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J. Schweinzer, A.C.C. Sips,
G. Tardini,
P.A. Schneider,
R. Fischer,
J.C. Fuchs,
O. Gruber,
J. Hobirk,
A. Kallenbach,
R.M. McDermott,
R. Neu,
T. Pütterich,
S.K. Rathgeber,
J. Stober,
J. Vicente,
the ASDEX Upgrade Team
[show abstract]
[hide abstract]
ABSTRACT: In ASDEX Upgrade the compatibility of improved H-modes with an all-W wall has been demonstrated. Under boronized conditions light impurities and the radiated power fraction in the divertor were reduced, requiring N seeding to cool the divertor plasma. The impurity seeding does not only protect the divertor tiles but also considerably improves the performance of improved H-mode discharges by up to 25%. The energy confinement increases to H98-factors up to 1.3 and thereby exceeds the best values in the carbon-dominated AUG at the same density and collisionality. This improvement is due to higher edge temperatures rather than to peaking of the electron density profile. Higher temperatures are reached at the pedestal top leading, via profile stiffness, to an increase in the total plasma pressure. There is no change to in the plasma core. The dilution at the plasma edge by nitrogen seems to play an important role since it allows higher ion temperatures at the same edge ion pressure as in the unseeded case. The dilution of the core plasma remains moderate.
Nuclear Fusion 09/2011; 51(11):113003. · 4.09 Impact Factor
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M. Murakami,
J.M. Park,
G. Giruzzi,
J. Garcia,
P. Bonoli,
R.V. Budny,
E.J. Doyle,
A. Fukuyama,
N. Hayashi,
M. Honda, [......],
T.H. Osborne,
V. Parail,
A. Polevoi,
R. Prater, A.C.C. Sips,
J. Snipes,
H.E. St. John,
P.B. Snyder,
I. Voitsekhovitch,
ITPA/Integrated Operation Scenario Group
[show abstract]
[hide abstract]
ABSTRACT: Recent progress on ITER steady-state (SS) scenario modelling by the ITPA-IOS group is reviewed. Code-to-code benchmarks as the IOS group's common activities for the two SS scenarios (weak shear scenario and internal transport barrier scenario) are discussed in terms of transport, kinetic profiles, and heating and current drive (CD) sources using various transport codes. Weak magnetic shear scenarios integrate the plasma core and edge by combining a theory-based transport model (GLF23) with scaled experimental boundary profiles. The edge profiles (at normalized radius ρ = 0.8–1.0) are adopted from an edge-localized mode-averaged analysis of a DIII-D ITER demonstration discharge. A fully noninductive SS scenario is achieved with fusion gain Q = 4.3, noninductive fraction fNI = 100%, bootstrap current fraction fBS = 63% and normalized beta βN = 2.7 at plasma current Ip = 8 MA and toroidal field BT = 5.3 T using ITER day-1 heating and CD capability. Substantial uncertainties come from outside the radius of setting the boundary conditions (ρ = 0.8). The present simulation assumed that βN (ρ) at the top of the pedestal (ρ = 0.91) is about 25% above the peeling–ballooning threshold. ITER will have a challenge to achieve the boundary, considering different operating conditions (Te/Ti ≈ 1 and density peaking). Overall, the experimentally scaled edge is an optimistic side of the prediction. A number of SS scenarios with different heating and CD mixes in a wide range of conditions were explored by exploiting the weak-shear steady-state solution procedure with the GLF23 transport model and the scaled experimental edge. The results are also presented in the operation space for DT neutron power versus stationary burn pulse duration with assumed poloidal flux availability at the beginning of stationary burn, indicating that the long pulse operation goal (3000 s) at Ip = 9 MA is possible. Source calculations in these simulations have been revised for electron cyclotron current drive including parallel momentum conservation effects and for neutral beam current drive with finite orbit and magnetic pitch effects.
