Speaker
Dr
Tatsuya Kobayashi
(National Institute for Fusion Science)
Description
Importance of role of the radial electric field was widely known for turbulent transport suppression across the L-H transition. Focusing on the ExB shear decorrelation effect, a possible model explaining the high confinement regime was proposed [1], which is nowadays subject to experimental validation [2,3]. Recently, not only the ExB shear but also the curvature of the radial electric field is regarded as an important player to suppress the turbulence transport [3,4]. At the radius of the radial electric field well, confinement improvement owing to the radial electric field curvature, possibly via a modulational coupling between turbulence and flow, was confirmed [4]. How the turbulent transport is reduced is also important issue. There are several routes to reach the reduced turbulent transport state in the H-mode, e.g., via turbulence amplitude suppression or via reduction of phase difference between the density and potential fluctuations. Here, we analyze a turbulence data set obtained with a heavy ion beam probe (HIBP) to investigate how the radial electric field shear and curvature affect the turbulent particle transport across the L-H transition in JFT-2M tokamak.
With the HIBP system, the electron density fluctuation and the electrostatic potential fluctuation are simultaneously and directly measured with a high time resolution. In the L-mode, turbulence amplitude is enhanced and the outward particle flux is observed, which results in the confinement degradation. After emergence of the radial electric field structure in the H-mode, the outward particle flux is significantly reduced. The particle flux is suppressed predominantly by reducing the density fluctuation amplitude and the cross phase between the density fluctuation and the potential fluctuation. Amplitude reduction of the potential fluctuation is only moderate. Both the shear and the curvature are found to play an important role to reduce the particle flux. Different time scale of changes in the density fluctuation amplitude and the cross phase between the density fluctuation and the potential fluctuation is also observed.
[1] H. Biglari, P. H. Diamond, and P. W. Terry, Phys. Fluids B 2, 1 (1990).
[2] J. A. Boedo et al., Nucl. Fusion 42, 117 (2002).
[3] R. A. Moyer et al., Phys. Plasmas 2, 2397 (1995).
[4] K. Kamiya et al., Sci. Rep. 6, 30585 (2016)
Primary author
Dr
Tatsuya Kobayashi
(National Institute for Fusion Science)
Co-authors
Dr
Akihide Fujisawa
(Kyushu University)
Dr
Katsumi Ida
(National Institute for Fusion Science)
Dr
Kensaku Kamiya
(National Institutes for Quantum and Radiological Science and Technology)
Dr
Kimitaka Itoh
(Chubu University)
Dr
Sanae-I Itoh
(Kyushu University)
Dr
Shigeru Inagaki
(Kyushu University)
Dr
Takeshi Ido
(National Institute for Fusion Science)
Dr
Yoshihiko Nagashima
(Kyushu University)
Dr
Yukitoshi Miura
(Japan Atomic Energy Agency)
