Long-time simulation of N-NB-driven JT-60U plasmas; Validation and explanation for chirping modes (n=1 EPM) and ALE (multi-n)

Bierwage, A.

Results of long-time simulations of N-NB-driven JT-60U plasmas are presented. The simulations are performed with an extended version of the MEGA code that includes MHD activity, fast ion sources, collisions and a realistic particle boundary (wall). The plasmas studied exhibit two important phenomena: rapidly chirping modes and Abrupt Large Events (ALE). The long-time MEGA simulations reproduce many of the observed properties both qualitatively and quantitatively. The simulations even predict features that were subsequently confirmed by experimental data mining. This constitutes a successful validation of the code and a demonstration of its predictive capability. An analysis of the simulation results allows us to offer explanations for both phenomena. Chirping modes are interpreted as Energetic Particle Modes (EPM) with single toroidal mode number , whereas ALEs occur due to interactions between modes with , 2 and 3.