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Confinement transitions in TJ-II under Li-coated wall conditions

Date

2009

Authors

Sanchez, J.
Acedo, M.
Alonso, A.
Alonso, J.
Alvarez, P.
Ascasibar, E.
Baciero, A.
Balbin, R.
Barrera, L.
Blanco, E.

Journal Title

Journal ISSN

Volume Title

Publisher

IOP Publishing

Abstract

This paper presents the latest results on confinement studies in the TJ-II stellarator. 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 special relevance 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 × 1019 m-3 and Te ≈ 250-300 eV, with peaked density, rather flat Te profiles and higher ion temperatures. Due to the achieved density control, a second type of transition has been added to the low density ones previously observed in ECRH plasmas: higher density transitions characterized by the fall in Hα emission, the onset of steep density gradient and the reduction in the turbulence; which are characteristics of transition to the H mode. Confinement studies in ECH plasmas indicate that lowest order magnetic resonances, even in a low shear environment, locally reduce the effective electron heat diffusivities, while Alfven eigenmodes destabilized in NBI plasmas can influence fast ion confinement.

Description

Keywords

Keywords: Alfven eigenmodes; Confinement transitions; Density control; Density transition; Effective density; Electron heat diffusivity; Fast-ion confinement; Ion temperature; Low density; Plasma performance; Plasma wall interaction; Shear environments; Steep densi

Citation

Source

Nuclear Fusion

Type

Journal article

Book Title

Entity type

Access Statement

License Rights

DOI

10.1088/0029-5515/49/10/104018

Restricted until

2037-12-31