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Prediction of nonlinear evolution character of energetic-particle-driven instabilities

  • Author(s): Duarte, VN
  • Berk, HL
  • Gorelenkov, NN
  • Heidbrink, WW
  • Kramer, GJ
  • Nazikian, R
  • Pace, DC
  • Podestà, M
  • Tobias, BJ
  • Van Zeeland, MA
  • et al.

A general criterion is proposed and found to successfully predict the emergence of chirping oscillations of unstable Alfvénic eigenmodes in tokamak plasma experiments. The model includes realistic eigenfunction structure, detailed phase-space dependences of the instability drive, stochastic scattering and the Coulomb drag. The stochastic scattering combines the effects of collisional pitch angle scattering and micro-turbulence spatial diffusion. The latter mechanism is essential to accurately identify the transition between the fixed-frequency mode behavior and rapid chirping in tokamaks and to resolve the disparity with respect to chirping observation in spherical and conventional tokamaks.

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