Internal, nonperturbing, radio frequency wave monitor reflectometer system on the DIII-D tokamaka)

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Abstract
A new reflectometer system designed to monitor density fluctuations associated with rf waves has been successfully demonstrated on the DIII‐D tokamak. It is a direct, internal, and nonperturbing diagnostic with access into the plasma core. This new diagnostic is motivated by a desire to improve understanding of rf wave physics issues, such as wave trajectory, heating mechanisms, rf wave deposition profile, and wave number, and is highly relevant to planned tokamaks such as ITER and TPX. This work is the first application of reflectometry to rf wave studies in a tokamak. Feedforward tracking receiver techniques are employed to remove frequency instabilities due to inherent drifts in the microwave sources and frequency pulling. In order to minimize spurious pickup of the rf pulse (∼60 MHz), heterodyne detection techniques are utilized, and all components are installed inside an rf shielding box. The system operates in the extraordinary mode (X‐mode) at 70 GHz. In this paper, a detailed description of the system, and data illustrating its successful operation will be presented.

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