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ABSTRACT: Good confinement at low values of q0.95 and at high values of total beta is crucial for the economical development of a fusion reactor. It is shown that an extension of the domain of H-mode operation in JET to values of q0.95 ≥ 2.0 (i.e. a plasma current of 3 MA and a toroidal field of 1.2 T), with additional heating at a power of up to 12 MW, does not lead to an appreciable confinement deterioration when q0.95 is decreased, for total beta values of up to 4.2%, corresponding to 90% of the Troyon limit. Pressure profiles with a peaking factor p0/p ~ 3 can be achieved for such low values of q0.95. Analysis of the MHD equilibrium and stability shows that the conditions of marginal ballooning instability near the plasma edge are reached in a discharge with β ~ 4.2%.
Nuclear Fusion 01/2011; 30(10):2157. · 4.09 Impact Factor
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38th EPS Conference on Plasma Physics, Strasbourg, France; 01/2011
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ABSTRACT: In nonlinear MHD simulations of edge localized modes (ELMs) with the code JOREK, a strong m = n = 0 poloidal flow localized in the H-mode pedestal region shears density filaments off the separatrix. This flow is nonlinearly induced by the ballooning instability (Huysmans and Czarny 2007 Nucl. Fusion 47 659, Huysmans et al 2009 Plasma Phys. Control. Fusion 51 124012). An approach of the reduced resistive MHD equations used in JOREK leads to an analytical interpretation of the equilibrium flow in both circular and X-point plasmas. Transitions between two different flow structures have been found. Similar transitions between equilibrium flow states had been predicted by Strauss (1995 Phys. Plasmas 2 1229). Finally, results concerning the influence of the equilibrium flow on the linear and nonlinear stabilities of the ELM are presented. ELM-like multiple crashes were simulated.
Plasma Physics and Controlled Fusion 05/2010; 52(7):075006. · 2.42 Impact Factor
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J.F. Artaud,
V. Basiuk,
F. Imbeaux,
M. Schneider,
J. Garcia,
G. Giruzzi,
P. Huynh,
T. Aniel,
F. Albajar,
J.M. Ané, [......],
F. Köchl,
J. Lister,
X. Litaudon,
P. Maget,
R. Masset,
B. Pégourié,
Y. Peysson,
P. Thomas,
E. Tsitrone,
F. Turco
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ABSTRACT: CRONOS is a suite of numerical codes for the predictive/interpretative simulation of a full tokamak discharge. It integrates, in a modular structure, a 1D transport solver with general 2D magnetic equilibria, several heat, particle and impurities transport models, as well as heat, particle and momentum sources. This paper gives a first comprehensive description of the CRONOS suite: overall structure of the code, main available models, details on the simulation workflow and numerical implementation. Some examples of applications to the analysis of experimental discharges and the predictions of ITER scenarios are also given.
Nuclear Fusion 03/2010; 50(4):043001. · 4.09 Impact Factor
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ABSTRACT: The plasma response to externally imposed resonant magnetic perturbations (RMPs) is investigated through quasi-linear MHD modelling in the case where the resonant surfaces are located in the pedestal of an H-mode plasma. The pedestal is a particular region regarding the question of plasma response to RMPs because of its strong E × B and electron diamagnetic rotations. It is found that a strong rotational screening takes place in most of the pedestal. The RMPs may, however, penetrate in a narrow layer at the very edge, where the plasma is cold and resistive. The possibility that one harmonic of the RMPs may also penetrate if its resonant surface is at a particular location, close to the top of the pedestal, where the E × B and electron diamagnetic rotations compensate each other, is discussed. Finally, the RMPs are found to produce some additional transport, even though they do not penetrate.
Nuclear Fusion 02/2010; 50(3):034002. · 4.09 Impact Factor
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ABSTRACT: A new concept of steady-state scenario for tokamak reactors is proposed. It is based on cyclic operations, alternating phases of positive and negative loop voltage with no magnetic flux consumption on average. Localized non-inductive current drive by electron cyclotron waves is used to trigger and sustain an internal transport barrier (ITB), whereas neutral beam current drive is used to periodically recharge the tokamak transformer. The fact of operating in cycles relaxes the hard constraint of simultaneous fusion performance maximization and full non-inductive operation, within the MHD stability limits. Integrated modelling simulations are performed to apply this concept for the ITER steady-state regime. A linear MHD analysis of the instabilities that could appear in this type of scenario is performed, showing that MHD stability would be strongly improved with respect to a steady regime with a strong ITB.