Nuclear Fusion 08/2011; 51(10):103006. · 4.09 Impact Factor
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J. Stober,
G.L. Jackson,
E. Ascasibar,
Y.-S. Bae,
J. Bucalossi,
A. Cappa,
T. Casper,
M.-H. Cho,
Y. Gribov,
G. Granucci, [......],
T. Lunt,
W. Namkung,
S.-I. Park,
P.A. Politzer,
J. Schweinzer, A.C.C. Sips,
the ASDEX Upgrade Team,
the TJ-II Team,
the ITPA 'Integrated Operations Scenarios' Group Members,
Experts
[show abstract]
[hide abstract]
ABSTRACT: Electron cyclotron resonance heating (ECRH)-assisted plasma breakdown is foreseen with full and half magnetic field in ITER. As reported earlier, the corresponding O1- and X2-schemes have been successfully used to assist pre-ionization and breakdown in present-day devices. This contribution reports on common experiments studying the effect of toroidal inclination of the ECR beam, which is ≥20° in ITER. All devices could demonstrate successful breakdown assistance for this case also, although in some experiments the necessary power was almost a factor of 2 higher compared with perpendicular launch. Differences between the devices with regard to the required power and vertical field are discussed and analysed. In contrast to most of these experiments, ITER will build up loop voltage prior to the formation of the field null due to the strong shielding by the vessel. Possible consequences of this difference are discussed.
Nuclear Fusion 07/2011; 51(8):083031. · 4.09 Impact Factor
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R Neu,
M Balden,
V Bobkov,
R Dux,
O Gruber,
A Herrmann,
A Kallenbach,
M Kaufmann,
C F Maggi,
H Maier, [......],
L Giannone,
S Gori,
S da Graca,
H Greuner,
A Gude,
S Günter,
G Haas,
J Harhausen,
B Heinemann,
N Hicks
Plasma Physics and Controlled Fusion 07/2011; · 2.42 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: Sawtooth induced heat and density pulse measurements reported in the literature for the JET and TEXT experiments are discussed. In JET the heat pulse travels ten times faster than the density pulse, but in TEXT both pulses travel at the same speed. The measurements are analysed using coupled transport equations for energy and particles. It is shown that the different behaviour of the density pulse in the two experiments can be attributed to differences in the off-diagonal elements of the transport matrix. If the perturbed fluxes of heat and particles are expressed as linear combinations of the thermodynamic forces ∇p and ∇T (rather than ∇n and ∇T), the corresponding transport matrices are remarkably similar. However, minor differences in this transport matrix between JET and TEXT account for the qualitative difference in the density pulses.
Nuclear Fusion 01/2011; 31(8):1545. · 4.09 Impact Factor
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[show abstract]
[hide abstract]
ABSTRACT: The perturbations of electron density and temperature profiles in a tokamak following a sawtooth collapse are considered. An analytic model for the interpretation of such perturbations is presented. It is shown that the perturbation can be decomposed into two contributions, which are eigenmodes of the linearized coupled diffusion equations for particles and energy. The approximations made in the analytic treatment are checked using computer simulations. Measurements of heat and density pulses in JET are used to illustrate the power of the new approach. It is shown that with the coupled equations an improved description of the heat and density pulses is obtained. The analysis yields the four diffusion coefficients in the linearized transport matrix. The non-zero off-diagonal elements explain certain salient features of the measurements, notably a marked decrease of the local density which occurs during the maximum of the temperature pulse.
