High-resolution multichannel interferometric measurement of sawtooth density-pulse propagation (invited)

A unique high-resolution far-infrared multichannel interferometer system has been developed and successfully operated on the Texas Experimental Tokamak. Two sets of cylindrical parabolic mirrors are employed to expand both the local oscillator and probe beams in one dimension to cover the plasma cross section accessible through the vertical ports. A maximum of 29 mixers is configured on a linear array which provides a spatial resolution of 1.5 cm. The overall density resolution is ≤5×1010 cm−3 with a time response of 50 μs. The high resolution of the system permits detailed measurements of small-amplitude fine-structure density effects such as MHD activity during disruptions and sawteeth. Detailed observations of density-pulse propagation processes induced from sawtooth internal disruptions are described. Analysis of sawtooth density-pulse propagation measurements based on a diffusive model has led to a direct estimate of the internal electron particle diffusion coefficient.