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T.W. Versloot,
R. Sartori,
F. Rimini,
P.C. de Vries,
G. Saibene,
V. Parail,
M.N.A. Beurskens,
A. Boboc, R. Budny,
K. Crombé, [......],
V. Kiptily,
T. Johnson,
P. Mantica,
M.-L. Mayoral,
D.C. McDonald,
I. Monakhov,
M.F.F. Nave,
I. Voitsekhovitch,
K.-D. Zastrow,
JET EFDA Contributors
[show abstract]
[hide abstract]
ABSTRACT: 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.
Nuclear Fusion 09/2011; 51(10):103033. · 4.09 Impact Factor
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T Tala,
K Crombé,
P C de Vries,
J Ferreira,
P Mantica,
A G Peeters,
Y Andrew, R Budny,
G Corrigan,
A Eriksson, [......],
M F F Nave,
V Parail,
K Rantamäki,
B D Scott,
P Strand,
G Tardini,
A Thyagaraja,
J Weiland,
K-D Zastrow,
JET-EFDA Contributors
[show abstract]
[hide abstract]
ABSTRACT: The present status of understanding of toroidal and poloidal momentum transport in tokamaks is presented in this paper. Similar energy confinement and momentum confinement times, i.e. τE/τ ≈ 1 have been reported on several tokamaks. It is more important though, to study the local transport both in the core and edge plasma separately as, for example, in the core plasma, a large scatter in the ratio of the local effective momentum diffusivity to the ion heat diffusivity χeff/χi,eff among different tokamaks can be found. For example, the value of effective Prandtl number is typically around χeff/χi,eff ≈ 0.2 on JET while still τE/τ ≈ 1 holds. Perturbative NBI modulation experiments on JET have shown, however, that a Prandtl number χ/χi of around 1 is valid if there is an additional, significant inward momentum pinch which is required to explain the amplitude and phase behaviour of the momentum perturbation. The experimental results, i.e. the high Prandtl number and pinch, are in good qualitative and to some extent also in quantitative agreement with linear gyro-kinetic simulations. In contrast to the toroidal momentum transport which is clearly anomalous, the poloidal velocity is usually believed to be neo-classical. However, experimental measurements on JET show that the carbon poloidal velocity can be an order of magnitude above the predicted value by the neo-classical theory within the ITB. These large measured poloidal velocities, employed for example in transport simulations, significantly affect the calculated radial electric field and therefore the E × B flow shear and hence modify and can significantly improve the simulation predictions. Several fluid turbulence codes have been used to identify the mechanism driving the poloidal velocity to such high values. CUTIE and TRB turbulence codes and also the Weiland model predict the existence of an anomalous poloidal velocity, peaking in the vicinity of the ITB and driven dominantly by the flow due to the Reynold's stress. It is worth noting that these codes and models treat the equilibrium in a simplified way and this affects the geodesic curvature effects and geodesic acoustic modes. The neo-classical equilibrium is calculated more accurately in the GEM code and the simulations suggest that the spin-up of poloidal velocity is a consequence of the plasma profiles steepening when the ITB grows, following in particular the growth of the toroidal velocity within the ITB.
Plasma Physics and Controlled Fusion 11/2007; 49(12B):B291. · 2.42 Impact Factor
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W M Solomon,
K H Burrell,
J S Degrassie, R Budny,
R J Groebner,
W W Heidbrink,
J E Kinsey,
G J Kramer,
M A Makowski,
D Mikkelsen,
R Nazikian,
C C Petty,
P A Politzer,
S D Scott,
M A Van Zeeland,
M C Zarnstorff
01/2007;
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Physics of Plasmas 01/2006; 13(5):056116. · 2.15 Impact Factor
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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
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J.E. Kinsey,
F. Imbeaux,
G.M. Staebler, R. Budny,
C. Bourdelle,
A. Fukuyama,
X. Garbet,
T. Tala,
V. Parail,
for the ITPA Topical Group on Transport Physics,
the ITB Database Working Group
[show abstract]
[hide abstract]
ABSTRACT: Predictive transport modelling and gyrokinetic stability analyses of demonstration hybrid (HYBRID) and advanced tokamak (AT) discharges from the International Tokamak Physics Activity (ITPA) profile database are presented. Both regimes have exhibited enhanced core confinement (above the conventional ITER reference H-mode scenario) but differ in their current density profiles. Recent contributions to the ITPA database have facilitated an effort to study the underlying physics governing confinement in these advanced scenarios. In this paper, we assess the level of commonality of the turbulent transport physics and the relative roles of the transport suppression mechanisms (i.e. E × B shear and Shafranov shift (α) stabilization) using data for select HYBRID and AT discharges from the DIII-D, JET and AUG tokamaks. GLF23 transport modelling and gyrokinetic stability analysis indicate that E × B shear and Shafranov shift stabilization play essential roles in producing the improved core confinement in both HYBRID and AT discharges. Shafranov shift stabilization is found to be more important in AT discharges than in HYBRID discharges. We have also examined the competition between the stabilizing effects of E × B shear and Shafranov shift stabilization and the destabilizing effects of higher safety factors and parallel velocity shear. Linear and nonlinear gyrokinetic simulations of idealized low and high safety factor cases reveal some interesting consequences. A low safety factor (i.e. HYBRID relevant) is directly beneficial in reducing the transport, and E × B shear stabilization can dominate parallel velocity shear destabilization allowing the turbulence to be quenched. However, at low-q/high current, Shafranov shift stabilization plays less of a role. Higher safety factors (as found in AT discharges), on the other hand, have larger amounts of Shafranov shift stabilization, but parallel velocity shear destabilization can prevent E × B shear quenching of the turbulent transport, and only E × B suppression is achieved.
