High resolution temperature and density profiles during the energy quench of density limit disruptions in Rijnhuizen tokamak project

Salzedas, F.; Hokin, S.; Schüller, F. C.; Oomens, A.A.M.

doi:10.1063/1.1489675

Cited by 10 publications

(11 citation statements)

References 21 publications

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“…Furthermore, the correlation between the evolution of SODs and the ensuing disruption is investigated; multi-channel ECE contour and the perturbation structure during SODs are analyzed. The temperature perturbation behavior is found to be somewhat similar with that is found by Salzedas et al [27][28][29], although in our most cases only one 2/1 mode and its higher order harmonics exist before disruption, and it is inferred that their nonlinear evolution triggered the thermal quench. The possible physics mechanism behind SODs is also discussed in this section.…”

Section: Introductionsupporting

confidence: 88%

Synchronous oscillation prior to disruption caused by kink modes in HL-2A tokamak plasmas

Jiang

Wang

et al. 2015

Nucl. Fusion

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A class of evident MHD activities prior to major disruption has been observed during recent radiation induced disruptions of the HL-2A tokamak discharges. It can be named SOD, synchronous oscillations prior to disruption, characterized by synchronous oscillation of electron cyclotron emission (ECE), core soft x-ray, Mirnov coil, and a D radiation signals at the divertor plate. The SOD activity is mostly observed in a parametric regime where the poloidal beta is low enough before disruption, typically corresponding to those radiationinduced disruptions. It has been found that the m/n = 2/1 mode is dominant during the SODs, and consequently it is the drop of the mode frequency and the final mode locking that lead to thermal quench. The mode frequency before the mode locking corresponds to the toroidal rotation frequency of the edge plasma. It is also found that during SODs, the location of the q = 2 surface is moving outward, and most of the plasma current is enclosed within the surface. This demonstrates that the current channel lies inside the rational surface during SOD, and thus the resistive kink mode is unstable. Further analysis of the electron temperature perturbation structure shows that the plasma is indeed dominated by the resistive kink mode, with kink-like perturbation in the core plasma region. It suggests that it is the nonlinear growth of the m/n = 2/1 resistive kink mode and its higher order harmonics, rather than the spontaneous overlapping of multiple neighboring islands, that ultimately triggered the disruption.

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Section: Introductionsupporting

confidence: 88%

Synchronous oscillation prior to disruption caused by kink modes in HL-2A tokamak plasmas

Jiang

Wang

et al. 2015

Nucl. Fusion

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“…It may be driven by the pressure/ current profile change by the 2/1 instability. Similar multiple modes (1/1 and 2/1) interaction through the profile modification between the q = 1 and q = 2 magnetic flux surfaces was observed in the disruptions in RTP [6]. Magnetic coupling from the high level m/n = 2/1 perturbation [7, 9, 13] may be another possible drive for the core instability.…”

Section: Discussion and Summarymentioning

confidence: 66%

“…The m/n = 2/1 magnetic island (m is the poloidal mode number and n is the toroidal mode number) is the most frequently observed case in MHD instability driven disruptions. The catastrophic growth of the 2/1 magnetic island without the saturation is often observed regardless of the plasma beta [5][6][7][8][9][10], and various models are devised to suggest the possible physical mechanism. They are reduction of plasma rotation through the wall interaction [11], the impurity radiation cooling in the magnetic island [12], the magnetic field stochastization through multiple mode coupling [13] and the external or internal kink driven cold bubble formation [14,15].…”

Section: Introductionmentioning

confidence: 99%

2D/3D electron temperature fluctuations near explosive MHD instabilities accompanied by minor and major disruptions

et al. 2016

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Minor and major disruptions by explosive MHD instabilities were observed with the novel quasi 3D electron cyclotron emission imaging (ECEI) system in the KSTAR plasma. The fine electron temperature (T e) fluctuation images revealed two types of minor disruptions: a small minor disruption is a q ∼ 2 localized fast transport event due to a single m/n = 2/1 magnetic island growth, while a large minor disruption is partial collapse of the q ⩽ 2 region with two successive fast heat transport events by the correlated m/n = 2/1 and m/n = 1/1 instabilities. The m/n = 2/1 magnetic island growth during the minor disruption is normally limited below the saturation width. However, as the additional interchange-like perturbation grows near the inner separatrix of the 2/1 island, the 2/1 island can expand beyond the limit through coupling with the cold bubble formed by the interchange-like perturbation.

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“…A sudden internal degradation of the energy confinementa frequently observed feature of 'density limit' disruptions (e.g. a disruption caused by proximity to the Greenwald limit and/or by an excessive plasma edge fuelling rate)-has now been observed to initiate close to the q = 2 surface in small [302], medium [303] and large-sized [304] tokamaks. In each instance, a flattening of the electron temperature profile spreads inwards from the outboard (large-R) O-point of the 2/1 mode.…”

Section: Mechanisms For Major Disruptionmentioning

confidence: 99%

Chapter 3: MHD stability, operational limits and disruptions

Hender¹,

Wesley²,

Bialek³

et al. 2007

Nucl. Fusion

1,013

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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High resolution temperature and density profiles during the energy quench of density limit disruptions in Rijnhuizen tokamak project

Cited by 10 publications

References 21 publications

Synchronous oscillation prior to disruption caused by kink modes in HL-2A tokamak plasmas

Synchronous oscillation prior to disruption caused by kink modes in HL-2A tokamak plasmas

2D/3D electron temperature fluctuations near explosive MHD instabilities accompanied by minor and major disruptions

Chapter 3: MHD stability, operational limits and disruptions

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