We present an ultrafast neural network model, QLKNN, which predicts core tokamak transport heat and particle fluxes. QLKNN is a surrogate model based on a database of 3 × 108 flux calculations of the quasilinear gyrokinetic transport model, QuaLiKiz. The database covers a wide range of realistic tokamak core parameters. Physical features such as the existence of a critical gradient for the onset of turbulent transport were integrated into the neural network training methodology. We have coupled QLKNN to the tokamak modeling framework JINTRAC and rapid control-oriented tokamak transport solver RAPTOR. The coupled frameworks are demonstrated and validated through application to three JET shots covering a representative spread of H-mode operating space, predicting the turbulent transport of energy and particles in the plasma core. JINTRAC-QLKNN and RAPTOR-QLKNN are able to accurately reproduce JINTRAC-QuaLiKiz T i, e and ne profiles, but 3-5 orders of magnitude faster. Simulations which take hours are reduced down to only a few tens of seconds. The discrepancy in the final source-driven predicted profiles between QLKNN and QuaLiKiz is on the order of 1%-15%. Also the dynamic behavior was well captured by QLKNN, with differences of only 4%-10% compared to JINTRAC-QuaLiKiz observed at mid-radius, for a study of density buildup following the L-H transition. Deployment of neural network surrogate models in multi-physics integrated tokamak modeling is a promising route toward enabling accurate and fast tokamak scenario optimization, uncertainty quantification, and control applications. DOI dataset used for paper: 10.5281/zenodo.3497066

