self-consistently. The model is an extension of a previous bump-on-tail model [1,2], taking into account particle orbits and wave fields in realistic toroidal geometries. The model can be used in conjunction with an orbit averaged Monte Carlo code that handles heating and current drive (similar to e.g. the SELFO code), which enables modeling of the effects of MHD activity on plasma heating. For rapid particle tracing, the unperturbed guiding center orbits are described with canonical action-angle coordinates [3], and the perturbed Hamiltonian for wave-particle interaction is included as Fourier components in the same angles [4]. This allows the numerical integrator to take time steps over several transit periods, which efficiently resolves the relevant time scales for nonlinear wave-particle dynamics. The wave field is modeled by a static eigenfunction and a dynamic complex amplitude driven by the interactions with resonant and non-resonant particles.

    [1] E. Tholerus, T. Hellsten and T. Johnson, Phys. Plasmas 22, 082106 (2015)

    [2] S. Tholerus, T. Hellsten and T. Johnson, J. Phys.: Conf. Ser. 561, 012019 (2014)

    [3] A. N. Kaufman, Phys. Fluids 15, 1063 (1972)

    [4] H. L. Berk, B. N. Breizman and M. S. Pekker, Nucl. Fusion 35, 1713 (1995)

  • 154.
    Tholerus, Emmi
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Modeling the dynamics of toroidal Alfvén eigenmodes2013Conference paper (Other academic)
    Abstract [en]

    A model describing nonlinear dynamics of a single Alfvén eigenmode excited by an inverted energy distribution of energetic ions is presented, suitable for drift orbit averaged Monte Carlo codes. The nonlinear dynamics of the wave mode is modeled with a complex wave amplitude, and is characterized by the formation of coherent structures in phase space, caused by wave-particle interaction. The transition to a quasilinear regime is modeled with a phenomenological decorrelation of the wave-particle phase. As the decorrelation is increased the coherent phase-space structures diminishes, and frequency chirping events in the marginal stability region is limited. The strength of the decorrelation modifies the saturation level and saturation time of the eigenmode amplitude.

  • 155.
    Tholerus, Emmi
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    The effects of phase decorrelation on the dynamics of the bump-on-tail instability2015In: Physics of Plasmas, ISSN 1070-664X, E-ISSN 1089-7674, Vol. 22, no 8, article id 082106Article in journal (Refereed)
    Abstract [en]

    The dynamics of the bump-on-tail instability has been studied. The novelty of the work is the analysis of how the bump-on-tail dynamics is affected by an extrinsic stochastisation of the phase of the wave-particle interaction; here referred to as phase decorrelation. For this purpose, a nonlinear Monte Carlo model has been developed. When the characteristic time scale for macroscopic phase decorrelation becomes shorter than time scales of nonlinear wave-particle dynamics, the system may be described quasilinearly, with the phase decorrelation being replaced by a quasilinear diffusion coefficient in particle energy. A purely quasilinear Monte Carlo model, which is typically less computationally demanding than the fully nonlinear description due to the reduced dimensionality of phase space, has been developed for comparison. In this paper, parameter regimes, where the nonlinear and the quasilinear descriptions quantitatively agree on a macroscopic level, have been investigated, using combined theoretical and numerical analyses. Qualitative effects on the macroscopic dynamics by the presence of phase decorrelation and/or by structures of the energy distribution function in the proximity of the wave-particle resonance are also studied.

  • 156.
    Tholerus, Emmi
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    FOXTAIL: Modeling the nonlinear interaction between Alfven eigenmodes and energetic particles in tokamaks2017In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944, Vol. 214, p. 39-51Article in journal (Refereed)
    Abstract [en]

    FOXTAIL is a new hybrid magnetohydrodynamic-kinetic code used to describe interactions between energetic particles and Alfven eigenmodes in tokamaks with realistic geometries. The code Simulates the nonlinear dynamics of the amplitudes of individual eigenmodes and of a set of discrete markers in five dimensional phase space representing the energetic particle distribution. Action angle coordinates of the equilibrium system are used for efficient tracing of energetic particles, and the particle acceleration by the wave fields of the eigenmodes is Fourier decomposed in the same angles. The eigenmodes are described using temporally constant eigenfunctions with dynamic complex amplitudes. Possible applications of the code are presented, e.g., making a quantitative validity evaluation of the one-dimensional bump-on-tail approximation of the system. Expected effects of the fulfillment of the Chirikov criterion in two-mode scenarios have also been verified.

