-
J Hillairet,
J Achard,
Y S Bae,
X Bai,
C Balorin,
Y Baranov,
V Basiuk, A Becoulet,
J Belo,
G Berger-By, [......],
T Oosako,
V Petrzilka,
Y Peysson,
S Poli,
M Preynas,
M Prou,
F Saint-Laurent,
F Samaille,
B Saoutic,
P K Sharma
Antennas and Propagation (EUCAP), 2012 6th European Conference on; 01/2012
-
D.J. Gambier,
M.P. Evrard,
J. Adam, A. Becoulet,
S. Corti,
P. Hennequin,
J. Jacquinot,
D.F.H. Start,
K. Thomsen,
B.J.D. Tubbing,
V. Zanza
[show abstract]
[hide abstract]
ABSTRACT: The power deposition profile in the ion cyclotron range of frequencies (ICRF) has been investigated experimentally in JET by means of a square wave modulated RF perturbation. The study has been conducted in D(H) and D(3He) plasmas for two heating scenarios. In D(3He) plasmas and for central heating in a scenario where mode conversion to Bernstein waves is accessible, the direct power deposition profile on electrons has been derived. It accounts for 15% of the total coupled power and extends over 25% of the minor radius. Outside the RF power deposition zone, the electron thermal diffusivity χe inside the inversion radius surface (ri) can be estimated through observation of the diffusive electronic transport. In discharges without monster sawteeth and for a low central temperature gradient (∇Te(r ≤ ri) ≤ ∇Te(r ≥ ri) ≈ 5 keVm−1) the value obtained is small (≈ 0.24 ± 0.05 m2s−1), typically ten times ower than χe values deduced from heat pulse propagation in similar discharges at radii larger than the inversion radius. For the D(H) minority heating scheme, a large fraction of the ICRF modulated power is absorbed by minority ions, and the minority tail is modulated with a characteristic ion-electron (i–e) slowing-down time. In this scheme, electron heating occurs only through collisions with the minority ion tail and no modulation of the electron temperature is observed in sawtoothing discharges. This is interpreted as a consequence of the long i–e equipartition time, acting as an integrator for the modulated ICRF signal. Finally, a correlation between the time of the sawtooth crash and the periodic turn-off of the ICRF power is found and its consequence for modulation experiments is reviewed.
Nuclear Fusion 01/2011; 30(1):23. · 4.09 Impact Factor
-
J Decker,
Y Peysson,
J Hillairet,
J -F Artaud,
V Basiuk, A Becoulet,
A Ekedahl,
M Goniche,
G T Hoang,
F Imbeaux,
A K Ram,
M Schneider
Nuclear Fusion. 01/2011; 51(7):073025.
-
[show abstract]
[hide abstract]
ABSTRACT: Preliminary laboratory testing of ICRH antennas is a very useful step before their commissioning. Traditionally, pure water, salt water or baking soda water loads are used. These 'water' loads are convenient but strongly limited in terms of performance testing. We have started two feasibility studies for advanced ICRH loads made of ferroelectric ceramics (passive loads) and meta materials (active loads). Preliminary results are very encouraging.
AIP Conference Proceedings 11/2009; 1187(1).
-
G.S. Lee,
Yong-Su Na, A. Becoulet,
S. Ide,
C.E. Kessel,
A. Komori,
B.V. Kuteev,
G. Mank,
R.A. Olstad,
B. Sarkar,
A.C.C. Sips,
D. van Houtte,
V.L. Vdovin
[show abstract]
[hide abstract]
ABSTRACT: This report summarizes the contributions presented at the 5th IAEA Technical Meeting on Steady State Operation of Magnetic Fusion Devices, held in Daejeon, Republic of Korea, 14–17 May 2007. The main topics of the meeting were overview and superconducting devices, long pulse operation and advanced tokamak, steady state fusion technology, heating and current drive, particle control and power exhaust and ITER-related issues.