VL - 27 UR - https://arxiv.org/abs/1911.05617 IS - 2 U1 -FP

U2 -IMT

U5 - ec86515e5a6b89214cdee1922d2f857d ER - TY - JOUR T1 - Predictive multi-channel flux-driven modelling to optimise ICRH tungsten control and fusion performance in JET JF - Nuclear Fusion Y1 - 2020 A1 - Casson, F. J. A1 - Patten, H. A1 - Bourdelle, C. A1 - Breton, S. A1 - Citrin, J. A1 - Koechl, F. A1 - Sertoli, M. A1 - Angioni, C. A1 - Baranov, Y. A1 - Bilato, R. A1 - Belli, E. A1 - Challis, C. D. A1 - Corrigan, G. A1 - Czarnecka, A. A1 - Ficker, O. A1 - Frassinetti, L. A1 - Garzotti, L. A1 - Goniche, M. A1 - Graves, J. P. A1 - Johnson, T. A1 - Kirov, K. A1 - Knight, P. J. A1 - Lerche, E. A1 - Mantsinen, M. A1 - Mylnar, J. A1 - Valisa, M. A1 - JET Contributors AB - The evolution of the JET high performance hybrid scenario, including central accumulation of the tungsten (W) impurity, is reproduced with predictive multi-channel integrated modelling over multiple confinement times using first-principle based core transport models. Eight transport channels (Ti,Te,j,nD,nBe,nNi,nW, omega) are modelled predictively, with self-consistent sources, radiation and magnetic equilibrium, yielding a system with multiple non-linearities: This system can reproduce the observed radiative temperature collapse after several confinement times. W is transported inward by neoclassical convection driven by the main ion density gradients and enhanced by poloidal asymmetries due to centrifugal acceleration. The slow evolution of the bulk density profile sets the timescale for W accumulation. Modelling this phenomenon requires a turbulent transport model capable of accurately predicting particle and momentum transport (QuaLiKiz) and a neoclassical transport model including the effects of poloidal asymmetries (NEO) coupled to an integrated plasma simulator (JINTRAC). The modelling capability is applied to optimise the available actuators to prevent W accumulation, and to extrapolate in power and pulse length. Central NBI heating is preferred for high performance, but gives central deposition of particles and torque which increase the risk of W accumulation by increasing density peaking and poloidal asymmetry. The primary mechanism for ICRH to control W in JET is via its impact through turbulence in reducing main ion density peaking (which drives inward neoclassical convection), increased temperature screening and turbulent W diffusion. The anisotropy from ICRH also reduces poloidal asymmetry, but this effect is negligible in high rotation JET discharges. High power ICRH near the axis can sensitively mitigate against W accumulation, and dominant ion heating (e.g. He-3 minority) is predicted to provide more resilience to W accumulation than dominant electron heating (e.g. H minority) in the JET hybrid scenario. Extrapolation to DT plasmas finds 17.5 MW of fusion power and improved confinement compared to DD, due to reduced ion-electron energy exchange, and increased Ti/Te stabilisation of ITG instabilities. The turbulence reduction in DT increases density peaking and accelerates the arrival of W on axis; this may be mitigated by reducing the penetration of the beam particle source with an increased pedestal density. PB - IOP Publishing VL - 60 IS - 6 U1 - FP U2 - IMT U5 - 85e09691b3e9df9d0bb4bc6800d91b57 ER - TY - JOUR T1 - Isotope dependence of energy, momentum and particle confinement in tokamaks JF - Journal of Plasma Physics Y1 - 2020 A1 - Weisen, H. A1 - Maggi, C. F. A1 - Oberparleiter, M. A1 - Casson, F. J. A1 - Camenen, Y. A1 - Menmuir, S. A1 - Horvath, L. A1 - Auriemma, F. A1 - Bache, T. A1 - Marin, M. A1 - Bonanomi, N. A1 - Chankin, A. A1 - Delabie, E. A1 - Frassinetti, L. A1 - Garcia, J. A1 - Giroud, C. A1 - King, D. A1 - Lorenzini, R. A1 - Schneider, P. A. A1 - Siren, P. A1 - Varje, J. A1 - Viezzer, E. A1 - JET Contributors AB - The isotope dependence of plasma transport will have a significant impact on the performance of future D-T experiments in JET and ITER and eventually on the fusion gain and economics of future reactors. In preparation for future D-T operation on JET, dedicated experiments and comprehensive transport analyses were performed in H, D and H-D mixed plasmas. The analysis of the data has demonstrated an unexpectedly strong and favourable dependence of the global confinement of energy, momentum and particles in ELMy H-mode plasmas on the atomic mass of the main ion species, the energy confinement time scaling as tau(E) similar to