### Abstract

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 m_{1}+m_{2}=m_{3} and n _{1}+n_{2}=n_{3} 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 language | English (US) |
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Pages (from-to) | 2540-2545 |

Number of pages | 6 |

Journal | Physics of Fluids B |

Volume | 5 |

Issue number | 7 |

DOIs | |

State | Published - Jan 1 1993 |

Externally published | Yes |

### All Science Journal Classification (ASJC) codes

- Computational Mechanics
- Condensed Matter Physics
- Mechanics of Materials
- Physics and Astronomy(all)
- Fluid Flow and Transfer Processes

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## Cite this

*Physics of Fluids B*,

*5*(7), 2540-2545. https://doi.org/10.1063/1.860741