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(THP2/20) Energetic Particle Mode Dynamics in Tokamaks

F. Zonca¹⁾, S. Briguglio¹⁾, L. Chen²⁾, G. Fogaccia¹⁾, G. Vlad¹⁾, L.-J. Zheng^2)
 
1) ENEA C. R. Frascati, C.P. 65, 00044 Frascati, Rome, Italy
²⁾ Department of Physics and Astronomy, University of California, Irvine, CA 92717-4575, USA

Abstract.  Energetic Particle Modes (EPM) are strongly driven oscillations excited via wave-particle resonant interactions at the characteristic frequencies of the energetic ions, $\omega_{tE}^{}$, $\omega_{BE}^{}$ and/or $\bar{\omega}_{dE}^{}$, i.e., respectively the transit frequency for circulating particles and the bounce and precessional drift frequencies for trapped ions. A sharp transition in the plasma stability at the critical EPM excitation threshold has been observed by nonperturbative gyrokinetic codes in terms of changes in normalized growth rate ( $\gamma$/$\omega_{A}^{}$, with $\omega_{A}^{}$ = v_A/qR₀), real frequency ( $\omega_{r}^{}$/$\omega_{A}^{}$) and parallel wave vector ( k_|qR₀) both as $\alpha$ = - R₀q²$\beta{^\prime}$ of the thermal plasma and that, $\alpha_{E}^{}$ of fast ions are varied. The present work further explores theoretical aspects of EPM excitations by spatially localized particle sources, possibly associated with frequency chirping, which can radially trap the EPM in the region where the free energy source is strongest. Results of a nonperturbative 3D Hybrid MHD Gyrokinetic code are also presented to emphasize that nonlinear behaviors of EPM's are different from those of Toroidal Alfvén Eigenmodes (TAE) and Kinetic TAE (KTAE) and that particle losses and mode saturation are consistent with the mode-particle pumping model (particle radial convection). Results of theoretical analyses of nonlinear EPM dynamics are also presented and the possible overlap with more general nonlinear dynamics problems is discussed.

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