Nuclear Fusion 07/2008; 48(8):087001. · 4.09 Impact Factor
-
D A Batchelor,
M Beck, A Becoulet,
R V Budny,
C S Chang,
P H Diamond,
J Q Dong,
G Y Fu,
A Fukuyama,
T S Hahm, [......],
T Ozeki,
N Podhorszki,
Tang,
M A Vouk,
R E Waltz,
S J Wang,
H R Wilson,
X Q Xu,
M Yagi,
Zonca
[show abstract]
[hide abstract]
ABSTRACT: I. Introduction (Z. Lin, G. Y. Fu, J. Q. Dong) II. Role of theory and simulation in fusion sciences 1. The Impact of theory and simulation on tokomak experiments (H. R. Wilson, T.S. Hahm and F. Zonca) 2. Tokomak Transport Physics for the Era of ITER: Issues for Simulations (P.H. Diamond and T.S. Hahm) III. Status of fusion simulation and modeling 1. Nonlinear Governing Equations for Plasma Simulations (T. S. Hahm) 2. Equilibrium and stability (L.L. Lao, J. Manickam) 3. Transport modeling (R.E. Waltz) 4. Nonlinear MHD (G.Y. Fu) 5. Turbulence (Z. Lin and R.E. Waltz) 6. RF heating and current drive (D.A. Batchelor) 7. Edge physics Simulations (X.Q. Xu and C.S. Chang) 8. Energetic particle physics (F. Zonca, G.Y. Fu and S.J. Wang) 9. Time-dependent Integrated Modeling (R.V. Budny) 10. Validation and verification (J. Manickam) IV. Major initiatives on fusion simulation 1. US Scientific Discovery through Advanced Computing (SciDAC) Program & Fusion Energy Science (W. Tang) 2. EU Integrated Tokamak Modelling (ITM) Task Force (A. Becoulet) 3. Fusion Simulations Activities in Japan (A. Fukuyama, N. Nakajima, Y. Kishimoto, T. Ozeki, and M. Yagi) V. Cross-disciplinary research in fusion simulation 1. Applied mathematics: Models, Discretizations, and Solvers (D.E. Keyes) 2. Computational Science (K. Li) 3. Scientific Data and Workflow Management (S. Klasky, M. Beck, B. Ludaescher, N. Podhorszki, M.A. Vouk) 4. Collaborative tools (J. Manickam)
Plasma Science and Technology 06/2007; 9(3):312. · 0.41 Impact Factor
-
P Buratti,
B Alper,
S V Annibaldi, A Becoulet,
P Belo,
J Bucalossi,
M de Baar,
P de Vries,
D Frigione,
C Gormezano,
E Joffrin,
P Smeulders,
JET-EFDA contributors
[show abstract]
[hide abstract]
ABSTRACT: Experiments designed for the attainment of the hybrid advanced mode of operation in JET revealed the existence of a new form of reconnecting modes with toroidal number n = 1 and poloidal number m = 1, which have the same radial structure as sawtooth precursors but are characterized by small growth rate and low saturation amplitude. These modes develop in repetitive cycles with typical growth times of 100 ms. Temperature perturbations are not in the form of sawteeth; in fact, there is slow and mild erosion of the central temperature without any crash. Comparison with theory of m = 1 modes indicates that the slow growth observed in the hybrid regime is caused by low magnetic shear (a measure of the radial variation of field line inclination) and possibly by diamagnetic effects in the plasma core.