Nuclear Fusion 05/2005; 45(6):450. · 4.09 Impact Factor
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I. Voitsekhovitch,
X. Garbet,
D. C. McDonald,
K.-D. Zastrow,
M. Adams,
Yu. Baranov,
P. Belo,
L. Bertalot, R. Budny,
S. Conroy,
J. G. Cordey,
L. Garzotti,
P. Mantica,
D. McCune,
J. Ongena,
V. Parail,
S. Popovichev,
D. Stork,
A. D. Whiteford
[show abstract]
[hide abstract]
ABSTRACT: Tritium transport in edge localized mode (ELM) high confinement (H-mode) plasmas is analyzed here as a function of density for discharges from the recent trace tritium experimental campaign performed on Joint European Torus. In this campaign small amounts of tritium have been puffed or injected (with neutral beam injectors) into deuterium plasmas [
K.-D. Zastrow, J. M. Adams, Yu. Baranov et al., Plasma Phys. Controlled Fusion 46, B255 (2004)
]. Information about the tritium has been obtained from the evolution of the profiles of neutron emission simulated via the TRANSP [
R. J. Goldston, D. C. McCune, H. H. Towner, S. L. Davis, R. J. Hawryluk, and G. L. Schmidt, J. Comput. Phys. 43, 61 (1981)
] and SANCO (L. Lauro-Taroni, B. Alper, R. Giannella, K. Lawson, F. Marcus, M. Mattioli, P. Smeulders, and M. Von Hellermann, Proceedings of the 21st European Conference on Controlled Fusion and Plasma Physics, Montpelier, France, 1994) codes. A strong inverse correlation of tritium transport with plasma density is found in this analysis. The low tritium transport at high density is close to neoclassical values while the transport becomes strongly anomalous in low density plasmas. The thermal transport does not exhibit such a strong density dependence, leading to a varying ratio of thermal to tritium transport in these discharges. An interpretation of the density effects on the trace tritium transport, partially based on the test particle simulations in plasmas with stochastic magnetic field, is proposed. A simple model for the tritium diffusion coefficient and convective velocity, which includes the modification of the neoclassical particle diffusion in presence of electromagnetic turbulence [
A. I. Smolyakov and P. N. Yushmanov, Nucl. Fusion 35, 383 (1993)
] completed with an empirical density dependence, is developed. This model has positive β dependence in agreement with the results of the similarity experiments performed for trace tritium transport.
Physics of Plasmas 04/2005; 12(5):052508-052508-12. · 2.15 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Alfvén instabilities excited by energetic ions are used as a means to reduce the central magnetic shear in a tokamak via redistribution of energetic ions. When the central magnetic shear is low enough, ballooning modes become stable for any plasma pressure gradient and an internal transport barrier (ITB) with a steep pressure gradient can exist. This mechanism can sustain a steady-state ITB as demonstrated by experimental data from the DIII-D tokamak. It can also produce a shear in toroidal and poloidal plasma rotation. Possible application of this technique to use the energetic α particles for improvement of burning plasma performance is discussed.
Nuclear Fusion 12/2004; 45(1):30. · 4.09 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Alfvén instabilities can reduce the central magnetic shear via redistribution of energetic ions. They can sustain a steady state internal transport barrier as demonstrated in this DIII-D tokamak experiment. Improvement in burning plasma performance based on this mechanism is discussed.