Nuclear Fusion 01/2010; 50(2):025025. · 4.09 Impact Factor
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R. Sabot,
A. Macor,
C. Nguyen,
J. Decker,
D. Elbeze,
L.-G. Eriksson,
X. Garbet,
M. Goniche, G. Huysmans,
Y. Ladroit,
P. Maget,
J.L. Segui
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ABSTRACT: Energetic particles driven modes are one of the concerns for burning plasmas. On Tore-Supra, fast ions and electrons are generated by the RF heating systems and fast particles driven modes are detected with ECE and reflectometry diagnostics. In ICRH heated plasmas, modes are observed in the acoustic frequency range 30–70 kHz. The observed frequency agrees with the frequency predicted for both geodesic acoustic modes and beta Alfvén eigenmodes (BAE), but their structure and their excitation by fast ions advocate for an identification as BAE. Experimental analysis displays the existence of an excitation threshold depending on various parameters such as the ICRH power, the minority fraction and the density, in agreement with the theoretical prediction resulting from a balance between the fast ion drive and Landau damping by thermal ions. In lower hybrid current drive plasmas, electron fishbones have been detected below 20 kHz. Evolution of the fishbone modes with LH power was studied. Precession fishbones are observed at moderate power to be replaced by a mode at diamagnetic frequency at higher power. Precession fishbone frequency exhibits periodical jumps (0.1 s). These jumps are linked to spontaneous transitions between modes at different wavenumbers and a redistribution of the fast electrons in resonance with these modes. The number of excited modes and their wave number change with the LH power.
Nuclear Fusion 07/2009; 49(8):085033. · 4.09 Impact Factor
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M. Bécoulet, G. Huysmans,
X. Garbet,
E. Nardon,
D. Howell,
A. Garofalo,
M. Schaffer,
T. Evans,
K. Shaing,
A. Cole,
J.-K. Park,
P. Cahyna
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ABSTRACT: Non-linear reduced MHD modelling of the toroidally rotating plasma response to resonant magnetic perturbations (RMPs) is presented for DIII-D and ITER-like typical parameter and RMP coils. The non-linear cylindrical reduced MHD code was adapted to take into account toroidal rotation and plasma braking mechanisms such as resonant one (~j × B) and the neoclassical toroidal viscosity (NTV) calculated for low collisionality regimes ('1/ν' and 'ν'). Counter toroidal rotation by NTV is predicted for ITER with the proposed RMP coils in 1/ν-limit. Resonant braking is localized near resonant surfaces and is weak compared with NTV in the 1/ν regime for typical DIII-D and ITER parameters. Toroidal rotation leads to the effective screening of RMPs that is larger for stronger rotation and lower resistivity, resulting mainly in central islands screening. Non-resonant helical harmonics (q ≠ m/n) in RMP spectrum are not influenced by plasma rotation, and hence penetrate and are important in NTV mechanism.
Nuclear Fusion 07/2009; 49(8):085011. · 4.09 Impact Factor
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ABSTRACT: The COMPASS tokamak, recently transferred from UKAEA Culham to IPP Prague, is equipped with a set of saddle coils for producing controlled resonant magnetic perturbations (RMPs). In the future experimental programme of COMPASS we plan to focus on studies of RMPs, especially in view of their application as an ELM control mechanism and their considered use in ITER. In the present contribution we describe the preparatory calculations for the planned experiments. We computed the spectra of perturbations for several different equilibria predicted by MHD simulations and determined the positions and sizes of the resulting islands. It is shown how the saddle coils of COMPASS can be adapted to our equilibria to obtain good island overlap at the edge, which is believed to be a key component in the ELM mitigation effect. The techniques used for adapting the coils to achieve this result are described. Those are fairly general and could be used in the design of RMP coils on other machines.