Plasma Physics and Controlled Fusion 06/2006; 48(7):1005. · 2.42 Impact Factor
-
A.A. Tuccillo,
F. Crisanti,
X. Litaudon,
Yu.F. Baranov, A. Becoulet,
M. Becoulet,
L. Bertalot,
C. Castaldo,
C.D. Challis,
R. Cesario, [......],
D. Moreau,
A. Murari,
V. Pericoli-Ridolfini,
F. Rimini,
A.C.C. Sips,
C. Sozzi,
O. Tudisco,
D. Van Eester,
K-D. Zastrow,
JET-EFDA work-programme contributors
-
A.A. Tuccillo,
F. Crisanti,
X. Litaudon,
Yu.F. Baranov, A. Becoulet,
M. Becoulet,
L. Bertalot,
C. Castaldo,
C.D. Challis,
R. Cesario, [......],
D. Moreau,
A. Murari,
V. Pericoli-Ridolfini,
F. Rimini,
A.C.C. Sips,
C. Sozzi,
O. Tudisco,
D. Van Eester,
K-D. Zastrow,
JET-EFDA work-programme contributors
[show abstract]
[hide abstract]
ABSTRACT: Recent research on advanced tokamak in JET has focused on scenarios with both monotonic and reversed shear q-profiles having plasma parameters as relevant as possible for extrapolation to ITER. Wide internal transport barriers (ITBs), r/a ~ 0.7, are formed at ITER relevant triangularity δ ~ 0.45 and moderate plasma current, IP = 1.5–2.5 MA, with ne/nG ~ 60% when ELMs are moderated by Ne injection. At higher current (IP ≤ 3.5 MA, δ ~ 0.25) wide ITBs sitting at r/a ≥ 0.5, in the positive shear region, have been developed. Generally MHD events terminate these barriers otherwise limited in strength by power availability. ITBs with core density close to Greenwald value, Te ~ Ti and low toroidal rotation (4 times lower than standard ITBs) are obtained in plasma target preformed by opportune timing of lower hybrid current drive (LHCD), pellet injection and a small amount of NBI power. Wide ITBs, r/a ~ 0.6, of moderate strength, can be sustained without impurities accumulation for a time close to neoclassical resistive time in 3 T/1.8 MA discharges that exhibit reversed magnetic shear profiles and type-III ELMy edge. These discharges have been extended to the maximum duration allowed by JET subsystems (20 s) bringing to the record of injected energy in a JET discharge: E ~ 330 MJ. Portability of ITB physics has been addressed through dedicated similarity experiments. The ITB is identified as a layer of reduced diffusivity studying the propagation of the heat wave generated by modulating the ICRF mode conversion (MC) electron heating. Impressive results, QDT ~ 0.25, are obtained in these deuterium discharges with 3He minority when the MC layer is located in the core. The ion behaviour has been investigated in pure LHCD electron ITBs optimizing the 3He minority concentration for direct ion heating. Preliminary results of particle transport, studied via injection of a trace of tritium and an Ar–Ne mixture, will be presented.
Nuclear Fusion 01/2006; 46(2):214. · 4.09 Impact Factor
-
W.A. Houlberg,
C. Gormezano,
J.F. Artaud,
E. Barbato,
V. Basiuk, A. Becoulet,
P. Bonoli,
R.V. Budny,
L.G. Eriksson,
D. Farina, [......],
A. Polevoi,
E. Poli,
R. Prater,
H. St. John,
F. Volpe,
E. Westerhof,
A. Zvonkov,
ITPA Steady State Operation Topical Group,
ITPA Confinement Database,
Modeling Topical Group
[show abstract]
[hide abstract]
ABSTRACT: We present integrated modelling of steady-state and hybrid scenarios for ITER parameters using several predictive transport codes. These employ models for non-inductive current drive sources in conjunction with various theory-based and semi-empirical transport models. In conjunction with the simulation effort, the current drive models are being evaluated in a series of cross-code and code-experiment comparisons under ITER-relevant conditions. New benchmark evaluations of current drive from injection of neutral beams (NBCD), electron cyclotron waves (ECCD) and lower hybrid waves (LHCD) are reported. Simulations using several transport modelling codes self-consistently calculate the heating and current drive sources using ITER design parameters. Operating constraints are also taken into account, although the calculations reported here still require further refinement. The modelling addresses both the final stationary state and dynamic access to it. The simulations indicate that generation and control of internal and edge barriers to access and maintain high confinement will be a major undertaking for future simulations, as well as a challenge for the ITER steady-state and hybrid experimental programme.
