The effects of electron cyclotron heating and current drive on toroidal Alfvén eigenmodes in tokamak plasmas

Sharapov, S. E.; García-Muñoz, M.; Zeeland, M. A. Van; Bobkov, B.; Classen, I. G. J.; Ferreira, J.; Figueiredo, A.; Fitzgerald, Michael L.; Galdón-Quiroga, J.; Gallart, D.; Geiger, B.; Gonzalez-Martin, J.; Johnson, T.; Lauber, P.; Mantsinen, M.; Nabais, F.; Nikolaeva, V.; Rodriguez-Ramos, M.; Sanchis-Sanchez, L.; Schneider, P. A.; Snicker, A.; Vallejós, P.

doi:10.1088/1361-6587/aa90ee

Cited by 33 publications

(35 citation statements)

References 24 publications

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“…Studies have been made on the physical properties of specific modes, and several external actuators have been proposed and demonstrated in tokamaks and helical devices for controlling and/or stabilizing EP-driven modes [4]. Promising control techniques are based on (i) varying the energetic-ion sources to modify the gradients in the energetic ion-distribution [5][6][7][8][9][10], (ii) localized electron cyclotron heating (ECH) to modify the energetic-ion slowing-down distribution [11][12][13][14][15][16][17][18], (iii) a localized electron cyclotron current drive (ECCD) for modifying the equilibrium [19,20] and (iv) externally applied 3D perturbative magnetic fields for manipulating the energetic-ion distribution and thus the wave drive [21,22].…”

Section: Introductionmentioning

confidence: 99%

Effect of ECH/ECCD on energetic-particle-driven MHD modes in helical plasmas

et al. 2020

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The effect of electron cyclotron heating (ECH) and electron cyclotron current drive (ECCD) on energetic-particle (EP)-driven magnetohydrodynamic (MHD) modes is studied in the helical devices LHD, TJ-II and Heliotron J. We demonstrate that EP-driven MHD modes, including Alfvén eigenmodes (AEs) and energetic particle modes (EPMs), can be controlled by ECH/ECCD. In the LHD device, which has a moderate rotational transform and a high magnetic shear, co-ECCD enhances toroidal AEs (TAEs) and global AEs (GAEs), while counter-ECCD stabilizes them, which improves the neutron rate compared with the co-ECCD case. Counter-ECCD decreases the core rotational transform and increases the magnetic shear, strengthening the continuum damping on the shear Alfvén continua (SAC). In the TJ-II device, which has a high rotational transform, moderate magnetic shear and low toroidal field period, helical AEs (HAEs) appear when the HAE frequency gap of the SAC is changed by counter-ECCD combined with a bootstrap current and neutral-beam-driven current. On the other hand, both co- and counter-ECCD are effective in stabilizing GAEs and EPMs in the Heliotron J device, which has a low rotational transform and low magnetic shear. The experimental results indicate that the magnetic shear has a stabilizing effect regardless of its sign. Modeling analysis using the FAR3d code shows that the growth rates are reduced by both co- and counter-ECCD in Heliotron J, reproducing the experimental results. ECH only affects EP-driven MHD modes, and the experimental results show that the effect depends on the magnetic configuration. In Heliotron J, some modes are stabilized with an increase in ECH power in the low-bumpiness magnetic configuration, while some modes are destabilized in the high- and medium-bumpiness magnetic configurations.

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Section: Introductionmentioning

confidence: 99%

Effect of ECH/ECCD on energetic-particle-driven MHD modes in helical plasmas

et al. 2020

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“…The non inductive current drive is a promising mechanism to achieve steady state operation in advanced tokamaks where large bootstrap currents replace the magnetic field component generated by the transformer coils [10,11,12]. In addition, the non inductive current drive is used to modify the magnetic field configuration of the fusion devices, for example by the electron cyclotron current drive (ECCD) [13,14] and the neutral beam current drive (NBCD) [15,16,17,18], leading to an improved stability of the pressure and current gradient driven modes (PM) [19,20,21,22,23,24] as well as the Alfvén Eigenmodes (AE) [25,26]. ECCD is also used in stellarators [27,28,29,30] to improve the stability properties of the plasma with respect to the PM and AE [31,32,33,34,35,36,37,38,39].…”

