The dynamics of the formation of the edge particle transport barrier at TJ-II

Pedrosa, M. A.; Hidalgo, C.; Carreras, B. A.; Estrada, T.; Alonso, A.; Pablos, J.L. de; Melnikov, A. V.; Krupnik, L. I.; Eliseev, L.G.; Perfilov, S.V.

doi:10.1088/0029-5515/51/11/113002

Cited by 16 publications

(23 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The dominant frequency of the corresponding mode is indicated, and when a given mode (8/5 or 3/2) is further inward, the frequency is higher due to a higher rotation velocity. This is in accordance with earlier work, which showed the existence of a rotation velocity profile that increases from the edge inward [35]. The decay of magnetic activity associated with confinement transitions (Fig.…”

Section: B Evolution Of Magnetic Activity During L-h Transitionssupporting

confidence: 93%

“…However, the magnetic field is normalized to 0.95 T on the magnetic axis at the ECRH injection point in order to guarantee central absorption of the ECR heating power, so only three independent numbers are left, and these are compounded into a label to identify each configuration [35]. At TJ-II, the normalized pressure β is generally low, even in discharges with Neutral Beam Injection (NBI), and currents flowing inside the plasma are generally quite small (unless explicitly driven), so that the actual magnetic configuration is typically rather close to the vacuum magnetic configuration [36].…”

Section: Statistics Of L-h Transitions At Tj-iimentioning

confidence: 99%

See 1 more Smart Citation

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Estrada

Carreras²,

Ascasíbar

et al. 2016

Physics of Plasmas

Self Cite

View full text Add to dashboard Cite

This work focuses on the relationship between L-H (or L-I) transitions and MHD activity in the low magnetic shear TJ-II stellarator. It is shown that the presence of a low order rational surface in the plasma edge (gradient) region lowers the threshold density for H-mode access. MHD activity is systematically suppressed near the confinement transition.We apply a causality detection technique (based on the Transfer Entropy) to study the relation between magnetic oscillations and locally measured plasma rotation velocity (related to Zonal Flows). For this purpose, we study a large number of discharges in two magnetic configurations, corresponding to 'fast' and 'slow' transitions. With the 'slow' transitions, the developing Zonal Flow prior to the transition is associated with the gradual reduction of magnetic oscillations. The transition itself is marked by a strong spike of 'information transfer' from magnetic to velocity oscillations, suggesting that the magnetic drive may play a role in setting up the final sheared flow responsible for the H-mode transport barrier. Similar observations were made for the 'fast' transitions. Thus, it is shown that magnetic oscillations associated with rational surfaces play an important and active role in confinement transitions, so that electromagnetic effects should be included in any complete transition model.

show abstract

Section: B Evolution Of Magnetic Activity During L-h Transitionssupporting

confidence: 93%

Section: Statistics Of L-h Transitions At Tj-iimentioning

confidence: 99%

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Estrada

Carreras²,

Ascasíbar

et al. 2016

Physics of Plasmas

Self Cite

View full text Add to dashboard Cite

show abstract

“…The reconstructed time evolution of the density profile in the biasing discharges clearly shows the formation of an edge transport barrier in response to the biasing. The success of this analysis has prompted the study of such behaviour also in other (spontaneous) confinement transitions at TJ-II, providing enhanced insight into the mechanisms producing such transitions 32 . The NBI heated discharges were selected to provide an example of density profiles before and after an L-H transition.…”

Section: Discussionmentioning

confidence: 99%

Integrated data analysis at TJ-II: The density profile

Milligen

Estrada

Ascasíbar

et al. 2011

Review of Scientific Instruments

Self Cite

View full text Add to dashboard Cite

An integrated data analysis system based on Bayesian inference has been developed for the TJ-II stellarator. It reconstructs the electron density profile at a single time point, using data from interferometry, reflectometry, Thomson Scattering, and the Helium beam, while providing a detailed error analysis. In this work, we present a novel analysis of the ambiguity inherent in profile reconstruction from reflectometry, and show how the Integrated Data Analysis approach elegantly resolves it. Several examples of the application of the technique are provided, in both low-density discharges with and without electrode biasing, and in high-density discharges with an (L-H) confinement transition.

show abstract

“…The TJ-II stellarator exhibits such a bifurcation in low density plasmas with Electron Cyclotron Heating (ECH), see reference [9] and references therein. When a critical density n cr is reached, a spontaneous confinement transition takes place, associated with the formation of a shear layer.…”

Section: Introductionmentioning

confidence: 99%

Damping of radial electric field fluctuations in the TJ-II stellarator

Velasco¹,

Alonso²,

Calvo³

et al. 2013

Plasma Phys. Control. Fusion

View full text Add to dashboard Cite

The drift kinetic equation is solved for low density TJ-II plasmas employing slowly varying, time-dependent profiles. This allows to simulate density ramp-up experiments and to describe from first principles the formation and physics of the radial electric field shear, which is associated to the transition from electron to ion root. We show that the range of frequencies of plasma potential fluctuations in which zonal flows are experimentally observed is neoclassically undamped in a neighborhood of the transition. This makes the electron root regime of stellarators, close to the transition to ion root, a propitious regime for the study of zonal-flow evolution. We present simulations of collisionless relaxation of zonal flows, in the sense of the Rosenbluth and Hinton test, that show an oscillatory behaviour in qualitative agreement with the experiment close to the transition.

show abstract

The dynamics of the formation of the edge particle transport barrier at TJ-II

Cited by 16 publications

References 35 publications

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Causal impact of magnetic fluctuations in slow and fast L–H transitions at TJ-II

Integrated data analysis at TJ-II: The density profile

Damping of radial electric field fluctuations in the TJ-II stellarator

Contact Info

Product

Resources

About