Nuclear Fusion 04/2009; 49(5):055024. · 4.09 Impact Factor
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ABSTRACT: Non‐inductive tokamak discharges with a flat or hollow current profile are prone to the triggering of large tearing modes when the minimum of the safety factor is just below a low order rational. This issue is of particular importance for discussing the optimal safety factor for MHD modes avoidance in Steady‐State reactor plasmas. Different non‐linear regimes of such magnetic configurations in Tore Supra are studied using the full MHD code XTOR [1]. Numerical simulations show that the non‐linear stage of the Double‐Tearing Mode (DTM) is governed by the full reconnection model, but a single tearing mode in a low magnetic shear configuration can have a similar impact on the confinement. The different regimes observed experimentally are recovered in the simulations: a small amplitude (2,1) DTM for close resonant surfaces as seen in Tore Supra [2], a sawtooth‐like behaviour of the (2,1) Double‐Tearing Mode as first seen in TFTR [3], or a large amplitude (2,1) tearing mode that severely degrades the energy confinement, as reported in Tore Supra [4], JET [5] or DIII‐D [6]. Situations where qmin ≈ 1.5 with a stable n = 1 mode, as seen in Tore Supra longest discharges, seem to put specific constraints on the MHD model that is used. Indeed, curvature stabilisation without transport terms as derived in [7] could explain linear stability, but such effect vanishes in presence of heat transport [8]. Electron diamagnetic rotation effect is investigated as a possible mechanism for n = 1 mode stabilization.
AIP Conference Proceedings. 10/2008; 1069(1):153-164.
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M. Bécoulet,
E. Nardon, G. Huysmans,
W. Zwingmann,
P. Thomas,
M. Lipa,
R. Moyer,
T. Evans,
V. Chuyanov,
Y. Gribov,
A. Polevoi,
G. Vayakis,
G. Federici,
G. Saibene,
A. Portone,
A. Loarte,
C. Doebert,
C. Gimblett,
J. Hastie,
V. Parail
[show abstract]
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ABSTRACT: A number of possible designs of external and in-vessel coils generating resonant magnetic perturbations (RMPs) for Type I edge localized modes (ELMs) control in ITER are analysed for the reference scenarios (H-mode, Hybrid and Steady-State) taking into account physical, technical and spatial constraints. The level of stochasticity (Chirikov parameter ~1 at ψ1/2 ~ 0.95) generated by the I-coils in the DIII-D experiments on ELMs suppression was taken as a reference. Designs with a toroidal symmetry n = 3 were considered to avoid lower n numbers producing larger central islands, a potential trigger of MHD instabilities. The evaluation of RMP coils designs is done with respect to the RMPs spectrum that should produce enough edge ergodisation and minimum central perturbations at minimum current. The proposed designs include in-vessel, mid-ports and external coils. Changes in the equilibrium due to changes in the internal inductance li, the poloidal beta βp and the edge magnetic shear in a reasonable range for ITER scenarios were demonstrated to have a small effect on the edge ergodisation. Present estimations were done without margins and for vacuum fields neglecting plasma response on RMPs. The validity of the vacuum approach was estimated analytically in the visco-resistive linear response regime using [1]. The typical radial magnetic field amplitudes produced by RMP coils in DIII-D and ITER are an order of magnitude or slightly above the critical values for the 'downward' bifurcation to the reconnected stage indicating the possibility of the islands formation in the pedestal region. Central islands (from the top of the pedestal) are expected to be screened.
Nuclear Fusion 01/2008; 48(2):024003. · 4.09 Impact Factor
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ABSTRACT: Electron cyclotron current drive (ECCD) at a low power level has been used on Tore Supra to induce local perturbations of the current density profile. Regimes with strong MHD activity have been analysed, and compared with similar stable discharges, in order to investigate the possible causes of their instability and relate the evolution of the discharge to the localization of EC power deposition. Both co- and counter-current drive pulses have been applied to dominantly or fully non-inductive discharges, sustained by a lower hybrid current drive. Detailed reconstructions by current diffusion calculations have been performed and the error bars evaluated. This method has proved valuable for shedding light on the complex interplay between the evolutions of temperature and safety factor profiles in steady-state tokamak plasmas. The crucial role of the dynamic evolution of rational surfaces has been identified. Moreover, we demonstrate that the operational domain in which ECCD can be employed must cope with the overall current profile characteristics, in particular the position where the safety factor has a minimum.