Nuclear Fusion 10/2005; 45(11):1309. · 4.09 Impact Factor
-
E. Joffrin,
A.C.C. Sips,
J.F. Artaud, A. Becoulet,
L. Bertalot,
R. Budny,
P. Buratti,
P. Belo,
C.D. Challis,
F. Crisanti, [......],
X. Litaudon,
P.J. Lomas,
D.C. McDonald,
Y.S. Na,
S.D. Pinches,
A. Staebler,
T. Tala,
A. Tuccillo,
K.-D. Zastrow,
JET-EFDA Contributors to the Work Programme
[show abstract]
[hide abstract]
ABSTRACT: In 2003, the performance of the 'hybrid' regime was successfully validated in JET experiments up to βN = 2.8 at low toroidal field (1.7 T), with plasma triangularity and normalized Larmor radius (ρ*) corresponding to identical ASDEX Upgrade discharges. Stationary conditions have been achieved with the fusion figure of merit ( ) reaching 0.42 at q95 = 3.9. The JET discharges show similar MHD, edge and current profile behaviour, when compared with the ASDEX Upgrade. In addition, the JET experiments have extended the hybrid scenario operation at higher toroidal field of 2.4 T and lower ρ* towards the projected ITER values. Using this database, transport and confinement properties are characterized with respect to the standard H-mode regime. Moreover, trace tritium has been injected to assess the diffusion and convective coefficients of the fusion fuel. The maximization of confinement and stability properties provides, to this scenario, a good probability of achieving a high fusion gain at reduced plasma current for durations of up to 2000 s in ITER.
Nuclear Fusion 06/2005; 45(7):626. · 4.09 Impact Factor
-
V.S. Udintsev,
G. Giruzzi,
F. Imbeaux,
J. F. Artaud,
X. Garbet,
G. Huysmans,
P. Maget,
J. L. Segui, A. Becoulet,
G. T. Hoang,
E. Joffrin,
X. Litaudon,
B. Saoutic,
The Tore Supra Team
[show abstract]
[hide abstract]
ABSTRACT: Regular oscillations of the central electron temperature have been observed by means of ECE and SXR diagnostics during non-inductively driven discharges on Tore Supra. These oscillations are sustained by LHCD, do not have a helical structure and, therefore, cannot be ascribed as MHD phenomena. The most probable explanation of this oscillating regime (O-regime) is the assumption that the plasma current density (and, thus, the q-profile) and the electron temperature evolve as a non-linearly coupled predator-pray system. The integrated modelling code CRONOS has been used to demonstrate that the coupled heat transport and resistive diffusion equations admit solutions for the electron temperature and the current density which have a cyclic behaviour. Recent experimental results in which the O-regime co-exists with MHD modes will be presented. Because both phenomena are linked to details of the q-profile, some interplay between MHD and oscillations may occur. The localisation of magnetic islands allows to obtain an accurate picture of the q-profile in the plasma core. In some case, MHD-driven reconnection helps in maintaining a weakly inverted q-profile that is found to be, in the CRONOS simulations, a necessary condition to trigger the oscillations.
11/2004;
-
C Gormezano, A Becoulet,
P Buratti,
L Carraro,
F Crisanti,
B Esposito,
G Giruzzi,
R Guirlet,
G T Hoang,
E Joffrin,
X Litaudon,
T Luce,
V Pericoli-Ridolfini,
O Sauter,
A C C Sips,
A Tuccillo,
the JET EFDA Contributors
[show abstract]
[hide abstract]
ABSTRACT: A 'hybrid' scenario for ITER is defined through its objectives: a large fusion yield for a long time duration. In many tokamaks, discharges characterized by a stationary current density profile, enclosing a large volume of low magnetic shear with q0 near 1, have achieved improved confinement and higher beta limits. Their extrapolation to ITER from existing data corresponds to the ITER hybrid scenario. These discharges are characterized by soft MHD events. Physics issues relevant to the existence and extrapolation of this scenario will be addressed. New JET experiments with a large component of RF heating have answered some of these issues: injected momentum is not essential, hybrid scenarios are achievable at low ρ*, hybrid regimes have been achieved with ITER-relevant Te/Ti and they are compatible with a very low edge activity/low pressure pedestal. Data from pure RF discharges in other tokamaks (FTU, TS, TCV) seem to confirm that a large volume of low magnetic shear with q0 close to 1 is the key to achieving hybrid scenarios. Issues needing resolution in the extrapolation to ITER are discussed. The present understanding provides encouraging prospects for the use of this scenario in ITER.