A(0.5) (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045; JET Team, Nucl. Fusion, vol. 39, 1999, pp. 1227-1244), i.e. opposite to the expectations based only on local gyro-Bohm (GB) scaling, tau(E) similar to A(-0.5), and stronger than in the commonly used H-mode scaling for the energy confinement (Saibene et al., Nucl. Fusion, vol. 39, 1999, 1133; ITER Physics Basis, Nucl. Fusion, vol. 39, 1999, 2175). The scaling of momentum transport and particle confinement with isotope mass is very similar to that of energy transport. Nonlinear local GENE gyrokinetic analysis shows that the observed anti-GB heat flux is accounted for if collisions, ExB shear and plasma dilution with low-Z impurities (Be-9) are included in the analysis (E and B are, respectively the electric and magnetic fields). For L-mode plasmas a weaker positive isotope scaling tau(E) similar to A(0.14) has been found in JET (Maggi et al., Plasma Phys. Control. Fusion, vol. 60, 2018, 014045), similar to ITER97-L scaling (Kaye et al., Nucl. Fusion, vol. 37, 1997, 1303). Flux-driven quasi-linear gyrofluid calculations using JETTO-TGLF in L-mode show that local GB scaling is not followed when stiff transport (as is generally the case for ion temperature gradient modes) is combined with an imposed boundary condition taken from the experiment, in this case predicting no isotope dependence. A dimensionless identity plasma pair in hydrogen and deuterium L-mode plasmas has demonstrated scale invariance, confirming that core transport physics is governed, as expected, by the 4 dimensionless parameters rho*, nu*, beta, q (normalised ion Larmor radius, collisionality, plasma pressure and safety factor) consistently with global quasi-linear gyrokinetic TGLF calculations (Maggi et al., Nucl. Fusion, vol. 59, 2019, 076028). We compare findings in JET with those in different devices and discuss the possible reasons for the different isotope scalings reported from different devices. The diversity of observations suggests that the differences may result not only from differences affecting the core, e.g. heating schemes, but are to a large part due to differences in device-specific edge and wall conditions, pointing to the importance of better understanding and controlling pedestal and edge processes. VL - 86 IS - 5 U1 - FP U2 - IMT U5 - aeea7a42aad255ffb5c80fd74b345366 ER - TY - JOUR T1 - Flux-driven integrated modelling of main ion pressure and trace tungsten transport in ASDEX Upgrade JF - Nuclear Fusion Y1 - 2019 A1 - Linder, O. A1 - Citrin, J. A1 - Hogeweij, G. M. D. A1 - Angioni, C. A1 - Bourdelle, C. A1 - Casson, F. J. A1 - Fable, E. A1 - Ho, A. A1 - Koechl, F. A1 - Sertoli, M. A1 - EUROfusion MST1 Team A1 - ASDEX Upgrade Team AB -Neoclassical and turbulent heavy impurity transport in tokamak core plasmas are determined by main ion temperature, density and toroidal rotation profiles. Thus, in order to understand and prevent experimental behaviour of W accumulation, flux-driven integrated modelling of main ion heat and particle transport over multiple confinement times is a vital prerequisite. For the first time, the quasilinear gyrokinetic code QuaLiKiz is applied for successful predictions of core kinetic profiles in an ASDEX Upgrade H-mode discharge in the turbulence dominated region within the integrated modelling suite JETTO. Neoclassical contributions are calculated by NCLASS; auxiliary heat and particle deposition profiles due to NBI and ECRH are prescribed from previous analysis with TRANSP. Turbulent and neoclassical contributions are insufficient in explaining main ion heat and particle transport inside the q = 1 surface, necessitating the prescription of further transport coefficients to mimic the impact of MHD activity on central transport. The ion to electron temperature ratio at the simulation boundary at p tor=0.85 stabilizes ion scale modes while destabilizing ETG modes when significantly exceeding unity. Careful analysis of experimental measurements using Gaussian process regression techniques is carried out to explore reasonable uncertainties. In following trace W impurity transport simulations performed with additionally NEO, neoclassical transport under consideration of poloidal asymmetries alone is found to be insufficient to establish hollow central W density profiles. Reproduction of these conditions measured experimentally is found possible only when assuming the direct impact of a saturated (m, n) = (1, 1) MHD mode on heavy impurity transport.

