Plasma drift-kinetic equation calculations in three-dimensional magnetic geometries

Reynolds, J. M.; López‐Bruna, D.

doi:10.1063/1.3454362

Cited by 5 publications

(4 citation statements)

References 25 publications

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“…This indicates that a proper calculation of electron and ion neoclassical fluxes including threedimensional features-that affect differently the plasma species-is as important as checking for the generation of rotating flows via other mechanisms (e.g. Reynolds stress [15]); a task that has been started indeed for the TJ-II [16]. Note that all the effects exposed above are compatible with the existence of a layer, related to the resonances, where the larger mobility of electrons would force a more positive electric field to maintain ambipolarity.…”

Section: Practical Consequencesmentioning

confidence: 99%

Magnetic resonances and electric fields in the TJ-II Heliac

López‐Bruna¹,

Pedrosa²,

Ochando³

et al. 2011

Plasma Phys. Control. Fusion

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TJ-II is a medium-sized Heliac-type stellarator operating at low magnetic shear. Low-order rational values of the rotational transform ι = 1/q (magnetic resonances, for brevity) can be introduced anywhere in its plasmas causing modifications in the electric potential and, consequently, radial structures in the radial electric fields that can be used to alter transport and stability in an externally controllable way. The ability of the Heliac to perform dynamic configuration scans has been used to illustrate these aspects and find practical realizations, such as exerting control on the L-H transition.

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Section: Practical Consequencesmentioning

confidence: 99%

Magnetic resonances and electric fields in the TJ-II Heliac

López‐Bruna¹,

Pedrosa²,

Ochando³

et al. 2011

Plasma Phys. Control. Fusion

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“…In the case of the NC calculations this is not surprising because they are performed under the assumption of nested flux surfaces, thus excluding possibly important contributions to the nonambipolar fluxes coming from a broken topology. These results encourage continuing the development of collisional transport calculations in arbitrary magnetic fields considering electron and ion fluxes [38,39]. Indeed, low order rational values of ι inside TJ-II plasmas are known to modify locally the electric field and act as powerful triggers of the transition process; they can even abort it when removed from the favorable location near ρ = 0.8 [41].…”

Section: Discussionmentioning

confidence: 85%

Transport in threshold plasmas for a confinement transition in the TJ-II stellarator

López‐Bruna

Velasco

Ochando³

et al. 2012

Plasma Phys. Control. Fusion

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A description and transport analysis (energy and particles) of neutral beam heated plasmas is shown for two almost identical magnetic configurations except for a ≈1% difference in their rotational transform, ι. Due to the low magnetic shear of TJ-II magnetic fields, such difference takes the low order rational ι = 8/5 to the plasma edge in one of them, while in the other the 8/5 value is near the edge but inside the plasma. A transport transition happens at lower density and plasma energy for the configuration that includes the ι = 8/5, which exhibits better particle confinement already before the transition.

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“…The plasmas behave as if the resonances happened in an environment of 'healed' islands, which is part of the motivation to study the healing of islands in helical devices jointly with other devices [24]. Kinetic calculations [25] in the geometry of the standard TJ-II magnetic configuration, based on collisional transport alone, show 3D plasma current densities able to modify the magnetic structure in the resonant regions, even in the absence of electric fields [22]. Both elements, radial electric field and plasma current in the resonant regions, are also important in other phenomena such as the formation of internal electronheat barriers and have been proposed as tools to control plasma performance.…”

Section: Confinement and Configuration Effectsmentioning

confidence: 99%

Overview of TJ-II experiments

Sánchez¹,

Acedo²,

Alegre³

et al. 2011

Nucl. Fusion

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This paper presents the last results on confinement studies in the TJ-II stellarator. The research of the dependence of spatially resolved transport coefficients on plasma parameters for ECH plasmas with Boronised wall shows that the heat confinement increases linearly with density while particle confinement increases sharply a factor four above a certain density threshold associated with the positive electric field. Remarkably, lowest order magnetic resonances, even in a low shear environment, reduce locally the effective diffusivities. The inherently strong plasma wall interaction of TJ-II has been successfully reduced after Lithium coating by vacuum evaporation. Besides H-retention and low Z, Li was chosen because there exists a reactor-oriented interest in this element, thus giving especial interest to the investigation of its properties. The Li-coating has led to important changes in plasma performance. Particularly, the effective density limit in NBI plasmas has been extended reaching central values of 8 x 10 19 m-3 and Te≈250-300 eV, with peaked density, rather flat Te profiles and increased ion temperatures. Alfvén modes are destabilised and their influence on fast ion confinement is studied in NBI discharges. Due to the achieved density control, a second type of transitions has been added to the low density ones previously observed in boronised wall. The high density transitions, under NBI with Li-coated walls are characterised by the fall of Hα emission, the onset of steep density gradient, and the reduction of the turbulence, which are characteristics of transition to H mode. TJ-II is therefore a unique device where first and second order phase transitions can be investigated.

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Plasma drift-kinetic equation calculations in three-dimensional magnetic geometries

Cited by 5 publications

References 25 publications

Magnetic resonances and electric fields in the TJ-II Heliac

Magnetic resonances and electric fields in the TJ-II Heliac

Transport in threshold plasmas for a confinement transition in the TJ-II stellarator

Overview of TJ-II experiments

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