Section: Introductionmentioning

confidence: 99%

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Varela¹,

Cooper²,

Nagaoka³

et al. 2020

Nucl. Fusion

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The aim of the present study is to analyze the stability of the pressure gradient driven modes (PM) and Alfvén eigenmodes (AE) in the Large Helical Device (LHD) plasma if the rotational transform profile is modified by the current drive of the tangential neutral beam injectors (NBI). This study forms a basic search for optimized operation scenarios with reduced mode activity. The analysis is performed using the code FAR3d which solves the reduced MHD equations describing the linear evolution of the poloidal flux and the toroidal component of NBI current drive 2 the vorticity in a full 3D system, coupled with equations for density and parallel velocity moments of the energetic particle (EP) species, including the effect of the acoustic modes. The Landau damping and resonant destabilization effects are added via the closure relation. On-axis and off-axis NBI current drive modifies the rotational transform which becomes strongly distorted as the intensity of the neutral beam current drive (NBCD) increases, leading to wider continuum gaps and modifying the magnetic shear. The simulations with on-axis NBI injection show that a counter (ctr-) NBCD in inward shifted and default configurations leads to a lower growth rate of the PM, although strong n = 1 and 2 AEs can be destabilized. For the outward shifted configurations, a co-NBCD improves the AEs stability but the PM are further destabilized if the co-NBCD intensity is 30 kA/T. If the NBI injection is off-axis, the plasma stability is not significantly improved due to the further destabilization of the AE and energetic particle modes (EPM) in the middle and outer plasma region.

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“…Theoretical investigations [61,72,73] of the plasma pressure gradient effect upon the TAE stability have shown that the core localized TAEs can be suppressed when the normalized pressure gradient (α) exceeds a critical level (α c ) as described in equations ( 1) and ( 2), considering finite aspect ratio at finite beta [24][25][26]:…”

Section: Damping Effectmentioning

confidence: 99%

“…The correlation between performance degradation and AE activities has been investigated widely. At present-day experiments, various AE control tools such as electron-cyclotron (EC) waves, external magnetic perturbations and fast-ion pressure gradient change have been investigated and tested in tokamaks [20][21][22][23][24][25][26] and helical devices [27][28][29][30]. Among the various control tools, the electron cyclotron current drive (ECCD) is one of the most promising techniques because a flexible deposition of the EC waves is possible on the location where the AEs are excited.…”

Section: Introductionmentioning

confidence: 99%

Suppression of toroidal Alfvén eigenmodes by the electron cyclotron current drive in KSTAR plasmas

et al. 2022

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Advanced operation scenarios such as high poloidal beta (βP) or high q min are promising concepts to achieve the steady-state high-performance fusion plasmas. However, those scenarios are prone to substantial Alfvénic activity, causing fast-ion transport and losses. Recent experiments with the advanced operation scenario on KSTAR tokamak have shown that the electron cyclotron current drive (ECCD) is able to mitigate and suppress the beam-ion driven toroidal Alfvén eigenmodes (TAEs) for over several tens of global energy confinement time. Co-current directional intermediate off-axis ECCD lowers the central safety factor slightly and tilts the central q-profile shape so that the continuum damping in the core region increases. Besides, the rise of central plasma pressure and increased thermal-ion Landau damping contribute to TAE stabilization. While the TAEs are suppressed, neutron emission rate and total stored energy increase by approximately 45% and 25%, respectively. Fast-ion transport estimated by TRANSP calculations approaches the classical level during the TAE suppression period. Substantial reduction in fast-ion loss and neutron deficit is also observed. Enhancement of fast-ion confinement by suppressing the TAEs leads to an increase of non-inductive current fraction and will benefit the sustainment of the long-pulse high-performance discharges.

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The effects of electron cyclotron heating and current drive on toroidal Alfvén eigenmodes in tokamak plasmas

Abstract: View the article online for updates and enhancements. Recent citations Kinetic equilibrium reconstruction for the NBI-and ICRH-heated H-mode plasma on EAST tokamak Zhen ZHENG et al

Cited by 33 publications

References 24 publications

Effect of ECH/ECCD on energetic-particle-driven MHD modes in helical plasmas

Effect of ECH/ECCD on energetic-particle-driven MHD modes in helical plasmas

Effect of the tangential NBI current drive on the stability of pressure and energetic particle driven MHD modes in LHD plasma

Suppression of toroidal Alfvén eigenmodes by the electron cyclotron current drive in KSTAR plasmas

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