Advances in reflectometric density profile measurements on the DIII-D tokamaka)

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Abstract
Significant improvements have been achieved in the accuracy and reliability of broadband frequency‐swept (FM) reflectometer measurements on DIII‐D. This has been achieved through several improvements, the most important of which has been the application of digital complex demodulation (CDM) analysis software, which can extract signal phase with subfringe accuracy. Using this new analysis technique, results from the broadband FM system look very promising: reflectometer measurements show excellent agreement with Thomson profiles in Ohmic and H‐mode plasmas, and good agreement with Thomson data in L‐mode. Clear resolution of the steep edge density profile in H‐mode plasmas, where very small phase shifts are involved, confirm the accuracy of the system calibration and performance.