Nuclear Fusion 01/2011; 31(7):1261. · 4.09 Impact Factor
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Fusion Engineering and Design 01/2011; 86:1103-1106. · 1.49 Impact Factor
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I Voitsekhovitch, A C C Sips,
B Alper,
M Beurskens,
I Coffey,
J Conboy,
T Gerbaud,
C Giroud,
T Johnson,
F Köchl,
E de la Luna,
D C McDonald,
I Pavlenko,
G V Pereverzev,
S Popovichev,
A N Saveliev,
G Sergienko,
S Sharapov,
M Stamp,
JET-EFDA Contributors
[show abstract]
[hide abstract]
ABSTRACT: The current ramp-up phase of ITER demonstration discharges, performed at JET, is analysed and the capability of the empirical L-mode Bohm–gyroBohm and Coppi–Tang transport models as well as the theory-based GLF23 model to predict the temperature evolution in these discharges is examined. The analysed database includes ohmic (OH) plasmas with various current ramp rates and plasma densities and the L-mode plasmas with the ion cyclotron radio frequency (ICRF) and neutral beam injection (NBI) heating performed at various ICRF resonance positions and NBI heating powers. The emphasis of this analysis is a data consistency test, which is particularly important here because some parameters, useful for the transport model validation, are not measured in OH and ICRF heated plasmas (e.g. ion temperature, effective charge). The sensitivity of the predictive accuracy of the transport models to the unmeasured data is estimated. It is found that the Bohm–gyroBohm model satisfactorily predicts the temperature evolution in discharges with central heating (the rms deviation between the simulated and measured temperature is within 15%), but underestimates the thermal electron transport in the OH and off-axis ICRF heated discharges. The Coppi–Tang model strongly underestimates the thermal transport in all discharges considered. A re-normalization of these empirical models for improving their predictive capability is proposed. The GLF23 model, strongly dependent on the ion temperature gradient and tested only for NBI heated discharges with measured ion temperatures, predicts accurately the temperature in the low power NBI heated discharge (rms < 10%) while the discrepancy with the data increases at high power. Based on the analysis of the JET discharges, the modelling of the current ramp-up phase for the H-mode ITER scenario is performed with particular emphasis on the sensitivity of the sawtooth-free duration of this phase to transport model.
Plasma Physics and Controlled Fusion 09/2010; 52(10):105011. · 2.42 Impact Factor
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M Baruzzo,
B Alper,
T Bolzonella,
M Brix,
P Buratti,
C D Challis,
F Crisanti,
E de la Luna,
P C de Vries,
C Giroud,
N C Hawkes,
D F Howell,
F Imbeaux,
E Joffrin,
H R Koslowski,
X Litaudon,
J Mailloux, A C C Sips,
O Tudisco,
JET-EFDA contributors
[show abstract]
[hide abstract]
ABSTRACT: An experimental study on the poloidal mode number (m) spectrum produced by a single toroidal mode number (n) neoclassical tearing mode (NTM) in the JET tokamak is presented. Clear evidence of the existence of more than one significant m component is given. The analysis is performed comparing several methods and diagnostics; among the latter we mention high frequency magnetic pick-up coils and an electron cyclotron emission radiometer, which measures detailed electron temperature radial profiles at high time resolution. The two diagnostics are also used together in a cross coherence calculation technique. The issue of the interaction of this multiple m structure with the plasma is addressed as well, with particular attention paid to plasma toroidal rotation and rotation shear, obtained from charge exchange spectroscopy data. This effect has been studied under two different operational plasma scenarios on JET in order to investigate both dependences on plasma parameters and consequences on the scenario itself.
