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Director:
Prof. N.C. Luhmann, Jr.









Last update:
April 25, 2012

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ECEI is inherently well suited to diagnosing MHD activity and interactions across multiple scales. Shown above are images from a single DIII-D discharge comparing the fine scale structure of an Alfvén eigenmode to meso-scale perturbations due to a core-localized kink instability. Covering a large region of the plasma in 2D, ECEI enables reconstruction of helically symmetric structures in the entire poloidal plane.

    

Imaging the sawtooth crash at the inboard, or high field side, shows that thermal transport occurs along a localized conduction channel, consistent with a model for local magnetic reconnection. The hot plasma is carried leftward, across the temperature inversion radius, and ejected from the tokamak core. The image is unambiguous, composed of localized measurements, and is not subject to the uncertainties associated with the inversion of line integrated measurements.

ECE-Imaging systems acquire data with micro-second resolution, allowing for accurate discrimination among coupled and closely spaced eigenmodes. In this case, the linear superposition of two separate Alfvén eigenmodes produces a complicated structure. But, the quality of ECEI data allows these modes to be imaged separately for better understanding of their linear and non-linear stability properties.

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