Intra-shot MSE Calibration Technique For LHCD Experiments
Authors: Jinseok Ko, Steve Scott, Syun'ichi Shiraiwa, Martin Greenwald, Ronald Parker, and Gregory Wallace
Abstract:
The spurious drift in pitch angle of order several degrees measured by the Motional Stark Effect (MSE) diagnostic in the Alcator C-Mod tokamak1 over the course of an experimental run day has precluded direct utilization of independent absolute calibrations. Recently, the underlying cause of the drift has been identified as thermal stress-induced birefringence in a set of in-vessel lenses. The shot-to-shot drift can be avoided by using MSE to measure only the change in pitch angle between a reference phase and a phase of physical interest within a single plasma discharge. This intra-shot calibration technique has been applied to the Lower Hybrid Current Drive (LHCD) experiments and the measured current profiles qualitatively demonstrate several predictions of LHCD theory such as an inverse dependence of current drive efficiency on the parallel refractive index and the presence of off-axis current drive.
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Submitted to: Review of Scientific Instruments (November, 2009)
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Download PPPL-4474 (pdf 842 KB 8 pp)
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