Plasma Physics and Controlled Fusion 11/2004; 46(12B):B435. · 2.42 Impact Factor
-
B Esposito,
F Crisanti,
V Parail,
P Maget,
Y Baranov, A Becoulet,
C Castaldo,
C D Challis,
R De Angelis,
X Garbet,
C Giroud,
N Hawkes,
E Joffrin,
X Litaudon,
D Mazon,
M Riva,
K D Zastrow,
contributors to the EFDA JET Workprogramme
[show abstract]
[hide abstract]
ABSTRACT: A large variety of JET discharges with internal transport barriers (ITBs) has been analysed in order to determine the main features which characterize turbulence stabilization at the barrier. It is found that the location of barriers is well correlated with regions where the E×B flow shearing rate exceeds the linear growth rate of the ion temperature gradient mode instability (γηi). A key point is the dependence of γηi on the magnetic shear: in the discharges of this database the reduction of γηi associated to very low or null magnetic shear favours the formation of an ITB. After the ITB formation a positive feedback occurs in which the E×B flow shear mechanism has the leading role and the position of the barrier may be no longer linked to the low shear region.
Plasma Physics and Controlled Fusion 05/2003; 45(6):933. · 2.42 Impact Factor
-
J. Pamela,
E. R. Solano,
J M Adams,
G. Agarici,
M. Agarici,
H. Akhter,
R. Albanese,
S. Alberti,
S. Allfrey,
B. Alper, [......],
F. Zacek,
L. Zakharov,
P. Zanca,
K. D. Zastrow,
W. Zeidner,
M. Zerbini,
H. Zohm,
S. Zoletnik,
F. Zonca,
W. Zwingman
[show abstract]
[hide abstract]
ABSTRACT: Scientific and technical activities on JET focus on the issues likely to affect the ITER design and operation. Our understanding of the ITER reference mode of operation, the ELMy H-mode, has progressed significantly. The extrapolation of ELM size to ITER has been re-evaluated. Neoclassical tearing modes have been shown to be meta-stable in JET, and their beta limits can be raised by destabilization (modification) of sawteeth by ion cyclotron radio frequency heating (ICRH). Alpha simulation experiments with ICRH accelerated injected 4 (He) beam ions provide a new tool for fast particle and magnetohydrodynamic studies, with up to 80-90% of plasma heating by fast 4 He ions. With or without impurity seeding, a quasi-steady-state high confinement (H-98 = 1), high density(n(e)/n(GW) = 0.9-1) and high beta (betaN = 2) ELMy H-mode has been achieved by operating near the ITER triangularity ( similar to 0.40-0.5) and safety factor (q(95) similar to 3), at Z(eff) similar to 1.5-2. In advanced tokamak (AT) scenarios, internal transport barriers (ITBs) are now characterized in real time with a new criterion, rhoT(*). Tailoring of the current profile with T lower hybrid current drive provides reliable access to a variety of q profiles, lowering access power for barrier formation. Rational q surfaces appear to be associated with ITB formation. Alfven cascades were observed in reversed shear plasmas, providing identification of q profile evolution. Plasmas with 'current holes' were observed and modelled. Transient high confinement AT regimes with H-89 = 3.3, beta(N) = 2.4 and ITER-relevant q < 5 were achieved with reversed magnetic shear. Quasi-stationary ITBs are developed with full non-inductive current drive, including similar to 50% bootstrap current. A record duration of ITBs was achieved, up to 11 s, approaching the resistive time. For the first time, pressure and current profiles of AT regimes are controlled by a real-time feedback system, in separate experiments. Erosion and co-deposition studies with a quartz micro-balance show reduced co-deposition. Measured divertor thermal loads during disruptions in JET could modify ITER assumptions.