  • 157.
    Tholerus, Emmi
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    FOXTAIL: Modeling the nonlinear interaction between Alfvén eigenmodes and energetic particles in tokamaks2016In: Computer Physics Communications, ISSN 0010-4655, E-ISSN 1879-2944Article in journal (Refereed)
    Abstract [en]

    FOXTAIL is a new hybrid magnetohydrodynamic-kinetic code used to describe interactions between energetic particles and Alfvén eigenmodes in tokamaks with realistic geometries. The code simulates the nonlinear dynamics of the amplitudes of individual eigenmodes and of a set of discrete markers in five-dimensional phase space representing the energetic particle distribution. Action-angle coordinates of the equilibrium system are used for efficient tracing of energetic particles, and the particle acceleration by the wave fields of the eigenmodes is Fourier decomposed in the same angles. The eigenmodes are described using temporally constant eigenfunctions with dynamic complex amplitudes. Possible applications of the code are presented, e.g., making a quantitative validity evaluation of the one-dimensional bump-on-tail approximation of the system. Expected effects of the fulfillment of the Chirikov criterion in two-mode scenarios have also been verified.

  • 158.
    Tholerus, Emmi
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Modelling the Dynamics of Energetic Ions and MHD Modes Influenced by ICRH2016Report (Other academic)
    Abstract [en]

    FOXTAIL is a code used to describe the nonlinear interactions between toroidal Alfvén eigenmodes and an ensemble of resonant energetic particles in tokamaks with realistic geometries. This report introduces an extension of the code, including effects from ion cyclotron resonance heating (ICRH) of energetic ions using a quasilinear diffusion operator in adiabatic invariant space. First results of the effects of ICRH diffusion on the system consisting of a single Alfvén eigenmode linearly excited by resonant ions are presented. It is shown that the presence of ICRH diffusion allows for the mode amplitude to grow larger than in the case of nonlinear saturation in the absence of sources and sinks. Gradually increasing the strength of ICRH diffusion also decreases the linear growth rate of the mode. Both these phenomena are previously observed also for the case of a finite phase decorrelation operator in bump-on-tail systems with a single eigenmode.

  • 159.
    Tholerus, Simon
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Comparisons of the nonlinear and the quasilinear model for the bump-on-tail instability with phase decorrelation2014Conference paper (Refereed)
    Abstract [en]

    The dynamics of discrete global modes in a toroidal plasma interacting with an energetic particle distribution is studied, and in particular when the dynamics of the system using the nonlinear and quasilinear descriptions are macroscopically similar. The dynamics can be described with a nonlinear bump-on-tail model in a two-dimensional phase space of particles. A Monte Carlo framework is developed for this model with an included decorrelation of the wave-particle phase, which is used to model extrinsic stochastisation of the wave-particle interactions. From this description, a quasilinear version of the model is also developed, which is described by a diffusive process in energy space due to the added phase decorrelation. Due to the reduced dimensionality of phase space, the quasilinear description is typically less computationally demanding than the nonlinear description. The purpose of the studies is to find conditions when a quasilinear model sufficiently describes the same phenomena of the wave-plasma interactions as a nonlinear model does. Via numerical and theoretical parameter studies, regimes where the two models overlap macroscopically are found. These regimes exist above a given threshold of the strength of the decorrelation, where coherent phase space structures are destroyed on time scales shorter than characteristic time scales of nonlinear particle motion in phase space close to the wave-particle resonance. Specifically for the quasilinear model, a theoretical value of the time scale of quasilinear flattening is derived and numerically verified.

  • 160.
    Vallejos, Pablo
    et al.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    An iterative method to include spatial dispersion for waves in nonuniform plasmas using wavelet decomposition2016In: Journal of Physics, Conference Series, ISSN 1742-6588, E-ISSN 1742-6596, Vol. 775, no 1, article id 012016Article in journal (Refereed)
    Abstract [en]

    A novel method for solving wave equations with spatial dispersion is presented, suitable for applications to ion cyclotron resonance heating. The method splits the wave operator into a dispersive and a non-dispersive part. The latter can be inverted with e.g. finite element methods. The spatial dispersion is evaluated using a wavelet representation of the dielectric kernel and added by means of iteration. The method has been successfully tested on a low frequency kinetic Alfvén wave with second order Larmor radius effects in a nonuniform plasma slab.

