Time–frequency analysis of nonstationary complex magneto-hydro-dynamics in fusion plasma signals using the Choi–Williams distribution

Abstract The Choi–Williams distribution is applied to the time–frequency analysis of signals describing rapid magneto-hydro-dynamic (MHD) modes and events in tokamak plasmas. A comparison is made with Soft X-ray (SXR) signals as well as Mirnov signal that shows the advantages of the Choi–Williams distribution over both continuous wavelets transform scalogram and the short-time Fourier transform spectrogram. Examples of MHD activities in HT-7 and EAST tokamak are shown, namely the onset of coupling tearing modes, high frequency precursors of sawtooth, and low frequency MHD instabilities in edge localized mode (ELM) free in H mode discharge.

[1]  T. Tokuzawa,et al.  Wavelet analysis of plasma fluctuations in microwave reflectometry , 1999 .

[2]  B. Wan,et al.  Study on H-mode access at low density with lower hybrid current drive and lithium-wall coatings on the EAST superconducting tokamak , 2011 .

[3]  Ingrid Daubechies,et al.  Ten Lectures on Wavelets , 1992 .

[4]  Liqun Hu,et al.  Evidence for a resonant cyclotron interaction between runaway electrons and MHD modes in the experimental advanced superconducting tokamak , 2011 .

[5]  William J. Williams,et al.  Improved time-frequency representation of multicomponent signals using exponential kernels , 1989, IEEE Trans. Acoust. Speech Signal Process..

[6]  L. Cohen,et al.  Time-frequency distributions-a review , 1989, Proc. IEEE.

[7]  Jorge Ferreira,et al.  A signal processing tool to compute and visualize the Choi–Williams distribution and the Hilbert–Huang transform of nonstationary signals in fusion research , 2008 .

[8]  A. C. A. Figueiredo,et al.  Time–frequency analysis of nonstationary fusion plasma signals: A comparison between the Choi–Williams distribution and wavelets , 2004 .

[9]  H. Zohm,et al.  Stochastization as a possible cause for fast reconnection during MHD mode activity in the ASDEX Upgrade tokamak , 2006 .

[10]  New findings about sawtooth oscillations in LHCD plasmas on the HT-7 tokamak using tomography of soft x-ray signals , 2011 .

[11]  O. Dumbrajs,et al.  Understanding complex magnetohydrodynamic activities associated with a relaxation in the HT-7 tokamak , 2011 .

[12]  A. C. A. Figueiredo,et al.  Time–frequency analysis of fusion plasma signals beyond the short-time Fourier transform paradigm: An overview , 2008 .

[13]  Time-frequency analysis for microwave reflectometry data processing in the HL-2A tokamak. , 2011, The Review of scientific instruments.

[14]  J. Manickam,et al.  Chapter 3: MHD stability, operational limits and disruptions , 2007 .

[15]  Hidalgo,et al.  Nonlinear phenomena and intermittency in plasma turbulence. , 1995, Physical review letters.

[17]  A. C. A. Figueiredo,et al.  Time–frequency analysis of non-stationary signals in fusion plasmas using the Choi–Williams distribution , 2004 .

[18]  V. Altuzar,et al.  Atmospheric pollution profiles in Mexico City in two different seasons , 2003 .

[19]  I. Caldas,et al.  Time‐resolved analysis of Mirnov oscillations , 1992 .

[20]  Truong Q. Nguyen,et al.  Wavelets and filter banks , 1996 .