Plasma Physics and Controlled Fusion 01/2008; 50(3):035001. · 2.42 Impact Factor
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D Kalupin,
JF Artaud,
D Coster,
S Glowacz,
S Moradi,
G Perverzev,
R Stankiewicz,
M Tokar,
V Basiuk, G Huysmans,
others
Proc. 35th EPS Conf. Plasma Phys. 01/2008; 32.
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ABSTRACT: The early phase of a tokamak plasma discharge can have a dramatic impact on the main heating phase. This has been a persistent problem for the development of the steady state, fully non-inductive scenario using lower hybrid current drive (LHCD) on Tore Supra. The present paper reports on recent experimental and numerical investigations showing that a tearing mode coupled to the internal kink grows on q = 2 in the ohmic phase when the total current is too low, due to the weakening of field line curvature stabilization. Then, the application of LHCD drives the island to a larger size and undermines the development of the non-inductive phase. Decreasing the edge safety factor or increasing the Lundquist number S is found to be beneficial in both the linear and non-linear MHD analyses. The experimental database, which allows covering the edge safety factor dependence, supports this interpretation.
Nuclear Fusion 03/2007; 47(3):233. · 4.09 Impact Factor
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Physics of Plasmas 01/2007; 14:092501. · 2.15 Impact Factor
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J.‐S. Lönnroth,
G. Bateman,
M. Bécoulet,
P. Beyer,
G. Corrigan,
C. Figarella,
W. Fundamenski,
O. E. Garcia,
X. Garbet, G. Huysmans, [......],
G. W. Pacher,
H. D. Pacher,
A. Pankin,
V. Parail,
R. Pitts,
G. Saibene,
P. Snyder,
J. Spence,
D. Tskhakaya,
H. Wilson
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ABSTRACT: This paper presents a short overview of current trends and progress in integrated ELM modelling. First, the concept of integrated ELM modelling is introduced, various interpretations of it are given and the need for it is discussed. Then follows an overview of different techniques and methods used in integrated ELM modelling presented roughly according to physics approached in use and in order of increasing complexity. The paper concludes with a short discussion of open issues and future modelling requirements within the field of integrated ELM modelling. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
Beiträge aus der Plasmaphysik 08/2006; 46(7‐9):726 - 738.
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F Imbeaux,
G Giruzzi,
P Maget,
J L Ségui,
V S Udintsev,
J F Artaud,
D Elbèze, G Huysmans,
E Joffrin,
D Mazon,
R Sabot,
A Sirinelli
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ABSTRACT: During fully noninductively driven discharges in the Tore Supra tokamak, large spontaneous oscillations of the core electron temperature (DeltaTe/Te>50%) have been observed for the first time. They occurred during the standard O regime, which is itself characterized by periodic oscillations of much smaller amplitude. The "giant" oscillations appear to involve distinct mechanisms with respect to the O regime and provide a spectacular example of the complex nonlinear interactions between energy confinement, noninductive current sources, and MHD that may occur in a tokamak plasma during steady-state operation.
Physical Review Letters 02/2006; 96(4):045004. · 7.37 Impact Factor
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ABSTRACT: A 32-channel, 1 GHz spaced heterodyne radiometer is used on the Tore Supra tokamak to measure electron cyclotron emission (ECE) in the frequency range 78–110 GHz for the ordinary mode (O:E‖B,k⊥B) and 94–126 GHz for the extraordinary mode (X:E⊥B,k⊥B). The radial resolution is essentially limited by ECE relativistic effects, depending on electron temperature and density, and not by the channels’ frequency spacing. The time resolution depends on the acquisition scheme: the system allows for both 1 ms and 10 μs acquisition. For example, this leads to precise electron temperature mapping during MHD activity. First experimental results obtained with this upgraded 32-channel radiometer are presented.