Nuclear Fusion 01/2003; · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Velocity anisotropy of the suprathermal population created by heating (essentially ion cyclotron resonant heating (ICRH)) is known to influence sawtooth stabilization in tokamaks. However, studying such effects requires a realistic description of the hot ion distribution pitch angle dependence in terms of easily accessible experimental data. Such a description has been obtained for on-axis ICRH on Tore Supra. A simple analytic model, allowing an easy analysis of experimental data, is developed and applied to the above mentioned description of on-axis ICRH. It leads to the result that, contrary to common presumption, sawtooth stabilization with on-axis ICRH is driven by both passing and trapped hot ions. In Tore Supra discharges, the stabilizing effect of barely passing hot ions is found to be dominant
Nuclear Fusion 10/2002; 34(11):1489. · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Direct losses of ions trapped in the toroidal field ripple of Tore Supra were studied, using two techniques. The first (DRIPPLE I) correlates the ion loss current measured by an electric probe with the ion loss power measured by a calorimeter. As the calorimeter integrates over all particle energies and time, it yields only the averaged lost ion energy. The second technique (DRIPPLE II), still under development, uses a Faraday cup positioned and filtered so as to select ions by their Larmor radius. Preliminary results are useful but the currents measured are small (1-100 nA), aid improvements in instrumentation are needed to take full advantage of the data. During ICRH (hydrogen minority regime, resonance on-axis), a direct correlation between the lost ion mean energy and the density of hydrogen (nH) is observed. The energy increases when the hydrogen minority density decreases. Moreover, the line integrated density and the lower hybrid (LH) heating also affect the fast ion losses
Nuclear Fusion 10/2002; 35(12):1593. · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: The magnetic shear effect on thermal electron transport is studied in a large variety of non-inductive plasmas in Tore Supra. An improved confinement in the region of low and negative shear was observed and quantified with an exponential dependence on the magnetic shear (Litaudon, et al., Fusion Energy 1996 (Proc. 16th Int; Conf. Montreal, 1996), vol. 1, IAEA, Vienna (1997) 669). This is interpreted as a consequence of a decoupling of the global modes (Romanelli and Zonca, Phys. Fluids B 5 (1993) 4081) that are thought to be responsible for anomalous transport. This dependence is proposed in order to complete the Bohm-like L mode local electron thermal diffusivity so as to describe the transition from Bohm-like to gyroBohm transport in the plasma core. The good agreement between the predictive simulations of the different Tore Supra regimes (hot core lower hybrid enhanced performance, reversed shear plasmas and combined lower hybrid current drive and fast wave electron heating) and experimental data provides a basis for extrapolation of this magnetic shear dependence in the local transport coefficients to future machines. As an example, a scenario for non-inductive current profile optimization and control in ITER is presented
Nuclear Fusion 10/2002; 37(12):1715. · 4.09 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: Transport calculations illustrate that the lower hybrid current drive (LHCD) and off-axis electron cyclotron current drive (ECCD) are the only preheating methods that can create a wide, deeply reversed q-profile, i.e. large negative magnetic shear, on the JET tokamak. Off-axis neutral beam injection (NBI) and off-axis ion cyclotron resonance heating (ICRH) preheating yields a weakly reversed q-profile (small negative magnetic shear), whereas NBI and ICRH on-axis heating as well as ohmic preheating produce a monotonic q-profile in the preheating phase. Here, on-axis power deposition and current drive refers to heating and current drive at or close to magnetic axis and correspondingly, off-axis refers to heating and current drive deposited typically around the half minor radius (r/a = 0.3-0.6). The results on LHCD, ICRH and ohmic preheating have been verified in the recent JET experiments. The current drive efficiency scan shows that in the case of LHCD, ECCD and off-axis NBI, the driven current is absolutely crucial to obtain a reversed q-profile and to modify the current profile evolution drastically in the preheating phase. Taking into account only the direct electron heating effect, LHCD does not create a reversed q-profile. The timing scans indicate that the radial location of qmin at the end of the preheating phase is generally quite insensitive to the start time of the preheating, once started 0-2 s after the plasma initiation if the method relies upon the driven current. On the other hand, methods relying only upon electron heating are very sensitive to that. In both cases, the magnitude of the negative magnetic shear, however, seems to be very sensitive to the start time of the preheating.
Plasma Physics and Controlled Fusion 06/2002; 44(7):1181. · 2.42 Impact Factor
-
[show abstract]
[hide abstract]
ABSTRACT: A new model based on a combination of a Bohm-like term plus a gyro-Bohm-like term is proposed for the electron and ion heat diffusivity in the L mode regime, which is the commonest regime of operation of tokamaks. This model is derived using the dimensionless analysis technique taking into account the indications of scaling laws for the global confinement time and other experimental constraints on the diffusivity. The model has been successfully tested against data from several different experiments from the ITER database and the local Tore Supra database. Statistical analysis has shown it to perform better than purely Bohm or gyro-Bohm models and global scaling laws in the chosen dataset.
Nuclear Fusion 05/2002; 38(7):1013. · 4.09 Impact Factor
