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Dr Kenji Tanaka, NIFS (Japan)

Location: PS1.28
Particle confinement processes were studied in detail on LHD. Diffusion coefficients (D) and convection velocities (V) were estimated from density modulation experiments. The magnetic configuration and collsionality were widely scanned in order to investigate parameter dependences of D and V.  In order to study the effect of the magnetic configuration, magnetic axis positions (Rax) were scanned from 3.5 m to 3.9 m. This scan changed magnetic ripples quite significantly, enabling the effects of neoclassical property on measured values to be widely elucidated. Dependences of electron temperature (Te) and helically trapped normalized collsionality (νh*), where νh*=1 indicates a rough boundary between the 1/ν and plateau regimes, were examined using the heating power scan of neutral beam injection (NBI). It was found out that generally larger (or smaller) contributions of neoclassical transport resulted in more hollowed (or peaked) density profiles. The larger neoclassical contribution was found to be situated at more outwardly shifted Rax for the same Te, and higher Te or lower νh* at each Rax. However, it is to be noted that Rax=3.5 m showed a different characteristics from these trends in that this case showed a more peaked density profile at higher Te. This feature is similar with tokamak observation
Micro turbulence was measured by the two dimensional phase contrast imaging (2D PCI ) (Tanaka et al., RSI(2008)). Full spatial structure of the turbulence, of whick k range is kρs=0.1-0.5, were measured. Increase of fluctuation level was observed with increase of particle diffusion. Preliminary data showed switching of propagation from electron diamagnetic direction in plasma frame under electron dominant heating to ion diamagnetic direction in plasma frame under ion dominant heating. This suggests switching from TEM to ITG.  
Tags: CFSA Seminar

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