title: Intrashot motional Stark effect calibration technique for lower hybrid current drive experiments.
abstract: The spurious drift in pitch angle of order several degrees measured by the motional Stark effect (MSE) diagnostic in the Alcator C-Mod tokamak 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 intrashot 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.
authors.affiliation: MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139, USA.
authors.forename: Jinseok
authors.initials: J
authors.lastname: Ko
authors.forename: Steve
authors.initials: S
authors.lastname: Scott
authors.forename: Syun'ichi
authors.initials: S
authors.lastname: Shiraiwa
authors.forename: Martin
authors.initials: M
authors.lastname: Greenwald
authors.forename: Ronald
authors.initials: R
authors.lastname: Parker
authors.forename: Gregory
authors.initials: G
authors.lastname: Wallace