NTM stabilization by alternating O-point EC current drive using a high-power diplexer

Kasparek, W.; Doelman, Niek; Stober, J.; Maraschek, M.; Zohm, H.; Monaco, F.; Eixenberger, H.; Klop, W.; Wágner, D.; Schubert, M.; Schütz, H.; Grunwald, Gerhard; Plaum, B.; Munk, R.; Schlüter, K.

doi:10.1088/0029-5515/56/12/126001

Cited by 13 publications

(11 citation statements)

References 30 publications

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“…A practical steering of the rf beam across the target surface could probably be performed more easily developing a beam switch akin to the FADIS system [71] which as beeen used succesfully on ASDEX-U to switch the EC power transmission between the transmission lines connected to the upper and lower launchers, respectively, in synhronism with the mode rotation, so that the EC power could effectively be absorbed continuously close the O-point [72]. Another example of NTM amplitude control using a similar method is shown in Fig.11 [61].…”

Section: Eccd Magnetic Island Supression As Converse Of a Nonlineamentioning

confidence: 99%

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 Nonlineamentioning

confidence: 99%

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 present devices, typical diffusion times correspond to frequencies of ∼1kHz, coincidentally right around the natural island rotation rates to which pulse times are matched. The majority of modulation experiments report modest improvements, with stabilization made possible at lower average powers compared to continuous wave schemes 35,[43][44][45][46] . It has also been found that modulation seems to provide more a benefit when deposition is broad 43,47 .…”

Section: Discussionmentioning

confidence: 99%

Pulsed RF Schemes for Tearing Mode Stabilization

Jin,

Fisch,

Reiman

2020

Preprint

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The RF stabilization of tearing modes with current condensation has the potential to increase stabilization efficiency and loosen power localization requirements. Such benefits stem from the cooperative feedback between the RF deposition and resulting island temperature perturbation governed by diffusion. A self consistent treatment of the damping of an rf ray as it traverses the island shows that low damping scenarios can require unfavorably high powers to overcome initial power leakage and effectively capitalize on the nonlinear effect. In this work it is demonstrated that for such regimes, modulated stabilization schemes can achieve significant improvements in heating and current drive contributions to stabilization for the same average power as a continuous wave scheme. The impact of modulation frequency and duty cycle on the performance is explored, the results of which suggest modulation strategies in which the pulsing periods are kept on the order of a diffusive time.

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“…NTMs can be linearly stable and nonlinearly unstable and can be controlled with the injection of the current inside the island to compensate for the loss of the helical current inside the flattened island. While control of the 2/1 mode has been empirically successful with the injection of the current in the island using an ECCD system [79,80], the stability physics of the 2/1 mode has complex dependence on various plasma parameters and the cross-field transport has not been comprehensively validated yet. Among them, a comprehensive validation of the stability criteria of the 2/1 instability as well as the modified turbulence critical for the cross-field transport across the q~2 surface in the presence of the 2/1 island, has been attempted in the course of modeling studies.…”

Section: Brief Review Of Ntm Instabilitymentioning

confidence: 99%

Newly uncovered physics of MHD instabilities using 2-D electron cyclotron emission imaging system in toroidal plasmas

Park

2019

Advances in Physics: X

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Validation of physics models using the newly uncovered physics with a 2-D electron cyclotron emission imaging (ECEi) system for magnetic fusion plasmas has either enhanced the confidence or substantially improved the modeling capability. The discarded "full reconnection model" in sawtooth instability is vindicated and established that symmetry and magnetic shear of the 1/1 kink mode are critical parameters in sawtooth instability. For the 2/ 1 instability, it is demonstrated that the 2-D data can determine critical physics parameters with a high confidence and the measured anisotropic distribution of the turbulence and its flow in presence of the 2/1 island is validated by the modelled potential and gyro-kinetic calculation. The validation process of the measured reversed-shear Alfvéneigenmode (RSAE) structures has improved deficiencies of prior models. The 2-D images of internal structure of the ELMs and turbulence induced by the resonant magnetic perturbation (RMP) have provided an opportunity to establish firm physics basis of the ELM instability and role of RMPs. The importance of symmetry in determining the reconnection time scale and role of magnetic shear of the 1/1 kink mode in sawtooth instability may be relevant to the underlying physics of the violent kink instability of the filament ropes in a solar flare.

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NTM stabilization by alternating O-point EC current drive using a high-power diplexer

Cited by 13 publications

References 30 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

Pulsed RF Schemes for Tearing Mode Stabilization

Newly uncovered physics of MHD instabilities using 2-D electron cyclotron emission imaging system in toroidal plasmas

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