Active control of MHD instabilities by ECCD in ASDEX Upgrade

Maraschek, M.; Gantenbein, G.; Goodman, T.; Günter, S.; Howell, D. F.; Leuterer, F.; Mück, A.; Sauter, O.; Zohm, H.

doi:10.1088/0029-5515/45/11/018

Cited by 49 publications

(64 citation statements)

References 24 publications

(30 reference statements)

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“…ASDEX Upgrade, a medium size divertor tokamak (R 0 = 1.65 m, a = 0.5 m) with an ITERlike cross-section (single-null divertor, elongation up to 1.8, triangularity up to 0.5) and a versatile heating system, including a 140 GHz ECRH system with at present more than 2 MW of installed power, has a strong programme in this area [2], focussed directly on ITER needs. In this paper, we point out the requirements arising from the present theoretical understanding of the control of sawteeth and NTMs by ECCD and then present recent ASDEX Upgrade results that verify the basic predictions from theory.…”

Section: Introductionmentioning

confidence: 99%

Control of MHD instabilities by ECCD: ASDEX Upgrade results and implications for ITER

et al. 2007

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_______________________________________________________________This is a preprint of a paper intended for presentation at a scientific meeting. Because of the provisional nature of its content and since changes of substance or detail may have to be made before publication, the preprint is made available on the understanding that it will not be cited in the literature or in any way be reproduced in its present form. The views expressed and the statements made remain the responsibility of the named author(s); the views do not necessarily reflect those of the government of the designating Member State(s) or of the designating organization(s). In particular, neither the IAEA nor any other organization or body sponsoring this meeting can be held responsible for any material reproduced in this preprint. Abstract. The requirements for control of MHD instabilities by ECCD are reviewed. It is shown that localised current drive is needed for control of both sawteeth and Neoclassical Tearing Modes (NTMs). In the case of NTMs, the deposition width should be smaller than the island width for efficient control. At island widths smaller than the deposition width, as is predicted to occur in ITER, theory suggests that efficient control is possible only by modulating the ECCD power in phase with the island. These predictions are experimentally confirmed in ASDEX Upgrade for NTM control. Narrow deposition has also been used to extend the operational range of NTM stabilisation in ASDEX Upgrade to lower q 95 and in the improved H-mode scenario. Our results suggest that for the ITER ECCD system, good localisation of the driven curent profile as well as the capability to modulate the ECCD in phase with rotating modes will be needed for efficient MHD control by ECCD.

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Section: Introductionmentioning

confidence: 99%

Control of MHD instabilities by ECCD: ASDEX Upgrade results and implications for ITER

et al. 2007

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“…Since both I ECCD and d usually increase with toroidal launch angle, but not with the same power, an optimum toroidal launch angle can be found that maximizes j ECCD . Experiments in ASDEX Upgrade [28] have, by scanning the toroidal launch angle, convincingly verified this optimization strategy. It was found that the power requirement for complete (3,2) NTM suppression was indeed lowest when the current density was maximized, while at even higher launch angle and therefore higher I ECCD but lower j ECCD , the power requirement was found to increase.…”

Section: Progress In Understanding the Physics Of Ntm Stabilization Bmentioning

confidence: 75%

“…Also, first attempts at feedback control of the deposition had been made. Since then, full suppression of the (2,1) NTM has been demonstrated in several devices [27], [28], [29] and feedback control has been developed further. Based on this success, ECCD suppression of NTMs is now a major goal for the ITER ECCD system and recent experimental work has been geared towards establishing the physics base for the design of the ITER ECCD system with respect to this particular point.…”

Section: Application Of Ecrh and Eccd For Optimization Of Plasma Stabmentioning

confidence: 99%

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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“…Active control of the resistive wall mode (RWM) [53,54] has been demonstrated using magnetic mode detection and applied 3D fields [55][56][57][58][59][60]. Control of the m/n=2/1 neoclassical tearing mode [61,62] has been demonstrated using gyrotrons to drive currents inside the magnetic island [62][63][64][65][66][67]. Furthermore, even when instabilities grow large and result in significant modifications of the plasma state, active control "recovery techniques" can be envisioned, for instance, using ECCD on locked modes in DIII-D [68], or ECH as demonstrated on AUG [69,70] and FTU [69] to recover from locked mode and density limit disruptions.…”

Section: : Introductionmentioning

confidence: 99%