VL - 59 IS - 1 U1 -FP

U2 -IMT

U5 - 6d42c99c474c747f17f4b44236cecb27 ER - TY - JOUR T1 - Application of Gaussian process regression to plasma turbulent transport model validation via integrated modelling JF - Nuclear Fusion Y1 - 2019 A1 - Ho, A. A1 - Citrin, J. A1 - Auriemma, F. A1 - Bourdelle, C. A1 - Casson, F. J. A1 - Kim, H. T. A1 - Manas, P. A1 - Szepesi, G. A1 - Weisen, H. A1 - JET Contributors AB -This paper outlines an approach towards improved rigour in tokamak turbulence transport model validation within integrated modelling. Gaussian process regression (GPR) techniques were applied for profile fitting during the preparation of integrated modelling simulations allowing for rigourous sensitivity tests of prescribed initial and boundary conditions as both fit and derivative uncertainties are provided. This was demonstrated by a JETTO integrated modelling simulation of the JET ITER-like-wall H-mode baseline discharge #92436 with the QuaLiKiz quasilinear turbulent transport model, which is the subject of extrapolation towards a deuterium–tritium plasma. The simulation simultaneously evaluates the time evolution of heat, particle, and momentum fluxes over ~10 confinement times, with a simulation boundary condition at rho tor=0.85. Routine inclusion of momentum transport prediction in multi-channel flux-driven transport modelling is not standard and is facilitated here by recent developments within the QuaLiKiz model. Excellent agreement was achieved between the fitted and simulated profiles for n e , T e , T i , and omega tor within 2x, but the simulation underpredicts the mid-radius T i and overpredicts the core n e and T e profiles for this discharge. Despite this, it was shown that this approach is capable of deriving reasonable inputs, including derivative quantities, to tokamak models from experimental data. Furthermore, multiple figures-of-merit were defined to quantitatively assess the agreement of integrated modelling predictions to experimental data within the GPR profile fitting framework.

VL - 59 IS - 5 U1 -FP

U2 -IMT

U5 - 9b651392bcad55886e0c0848df55a9f0 ER - TY - JOUR T1 - High Z neoclassical transport: Application and limitation of analytical formulae for modelling JET experimental parameters JF - Physics of Plasmas Y1 - 2018 A1 - Breton, S. A1 - Casson, F. J. A1 - Bourdelle, C. A1 - Angioni, C. A1 - Belli, E. A1 - Camenen, Y. A1 - Citrin, J. A1 - Garbet, X. A1 - Sarazin, Y. A1 - Sertoli, M. A1 - JET Contributors AB -Heavy impurities, such as tungsten (W), can exhibit strongly poloidally asymmetric density profiles in rotating or radio frequency heated plasmas. In the metallic environment of JET, the poloidal asymmetry of tungsten enhances its neoclassical transport up to an order of magnitude, so that neoclassical convection dominates over turbulent transport in the core. Accounting for asymmetries in neoclassical transport is hence necessary in the integrated modeling framework. The neoclassical drift kinetic code, NEO [E. Belli and J. Candy, Plasma Phys. Controlled Fusion P50, 095010 (2008)], includes the impact of poloidal asymmetries on W transport. However, the computational cost required to run NEO slows down significantly integrated modeling. A previous analytical formulation to describe heavy impurity neoclassical transport in the presence of poloidal asymmetries in specific collisional regimes [C. Angioni and P. Helander, Plasma Phys. Controlled Fusion 56, 124001 (2014)] is compared in this work to numerical results from NEO. Within the domain of validity of the formula, the factor for reducing the temperature screening due to poloidal asymmetries had to be empirically adjusted. After adjustment, the modified formula can reproduce NEO results outside of its definition domain, with some limitations: When main ions are in the banana regime, the formula reproduces NEO results whatever the collisionality regime of impurities, provided that the poloidal asymmetry is not too large. However, for very strong poloidal asymmetries, agreement requires impurities in the Pfirsch-Schlüter regime. Within the JETTO integrated transport code, the analytical formula combined with the poloidally symmetric neoclassical code NCLASS [W. A. Houlberg et al., Phys. Plasmas 4, 3230 (1997)] predicts the same tungsten profile as NEO in certain cases, while saving a factor of one thousand in computer time, which can be useful in scoping studies. The parametric dependencies of the temperature screening reduction due to poloidal asymmetries would need to be better characterised for this faster model to be extended to a more general applicability.