  • 161. Van Eester, D.
    et al.
    Lerche, E.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ongena, J.
    Mayoral, M. -L
    Frigione, D.
    Sozzi, C.
    Calabro, G.
    Lennholm, M.
    Beaumont, P.
    Blackman, T.
    Brennan, D.
    Brett, A.
    Cecconello, M.
    Coffey, I.
    Coyne, A.
    Crombe, K.
    Czarnecka, A.
    Felton, R.
    Gatu Johnson, M.
    Giroud, C.
    Gorini, G.
    Hellesen, C.
    Jacquet, P.
    Kazakov, Y.
    Kiptily, V.
    Knipe, S.
    Krasilnikov, A.
    Lin, Y.
    Maslov, M.
    Monakhov, I.
    Noble, C.
    Nocente, M.
    Pangioni, L.
    Proverbio, I.
    Stamp, M.
    Studholme, W.
    Tardocchi, M.
    Versloot, T. W.
    Vdovin, V.
    Whitehurst, A.
    Wooldridge, E.
    Zoita, V.
    Mode conversion heating in JET plasmas with multiple mode conversion layers2010In: 37th EPS Conference on Plasma Physics 2010, EPS 2010: Volume 3, 2010, p. 1816-1819Conference paper (Refereed)
  • 162. Van Eester, D.
    et al.
    Lerche, E.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ongena, J.
    Mayoral, M. -L
    Frigione, D.
    Sozzi, C.
    Calabro, G.
    Lennholm, M.
    Beaumont, P.
    Blackman, T.
    Brennan, D.
    Brett, A.
    Cecconello, M.
    Coffey, I.
    Coyne, A.
    Crombe, K.
    Czarnecka, A.
    Felton, R.
    Johnson, M. G.
    Giroud, C.
    Gorini, G.
    Hellesen, C.
    Jacquet, P.
    Kazakov, Y.
    Kiptily, V.
    Knipe, S.
    Krasilnikov, A.
    Lin, Y.
    Maslov, M.
    Monakhov, I.
    Noble, C.
    Nocente, M.
    Pangioni, L.
    Proverbio, I.
    Stamp, M.
    Studholme, W.
    Tardocchi, M.
    Versloot, T. W.
    Vdovin, V.
    Whitehurst, A.
    Wooldridge, E.
    Zoita, V.
    Enhancing the mode conversion efficiency in JET plasmas with multiple mode conversion layers2011In: AIP Conf. Proc., 2011, p. 301-308Conference paper (Refereed)
    Abstract [en]

    The constructive interference effect described by Fuchs et al. [1] shows that the mode conversion and thereby the overall heating efficiency can be enhanced significantly when an integer number of fast wave wavelengths can be folded in between the high field side fast wave cutoff and the ion-ion hybrid layer(s) at which the ion Bernstein or ion cyclotron waves are excited. This effect was already experimentally identified in ( 3He)-D plasmas [2] and was recently tested in ( 3He)-H JET plasmas. The latter is an 'inverted' scenario, which differs significantly from the ( 3He)-D scenarios since the mode-conversion layer is positioned between the low field side edge of the plasma and the ion-cyclotron layer of the minority 3He ions (whereas the order in which a wave entering the plasma from the low field side encounters these layers is inverted in a 'regular' scenario), and because much lower 3He concentrations are needed to achieve the mode-conversion heating regime. The presence of small amounts of 4He and D in the discharges gave rise to an additional mode conversion layer on top of the expected one associated with 3He-H, which made the interpretation of the results more complex but also more interesting: Three different regimes could be distinguished as a function of X[ 3He], and the differing dynamics at the various concentrations could be traced back to the presence of these two mode conversion layers and their associated fast wave cutoffs. Whereas (1-D and 2-D) numerical modeling yields quantitative information on the RF absorptivity, recent analytical work by Kazakov [3] permits to grasp the dominant underlying wave interaction physics.

  • 163. Van Eester, D.
    et al.
    Lerche, E.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Hellsten, Torbjörn
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Ongena, J.
    Mayoral, M-L
    Frigione, D.
    Sozzi, C.
    Calabro, G.
    Lennholm, M.
    Beaumont, P.
    Blackman, T.
    Brennan, D.
    Brett, A.
    Cecconello, M.
    Coffey, I.
    Coyne, A.
    Crombe, K.
    Czarnecka, A.
    Felton, R.
    Johnson, M. Gatu
    Giroud, C.
    Gorini, G.
    Hellesen, C.
    Jacquet, P.
    Kazakov, Ye
    Kiptily, V.
    Knipe, S.
    Krasilnikov, A.
    Lin, Y.
    Maslov, M.
    Monakhov, I.
    Noble, C.
    Nocente, M.
    Pangioni, L.
    Proverbio, I.
    Stamp, M.
    Studholme, W.
    Tardocchi, M.
    Versloot, T. W.
    Vdovin, V.
    Whitehurst, A.
    Wooldridge, E.
    Zoita, V.
    Minority and mode conversion heating in (He-3)-H JET plasmas2012In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 54, no 7, p. 074009-Article in journal (Refereed)
    Abstract [en]

