Speaker
Dr
Frederic Clairet
(CEA)
Description
The foreseen plasma operation in future tokamak devices to reach fusion would be in H-mode. It is desirable to understand the underlined physic, and particularly the turbulence, that provides the improvement of the plasma confinement. Major modification occurs close the plasma edge into the pedestal region where the turbulence not only reduces dramatically but also changes in nature. In this work, experimental observation of these changes have been performed using reflectometry diagnostic which provides high radial (in the mm range) and temporal resolution (in the µs range). During the L to H transition the density fluctuation level (n/n) drops significantly at the edge and the frequency spectra turn from broadband to coherent modes in a narrow region of the pedestal. This change occurs at the position of the Er well position (calculated from the diamagnetic contribution) along with its growth. Moreover, a detailed analysis of the complex reflected signal displays a single side band feature at low frequency around few kHz in the spectra which reverses of sign radially. This feature is discussed in terms of eddy tilting in changing ExB poloidal shear flow. This shear decorrelation mechanism of the turbulence is suspected to be at the origin of the observed particle transport reduction.
Primary author
Dr
Frederic Clairet
(CEA)