VL - 25 IS - 1 U1 -FP

U2 -IMT

U5 - 4124380d82634de2c37d95ae7f073ef4 ER - TY - JOUR T1 - Fast H isotope and impurity mixing in ion-temperature-gradient turbulence JF - Nuclear Fusion Y1 - 2018 A1 - Bourdelle, C. A1 - Camenen, Y. A1 - Citrin, J. A1 - Marin, M. A1 - Casson, F. J. A1 - Kochl, F. A1 - Maslov, M. A1 - JET Contributors AB - In ion-temperature-gradient (ITG) driven turbulence, the resonance condition leads to ion particle turbulent transport coefficients significantly larger than electron particle turbulent transport coefficients. This is shown in nonlinear gyrokinetic simulations and explained by an analytical quasilinear model. It is then illustrated by JETTO-QuaLiKiz integrated modelling. Large ion particle transport coefficients implies that the ion density profiles are uncorrelated to the corresponding ion source, allowing peaked isotope density profiles even in the absence of core source. This also implies no strong core accumulation of He ash. Furthermore, the relaxation time of the individual ion profiles in a multi-species plasma can be significantly faster than the total density profile relaxation time which is constrained by the electrons. This leads to fast isotope mixing and fast impurity transport in FM regimes. In trapped-electron- mode (TEM) turbulence, in presence of electron heating about twice the ion heating, the situation is the inverse: ion particle turbulent transport coefficients are smaller than their electron counterpart. VL - 58 IS - 7 U1 - FP U2 - IMT U5 - 412f415e9060f52a4a0e26b173073035 ER - TY - JOUR T1 - Tractable flux-driven temperature, density, and rotation profile evolution with the quasilinear gyrokinetic transport model QuaLiKiz JF - Plasma Physics and Controlled Fusion Y1 - 2017 A1 - Citrin, J. A1 - Bourdelle, C. A1 - Casson, F. J. A1 - Angioni, C. A1 - Bonanomi, N. A1 - Camenen, Y. A1 - Garbet, X. A1 - Garzotti, L. A1 - Gorler, T. A1 - Gurcan, O. D. A1 - Koechl, F. A1 - Imbeaux, F. A1 - Linder, O. A1 - van de Plassche, K. A1 - Strand, P. A1 - Szepesi, G. A1 - JET Contributors AB - Quasilinear turbulent transport models are a successful tool for prediction of core tokamak plasma profiles in many regimes. Their success hinges on the reproduction of local nonlinear gyrokinetic fluxes. We focus on significant progress in the quasilinear gyrokinetic transport model QuaLiKiz (Bourdelle et al 2016 Plasma Phys. Control. Fusion 58 014036), which employs an approximated solution of the mode structures to significantly speed up computation time compared to full linear gyrokinetic solvers. Optimisation of the dispersion relation solution algorithm within integrated modelling applications leads to flux calculations x10 6-7 faster than local nonlinear simulations. This allows tractable simulation of flux-driven dynamic profile evolution including all transport channels: ion and electron heat, main particles, impurities, and momentum. Furthermore, QuaLiKiz now includes the impact of rotation and temperature anisotropy induced poloidal asymmetry on heavy impurity transport, important for W-transport applications. Application within the JETTO integrated modelling code results in 1 s of JET plasma simulation within 10 h using 10 CPUs. Simultaneous predictions of core density, temperature, and toroidal rotation profiles for both JET hybrid and baseline experiments are presented, covering both ion and electron turbulence scales. The simulations are successfully compared to measured profiles, with agreement mostly in the 5%–25% range according to standard figures of merit. QuaLiKiz is now open source and available at www.qualikiz.com. VL - 59 UR - https://arxiv.org/abs/1708.01224 IS - 12 U1 - FP U2 - IMT U5 - 5234d3fadaa3c4d0ad98a555a43c362c ER - TY - JOUR T1 - Optimization of ICRH for core impurity control in JET-ILW JF - Nuclear Fusion Y1 - 2016 A1 - Lerche, E. A1 - Goniche, M. A1 - Jacquet, P. A1 - Van Eester, D. A1 - Bobkov, V. A1 - Colas, L. A1 - Giroud, C. A1 - Monakhov, I. A1 - Casson, F. J. A1 - Tsalas, M. A1 - Rimini, F. A1 - Angioni, C. A1 - Baruzzo, M. A1 - Blackman, T. A1 - Brezinsek, S. A1 - Brix, M. A1 - Czarnecka, A. A1 - Crombe, K. A1 - Challis, C. A1 - Dumont, R. A1 - Eriksson, J. A1 - Fedorczak, N. A1 - Graham, M. A1 - Graves, J. P. A1 - Gorini, G. A1 - Hobirk, J. A1 - Joffrin, E. A1 - Johnson, T. A1 - Kazakov, Y. A1 - Kiptily, V. A1 - Krivska, A. A1 - Lennholm, M. A1 - Lomas, P. A1 - Maggi, C. A1 - Mantica, P. A1 - Mathews, G. A1 - Mayoral, M. A1 - Meneses, L. A1 - Mlynar, J. A1 - Monier-Garbet, P. A1 - Nave, M. F. A1 - Noble, C. A1 - Nocente, M. A1 - Nunes, I. A1 - Ongena, J. A1 - Petravich, G. A1 - Petrzilka, V. A1 - Putterich, T. A1 - Reich, M. A1 - Santala, M. A1 - Solano, E. R. A1 - Shaw, A. A1 - Sips, G. A1 - Stamp, M. A1 - Tardocchi, M. A1 - Valisa, M. A1 - JET Contributors AB -Ion cyclotron resonance frequency (ICRF) heating has been an essential component in the development of high power H-mode scenarios in the Jet European Torus ITER-like wall (JET-ILW). The ICRF performance was improved by enhancing the antenna-plasma coupling with dedicated main chamber gas injection, including the preliminary minimization of RF-induced plasma-wall interactions, while the RF heating scenarios where optimized for core impurity screening in terms of the ion cyclotron resonance position and the minority hydrogen concentration. The impact of ICRF heating on core impurity content in a variety of 2.5 MA JET-ILW H-mode plasmas will be presented, and the steps that were taken for optimizing ICRF heating in these experiments will be reviewed.

