Steady state advanced scenarios at ASDEX Upgrade

Sips, A. C. C.; Arslanbekov, Robert; Atanasiu, C. V.; Becker, Werner; Becker, G.; Behler, K.; Behringer, K.; Bergmann, Andreas; Bilato, R.; Bolshukhin, D.; Borraß, K.; Braams, Bastiaan J.; Brambilla, M.; Braun, F.; Buhler, A.; Conway, G. D.; Coster, D.; Drube, R.; Dux, R.; Egorov, S.M.; Eich, T.; Engelhardt, K.; Fahrbach, H.‐U.; Fantz, U.; Faugel, H.; Foley, M.; Fournier, K. B.; Franzen, P.; Fuchs, Julien; Gafert, J.; Gantenbein, G.; Gehre, O.; Geier, A.; Gernhardt, J.; Gruber, O.; Gude, A.; Günter, S.; Haas, G.; Hartmann, D.; Heger, B.; Heinemann, B.; Herrmann, A.; Hobirk, J.; Hofmeister, F.; Hohenöcker, H.; Horton, L. D.; Igochine, V.; Jacobi, D.; Jakobi, Martin; Jenko, F.; Kallenbach, A.; Kardaun, O.; Kaufmann, Michael; Keller, Andrei; Kendl, A.; Kim, J. W.; Kirov, K.; Kochergov, R.; Kollotzek, H.; Kraus, Werner; Krieger, K.; Kurzan, B.; Lang, P. T.; Lauber, P.; Laux, M.; Leuterer, F.; Lohs, A.; Lorenz, A.; Maggi, C. F.; Maier, H.; Mank, K.; Manso, M. E.; Maraschek, M.; Mast, K. F.; McCarthy, Patrick J.; Meisel, D.; Meister, H.; Méo, F.; Merkel, R.; Merkl, D.; Mertens, V.; Monaco, F.; Mück, A.; Müller, Hans; Münich, M.; Mürmann, H.; Na, Y. S.; Neu, G.; Neu, R.; Neuhäuser, J.; Noterdaeme, Jean-Marie; Nunes, I.; Pautasso, G.; Peeters, A. G.; Pereverzev, G.; Pinches, S. D.; Poli, E.; Proschek, M.; Pugno, R.; Quigley, E.; Raupp, G.; Ribeiro, Tiago; Riedl, R.; Riondato, S.; Rohde, V.; Roth, J.; Ryter, F.; Saarelma, S.; Sandmann, W.; Schade, S.; Schilling, H.-B.; Schneider, W.; Schramm, G.; Schweizer, Sabine; Scott, B.; Seidel, U.; Serra, F.; Šesnić, S.; Sihler, C.; Silva, A.; Speth, E.; Stäbler, A.; Steuer, K.-H.; Stober, J.; Streibl, B.; Strumberger, E.; Suttrop, W.; Tabasso, A.; Tanga, A.; Tardini, G.; Tichmann, C.; Treutterer, W.; Troppmann, M.; Varela, P.; Vollmer, O.; Wágner, D.; Wenzel, U.; Wesner, F.; Wolf, R. C.; Wolfrum, E.; Würsching, E.; Yu, Q.; Zasche, D.; Zehetbauer, T.; Zehrfeld, H. P.; Zohm, H.

doi:10.1088/0741-3335/44/12b/306

Cited by 111 publications

(77 citation statements)

References 40 publications

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“…Thus, (3,2) NTMs might not be a very serious problem for ITER for β N > 2.3; though current and density profiles may influence the exact β N for transition to the FIR NTM regime. A weak magnetic shear that is characteristic of the recently developed advanced Hmodes [106,116] would be additionally beneficial as it reduces the influence of the NTMs on confinement. The weak shear is destabilizing for the (4,3) mode and thus might decrease the critical β N value for the FIR-NTMs.…”