Physical Review Letters 09/2004; 93(8):085002. · 7.37 Impact Factor
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D C McDonald,
J G Cordey,
C C Petty,
M Beurskens, R Budny,
I Coffey,
M de Baar,
C Giroud,
E Joffrin,
P Lomas,
A Meigs,
J Ongena,
G Saibene,
R Sartori,
I Voitsekhovitch,
JET EFDA contributors
[show abstract]
[hide abstract]
ABSTRACT: The disagreement between the weak dependence of the energy confinement time on normalized pressure, β, observed in dedicated scans and the strongly negative dependence in the confinement scaling laws used for the design of next step tokamaks and future reactors, remains an outstanding problem. As such, scans of β have been undertaken in single null, low triangularity (δ ≈ 0.2) ELMy H-mode plasmas in JET with the MarkIIGB-SRP divertor. The scans varied β by a factor of 2.8 (normalized β from 0.72 to 2.04) and covered a range of magnetic fields (1.5–2.3 T), plasma currents (1.5–2.75 MA) and safety factors (q95 = 2.8 and 3.3). A weak β dependence was observed both globally (B0τE varied less than 9% across any one scan) and locally. A scan within Type I ELMy H-modes suggests that this weaker dependence is not due to ELM regimes. A statistical analysis indicates that these results are consistent with log–linear regressions performed on a wide JET database of ELMy H-modes, if correlations in this database are considered.
Plasma Physics and Controlled Fusion 04/2004; 46(5A):A215. · 2.42 Impact Factor
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M.F.F. Nave,
J. Rapp,
T. Bolzonella,
R. Dux,
M.J. Mantsinen, R. Budny,
P. Dumortier,
M. von Hellermann,
S. Jachmich,
H.R. Koslowski, [......],
A. Messiaen,
P. Monier-Garbet,
J. Ongena,
M.E. Puiatti,
J. Strachan,
G. Telesca,
B. Unterberg,
M. Valisa,
P. de Vries,
contributors to the JET-EFDA Workprogramme
[show abstract]
[hide abstract]
ABSTRACT: Impurity injection in the JET ELMy H-mode regime has produced high-confinement, quasi-steady-state plasmas with densities close to the Greenwald density. However, at large Ar densities, a sudden loss of confinement is observed. A possible correlation between loss of confinement and the observed MHD phenomena, both in the core and in the edge of the plasma, was considered. The degradation in confinement coincided with impurity profile peaking following the disappearance of sawtooth activity. In addition, impurity density profile analysis confirmed that central MHD modes prevented impurity peaking. Experiments were designed to understand the role of sawtooth crashes in re-distributing impurities. Ion-cyclotron radio frequency heating was used to control the central q-profile and maintain sawtooth activity. This resulted in quasi-steady-state, high-performance plasmas with high Ar densities. At and high Ar injection rates, quasi-steady-states, which previously only lasted <1τE, were now maintained for the duration of the heating (Δ t ~ 9τ E). The increased central heating may have an additional beneficial effect in opposing impurity accumulation by changing the core power balance and modifying the impurity transport as predicted by neo-classical theory.
Nuclear Fusion 09/2003; 43(10):1204. · 4.09 Impact Factor
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X. Garbet,
Y. Baranov,
G. Bateman,
S. Benkadda,
P. Beyer, R. Budny,
F. Crisanti,
B. Esposito,
C. Figarella,
C. Fourment, [......],
A. Pankin,
V. Parail,
A. Peeters,
T. Tala,
G. Tardini,
A. Thyagaraja,
I. Voitsekhovitch,
J. Weiland,
R. Wolf,
JET EFDA contributors
[show abstract]
[hide abstract]
ABSTRACT: The physics of internal transport barrier (ITB) formation in JET has been investigated using micro-stability analysis, profile modelling and turbulence simulations. The calculation of linear growth rates shows that magnetic shear plays a crucial role in the formation of the ITB. Shafranov shift, ratio of the ion to electron temperature, and impurity content further improve the stability. This picture is consistent with profile modelling and global fluid simulations of electrostatic drift waves. Turbulence simulations also show that rational q values may play a special role in triggering an ITB. The same physics also explains how double internal barriers can be formed.