Plasma Physics and Controlled Fusion 05/2010; 52(7):075001. · 2.42 Impact Factor
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C.F. Maggi,
R.J. Groebner,
C. Angioni,
T. Hein,
L.D. Horton,
C. Konz,
A.W. Leonard,
C.C. Petty, A.C.C. Sips,
P.B. Snyder,
J. Candy,
R.E. Waltz,
ASDEX Upgrade,
DIII-D Teams
[show abstract]
[hide abstract]
ABSTRACT: Pedestal and core confinement of hybrid discharges in ASDEX Upgrade (AUG) and DIII-D are studied in dedicated power scan experiments. The H98(y,2) confinement factor increases with total βN in both tokamaks and it is higher in DIII-D with higher δ plasma shape at a given βN. The pedestal beta, , increases linearly with total beta in AUG hybrid discharges, while it is roughly constant with βN at fixed shape in the DIII-D power scans. The confinement enhancement with power observed with respect to the IPB98(y,2) scaling is due to an increase in pedestal confinement in AUG hybrid discharges and to an increase in core confinement in the DIII-D hybrid power scans. The increase in pedestal pressure with power in AUG hybrid discharges is primarily due to an increase in the width of the edge transport barrier at constant pressure gradient. In the DIII-D discharges the widths of the Te and ne pedestals, and , are consistent with a scaling. In the AUG hybrid power scans a dependence of on βpol,PED cannot be excluded, while shows no dependence on βpol,PED In both machines increases with β. The maximum pedestal pressure achieved in the experiment prior to the onset of type I ELMs is consistent with predictions from ideal MHD; however, a physics model explaining the increase in the pedestal width with β is still missing. The increase in with β in the core of DIII-D is consistent with predictions by linear gyrokinetic simulations. In the plasma core, E × B shearing rate stabilization of the ITG modes is significant in both machines as beta is increased. Inclusion of electromagnetic effects in the gyrokinetic calculations provides additional stabilization at βN values achieved in the experiment. In AUG, proximity to the kinetic ballooning threshold and/or a stronger reduction in normalized ion heat flux with increasing input power are possible explanations for the constancy of at mid-radius as beta is increased.
Nuclear Fusion 01/2010; 50(2):025023. · 4.09 Impact Factor
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N. K. Hicks,
W.Suttrop,
K. Behler,
S. Cirant,
G. d’Antona,
M. García-‐Muñoz,
L. Giannone,
M. Maraschek,
G. Raupp,
M. Reich, A.C.C. Sips,
J. Stober,
W. Treutterer,
F. Volpe,
the ASDEX Upgrade Team
Fusion Science and Technology 01/2010; · 1.12 Impact Factor
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L. Giannone,
M. Cerna,
R. Cole,
M. Fitzek,
A. Kallenbach,
K. Lüddecke,
P.J. McCarthy,
A. Scarabosio,
W. Schneider, A.C.C. Sips, [......],
M. Reich,
J. Sachtleben,
K.H. Schuhbeck,
T. Zehetbauer,
S. Concezzi,
T. Debelle,
B. Marker,
M. Munroe,
N. Petersen,
D. Schmidt
[show abstract]
[hide abstract]
ABSTRACT: The existing VxWorks real-time system for the position and shape control in ASDEX Upgrade has been extended to calculate magnetic flux surfaces in real-time using a multi-core PCI Express system running LabVIEW RT 8.6. real-time signal processing of bolometers and manometers is performed with the on-board FPGA to calculate the measured radiated power flux and particle flux respectively from the raw data. Radiation feedback experiments use halo current measurements from the outer divertor with real-time median filter pre-processing to remove the excursions produced by ELMs. Integration of these plasma diagnostics into the control system by the exchange of XML sheets for communicating the real-time variables to be produced and consumed is in operation. Reflective memory and UDP are employed by the LabVIEW RT plasma diagnostics to communicate with the control system and other plasma diagnostics in a multi-platform real-time network.
Fusion Engineering and Design. 01/2010;
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R Neu,
V Bobkov,
R Dux,
J C Fuchs,
O Gruber,
A Herrmann,
A Kallenbach,
H Maier,
M Mayer,
T Pütterich,
V Rohde, A C C Sips,
J Stober,
K Sugiyama,
ASDE Upgrade Team
[show abstract]
[hide abstract]
ABSTRACT: Since 1999 ASDEX Upgrade increased its tungsten plasma-facing components (PFCs) and finally reached a full W coverage in 2007. Most of the initial goals of the investigations were successfully achieved. A highlight of the investigations was multiple start-ups and operation without any boronization demonstrating that performance and confinement similar to boronized operation with carbon PFCs can be reached in high power, high density discharges. This also allowed the investigation of the hydrogen retention without disturbing effects from the low-Z coating. A strong reduction of hydrogen retention was found in gas balance measurements as well as in post-mortem analyses. On the other hand, an almost complete suppression of low-Z divertor radiation was achieved after boronization, providing valuable information on the control requirements of radiative cooling by artificially introduced impurities. Among the challenges remains the strong increase of the W source and W concentration resulting from ICRH. At the same time it helped to identify the underlying physics and may lead to solutions superior to the presently used ones.
