Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

N.P. Basse; S. Zoletnik; S. Baumel; M. Endler; M. Hirsch; K. McCormick; A. Werner

doi:10.1088/0029-5515/43/1/305

Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

N.P. Basse, S. Zoletnik, S. Baumel, M. Endler, M. Hirsch, K. McCormick, A. Werner

Research output: Contribution to journal › Journal article › Research › peer-review

Abstract

Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper, measurements of short wavelength density fluctuations in the HDH-mode using collective scattering of infrared light are presented. These measurements will be contrasted to fluctuations during normal confinement operation (NC-mode). The autopower spectra of the measurements show a consistent increase of the fluctuation level associated with the transition from NC- to HDH-mode. Correlation calculations on a 20 mus timescale between magnetic and density fluctuations lead to the result that the fluctuations are correlated in NC- but not in HDH-mode. Finally, a comparative analysis between the enhanced D-alpha H-mode (EDA H-mode) found in the Alcator C-Mod tokamak and the HDH-mode in W7-AS is carried out.

Original language	English
Journal	Nuclear Fusion
Volume	43
Issue number	1
Pages (from-to)	40-48
ISSN	0029-5515
DOIs	https://doi.org/10.1088/0029-5515/43/1/305
Publication status	Published - 2003

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title = "Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas",

abstract = "Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper, measurements of short wavelength density fluctuations in the HDH-mode using collective scattering of infrared light are presented. These measurements will be contrasted to fluctuations during normal confinement operation (NC-mode). The autopower spectra of the measurements show a consistent increase of the fluctuation level associated with the transition from NC- to HDH-mode. Correlation calculations on a 20 mus timescale between magnetic and density fluctuations lead to the result that the fluctuations are correlated in NC- but not in HDH-mode. Finally, a comparative analysis between the enhanced D-alpha H-mode (EDA H-mode) found in the Alcator C-Mod tokamak and the HDH-mode in W7-AS is carried out.",

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T1 - Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

AU - Basse, N.P.

AU - Zoletnik, S.

AU - Baumel, S.

AU - Endler, M.

AU - Hirsch, M.

AU - McCormick, K.

AU - Werner, A.

PY - 2003

Y1 - 2003

N2 - Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper, measurements of short wavelength density fluctuations in the HDH-mode using collective scattering of infrared light are presented. These measurements will be contrasted to fluctuations during normal confinement operation (NC-mode). The autopower spectra of the measurements show a consistent increase of the fluctuation level associated with the transition from NC- to HDH-mode. Correlation calculations on a 20 mus timescale between magnetic and density fluctuations lead to the result that the fluctuations are correlated in NC- but not in HDH-mode. Finally, a comparative analysis between the enhanced D-alpha H-mode (EDA H-mode) found in the Alcator C-Mod tokamak and the HDH-mode in W7-AS is carried out.

AB - Recently a new improved confinement regime was found in the Wendelstein 7-AS (W7-AS) stellarator (Renner H. et al 1989 Plasma Phys. Control. Fusion 31 1579). The discovery of this high density high confinement mode (HDH-mode) was facilitated by the installation of divertor modules. In this paper, measurements of short wavelength density fluctuations in the HDH-mode using collective scattering of infrared light are presented. These measurements will be contrasted to fluctuations during normal confinement operation (NC-mode). The autopower spectra of the measurements show a consistent increase of the fluctuation level associated with the transition from NC- to HDH-mode. Correlation calculations on a 20 mus timescale between magnetic and density fluctuations lead to the result that the fluctuations are correlated in NC- but not in HDH-mode. Finally, a comparative analysis between the enhanced D-alpha H-mode (EDA H-mode) found in the Alcator C-Mod tokamak and the HDH-mode in W7-AS is carried out.

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JF - Nuclear Fusion

IS - 1

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Turbulence at the transition to the high density H-mode in Wendelstein 7-AS plasmas

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