New insights into the generalized Rutherford equation for nonlinear neoclassical tearing mode growth from 2D reduced MHD simulations

Westerhof, E.; Blank, de Hj Hugo; Pratt, J.

doi:10.1088/0029-5515/56/3/036016

Cited by 18 publications

(25 citation statements)

References 12 publications

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“…Note that given the relatively short time scale on TCV and the strong co-ECCD involved here ( (12) accounts for the change of the linear stability through a global change of the q profile by ECCD regardless of the appearance of a mode. This is different from the effect of small local off-axis ECCD depositions on ∆ [41,42]. Interpretative simulations with ASTRA show that the magnetic shear at the 2/1 surface, s 21 , increases with increasing I cd,tot (under constant I p ), which justifies equation (12) to some extent.…”

Section: Theoretical Modelmentioning

confidence: 80%

Control of neoclassical tearing modes and integrated multi-actuator plasma control on TCV

et al. 2019

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The control of 2/1 neoclassical tearing modes (NTMs) with electron cyclotron (EC) waves has been studied both experimentally and numerically on TCV. Dynamic evolutions of NTMs along with time-varying deposition locations of the control beam have been studied in detail. The prevention of NTMs by means of preemptive EC (i.e. the control beam is switched on before the mode onset) has also been explored. A small sinusoidal sweeping with full amplitude of 0.07 (normalized to the minor radius) has been added to the control beam in two of the experiments to facilitate the comparison between NTM stabilization and prevention. It is shown that the prevention of NTMs is more efficient than NTM stabilization in terms of the minimum EC power required. Interpretative simulations with the Modified Rutherford Equation (MRE) have been performed to better quantify various effects, with coefficients well defined by dedicated experiments. Specifically, in order to obtain more insight on the dominant dependencies, a simple ad-hoc analytical model has been proposed to evaluate the time-varying classical stability index ∆ in the test discharges, based on the ∆ -triggered nature of these 2/1 NTMs. This allows simulating well the entire island width evolution with the MRE, starting from zero width and including both NTM stabilization and prevention cases for the first time. The exploration of NTM physics and control has facilitated the development of an NTM controller that is independent of the particular features of TCV and has been included in a generic plasma control system (PCS) framework. Integrated control of 2/1 NTMs, plasma β (the ratio of plasma pressure to magnetic pressure) and model-estimated safety factor q profiles has been demonstrated on TCV.

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Section: Theoretical Modelmentioning

confidence: 80%

Control of neoclassical tearing modes and integrated multi-actuator plasma control on TCV

et al. 2019

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“…Indeed, the curvature stabilization Glasser et al (1975); Kotschenreuther et al (1985); Lütjens et al (2001) also plays a stabilizing role. The "with current case" appears as more stabilizing, as the contribution from the RF-current n = 0 harmonics is known to have a stabilizing effects Westerhof et al (2016), thus explaining why this case is more stabilizing than the "No-current case". On figure 2, bottom panel, we also have plotted the saturation width of a (2,1) seed island corresponding to the "No-current case", that is, the equilibrium modified by the ECCD deposition, the latter being then removed.…”

Section: Impact Of Preemption On Mode Stability and Growth Ratementioning

confidence: 98%

“…A possible solution to control the tearing modes is to prevent their apparition in the first place, which can be achieved by tailoring the current profile so as to increase the linear stability of the mode Glasser et al (1977); Pletzer and Perkins (1999). Moreover, computations show that the contribution of ∆ RF is non-null, and stabilizing, even in the absence of an island Hegna and Callen (1997); Westerhof et al (2016). The stability of the mode is evaluated in two ways.…”

Section: Impact Of Preemption On Mode Stability and Growth Ratementioning

confidence: 99%

Comparison of magnetic island stabilization strategies from magneto-hydrodynamic simulations

Février

Maget

Lütjens

et al. 2017

Plasma Phys. Control. Fusion

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The degradation of plasma confinement in tokamaks by magnetic islands motivates to better understand their possible suppression using Electron Cyclotron Current Drive (ECCD) and to investigate the various strategies relevant for this purpose. In this work, we evaluate the efficiency of several control methods through nonlinear simulations of this process with the toroidal MHD code XTOR Lütjens and Luciani (2010), which has been extended to incorporate in Ohm's law a source term modeling the RF driven current resulting from the interaction of the RF waves with the plasma. A basic control system has been implemented in the code, allowing testing advanced strategies that require feedback on island position or phase. We focus in particular on the robustness of the control strategies towards the uncertainties that apply on the control and ECCD systems, such as the risk of misalignment of the current deposition or the possible inability to generate narrow current deposition.

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“…The code interfaced in TRANSP solves a quasi-cylindrical version of this equation by using both the unperturbed current density J 0 (r) and safety factor q 0 (r) profiles from TRANSP. As TRANSP separately calculates the ECCD current, this term could be calculated excluding the contribution of the equilibrium ECCD perturbation to the total current, thus avoiding potential double counting [20]. The normalized discontinuity in the derivative at the resonant surface r s :…”

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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New insights into the generalized Rutherford equation for nonlinear neoclassical tearing mode growth from 2D reduced MHD simulations

Cited by 18 publications

References 12 publications

Control of neoclassical tearing modes and integrated multi-actuator plasma control on TCV

Control of neoclassical tearing modes and integrated multi-actuator plasma control on TCV

Comparison of magnetic island stabilization strategies from magneto-hydrodynamic simulations

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

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