Section: Mitigation Of Ntmsmentioning

confidence: 99%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

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1,000

947

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Progress in the area of MHD stability and disruptions, since the publication of the 1999 ITER Physics Basis document Nucl. Fusion 39 2137-2664, is reviewed. Recent theoretical and experimental research has made important advances in both understanding and control of MHD stability in tokamak plasmas. Sawteeth are anticipated in the ITER baseline ELMy H-mode scenario, but the tools exist to avoid or control them through localized current drive or fast ion generation. Active control of other MHD instabilities will most likely be also required in ITER. Extrapolation from existing experiments indicates that stabilization of neoclassical tearing modes by highly localized feedback-controlled current drive should be possible in ITER. Resistive wall modes are a key issue for S128 Chapter 3: MHD stability, operational limits and disruptions advanced scenarios, but again, existing experiments indicate that these modes can be stabilized by a combination of plasma rotation and direct feedback control with non-axisymmetric coils. Reduction of error fields is a requirement for avoiding non-rotating magnetic island formation and for maintaining plasma rotation to help stabilize resistive wall modes. Recent experiments have shown the feasibility of reducing error fields to an acceptable level by means of non-axisymmetric coils, possibly controlled by feedback. The MHD stability limits associated with advanced scenarios are becoming well understood theoretically, and can be extended by tailoring of the pressure and current density profiles as well as by other techniques mentioned here. There have been significant advances also in the control of disruptions, most notably by injection of massive quantities of gas, leading to reduced halo current fractions and a larger fraction of the total thermal and magnetic energy dissipated by radiation. These advances in disruption control are supported by the development of means to predict impending disruption, most notably using neural networks. In addition to these advances in means to control or ameliorate the consequences of MHD instabilities, there has been significant progress in improving physics understanding and modelling. This progress has been in areas including the mechanisms governing NTM growth and seeding, in understanding the damping controlling RWM stability and in modelling RWM feedback schemes. For disruptions there has been continued progress on the instability mechanisms that underlie various classes of disruption, on the detailed modelling of halo currents and forces and in refining predictions of quench rates and disruption power loads. Overall the studies reviewed in this chapter demonstrate that MHD instabilities can be controlled, avoided or ameliorated to the extent that they should not compromise ITER operation, though they will necessarily impose a range of constraints.

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Section: Mitigation Of Ntmsmentioning

confidence: 99%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

Self Cite

1,000

947

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“…In this hybrid scenario [19][20][21][22][23] plasma on DIII-D, increasing the normalized beta (β N ) from 2.6 to 3.2 at 4250 ms, causes a m/n = 3/2 NTM to be destabilized ≈350 ms later. A direct measurement of the safety factor minimum using the MSE pitch angles [15] shows an abrupt increase from q min < 1 to q min ≈ 1.1 after the destabilization of the m/n = 3/2 NTM (figure 1(c)); this is consistent with the disappearance of the sawtooth oscillation after 4700 ms.…”

Section: Measurement Of Missing Bootstrap Currentmentioning

confidence: 99%

Local formulae for combinatorial Pontryagin classes

Gaifullin¹

2004

Izv. Math.

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Using direct analysis of the motional Stark effect (MSE) signals, an explicit measurement of the 'missing' bootstrap current density around the island location of a neoclassical tearing mode (NTM) is made for the first time. When the NTM is suppressed using co-electron cyclotron current drive, the measured changes in the current profile that restore the bootstrap current are also directly found from the MSE measurements. Additionally, direct analysis of helical perturbations in the MSE signals during slowly rotating 'quasi-stationary' modes shows the first explicit measurement of the deficit in the toroidal current density in the island O-point.

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“…The observation of improved confinement with respect to the IPB98(y,2) scaling at high  has been reported on several tokamak devices, typically associated with an optimisation of the q-profile shape in plasma scenarios variously described as 'improved H-mode', 'advanced inductive' or 'hybrid' [e.g. [4][5][6]. The JET experiments used a 'current overshoot' technique before the main heating pulse to transiently shape the q-profile, suggesting that this was an important factor in the achievement of H 98 >1 [6].…”

Section: Introductionmentioning

confidence: 99%

Improved confinement in JET highβplasmas with an ITER-like wall

et al. 2015

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Abstract. The replacement of the JET carbon wall (C-wall) by a Be/W ITER-like wall (ILW) has affected the plasma energy confinement. To investigate this, experiments have been performed with both the C-wall and ILW to vary the heating power over a wide range for plasmas with different shapes. It was found that the power degradation of thermal energy confinement was weak with the ILW; much weaker than the IPB98(y,2) scaling and resulting in an increase in normalised confinement from H 98~0 .9 at  N~1 .5 to H 98~1 .2-1.3 at  N~2 .5-3.0 as the power was increased (where H 98 = E / IPB98(y,2) and  N = T B T /aI P in %T/mMA). This reproduces the general trend in JET of higher normalised confinement in the so-called 'hybrid' domain, where normalised  is typically above 2.5, compared with 'baseline' ELMy H-mode plasmas with  N~1 .5-2.0. This weak power degradation of confinement, which was also seen with the C-wall experiments at low triangularity, is due to both increased edge pedestal pressure and core pressure peaking at high power. By contrast, the high triangularity C-wall plasmas exhibited elevated H 98 over a wide power range with strong, IPB98(y,2)-like, power degradation. This strong power degradation of confinement appears to be linked to an increase in the source of neutral particles from the wall as the power increased, an effect that was not reproduced with the ILW. The reason for the loss of improved confinement domain at low power with the ILW is yet to be clarified, but contributing factors may include changes in the rate of gas injection, wall recycling, plasma composition and radiation. The results presented in this paper show that the choice of wall materials can strongly affect plasma performance, even changing confinement scalings that are relied upon for extrapolation to future devices.

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Steady state advanced scenarios at ASDEX Upgrade

Cited by 111 publications

References 40 publications

Chapter 3: MHD stability, operational limits and disruptions

Chapter 3: MHD stability, operational limits and disruptions

Local formulae for combinatorial Pontryagin classes

Improved confinement in JET highβplasmas with an ITER-like wall

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