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q-profile measurements with motional stark effect in DIII-D

By B. W. Rice

Abstract

Motional Stark Effect (MSE) has emerged as the most reliable technique for the measurement of q profiles in tokamaks equipped with neutral beams. On DIII-D, two separate 8-channel MSE instruments are utilized, giving 16 radial measurements. The viewing geometry for each instrument is designed to optimize radial resolution (1.5 cm < {delta}R < 6 cm) over the measurement range. Dual-frequency polarization modulators combined with lock-in detection provides maximum signal-to-noise with a time response of {approximately}1 ms. Special consideration has gone into the design of the collection optics to minimize undesirable polarization effects on reflectors and Faraday rotation in lenses. Examples of data from negative central magnetic shear, VH-mode, and sawtoothing discharges highlight the capabilities of the DIII-D MSE diagnostic

Topics: Signal-To-Noise Ratio, Sawtooth Oscillations, Plasma Diagnostics, 70 Plasma Physics And Fusion, Doublet-3 Device, Optical Systems, Neutral Atom Beam Injection, Magnetic Fields, Time Resolution, Shear, Stark Effect
Publisher: Lawrence Livermore National Laboratory
Year: 1996
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Provided by: UNT Digital Library
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