A novel rotating mask system has been designed and implemented on the DIII-D Phase Contrast Imaging diagnostic to produce the first spatially localized PCI measurements of a tokamak plasma. The localization technique makes use of the variation of the magnetic field component perpendicular to the viewing chord as a function of chord height. This new capability provides measurements in the range 2 < k < 30 cm −1 , 10 kHz < f < 10 MHz, 0.7 < r/a < 1. This technique provides a spatial resolution of 10 cm at k = 15 cm −1 and can realistically provide measurements at a rate of 10 profiles/second. Calibration measurements show accurate characterization of the system transfer function making feasible a time dependent analysis that results in improved localization. Initial measurements show turbulence to peak near the plasma edge. This upgrade is part of a broader program to operate the DIII-D PCI at wavenumbers up to 40 cm −1 to probe electron scale turbulence in the plasma core.
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