Comparison of Edge Turbulence Imaging at Two Different Poloidal Locations in the Scrape-off Layer of Alcator C-Mod
Authors: S.J. Zweben, et. al.
Abstract:
This paper describes 2-D imaging measurements of plasma turbulence made in
the scrape-off layer of the Alcator C-Mod tokamak simultaneously at two different
poloidal locations, one near the outer midplane and the other near the divertor X-point
region. These images were made with radial and poloidal resolution using two gas puff
imaging (GPI) diagnostics, which were not directly connected along a B field line. The
turbulence correlation structure has a significantly different tilt angle with respect to the
local flux surfaces for the midplane and X-regions, and a slightly different ellipticity and
size. The time-averaged turbulence velocities can be different in the midplane and Xregions,
even within the same flux surface in the same shot, and in most cases the
fluctuations in poloidal velocity in these two regions were not correlated. These
structures are partially consistent with a magnetic flux tube mapping model, and the
velocities are compared with various poloidal flow models.
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Submitted to: Physics of Plasmas (March 2013)
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