On the use of MHD mode analysis as a technique for determination of q-profiles in JET plasmas

Nave, M. F. F.; Alper, B.; Brix, M.; Hawkes, N.; Mailloux, J.; Smeulders, P.; Jofrin, E.; Hacquin, S.; Borba, D.; de la Luna, E.; Boswell, C.; Challis, C.; Gerasimov, S.

doi:10.1063/1.1791333

Journal Article

On the use of MHD mode analysis as a technique for determination of q-profiles in JET plasmas

Nave, M. F. F. ; Alper, B. ; Borba, D. ; Boswell, C. ; Challis, C. ; Brix, M.FZJ* ; Gerasimov, S. ; Hacquin, S. ; Hawkes, N. ; Jofrin, E. ; Mailloux, J. ; de la Luna, E. ; Smeulders, P.

2004
American Institute of Physics [S.l.]

Review of scientific instruments 75, 4274 (2004) [10.1063/1.1791333]

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Please use a persistent id in citations: http://hdl.handle.net/2128/1824 doi:10.1063/1.1791333

Abstract: JET plasmas show fluctuations from a large variety of MHD instabilities. A combination of spectral analysis, mode number analysis, and determination of mode radial position has the potential as a diagnostic for the plasma q profile. Mode frequencies and mode numbers are obtained from spectral and phase analysis from fast magnetic pickup signals. Cross correlation of magnetic and multiarray signals from ECE, SXR, and reflectometer systems provide the mode localization. The present status of the diagnostic systems used for fluctuation analysis is summarized, with particular emphasis on the fast magnetic pickup system. A new data collection system allows the magnetic signals to be recorded at 2 MHz for up to 32 s in each pulse. An example of q-profile validation from the observation of Alfven eigenmode cascades and a snake is given. At JET, Alfven cascades are used to determine q(min) in optimized shear discharges, while a variety of low frequency modes (such as the snake) allow the determination of the radial position of q integer values in monotonic and reversed shear q profiles. (C) 2004 American Institute of Physics.

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