Observation of low frequency electrostatic coherent oscillation in the proximity of the density limit in the TJ-II stellarator

Fernández-Ruiz, D.; Losada, U.; Ochando, M. A.; Liu, B.; Hidalgo, C.

doi:10.1088/1741-4326/ac3190

Cited by 4 publications

(3 citation statements)

References 34 publications

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“…The edge shear layer is controlled by the zonal flow screening response, collisional damping and input power. A recent experiment on TJ-II stellarator [70] shows edge cooling, decline in strored energy and LRCs at densities close to the DL. This is qualitatively consistent with our analysis and conclusions.…”

Section: Discussionmentioning

confidence: 93%

Zonal shear layer collapse and the power scaling of the density limit: old L-H wine in new bottles

Singh¹,

Diamond²

2022

Plasma Phys. Control. Fusion

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Edge shear layer collapse causes edge cooling and aggravates radiative effects. This paper details on the microscopic dynamics of the emergence of power (Q) scaling of density limit from the shear layer collapse transport bifurcation scenario. The analysis is based on a novel 4-field model which evolves turbulence energy, zonal flow energy, temperature gradient and density, including the neoclassical screening of zonal flow response. Bifurcation analysis yields power scaling of critical density for shear layer collapse as ncrit∼Q1/3. The favorable Q scaling of the density limit emerges from the fact that the shear layer strength increases with Q, thus preventing shear layer collapse. This in turn reduces particle transport and improves particle confinement. RMP induced ambient stochastic fields degrade the shear layer by inducing decoherence in the Reynolds stress. As a result the particle transport increases and particle confinement degrades. This leads to the emergence of unfavorable stochastic field intensity (bst 2) scaling of the critical density as ncrit∼(1+bst 2)-5/3 . All fields, including zonal flow shear, exhibit hysteresis when the power Q is ramped cyclically across the bifurcation point. The hysteresis is due to dynamical delay in bifurcation on account of critical slowing down. Thus, the dynamical hysteresis here is fundamentally different from the hysteresis associated with the existence of bi-stable states.

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Section: Discussionmentioning

confidence: 93%

Zonal shear layer collapse and the power scaling of the density limit: old L-H wine in new bottles

Singh¹,

Diamond²

2022

Plasma Phys. Control. Fusion

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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%

“…Furthermore, results point towards the amplification of low frequency, coherent, global fluctuations with similar properties as ZFs in the vicinity of the density limit. Whether the threshold radiation value for the density limit as well as the conditions to reach stationary regimes would be partially affected by the amplitude of (fluctuating and DC) ZFs is an open question [50].…”

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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Turbulence in the near scrape-off layer towards the L-mode density limit in ASDEX-Upgrade

Grenfell

Mänz

Conway

et al. 2022

Nuclear Materials and Energy

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Observation of low frequency electrostatic coherent oscillation in the proximity of the density limit in the TJ-II stellarator

Cited by 4 publications

References 34 publications

Zonal shear layer collapse and the power scaling of the density limit: old L-H wine in new bottles

Zonal shear layer collapse and the power scaling of the density limit: old L-H wine in new bottles

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

Turbulence in the near scrape-off layer towards the L-mode density limit in ASDEX-Upgrade

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