Nuclear Fusion 08/2003; 43(9):975. · 4.09 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The stability of α-particle driven shear Alfvén eigenmodes (AE) for nominal burning plasma (BP) parameters in the proposed international tokamak experimental reactor (ITER), fusion ignition research experiment (FIRE) and IGNITOR tokamaks is studied. JET plasma, where fusion αs were generated in tritium experiments, is also studied to compare the numerical predictions with the existing experiments. An analytic assessment of toroidal AE (TAE) stability is first presented, where the α-particle β due to the fusion reaction rate and electron drag is simply and accurately estimated in plasmas with central temperature in the range of 7–20 keV. In this assessment the hot particle drive is balanced against ion-Landau damping of the background deuterons, and electron collision effects and stability boundaries are determined. Then two numerical studies of AE instability are presented. In one, the HIgh-n STability (HINST) code is used to predict the instabilities of low and moderately high frequency Alfvén modes. HINST computes the non-perturbative solutions of the AE including effects of ion finite Larmor radius, orbit width, trapped electrons etc. The stability calculations are repeated using the global code NOVAK. We show that for these plasmas the spectrum of the least stable AE modes is at medium-/high-n numbers. In HINST, TAEs are locally unstable due to the α pressure gradient in all the devices under consideration except IGNITOR. However, NOVAK calculations show that the global mode structure enhances the damping mechanisms and produces stability for the nominal FIRE proposal and near-marginal stability for the nominal ITER proposal. NBI ions produce a strong stabilizing effect for JET. However, in ITER, the beam energies needed to penetrate to the core must be high (~1 MeV) so that a diamagnetic drift frequency comparable to that of α-particles is produced by the beam ions which induces a destabilizing effect. A serious question remains whether the perturbation theory used in NOVAK overestimates the stability predictions, so that it is premature to conclude that the nominal operation of all three BP proposals without neutral beam injection are stable (or marginally stable) to AEs.
Nuclear Fusion 07/2003; 43(7):594. · 4.09 Impact Factor
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X. Litaudon,
A. Bécoulet,
F. Crisanti,
R.C. Wolf,
Yu.F. Baranov,
E. Barbato,
M. Bécoulet, R. Budny,
C. Castaldo,
R. Cesario, [......],
M. Riva,
F. Rimini,
Y. Sarazin,
B.C. Stratton,
T.J.J. Tala,
G. Tresset,
O. Tudisco,
L. Zabeo,
K.-D. Zastrow,
JET-EFDA contributors
[show abstract]
[hide abstract]
ABSTRACT: In JET, advanced tokamak research mainly focuses on plasmas with internal transport barriers (ITBs) that are strongly influenced by the current density profile. A previously developed optimized shear regime with low magnetic shear in the plasma centre has been extended to deeply negative magnetic shear configurations. High fusion performance with wide ITBs has been obtained transiently with negative central magnetic shear configuration: HIPB98(y,2) ~ 1.9, βN = 2.4 at Ip = 2.5 MA. At somewhat reduced performance, electron and ion ITBs have been sustained in full current drive operation with 1 MA of bootstrap current: HIPB98(y,2) ~ 1, βN = 1.7 at Ip = 2.0 MA. The ITBs were maintained for up to 11 s for the latter case. This duration, much larger than the energy confinement time (37 times larger), is already approaching a current resistive time. New real-time measurements and feedback control algorithms have been developed and implemented in JET for successfully controlling the ITB dynamics and the current density profile in the highly non-inductive current regime.
Nuclear Fusion 06/2003; 43(7):565. · 4.09 Impact Factor
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J.-M. Noterdaeme, R. Budny,
A. Cardinali,
C. Castaldo,
R. Cesario,
F. Crisanti,
J. deGrassie,
D.A. D'Ippolito,
F. Durodié,
A. Ekedahl, [......],
J.R. Myra,
J. Paméla,
V. Pericoli,
Yu. Petrov,
O. Sauter,
Y. Sarazin,
S.E. Sharapov,
A.A. Tuccillo,
D. Van Eester,
JET EFDA Contributors
[show abstract]
[hide abstract]
ABSTRACT: This paper summarizes the recent work on JET in the three areas of heating, current drive and energetic particles. The achievements have extended the possibilities of JET, have a direct connection to ITER operation and provide new and interesting physics. Toroidal rotation profiles of plasmas heated far off axis with little or no refuelling or momentum input are hollow with only small differences on whether the power deposition is located on the low field side or on the high field side. With LH current drive the magnetic shear was varied from slightly positive to negative. The improved coupling (through the use of plasma shaping and CD4) allowed up to 3.4 MW of PLH in internal transport barrier (ITB) plasmas with more than 15 MW of combined NBI and ICRF heating. The q-profile with negative magnetic shear and the ITB could be maintained for the duration of the high heating pulse (8 s). Fast ions have been produced in JET with ICRF to simulate alpha particles: by using third harmonic 4He heating, beam injected 4He at 120 kV were accelerated to energies above 2 MeV, taking advantage of the unique capability of JET to use NBI with 4He and to confine MeV class ions. ICRF heating was used to replicate the dynamics of alpha heating and the control of an equivalent Q = 10 `burn' was simulated.
