The MAST motional Stark effect diagnostic

N.J. Conway, M.F.M. Bock, de, C.A. Michael, M.J. Walsh, P.G. Carolan, N.C. Hawkes, E. Rachlew, J.F.G. McCone, S. Shibaev, G. Wearing

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A motional Stark effect (MSE) diagnostic is now installed and operating routinely on the MAST spherical tokamak, with 35 radial channels, spatial resolution of ~ 2.5 cm, and time resolution of ~ 1 ms at angular noise levels of ~ 0.5°. Conventional (albeit very narrow) interference filters isolate p or s polarized emission. Avalanche photodiode detectors with digital phase-sensitive detection measure the harmonics of a pair of photoelastic modulators operating at 20 and 23 kHz, and thus the polarization state. The p component is observed to be significantly stronger than s, in reasonably good agreement with atomic physics calculations, and as a result, almost all channels are now operated on p. Trials with a wide filter that admits the entire Stark pattern (relying on the net polarization of the emission) have demonstrated performance almost as good as the conventional channels. MSE-constrained equilibrium reconstructions can readily be produced between pulses. © 2010 EURATOM
Original languageEnglish
Pages (from-to)10D738-1/6
Number of pages6
JournalReview of Scientific Instruments
Issue number10
Publication statusPublished - 2010

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