VL - 56 UR - http://www.euro-fusionscipub.org/wp-content/uploads/2015/09/WPJET1PR1528.pdf IS - 3 U1 -FP

U2 -TP

U5 - d602ccdf3e42dd82b551d41759691058 ER - TY - JOUR T1 - Progress at JET in integrating ITER-relevant core and edge plasmas within the constraints of an ITER-like wall JF - Plasma Physics and Controlled Fusion Y1 - 2015 A1 - Giroud, C. A1 - Jachmich, S. A1 - Jacquet, P. A1 - Jarvinen, A. A1 - Lerche, E. A1 - Rimini, F. A1 - Aho-Mantila, L. A1 - Aiba, N. A1 - Balboa, I. A1 - da Silva Aresta Belo, P. A1 - Angioni, C. A1 - Beurskens, M. A1 - Brezinsek, S. A1 - Casson, F. J. A1 - Coffey, I. A1 - Cunningham, G. A1 - Delabie, E. A1 - Devaux, S. A1 - Drewelow, P. A1 - Frassinetti, L. A1 - Figueiredo, A. A1 - Huber, A. A1 - Hillesheim, J. A1 - Garzotti, L. A1 - Goniche, M. A1 - Groth, M. A1 - Hyun-Tae Kim A1 - Leyland, M. A1 - Lomas, P. A1 - Maddison, G. A1 - Marsen, S. A1 - Matthews, G. A1 - Meigs, A. A1 - Menmuir, S. A1 - Putterich, T. A1 - G. van Rooij A1 - Saarelma, S. A1 - Stamp, M. A1 - Urano, H. A1 - Webster, A. A1 - JET-EFDA Contributors AB - This paper reports the progress made at JET-ILW on integrating the requirements of the reference ITER baseline scenario with normalized confinement factor of 1, at a normalized pressure of 1.8 together with partially detached divertor whilst maintaining these conditions over many energy confinement times. The 2.5 MA high triangularity ELMy H-modes are studied with two different divertor configurations with D-gas injection and nitrogen seeding. The power load reduction with N seeding is reported. The relationship between an increase in energy confinement and pedestal pressure with triangularity is investigated. The operational space of both plasma configurations is studied together with the ELM energy losses and stability of the pedestal of unseeded and seeded plasmas. The achievement of stationary plasma conditions over many energy confinement times is also reported. VL - 57 UR - http://www.iop.org/Jet/fulltext/EFDP14021.pdf IS - 3 U1 - FP U2 - PDG U5 - 4b7265a10a94f029cf4f14cd047251e2 ER - TY - JOUR T1 - Overview of ASDEX Upgrade results JF - Nuclear Fusion Y1 - 2013 A1 - Stroth, U. A1 - Adamek, J. A1 - Aho-Mantila, L. A1 - Akaslompolo, S. A1 - Amdor, C. A1 - Angioni, C. A1 - Balden, M. A1 - Bardin, S. A1 - L. Barrera Orte A1 - Behler, K. A1 - Belonohy, E. A1 - Bergmann, A. A1 - Bernert, M. A1 - Bilato, R. A1 - Birkenmeier, G. A1 - Bobkov, V. A1 - Boom, J. A1 - Bottereau, C. A1 - Bottino, A. A1 - Braun, F. A1 - Brezinsek, S. A1 - Brochard, T. A1 - M. Brüdgam A1 - Buhler, A. A1 - Burckhart, A. A1 - Casson, F. J. A1 - Chankin, A. A1 - Chapman, I. A1 - Clairet, F. A1 - Classen, I.G.J. A1 - Coenen, J. W. A1 - Conway, G. D. A1 - Coster, D. P. A1 - Curran, D. A1 - da Silva, F. A1 - P. de Marné A1 - D'Inca, R. A1 - Douai, D. A1 - Drube, R. A1 - Dunne, M. A1 - Dux, R. A1 - Eich, T. A1 - Eixenberger, H. A1 - Endstrasser, N. A1 - Engelhardt, K. A1 - Esposito, B. A1 - Fable, E. A1 - Fischer, R. A1 - H. Fünfgelder A1 - Fuchs, J. C. A1 - K. Gál A1 - M. García Muñoz A1 - Geiger, B. A1 - Giannone, L. A1 - T. Görler A1 - da Graca, S. A1 - Greuner, H. A1 - Gruber, O. A1 - Gude, A. A1 - Guimarais, L. A1 - S. Günter A1 - Haas, G. A1 - Hakola, A. H. A1 - Hangan, D. A1 - Happel, T. A1 - T. Härtl A1 - Hauff, T. A1 - Heinemann, B. A1 - Herrmann, A. A1 - Hobirk, J. A1 - H. Höhnle A1 - M. Hölzl A1 - Hopf, C. A1 - Houben, A. A1 - Igochine, V. A1 - Ionita, C. A1 - Janzer, A. A1 - Jenko, F. A1 - Kantor, M. A1 - C.-P. Käsemann A1 - Kallenbach, A. A1 - S. Kálvin A1 - Kantor, M. A1 - Kappatou, A. A1 - Kardaun, O. A1 - Kasparek, W. A1 - Kaufmann, M. A1 - Kirk, A. A1 - H.-J. Klingshirn A1 - Kocan, M. A1 - Kocsis, G. A1 - Konz, C. A1 - Koslowski, R. A1 - Krieger, K. A1 - Kubic, M. A1 - Kurki-Suonio, T. A1 - Kurzan, B. A1 - Lackner, K. A1 - Lang, P. T. A1 - Lauber, P. A1 - Laux, M. A1 - Lazaros, A. A1 - Leipold, F. A1 - Leuterer, F. A1 - Lindig, S. A1 - Lisgo, S. A1 - Lohs, A. A1 - Lunt, T. A1 - Maier, H. A1 - Makkonen, T. A1 - Mank, K. A1 - M.-E. Manso A1 - Maraschek, M. A1 - Mayer, M. A1 - McCarthy, P. J. A1 - McDermott, R. A1 - Mehlmann, F. A1 - Meister, H. A1 - Menchero, L. A1 - Meo, F. A1 - Merkel, P. A1 - Merkel, R. A1 - Mertens, V. A1 - Merz, F. A1 - Mlynek, A. A1 - Monaco, F. A1 - Müller, S. A1 - H.W. Müller A1 - M. Münich A1 - Neu, G. A1 - Neu, R. A1 - Neuwirth, D. A1 - Nocente, M. A1 - Nold, B. A1 - Noterdaeme, J. M. A1 - Pautasso, G. A1 - Pereverzev, G. A1 - B. Plöckl A1 - Podoba, Y. A1 - Pompon, F. A1 - Poli, E. A1 - Polozhiy, K. A1 - Potzel, S. A1 - M. J. Pueschel A1 - Putterich, T. A1 - Rathgeber, S. K. A1 - Raupp, G. A1 - Reich, M. A1 - Reimold, F. A1 - Ribeiro, T. A1 - Riedl, R. A1 - Rohde, V. A1 - G. J. van Rooij A1 - Roth, J. A1 - Rott, M. A1 - Ryter, F. A1 - Salewski, M. A1 - Santos, J. A1 - Sauter, P. A1 - Scarabosio, A. A1 - Schall, G. A1 - Schmid, K. A1 - Schneider, P. A. A1 - Schneider, W. A1 - Schrittwieser, R. A1 - Schubert, M. A1 - Schweinzer, J. A1 - Scott, B. A1 - Sempf, M. A1 - Sertoli, M. A1 - Siccinio, M. A1 - Sieglin, B. A1 - Sigalov, A. A1 - Silva, A. A1 - Sommer, F. A1 - A. Stäbler A1 - Stober, J. A1 - Streibl, B. A1 - Strumberger, E. A1 - Sugiyama, K. A1 - Suttrop, W. A1 - Tala, T. A1 - Tardini, G. A1 - Teschke, M. A1 - Tichmann, C. A1 - Told, D. A1 - Treutterer, W. A1 - Tsalas, M. A1 - VanZeeland, M. A. A1 - Varela, P. A1 - Veres, G. A1 - Vicente, J. A1 - Vianello, N. A1 - Vierle, T. A1 - Viezzer, E. A1 - Viola, B. A1 - Vorpahl, C. A1 - Wachowski, M. A1 - Wagner, D. A1 - Wauters, T. A1 - Weller, A. A1 - Wenninger, R. A1 - Wieland, B. A1 - Willensdorfer, M. A1 - Wischmeier, M. A1 - Wolfrum, E. A1 - E. Würsching A1 - Yu, Q. A1 - Zammuto, I. A1 - Zasche, D. A1 - Zehetbauer, T. A1 - Zhang, Y. A1 - Zilker, M. A1 - Zohm, H. AB - The medium size divertor tokamak ASDEX Upgrade (major and minor radii 1.65 m and 0.5 m, respectively, magnetic-field strength 2.5 T) possesses flexible shaping and versatile heating and current drive systems. Recently the technical capabilities were extended by increasing the electron cyclotron resonance heating (ECRH) power, by installing 2 × 8 internal magnetic perturbation coils, and by improving the ion cyclotron range of frequency compatibility with the tungsten wall. With the perturbation coils, reliable suppression of large type-I edge localized modes (ELMs) could be demonstrated in a wide operational window, which opens up above a critical plasma pedestal density. The pellet fuelling efficiency was observed to increase which gives access to H-mode discharges with peaked density profiles at line densities clearly exceeding the empirical Greenwald limit. Owing to the increased ECRH power of 4 MW, H-mode discharges could be studied in regimes with dominant electron heating and low plasma rotation velocities, i.e. under conditions particularly relevant for ITER. The ion-pressure gradient and the neoclassical radial electric field emerge as key parameters for the transition. Using the total simultaneously available heating power of 23 MW, high performance discharges have been carried out where feed-back controlled radiative cooling in the core and the divertor allowed the divertor peak power loads to be maintained below 5 MW m −2 . Under attached divertor conditions, a multi-device scaling expression for the power-decay length was obtained which is independent of major radius and decreases with magnetic field resulting in a decay length of 1 mm for ITER. At higher densities and under partially detached conditions, however, a broadening of the decay length is observed. In discharges with density ramps up to the density limit, the divertor plasma shows a complex behaviour with a localized high-density region in the inner divertor before the outer divertor detaches. Turbulent transport is studied in the core and the scrape-off layer (SOL). Discharges over a wide parameter range exhibit a close link between core momentum and density transport. Consistent with gyro-kinetic calculations, the density gradient at half plasma radius determines the momentum transport through residual stress and thus the central toroidal rotation. In the SOL a close comparison of probe data with a gyro-fluid code showed excellent agreement and points to the dominance of drift waves. Intermittent structures from ELMs and from turbulence are shown to have high ion temperatures even at large distances outside the separatrix. VL - 53 UR - http://hdl.handle.net/11858/00-001M-0000-0026-E166-7 IS - 10 U1 - FP U2 - PDG U5 - 0b5b08fdc590c85cc01e6d1db1958848 ER - TY - JOUR T1 - Overview of toroidal momentum transport JF - Nuclear Fusion Y1 - 2011 A1 - Peeters, A.G. A1 - Angioni, C. A1 - Bortolon, A. A1 - Camenen, Y. A1 - Casson, F. J. A1 - Duval, B. A1 - Fiederspiel, L. A1 - Hornsby, W. A. A1 - Idomura, Y. A1 - Hein, T. A1 - Kluy, N. A1 - Mantica, P. A1 - Parra, F. I. A1 - Snodin, A. P. A1 - Szepesi, G. A1 - Strintzi, D. A1 - Tala, T. A1 - Tardini, G. A1 - P. de Vries A1 - Weiland, J. KW - ALCATOR-C-MOD KW - ANGULAR-MOMENTUM KW - CYCLOTRON WAVE KW - FLOWS KW - INJECTION KW - ION TEMPERATURE KW - NEUTRAL-BEAM INJECTION KW - OFF-LAYER KW - OHMIC H-MODE KW - PLASMA ROTATION KW - RADIAL ELECTRIC-FIELD KW - TEMPERATURE-GRADIENT MODE AB -Toroidal momentum transport mechanisms are reviewed and put in a broader perspective. The generation of a finite momentum flux is closely related to the breaking of symmetry (parity) along the field. The symmetry argument allows for the systematic identification of possible transport mechanisms. Those that appear to lowest order in the normalized Larmor radius (the diagonal part, Coriolis pinch, E x B shearing, particle flux, and up-down asymmetric equilibria) are reasonably well understood. At higher order, expected to be of importance in the plasma edge, the theory is still under development.