    Radio frequency (RF) heating experiments have recently been conducted in JET (He-3)-H plasmas. This type of plasmas will be used in ITER's non-activated operation phase. Whereas a companion paper in this same PPCF issue will discuss the RF heating scenario's at half the nominal magnetic field, this paper documents the heating performance in (He-3)-H plasmas at full field, with fundamental cyclotron heating of He-3 as the only possible ion heating scheme in view of the foreseen ITER antenna frequency bandwidth. Dominant electron heating with global heating efficiencies between 30% and 70% depending on the He-3 concentration were observed and mode conversion (MC) heating proved to be as efficient as He-3 minority heating. The unwanted presence of both He-4 and D in the discharges gave rise to 2 MC layers rather than a single one. This together with the fact that the location of the high-field side fast wave (FW) cutoff is a sensitive function of the parallel wave number and that one of the locations of the wave confluences critically depends on the He-3 concentration made the interpretation of the results, although more complex, very interesting: three regimes could be distinguished as a function of X[He-3]: (i) a regime at low concentration (X[He-3] < 1.8%) at which ion cyclotron resonance frequency (ICRF) heating is efficient, (ii) a regime at intermediate concentrations (1.8 < X[He-3] < 5%) in which the RF performance is degrading and ultimately becoming very poor, and finally (iii) a good heating regime at He-3 concentrations beyond 6%. In this latter regime, the heating efficiency did not critically depend on the actual concentration while at lower concentrations (X[He-3] < 4%) a bigger excursion in heating efficiency is observed and the estimates differ somewhat from shot to shot, also depending on whether local or global signals are chosen for the analysis. The different dynamics at the various concentrations can be traced back to the presence of 2 MC layers and their associated FW cutoffs residing inside the plasma at low He-3 concentration. One of these layers is approaching and crossing the low-field side plasma edge when 1.8 < X[He-3] < 5%. Adopting a minimization procedure to correlate the MC positions with the plasma composition reveals that the different behaviors observed are due to contamination of the plasma. Wave modeling not only supports this interpretation but also shows that moderate concentrations of D-like species significantly alter the overall wave behavior in He-3-H plasmas. Whereas numerical modeling yields quantitative information on the heating efficiency, analytical work gives a good description of the dominant underlying wave interaction physics.

  • 164. Versloot, Thijs W.
    et al.
    Sartori, Roberta
    Rimini, Fernanda
    de Vries, Peter C.
    Saibene, Gabriella
    Parail, Vassili
    Beurskens, Mark N. A.
    Boboc, Alexander
    Budny, Robert
    Crombé, Kristel
    de la Luna, Elena
    Durodie, Frederic
    Eich, Thomas
    Giroud, Carine
    Kiptily, Vasily
    Johnson, Thomas
    Uppsala University, Association EURATOM-VR, Uppsala, Sweden.
    Mantica, Paula
    Mayoral, Marie-Line
    McDonald, Darren C.
    Monakov, Igor
    Nave, M. F. F.
    Voitsekhovitch, Irena
    Zastrow, Klaus-Dieter
    Comparison between dominant NB and dominant IC heated ELMy H-mode discharges in JET2011In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 51, no 10, p. 103033-Article in journal (Refereed)
    Abstract [en]

    The experiment described in this paper is aimed at characterization of ELMy H-mode discharges with varying momentum input, rotation, power deposition profiles and ion to electron heating ratio obtained by varying the proportion between ion cyclotron (IC) and neutral beam (NB) heating. The motivation for the experiment was to verify if the basic confinement and transport properties of the baseline ITER H-mode are robust to these changes, and similar to those derived mostly from dominant NB heated H-modes. No significant difference in the density and temperature profiles or in the global confinement were found. Although ion temperature profiles were seen to be globally stiff, some variation of stiffness was obtained in the experiment by varying the deposition profiles, but not one that could significantly affect the profiles in terms of global confinement. This analysis shows the thermal plasma energy confinement enhancement factor to be independent of the heating mix, for the range of conditions explored. Moreover, the response of the global confinement to changes in density and power were also independent of heating mix, reflecting the changes in the pedestal, which is in agreement with globally stiff profiles. Consistently, the pedestal characteristics (pressure and width) and their dependences on global parameters such as density and power were the same during NB only or with predominant IC heating.