Physica Scripta 12/2009; 2009(T138):014038. · 1.20 Impact Factor
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J A Romero,
C D Challis,
R Felton,
E Jachmich,
E Joffrin,
D Lopez-Bruna,
F Piccolo,
P Sartori, A C C Sips,
P De Vries,
L Zabeo,
Jet-Efda Contributors
[show abstract]
[hide abstract]
ABSTRACT: Plasma inductance control is an essential profile control tool for tokamaks that can be used to
extend pulse duration, access to advanced regimes, reduce vertical instability growth rate, and
improve experiment reproducibility. To better understand the inductance control problem, we
derive a lumped parameter model that approximates a process that is inherently a distributed
parameter system. This model is then used to design an inductance control system, and its
performance studied with simulations. Experiments done at JET in support of the controller
have help to identify some of the issues regarding the use of boundary flux as actuator.
Inductance control with neutral beams has been achieved with different degree of efficiency.
36th EPS Conference on Plasma Physics, Sofia; 06/2009
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[show abstract]
[hide abstract]
ABSTRACT: In this paper we discuss a procedure to evaluate the fusion performance of ASDEX Upgrade discharges scaled up to ITER. The kinetic profile shape is taken from the measured profiles. Multiplication factors are used to obtain a fixed Greenwald fraction and an ITER normalized thermal pressure as in the corresponding ASDEX Upgrade discharge. The toroidal field and the plasma geometry are taken from the ITER-FEAT design (scenario 2), whereas q95 is taken from the experiment. The confinement time is inferred assuming that the measured H-factor with respect to several existing scaling laws also holds for ITER. While retaining the information contained in the multi-machine databases underlying the different scaling laws, this approach adds profile effects and confinement improvement with respect to the ITER baseline, thus including recent experimental evidence such as the prediction of peaked density profiles in ITER. Under this set of assumptions, of course not unique, we estimate the ITER performance on the basis of a wide database of ASDEX Upgrade H-mode discharges, in terms of fusion power, fusion gain and triple product. According to the three scalings considered, there is a finite probability of reaching ignition, while more than half of the discharges require less auxiliary power than the one foreseen for ITER. For all the scaling laws, high values of the thermal βN up to 2.4 are accessible. A sensitivity study gives an estimate of the accuracy of the extrapolation. The impact of different levels of tungsten concentration on the fusion performance is also studied in this paper. This scaling method is used to verify some common 0D figures of merit of ITER's fusion performance.
Nuclear Fusion 05/2009; 49(7):075004. · 4.09 Impact Factor
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L. Giannone,
W. Schneider,
P.J. McCarthy, A.C.C. Sips,
W. Treutterer,
K.Behler,
T.Eich,
J.C. Fuchs,
N. Hicks,
A. Kallenbach, [......],
A. Mlynek,
G. Neu,
G. Pautasso,
G. Raupp,
M. Reich,
K.H. Schuhbeck,
J. Stober,
F. Volpe,
T. Zehetbauer,
ASDEX Upgrade Team
Fusion Engineering and Design 01/2009; · 1.49 Impact Factor
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D C McDonald,
L Laborde,
J C DeBoo,
F Ryter,
M Brix,
C D Challis,
P de Vries,
C Giroud,
J Hobirk,
D Howell,
E Joffrin,
T C Luce,
J Mailloux,
V Pericoli-Ridolfini, A C C Sips,
K Thomsen,
JET EFDA Contributors
[show abstract]
[hide abstract]
ABSTRACT: The ITER hybrid scenario aims to exploit non-inductive current drive to enable burn times in excess of 1000 s. To achieve this, and optimize fusion performance, requires high βN (the plasma pressure normalized to a stability scaling) and energy confinement equal to or greater than that predicted for the baseline scenario. This paper discusses results from the JET candidate hybrid scenario, where βN,MHD ≤ 3.6 plasmas have been produced. Despite a different initial phase, confinement relevant plasma parameters evolve rapidly towards those of equivalent ELMy H-modes and are well described by IPB98(y, 2). In contrast to previous ELMy H-mode studies, a dedicated β scan experiment in the JET hybrid candidate scenario shows a strong negative dependence of global confinement on βN. Analysis indicates that the core transport remains consistent with weakly dependent electrostatic transport, whilst the edge confinement decreases strongly with increasing βN. By combining global confinement data from ASDEX Upgrade, DIII-D and JET hybrid scenario discharges, a multi-machine database is produced. In contrast to the JET case, confinement in ASDEX Upgrade and DIII-D is shown to be inconsistent with IPB98(y, 2) and alternative dependences are explored.
