Nonlinear coupling of tearing fluctuations in the Madison Symmetric Torus

J. S. Sarff, S. Assadi, A. F. Almagri, M. Cekic, D. J. Den Hartog, G. Fiksel, S. A. Hokin, H. Ji, S. C. Prager, W. Shen, K. L. Sidikman, M. R. Stoneking

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Three-wave, nonlinear, tearing mode coupling has been measured in the Madison Symmetric Torus (MST) reversed-field pinch (RFP) [Fusion Technol. 19, 131 (1991)] using bispectral analysis of edge magnetic fluctuations resolved in "k-space." The strength of nonlinear three-wave interactions satisfying the sum rules m1+m2=m3 and n 1+n2=n3 is measured by the bicoherency. In the RFP, m=1, n∼2R/a (6 for MST) internally resonant modes are linearly unstable and grow to large amplitude. Large values of bicoherency occur for two m=1 modes coupled to an m=2 mode and the coupling of intermediate toroidal modes, e.g., n=6 and 7 coupled to n=13. These experimental bispectral features agree with predicted bispectral features derived from magnetohydrodynamic (MHD) computation. However, in the experiment, enhanced coupling occurs in the "crash" phase of a sawtooth oscillation concomitant with a broadened mode spectrum suggesting the onset of a nonlinear cascade.

Original languageEnglish (US)
Pages (from-to)2540-2545
Number of pages6
JournalPhysics of Fluids B
Issue number7
StatePublished - 1993

All Science Journal Classification (ASJC) codes

  • Computational Mechanics
  • Condensed Matter Physics
  • Mechanics of Materials
  • General Physics and Astronomy
  • Fluid Flow and Transfer Processes


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