  • 165. Voitsekhovitch, I.
    et al.
    Sips, A. C. C.
    Alper, B.
    Beurskens, M.
    Coffey, I.
    Conboy, J.
    Gerbaud, T.
    Giroud, C.
    Johnson, Thomas
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Koechl, F.
    de la Luna, E.
    McDonald, D. C.
    Pavlenko, I.
    Pereverzev, G. V.
    Popovichev, S.
    Saveliev, A. N.
    Sergienko, G.
    Sharapov, S.
    Stamp, M.
    Modelling of the JET current ramp-up experiments and projection to ITER2010In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 52, no 10, p. 105011-Article in journal (Refereed)
    Abstract [en]

    The current ramp-up phase of ITER demonstration discharges, performed at JET, is analysed and the capability of the empirical L-mode Bohm-gyroBohm and Coppi-Tang transport models as well as the theory-based GLF23 model to predict the temperature evolution in these discharges is examined. The analysed database includes ohmic (OH) plasmas with various current ramp rates and plasma densities and the L-mode plasmas with the ion cyclotron radio frequency (ICRF) and neutral beam injection (NB!) heating performed at various ICRF resonance positions and NBI heating powers. The emphasis of this analysis is a data consistency test, which is particularly important here because some parameters, useful for the transport model validation, are not measured in OH and ICRF heated plasmas (e.g. ion temperature, effective charge). The sensitivity of the predictive accuracy of the transport models to the unmeasured data is estimated. It is found that the Bohm-gyroBohm model satisfactorily predicts the temperature evolution in discharges with central heating (the rms deviation between the simulated and measured temperature is within 15%), but underestimates the thermal electron transport in the OH and off-axis ICRF heated discharges. The Coppi-Tang model strongly underestimates the thermal transport in all discharges considered. A re-normalization of these empirical models for improving their predictive capability is proposed. The GLF23 model, strongly dependent on the ion temperature gradient and tested only for NBI heated discharges with measured ion temperatures, predicts accurately the temperature in the low power NBI heated discharge (rms < 10%) while the discrepancy with the data increases at high power. Based on the analysis of the JET discharges, the modelling of the current ramp-up phase for the H-mode ITER scenario is performed with particular emphasis on the sensitivity of the sawtooth-free duration of this phase to transport model.

  • 166. von Thun, C. Perez
    et al.
    Perona, A.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Reich, M.
    Sharapov, S. E.
    Kiptily, V. G.
    Cecconello, M.
    Salmi, A.
    Goloborod'ko, V. Ya
    Pinches, S. D.
    Garcia-Munoz, M.
    Darrow, D.
    Brix, M.
    Voitsekhovitch, I.
    Numerical simulation of fast ion loss detector measurements for fishbones on JET2011In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 51, no 5, p. 053003-Article in journal (Refereed)
    Abstract [en]

    A synthetic diagnostic model for the simulation of energy and pitch angle resolved measurements of fast ion losses obtained by 2D scintillation-type detectors is presented and subsequently tested on a JET discharge with fishbones (previously documented in Perez von Thun et al 2010 Nucl. Fusion 50 084009). The simulated energy and pitch angle distributions at the detector are found to be in excellent agreement with the measurements. The simulations further suggest that nearly all the fast ion losses take place in the early growth phase of the fishbone cycle, and reach their maximum well ahead of the magnetic perturbation peak.

  • 167. von Thun, C. Perez
    et al.
    Perona, A.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sharapov, S. E.
    Reich, M.
    Kiptily, V. G.
    Cecconello, M.
    Salmi, A.
    Goloborod'ko, V. Ya
    Pinches, S. D.
    Garcia-Munoz, M.
    Darrow, D.
    Brix, M.
    Voitsekhovitch, I.
    MeV-range fast ion losses induced by fishbones on JET2010In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 50, no 8, p. 084009-Article in journal (Refereed)
    Abstract [en]

