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Study of the spectral properties of ELM precursors by means of wavelets

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European Fusion Development Agreement, JET Project (Including: Poli, F. M. (Francesca), Sharapov, S. E. (Sergei E.) and Chapman, Sandra C.). (2008) Study of the spectral properties of ELM precursors by means of wavelets. Plasma Physics and Controlled Fusion, Vol.50 (No.9). p. 5009. ISSN 0741-3335

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Official URL: http://dx.doi.org/10.1088/0741-3335/50/9/095009

Abstract

The high confinement regime (H-mode) in tokamaks is accompanied by the occurrence of bursts of MHD activity at the plasma edge, so-called edge localized modes (ELMs), lasting less than 1 ms. These modes are often preceded by coherent oscillations in the magnetic field, the ELM precursors, whose mode numbers along the toroidal and the poloidal directions can be measured from the phase shift between Mirnov pickup coils. When the ELM precursors have a lifetime shorter than a few milliseconds, their toroidal mode number and their nonlinear evolution before the ELM crash cannot be studied reliably with standard techniques based on Fourier analysis, since averaging in time is implicit in the computation of the Fourier coefficients. This work demonstrates significant advantages in studying spectral features of the short-lived ELM precursors by using Morlet wavelets. It is shown that the wavelet analysis is suitable for the identification of the toroidal mode numbers of ELM precursors with the shortest lifetime, as well as for studying their nonlinear evolution with a time resolution comparable to the acquisition rate of the Mirnov coils.

Item Type:	Journal Article
Subjects:	Q Science > QC Physics
Divisions:	Faculty of Science > Physics
Library of Congress Subject Headings (LCSH):	Plasma jets -- Research, Wavelets (Mathematics), Toroidal magnetic circuits, Plasma confinement devices, Tokamaks
Journal or Publication Title:	Plasma Physics and Controlled Fusion
Publisher:	Institute of Physics Publishing Ltd.
ISSN:	0741-3335
Date:	24 July 2008
Volume:	Vol.50
Number:	No.9
Page Range:	p. 5009
Identification Number:	10.1088/0741-3335/50/9/095009
Status:	Peer Reviewed
Access rights to Published version:	Open Access
Funder:	Engineering and Physical Sciences Research Council (EPSRC)
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URI:	http://wrap.warwick.ac.uk/id/eprint/2181