Nuclear Fusion 03/2003; 43(3):202. · 4.09 Impact Factor
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G P Maddison,
M Brix, R Budny,
M Charlet,
I Coffey,
J G Cordey,
P Dumortier,
S K Erents,
N C Hawkes,
M Von Hellermann, [......],
S Sharapov,
G M Staebler,
M Stamp,
J D Strachan,
W Suttrop,
G Telesca,
M Z Tokar,
B Unterberg,
M Valisa,
K.-D Zastrow
Nuclear Fusion 01/2003; 43(1):49. · 4.09 Impact Factor
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J -M Noterdaeme,
E Righi,
V Chan,
J deGrassie,
K Kirov,
M Mantsinen,
M F F Nave,
D Testa,
K -D Zastrow, R Budny,
R Cesario,
A Gondhalekar,
N Hawkes,
T Hellsten,
Ph. Lamalle,
F Meo,
F Nguyen,
EFDA-JET-EFDA contributors
[show abstract]
[hide abstract]
ABSTRACT: Plasmas heated by ICRF only in the JET tokamak show distinct structures in the toroidal rotation profile, with regions where do/dr$>$0 when the minority cyclotron resonance layer is far off-axis. The rotation is dominantly co-current with a clear off-axis maximum. There is only a slight difference between a high-field side (HFS) or a low-field side position of this resonance layer: the off-axis maximum in the rotation profile is modestly higher for the HFS position. This is in contrast to the predictions of theories that rely mainly on the effects arising from ICRF-driven fast ions to account for ICRF-induced plasma rotation. The differences due to the direction of the antenna spectrum (co- or counter-) are small. A more central deposition of the ICRF power in L-mode and operation in H-mode both lead to more centrally peaked profiles, both in the co-direction. Strong MHD modes brake the rotation and lead to overall flat rotation profiles.
Nuclear Fusion. 01/2003; 43(4):274-289.
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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
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[show abstract]
[hide abstract]
ABSTRACT: The scaling of energy transport with dimensionless parameters has been measured in high-temperature plasmas with the goals of guiding theory and predicting energy confinement in future fusion devices. Validation of this approach requires demonstration of similarity in plasmas with identical dimensionless parameters but very different physical parameters. Within measurement uncertainties, the heat diffusivities and global energy confinement exhibit similarity in high-confinement regimes on the DIII-D and JET tokamaks and in low-confinement regimes on the DIII-D and Alcator C-Mod tokamaks.
Nuclear Fusion 09/2002; 42(10):1193. · 4.09 Impact Factor
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G L Jackson,
M Murakami,
D R Baker, R Budny,
M Charlet,
M R deBaar,
P Dumortier,
T E Evans,
R J Groebner,
N C Hawkes, [......],
J Rapp,
F Sartori,
G M Staebler,
M Stamp,
J D Strachan,
M Tokar,
B Unterberg,
M von Hellerman,
M R Wade,
contributors to the EFDA-JET Work Programme
[show abstract]
[hide abstract]
ABSTRACT: Impurity seeding in both the Joint European Torus (JET) and DIII-D tokamaks has produced L-mode discharges with confinement enhancements comparable to H-mode and a near doubling of the core ion temperature when compared to similar unseeded discharges. Although Zeff increases with the neon injection, the total neutron rate is as high, or higher, than reference discharges and the calculated thermal neutron rate increases dramatically in both devices. Modelling with the gyrokinetic simulation code shows a reduction in low k turbulence growth rates with neon injection decreasing to less than the E×B shearing rate, consistent with stabilization of ion temperature gradient modes in both JET and DIII-D. Reductions in ion thermal diffusivity are also observed with impurity seeding. Neoclassical m/n = 3/2 tearing modes limit the duration of best performance in DIII-D with neon injection, while n = 1 and n = 2 magnetohydrodynamic modes limit the performance in JET.
Plasma Physics and Controlled Fusion 08/2002; 44(9):1893. · 2.42 Impact Factor
