Beta limit due to resistive tearing modes in T-10

Kislov, D. A.; Esipchuk, Yu. V.; Kirneva, N.; Klimanov, I.; Pavlov, Yu.D.; Субботин, А. А.; Alikaev, V. V.; Borshegovskiy, A.A.; Gott, Yu. V.; Kakurin, A. M.; Krilov, S V; Myalton, T.B.; Roy, I. N.; Trukhina, E.V.; Волков, В.В.; Team, the JT-60

doi:10.1088/0029-5515/41/11/311

Cited by 21 publications

(20 citation statements)

References 24 publications

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“…The understanding and relevance of each of these terms have been further developed since [1]: -The first term is the classical term, which has a weak dependence on W . It has been shown that classical tearing modes can provide the seed islands for NTMs [63,64], and this may be one of the possible explanations of the 'triggerless NTMs' observed in other machines like ASDEX Upgrade [65], JT-60U [55], T-10 [56] and TFTR [66]. This usually happens when the current profile is modified [63], and could become the main seed island trigger mechanism in hybrid scenarios, or when β approaches the ideal limit, as can become large and positive [64] and thus could become important in advanced scenarios.…”

Section: Neoclassical Tearing Modesmentioning

confidence: 98%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

980

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: Neoclassical Tearing Modesmentioning

confidence: 98%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

980

947

View full text Add to dashboard Cite

show abstract

“…For a q ¼ m=n island of full width w at rational surface q of poloidal mode m and toroidal mode n, the island growth or decay 4,6,20,[22][23][24][25][26][27][28][29][30][31][32][33][34][35][36] is here given by the MRE,…”

Section: Form Of the Modified Rutherford Equation Used For Empirimentioning

confidence: 99%

Aspect ratio effects on neoclassical tearing modes from comparison between DIII-D and National Spherical Torus Experiment

et al. 2012

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Neoclassical tearing mode islands are sustained by helically perturbed bootstrap currents arising at finite beta from toroidal effects that trap a fraction of the particles in non-circulating orbits. DIII-D and NSTX are here operated with similar shape and cross-sectional area but almost a factor of two difference in inverse aspect ratio a=R. In these experiments, destabilized n ¼ 1 tearing modes were self-stabilized (reached the "marginal point") by reducing neutral-beam power and thus beta. The measure of the marginal island gives information on the small-island stabilizing physics that in part (with seeding) governs onset. The marginal island width on NSTX is found to be about three times the ion banana width and agrees with that measured in DIII-D, except for DIII-D modes closer to the magnetic axis, which are about two times the ion banana width. There is a balance of the helically perturbed bootstrap term with small island effects with the sum of the classical and curvature terms in the modified Rutherford equation for tearing-mode stability at the experimental marginal point. Empirical evaluation of this sum indicates that while the stabilizing effect of the curvature term is negligible in DIII-D, it is important in NSTX. The mode temporal behavior from the start of neutral-beam injection reduction also suggests that NSTX operates closer to marginal classical tearing stability; this explains why there is little hysteresis in beta between mode onset, saturation, and self-stabilization (while DIII-D has large hysteresis in beta). NIMROD code module component calculations based on DIII-D and NSTX reconstructed experimental equilibria are used to diagnose and confirm the relative importance of the stabilizing curvature effect, an advantage for low aspect ratio; the relatively greater curvature effect makes for less susceptibility to NTM onset even if the classical tearing stability index is near marginal. V C 2012 American Institute of Physics. [http://dx.

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“…2008FEC (Geneva, Switzerland, 2008) (Vienna: IAEA). plasma current expressed in MA) have found this so-called soft β limit (in contrast to disruptive ones) on TFTR [1], ASDEX-Upgrade [2], DIII-D [3], JET [4], JT-60U [5], COMPASS-D [6], T-10 [7], TCV [8] or TEXTOR [9]. In these plasma with high pressure, the drive for island growth is dominated by a non-linear coupling between the pressure and the parallel current density, through the bootstrap current (driven by the pressure gradient), resulting in the emergence of a metastable branch called neoclassical tearing mode (NTM) [10].…”

Section: Introductionmentioning

confidence: 95%

Modelling of (2,1) NTM threshold in JET advanced scenarios

Maget

Lütjens

Coelho³

et al. 2010

Nucl. Fusion

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The limit to high performances advanced scenario discharges with q min above unity is generally set by the (2,1) magneto-hydro-dynamic (MHD) mode in JET. We investigate here the possibility that this mode is a (2,1) neoclassical tearing mode (NTM) by computing the critical island width at which such mode would be unstable, using a nonlinear MHD code where the relevant bootstrap current physics is accounted for. We show that the triggering of a (2,1) NTM is consistent with a lowering of the critical island width as the plasma current diffuses towards the centre. This is explained partly by the increase in the magnetic shear at the resonant surface, which weakens the curvature stabilization term, as found in the analytical framework of a generalized Rutherford equation. A comparison with experiment is made in the non-linear regime, showing encouraging results on the dynamics of the confinement degradation and mode structure.

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Beta limit due to resistive tearing modes in T-10

Cited by 21 publications

References 24 publications

Chapter 3: MHD stability, operational limits and disruptions

Chapter 3: MHD stability, operational limits and disruptions

Aspect ratio effects on neoclassical tearing modes from comparison between DIII-D and National Spherical Torus Experiment

Modelling of (2,1) NTM threshold in JET advanced scenarios

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