Plasma Physics and Controlled Fusion 11/2008; 50(12):124013. · 2.42 Impact Factor
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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
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A C C Sips,
P Lomas,
O Gruber,
J Hobirk,
G M D Hogeweij,
L D Horton,
F Imbeaux,
M Mattei,
F Köchl,
X Litaudon, [......],
Y-S Na,
I Nunes,
V Parail,
V Plyusnin,
J Kim,
J Romero,
G Saibene,
J Seol,
J Stober,
L Zabeo
35th EPS Conference on Plasma Physics, Hersonissos; 06/2008
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C P Perez von Thun,
M Maraschek,
S da Graça,
R J Buttery,
A Herrmann,
J Stober,
G Conway,
T Eich,
J C Fuchs,
L D Horton, [......],
A Kallenbach,
A Loarte,
H W Müller,
I Nunes,
G Saibene,
R Sartori, A C C Sips,
W Suttrop,
E Wolfrum,
the ASDEX Upgrade Team
[show abstract]
[hide abstract]
ABSTRACT: The properties of ASDEX Upgrade's type-II ELM regime, which combines good confinement with benign temporal variation of the power exhaust, make it an attractive candidate for ITER baseline scenario operation. As yet it is not understood what the physics origin of this regime is. In previous type-II ELM studies (Stober J et al 2001 Nucl. Fusion 41 1123, Stober J et al 2005 Nucl. Fusion 45 1213) a whole range of fluctuations have been reported. In this paper the properties of these fluctuations are inspected in more detail, and their relevance for the regime investigated. For the high frequency (~150–220 kHz) magnetic fluctuation activity, from its absence in certain type-II ELM scenarios and behaviour during regime transitions it is concluded that it is not an essential ingredient of type-II ELM regimes on ASDEX Upgrade. A stronger contender to explain the type-II ELM regime appears to be given by small repetitive electromagnetic bursts, and low frequency (~5–25 kHz) magnetic precursor activity associated with these bursts. It is demonstrated that these bursts give rise to small but frequent heat loads of the right order to influence ELM cycles. These are best detected in the vicinity of the inner strike point in the lower divertor through infrared thermography and Langmuir probes. Their properties further suggest that the bursts are neither small type-I ELMs nor type-III ELMs. However, it remains to be shown that the losses associated with these bursts are high enough to replace the type-I ELM losses. Other enhanced density fluctuation activity at low frequency (10–30 kHz) is detected by reflectometry near the plasma boundary. The information available about this mode is more limited, but so far a causal implication of this mode in the type-II ELM regime cannot be excluded. Overall it can be concluded that, of the three potential dissipation mechanisms, the low frequency electromagnetic burst behaviour seems to be the most promising candidate to account for type-II ELMs and their energy losses.
Plasma Physics and Controlled Fusion 05/2008; 50(6):065018. · 2.42 Impact Factor
