21st IAEA Fusion Energy Conference: summary of sessions EX/D, EX/S and EX/W

Zohm, H.

doi:10.1088/0029-5515/47/10/s03

Cited by 2 publications

(2 citation statements)

References 37 publications

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“…Similar results were also found when optimising the launch angle in JT-60U [29]. We note here that a narrower deposition profile is also predicted to be beneficial for sawtooth tailoring and first hints of this have recently been obtained on ASDEX Upgrade [33]. Another important point is that only helical current of the same helicity as the magnetic island has a stabilizing effect, so that current driven in the area of the island O-point is stabilizing while helical current around the X-point is predicted to have a destabilizing effect.…”

Section: Progress In Understanding the Physics Of Ntm Stabilization Bsupporting

confidence: 82%

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Zohm

2007

Fusion Science and Technology

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A review of recent experimental results in the area of ECRH and ECCD is given. Special emphasis is put on the recent developments of new schemes in which EC waves can heat and drive current in magnetically confined fusion plasmas. These comprise scenarios to overcome the density cutoff experienced in application of the classical O1 and X2 scheme as well as to increase the current drive efficiency of EC waves while maintaining their good localization. In particular, we discuss recent experimental progress in tokamaks, stellarators and spherical tori in the areas of the O2, X3 and EBW schemes (mostly OXB scheme) as well as experiments in which the combination of ECCD with Lower Hybrid Current Drive (LHCD) leads to a synergetic increase of the ECCD efficiency. A particular application of ECCD that has recently received a lot of attention and is therefore reviewed in this paper is the suppression of Neoclassical Tearing Modes (NTMs) by ECCD. We show that the theoretically predicted requirements for ECCD in terms of deposition (maximising the ECCD driven current density) and injection in phase with the O-point of the magnetic island associated with the NTM (which is needed when the island width falls below the deposition width) have been verified experimentally. Also, many of the elements needed for constructing a reliable, feedback controlled NTM suppression system for ITER based on ECCD have now been demonstrated experimentally and the next step, which is their integration into a reliable scheme, is well within reach.

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Section: Progress In Understanding the Physics Of Ntm Stabilization Bsupporting

confidence: 82%

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Zohm

2007

Fusion Science and Technology

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“…Simulations also predict that counter-ECCD close to but inside the q = 1 surface should stabilize sawteeth. This has been confirmed on ASDEX Upgrade [20,22] and perhaps on JT-60U. On ASDEX Upgrade, moving counter-ECCD further inside q = 1 leads to complete elimination of the sawtooth crashes; however, from the changed MHD signature, it can be concluded that the stabilizing mechanism is different than that due to off-axis co-ECCD.…”

Section: Sawtooth Controlmentioning

confidence: 77%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

997

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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21st IAEA Fusion Energy Conference: summary of sessions EX/D, EX/S and EX/W

Cited by 2 publications

References 37 publications

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Recent Experimental Progress in Electron Cyclotron Resonance Heating and Electron Cyclotron Current Drive in Magnetically Confined Fusion Plasmas

Chapter 3: MHD stability, operational limits and disruptions

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