    Energy and pitch angle resolved measurements of highly energetic (megaelectronvolt (MeV) range) suprathermal ions ejected from the plasma through interaction with fishbone oscillations are presented. The measurements are obtained with a 2D scintillator probe diagnostic installed on JET, which is designed to detect lost ions only above a certain energy threshold (E-min,E- D similar to 200 keV). In the case reported here the lost ions are identified as fast protons which had been accelerated to high energies by ICRF minority heating. The energy of the lost protons (similar to 0.5-4 MeV) is approximately one order of magnitude higher than the energy of the injected beam ions (maximum 130 keV) driving the fishbone. Losses arriving at the probe are enhanced by about a factor 10-20 with respect to MHD-quiescent levels, and are found to increase quadratically with the fishbone amplitude. Using a number of simplifying assumptions, numerical simulations have been performed which combine the HAGIS, MISHKA and SELFO codes (where the distribution function predicted by SELFO has been validated against neutral particle analyser measurements). The losses are found to originate from orbit stochastic diffusion of trapped protons near the plasma boundary or from counter-passing protons deep in the plasma core, which transit under the influence of the fishbone into an unconfined trapped orbit. The simulations show further that the losses are of non-resonant type. The simulated energy and pitch angle distribution of the losses, the temporal behaviour of the losses during a fishbone cycle and the scaling of the losses with the fishbone amplitude are compared with experiment. The simulation results are mostly in broad agreement with experiment, but some of the predictions could not be reconciled with experiment using this model.

  • 168. Westerhof, E.
    et al.
    Sauter, O.
    Mayoral, M. L.
    Howell, D. F.
    Mantsinen, M. J.
    Nave, M. F. F.
    Alper, B.
    Angioni, C.
    Belo, P.
    Buttery, R. J.
    Gondhalekar, A.
    Hellsten, Torbjörn A. K.
    KTH, Superseded Departments, Alfvén Laboratory.
    Hender, T. C.
    Johnson, Thomas J.
    KTH, Superseded Departments, Alfvén Laboratory.
    Lamalle, P.
    Maraschek, M. E.
    McClements, K. G.
    Nguyen, F.
    Pecquet, A. L.
    Podda, S.
    Rapp, J.
    Sharapov, S. E.
    Zabiego, M.
    Efda Jet Workprogramme,
    Control of sawteeth and triggering of NTMs with ion cyclotron resonance frequency waves in JET2002In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 42, no 11, p. 1324-1334Article in journal (Refereed)
    Abstract [en]

    A new scenario to delay or prevent neoclassical tearing mode (NTM) onset is presented. By active sawtooth destabilization, short period and low amplitude sawteeth are generated, such that the sawtooth produced NTM seed island is reduced and the threshold normalized plasma pressure for triggering of NTMs, beta(Nonset), is increased. The scenario has been explored experimentally in the Joint European Torus (JET). Ion cyclotron resonance frequency (ICRF) waves tuned to the 2nd harmonic H-minority resonance have been used for sawtooth control. Whereas ICRF waves generally induce sawtooth stabilization, favouring the triggering of NTMs and reducing beta(Nonset), the present experiments show that by toroidally directed waves, ion cyclotron current drive is produced, and that sawteeth can be destabilized by careful positioning of the 2nd harmonic H resonance layer with respect to the sawtooth inversion radius. As a result, NTM onset is delayed and beta(Nonset) is increased above its value obtained in discharges with additional heating from neutral beam injection alone.

  • 169. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas J.
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Sharapov, S. E.
    Testa, D. S.
    Kurbet, I. I.
    Suprathermal deuterium ions produced by nuclear elastic scattering of ICRH driven He-3 ions in JET plasmas2007In: Plasma Physics and Controlled Fusion, ISSN 0741-3335, E-ISSN 1361-6587, Vol. 49, no 11, p. 1747-1766Article in journal (Refereed)
    Abstract [en]

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

  • 170. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
    Kiptily, V. G.
    Sharapov, S. E.
    Simulations to elucidate suprathermal deuterium ion tail observed in He3 minority ICRF heated JET plasmas2008In: EPS Conf. Plasma Phys., EPS - Europhys. Conf. Abstr., 2008, no 1, p. 501-504Conference paper (Refereed)
  • 171. Zaitsev, F. S.
    et al.
    Gondhalekar, A.
    Johnson, Thomas Joe
    KTH, School of Electrical Engineering (EES), Fusion Plasma Physics. KTH, School of Electrical Engineering (EES), Centres, Alfvén Laboratory Centre for Space and Fusion Plasma Physics.
    Sharapov, S. E.
    Testa, D. S.
    Kurbet, I. I.
    Simulation of deuteron tails produced by close collisions with ICRH Accelerated He3 ions in JET2006In: EPS Conf. Plasma Phys., EPS, 2006, p. 412-415Conference paper (Refereed)
1234 151 - 171 of 171
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