Frequency and plasma condition dependent spatial structure of low frequency global potential oscillations in the TJ-II stellarator

Kobayashi, Tatsuya; Losada, U.; Liu, B.; Estrada, T.; Gerrú, R.; Sasaki, M.; Hidalgo, C.

doi:10.1088/1741-4326/ab0122

Cited by 7 publications

(11 citation statements)

References 168 publications

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“…While early measurements of potential fluctuations across the TJ-II edge, with LRC properties, showed no distinctive GAM peak [584] plus more recent global low frequency flows [585] (as expected for low q), there are several later reports of candidate GAMs in the core. For example, low frequency E r oscillations were triggered by the transition of the core radial electric field E r during density ramp experiments from the positive E r (electron-root) to the negative E r (ion-root) [586].…”

mentioning

confidence: 93%

Geodesic acoustic modes in magnetic confinement devices

Smolyakov

Ido

2021

Nucl. Fusion

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Geodesic acoustic modes (GAMs) are ubiquitous oscillatory flow phenomena observed in toroidal magnetic confinement fusion plasmas, such as tokamaks and stellarators. They are recognized as the non-stationary branch of the turbulence driven zonal flows which play a critical regulatory role in cross-field turbulent transport. GAMs are supported by the plasma compressibility due to magnetic geodesic curvature—an intrinsic feature of any toroidal confinement device. GAMs impact the plasma confinement via velocity shearing of turbulent eddies, modulation of transport, and by providing additional routes for energy dissipation. GAMs can also be driven by energetic particles (so-called EGAMs) or even pumped by a variety of other mechanisms, both internal and external to the plasma, opening-up possibilities for plasma diagnosis and turbulence control. In recent years there have been major advances in all areas of GAM research: measurements, theory, and numerical simulations. This review assesses the status of these developments and the progress made towards a unified understanding of the GAM behaviour and its role in plasma confinement. The review begins with tutorial-like reviews of the basic concepts and theory, followed by a series of topic orientated sections covering different aspects of the GAM. The approach adopted here is to present and contrast experimental observations alongside the predictions from theory and numerical simulations. The review concludes with a comprehensive summary of the field, highlighting outstanding issues and prospects for future developments.

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confidence: 93%

Geodesic acoustic modes in magnetic confinement devices

Smolyakov

Ido

2021

Nucl. Fusion

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“…Zonal flows are ubiquitous, and their spatio-temporal structures are important for turbulent transport. A detailed analysis of the low frequency global potential oscillations on the TJ-II stellarator indicated the spatial structure had high sensitivity to the mean electric field profile [41]. A data-driven DMD model for the evolution of the spatial structure of the zonal flows may facilitate future control over the turbulent transport properties mediated by this mode.…”

Section: Resultsmentioning

confidence: 99%

“…This implies that the evolution of coherent structures, and possibly the bulk evolution of the plasma, can be understood using a low-dimensional model, with implications for physical discovery, and real-time prediction and control [9]. Nearly all fusion-relevant experiments have coherent edge fluctuations and zonal flows with significant effects on transport, including the Alcator C-Mod tokamak [25], the DIII-D tokamak [14,27], the TJ-II stellarator [41], the High Recycling Steady H-mode in the JFT-2M tokamak [38], and the High-Density H-mode in the W7-AS stellarator [6].…”

Section: Introductionmentioning

confidence: 99%

Characterizing magnetized plasmas with dynamic mode decomposition

et al. 2020

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Accurate and efficient plasma models are essential to understand and control experimental devices. Existing magnetohydrodynamic or kinetic models are nonlinear, computationally intensive, and can be difficult to interpret, while often only approximating the true dynamics. In this work, data-driven techniques recently developed in the field of fluid dynamics are leveraged to develop interpretable reduced-order models of plasmas that strike a balance between accuracy and efficiency. In particular, dynamic mode decomposition (DMD) is used to extract spatio-temporal magnetic coherent structures from the experimental and simulation datasets of the HIT-SI experiment. Three-dimensional magnetic surface probes from the HIT-SI experiment are analyzed, along with companion simulations with synthetic internal magnetic probes. A number of leading variants of the DMD algorithm are compared, including the sparsity-promoting and optimized DMD. Optimized DMD results in the highest overall prediction accuracy, while sparsity-promoting DMD yields physically interpretable models that avoid overfitting. These DMD algorithms uncover several coherent magnetic modes that provide new physical insights into the inner plasma structure. These modes were subsequently used to discover a previously unobserved three-dimensional structure in the simulation, rotating at the second injector harmonic. Finally, using data from probes at experimentally accessible locations, DMD identifies a resistive kink mode, a ubiquitous instability seen in magnetized plasmas.

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“…The unique experimental system that is the TJ-II stellarator has made it possible to obtain direct experimental evidence of self-organization processes consistent with the concept of ZFs. Recent experiments, developed within the framework of intense international collaborations, have demonstrated the influence of plasma ECRH and NBI heating conditions [47], the entangled role between turbulence and particle orbits [48], the influence of isotopic mass [49] and proximity to operational (density) limits [50] on the properties and dynamics [51] of ZFs in the TJ-II stellarator.…”

Section: Edge Zonal Flows and Radial Electric Fieldsmentioning

confidence: 99%

“…Figures 13 and 14 show the radial scale of LRCs in hydrogen and deuterium plasmas [49] and the radial modulation of dynamical radial electric fields due to edge ZFs in the plasma edge [47]. In NBI plasma scenarios, the radial size increases with isotope mass.…”

Section: Edge Zonal Flows and Radial Electric Fieldsmentioning

confidence: 99%

Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

Hidalgo¹,

Ascasíbar²,

Alegre³

et al. 2022

Nucl. Fusion

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TJ-II stellarator results on modelling and validation of plasma flow asymmetries due to on-surface potential variations, plasma fuelling physics, Alfvén eigenmodes (AEs) control and stability, the interplay between turbulence and neoclassical (NC) mechanisms and liquid metals are reported. Regarding the validation of the neoclassically predicted potential asymmetries, its impact on the radial electric field along the flux surface has been successfully validated against Doppler reflectometry measurements. Research on the physics and modelling of plasma core fuelling with pellets and tracer encapsulated solid pellet injection has shown that, although post-injection particle radial redistributions can be understood qualitatively from NC mechanisms, turbulence and fluctuations are strongly affected during the ablation process. Advanced analysis tools based on transfer entropy have shown that radial electric fields do not only affect the radial turbulence correlation length but are also capable of reducing the propagation of turbulence from the edge into the scrape-off layer. Direct experimental observation of long range correlated structures show that zonal flow structures are ubiquitous in the whole plasma cross-section in the TJ-II stellarator. Alfvénic activity control strategies using ECRH and ECCD as well as the relation between zonal structures and AEs are reported. Finally, the behaviour of liquid metals exposed to hot and cold plasmas in a capillary porous system container was investigated.

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Frequency and plasma condition dependent spatial structure of low frequency global potential oscillations in the TJ-II stellarator

Cited by 7 publications

References 168 publications

Geodesic acoustic modes in magnetic confinement devices

Geodesic acoustic modes in magnetic confinement devices

Characterizing magnetized plasmas with dynamic mode decomposition

Overview of the TJ-II stellarator research programme towards model validation in fusion plasmas

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