Review of Scientific Instruments. 12/2005; 76(12):123501-123501-6.
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F.G. Rimini,
M. Bécoulet,
E. Giovannozzi,
P.J. Lomas,
O. Tudisco,
B. Alper,
F. Crisanti,
M. de Baar,
E. de La Luna,
P. de Vries,
A. Ekedahl,
N. Hawkes, G. Huysmans,
X. Litaudon,
V. Parail,
G. Saibene,
A.A. Tuccillo,
K.D. Zastrow,
EFDA-JET Workprogramme Contributors
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ABSTRACT: The development of scenarios characterized by H-mode confinement and internal transport barriers (ITBs) in high triangularity, δ ~ 0.4–0.5, discharges is of particular interest for ITER advanced tokamak operation. Previous JET experiments have shown that high triangularity favours H-modes which are ELM-free or develop type I edge localized mode (ELM) activity, which inhibits long lasting ITBs. The recent experiments reported here concentrate on integrated optimization of edge and core conditions. The stability of the edge pedestal was controlled using gas injection, deuterium or light impurities, and plasma current ramps. Both methods yield more ITB-friendly edge pedestal conditions, varying from small type I to type III ELMs and, in extreme cases, resulting in L-mode. In parallel, the conditions for triggering and sustaining ITBs encompassing a large proportion of the plasma volume (outer ITBs) were optimized, as opposed to less performing ITBs located closer to the plasma centre (inner ITB). These plasmas have deeply reversed target current profiles with qmin ~ 3 and a narrow inner ITB, located typically at a small normalized radius ρ < 0.5 and close to the reversed shear region, is routinely observed. Large radius outer ITBs are only triggered at an input power in excess of 20 MW, but they do not usually survive the transition into H-mode. The best results, in terms of sustained high confinement, have been obtained with neon injection; an outer ITB is triggered during the phase with L-mode edge and survives into H-mode for about 2 s, corresponding to ~10 times the global energy confinement time τE, at q95 = 7.5, H89βN ~ 3.5–4 and ~60% of the Greenwald density limit. In summary, a high triangularity scenario has been developed, which combines the desirable characteristics of controlled edge, long lasting wide ITBs and high performance at density higher than the low triangularity JET scenarios.
Nuclear Fusion 11/2005; 45(12):1481. · 4.09 Impact Factor
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M. Bécoulet, G. Huysmans,
P. Thomas,
P. Ghendrih,
E. Nardon,
A. Grosman,
X. Garbet,
W. Zwingman,
R. Moyer,
T. Evans,
M. Schaffer,
A. Leonard
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ABSTRACT: This paper describes a new approach for modelling the pedestal energy transport in the presence of a small radial magnetic perturbation. The cases of a ballooning instability leading to Type I edge localized modes (ELMs) and a magnetic perturbation generated by external coils are treated. The model for Type I ELMs is based on the linear ideal MHD code MISHKA coupled with the non-linear energy transport code TELM in a realistic tokamak geometry. The main mechanism of the increased transport through the external transport barrier in this model of ELMs is due to the appearance of a radial velocity and a radial magnetic field perturbation due to the MHD mode. Both lead to additional transport perpendicular to the magnetic surface and hence to a relaxation of the pressure profile in the unstable zone. The typical Type I ELM time-cycle was reproduced numerically including the destabilization of the ballooning modes leading to the fast (250 μ s) collapse of the pedestal pressure followed by the edge pressure profile re-building on a diffusive time scale. A possible mechanism for the control of Type I ELMs using a stochastic plasma boundary created by external coils is modelled in this paper using data on ELM suppression by I-coils from the DIII-D experiment. In the stochastic layer the transverse transport is effectively increased by diffusion of the magnetic field lines. The modelling results demonstrate the possibility of decreasing the edge pressure gradient to a value that is just below the ideal ballooning limit, leading to a high confinement regime without Type I ELMs.
Nuclear Fusion 10/2005; 45(11):1284. · 4.09 Impact Factor