VL - 51 SN - 0029-5515 IS - 9 N1 - ISI Document Delivery No.: 818DPTimes Cited: 1Cited Reference Count: 114SI U1 -FP

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U5 - 2efb8b4ed885eb95aa643b3d2cfd6e6b ER - TY - JOUR T1 - Parametric dependences of momentum pinch and Prandtl number in JET JF - Nuclear Fusion Y1 - 2011 A1 - Tala, T. A1 - Salmi, A. A1 - Angioni, C. A1 - Casson, F. J. A1 - Corrigan, G. A1 - Ferreira, J. A1 - Giroud, C. A1 - Mantica, P. A1 - Naulin, V. A1 - Peeters, A.G. A1 - Solomon, W. M. A1 - Strintzi, D. A1 - Tsalas, M. A1 - Versloot, T. W. A1 - de Vries, P. C. A1 - Zastrow, K. D. KW - COLLISIONALITY KW - DENSITY PEAKING KW - H-MODES KW - PLASMAS KW - PROFILE KW - ROTATION KW - SHEAR KW - TOKAMAKS KW - TRANSPORT KW - TURBULENCE AB -Several parametric scans have been performed to study momentum transport on JET. A neutral beam injection modulation technique has been applied to separate the diffusive and convective momentum transport terms. The magnitude of the inward momentum pinch depends strongly on the inverse density gradient length, with an experimental scaling for the pinch number being - Rv(pinch)/chi(phi) = 1.2R/L(n) + 1.4. There is no dependence of the pinch number on collisionality, whereas the pinch seems to depend weakly on q-profile, the pinch number decreasing with increasing q. The Prandtl number was not found to depend either on R/L(n), collisionality or on q. The gyro-kinetic simulations show qualitatively similar dependence of the pinch number on R/L(n), but the dependence is weaker in the simulations. Gyro-kinetic simulations do not find any clear parametric dependence in the Prandtl number, in agreement with experiments, but the experimental values are larger than the simulated ones, in particular in L-mode plasmas. The extrapolation of these results to ITER illustrates that at large enough R/L(n) > 2 the pinch number becomes large enough (>3-4) to make the rotation profile peaked, provided that the edge rotation is non-zero. And this rotation peaking can be achieved with small or even with no core torque source. The absolute value of the core rotation is still very challenging to predict partly due to the lack of the present knowledge of the rotation at the plasma edge, partly due to insufficient understanding of 3D effects like braking and partly due to the uncertainties in the extrapolation of the present momentum transport results to a larger device.

VL - 51 SN - 0029-5515 IS - 12 N1 - ISI Document Delivery No.: 865YKTimes Cited: 0Cited Reference Count: 70 U1 -FP

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U5 - 76d59f479b968143a6d6d759b5aaecd1 ER -