TH/P6-4 Particle Simulation Analysis of Energetic-Particle and Alfvén-Mode Dy- namics in JT-60U Discharges
نویسندگان
چکیده
The results of particle simulations of a typical NNB-heated JT-60U discharge (# E036378), performed by the HMGC particle-in-cell code, are presented. We observe that the linear-growth phase is dominated by a fast-growing mode, localized at half radius, near the maximum of the energetic-ion pressure gradient and with a significant coupling with the Alfvén continuum, showing the energetic-particle-driven nature of the mode. As the nonlinear effects become important, a macroscopic outward displacement of the energetic ions is observed, producing a significant reduction of their density in the central region. These results seem to match quite well the dynamics of the abrupt large-amplitude event (ALE) experimentally observed in the JT-60U discharge. The time scale and frequency spread of the ALE are well reproduced too. Then, the issue of the almost quiescent phase following the ALEs, characterized by weaker fast frequency sweeping (fast FS) modes, is investigated. We show that it is not possible to explain such a phase as the consequence of the mere relaxation of the energetic-ion density profile produced by the ALE. The decrease of the instability level of the system can however be fully accounted for by properly taking into account the nonlinear modification of the energetic-ion distribution function in the velocity space. An interpretation of the full JT-60U bursting-mode phenomenology is finally presented.
منابع مشابه
Particle simulation of bursting Alfvén modes in JT-60U
The results of particle-in-cell simulations of a negative neutral beam heated Alfvén-mode experiment in the Japan Atomic Energy Research Institute Tokamak-60 Upgrade JT-60U H. Ninomiya et al., Fusion Sci. Technol. 42, 7 2002 ; A. Kitsunezaki et al., ibid. 42, 179 2002 are presented. They seem to match quite well the dynamics of the abrupt large-amplitude event ALE experimentally observed in the...
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