Comparison of magnetic island stabilization strategies from magneto-hydrodynamic simulations

Février, O.; Maget, P.; Lütjens, H.; Beyer, Peter

doi:10.1088/1361-6587/aa5861

Cited by 11 publications

(13 citation statements)

References 43 publications

(102 reference statements)

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“…The parameters of the exercise are deduced from a real TCV discharge [70].The perturbation of the frequency decays on the timescale 1/a 22 .The Fig.8 (top) uncertainties.The procedure is expected to be effective also in more complex cases, with disturbances due, for instance,to mode coupling. The results of modelling with the extended MHD code XTOR [29], reproduced in Fig.9 are significantly similar to those of the above model.In both cases (Fig.8, Fig.9) the EC power was not modulated and the oscillations in the response (decaying mode rms amplitide) are just due to the beam sweeping close to the rational q surface. In Refs.…”

Section: Eccd Magnetic Island Supression As Converse Of a Nonlineasupporting

confidence: 81%

Physics conditions for robust control of tearing modes in a rotating tokamak plasma

Lazzaro¹,

Borgogno

Brunetti³

et al. 2017

Plasma Phys. Control. Fusion

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The disruptive collapse of the current sustained equilibrium of a tokamak is perhaps the single most serious obstacle on the path toward controlled thermonuclear fusion. The current disruption is generally too fast to be identified early enough and tamed efficiently, and may be associated with a variety of initial perturbing events. However, a common feature of all disruptive events is that they proceed through the onset of magnetohydrodynamic instabilities and field reconnection processes developing magnetic islands, which eventually destroy the magnetic configuration. Therefore the avoidance and control of magnetic reconnection instabilities is of foremost importance and great attention is focused on the promising stabilization techniques based on localized rf power absorption and current drive. Here a short review is proposed of the key aspects of high power rf control schemes (specifically electron cyclotron heating and current drive) for tearing modes, considering also some effects of plasma rotation. From first principles physics considerations, new conditions are presented and discussed to achieve control of the tearing perturbations by means of high power  (P P EC ohm ) in regimes where strong nonlinear instabilities may be driven, such as secondary island structures, which can blur the detection and limit the control of the instabilities. Here we consider recent work that has motivated the search for the improvement of some traditional control strategies, namely the feedback schemes based on strict phase tracking of the propagating magnetic islands.

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Section: Eccd Magnetic Island Supression As Converse Of a Nonlineasupporting

confidence: 81%

Physics conditions for robust control of tearing modes in a rotating tokamak plasma

Lazzaro¹,

Borgogno

Brunetti³

et al. 2017

Plasma Phys. Control. Fusion

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“…In practice, all simulations described here have an uncertainty on the results that is equal to the time step used for the update of the EC parameters, δt HCD . While some of these effects, like the evolution of the magnetic island over transport time scales, the inclusion of toroidal effects in the calculation of the tearing stability term, and corrections in the calculation of ∆ (w) to avoid counting the EC current twice [20], will be accounted for in future work, we note here that a self-consistent approach would be possible only within the context of 3D MHD simulations [26].…”

Section: Calculation Of Ntm Stability In Transp With Simulated Ec Fementioning

confidence: 99%

Electron cyclotron power management for control of neoclassical tearing modes in the ITER baseline scenario

et al. 2017

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Time-dependent simulations are used to evolve plasma discharges in combination with a modified Rutherford equation for calculation of neoclassical tearing mode (NTM) stability in response to electron cyclotron (EC) feedback control in ITER. The main application of this integrated approach is to support the development of control algorithms by analyzing the plasma response with physics-based models and to assess how uncertainties in the detection of the magnetic island and in the EC alignment affect the ability of the ITER EC system to fulfill its purpose. Simulations indicate that it is critical to detect the island as soon as possible, before its size exceeds the EC deposition width, and that maintaining alignment with the rational surface within half of the EC deposition width is needed for stabilization and suppression of the modes, especially in the case of modes with helicity (2, 1). A broadening of the deposition profile, for example due to wave scattering by turbulence fluctuations or not well aligned beams, could even be favorable in the case of the (2, 1)−NTM, by relaxing an over-focussing of the EC beam and improving the stabilization at the mode onset. Pre-emptive control reduces the power needed for suppression and stabilization in the ITER baseline discharge to a maximum of 5 MW, which should be reserved and available to the upper launcher during the entire flattop phase. Assuming continuous triggering of NTMs, with preemptive control ITER would be still able to demonstrate a fusion gain of Q = 10.

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“…2012; Fevrier et al. 2017) with ‘sweeping’ rf injection demonstrate a technique that can overcome the problems analysed in the present work.…”

Section: Introductionmentioning

confidence: 66%

“…2014) and simulations (Fevrier et al. 2017). The delivery of large, localized power to the system may however give rise to parasitic processes such as the possible onset of smaller scale structures in a non-constant flux regime (Comisso et al.…”

Section: Introductionmentioning

confidence: 99%

“…in experiments (Maraschek 2012;Koleman et al 2014) and simulations (Fevrier et al 2017). The delivery of large, localized power to the system may however give rise to parasitic processes such as the possible onset of smaller scale structures in a non-constant flux ψ regime (Comisso et al 2016), which may blur detection and hinder the feedback stabilization action.…”

Section: Introductionmentioning

confidence: 99%

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Magnetic island suppression by electron cyclotron current drive as converse of a forced reconnection problem

et al. 2018

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This paper addresses one aspect of the problem of the suppression of tearing mode magnetic islands by electron cyclotron current drive (ECCD) injection, formulating the problem as the converse of a forced reconnection problem. New physical conditions are discussed which should be considered in the technical approach towards a robust control strategy. Limits on the ECCD deposition are determined to avoid driving the system into regimes where secondary instabilities develop. Numerical simulations confirming the theory are also presented.

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Comparison of magnetic island stabilization strategies from magneto-hydrodynamic simulations

Cited by 11 publications

References 43 publications

Physics conditions for robust control of tearing modes in a rotating tokamak plasma

Physics conditions for robust control of tearing modes in a rotating tokamak plasma

Electron cyclotron power management for control of neoclassical tearing modes in the ITER baseline scenario

Magnetic island suppression by electron cyclotron current drive as converse of a forced reconnection problem

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