The results of a set of simulations of Alfvén modes driven by an energetic particle population are presented, with the specific aim of comparing single-n and multiple-n simulations (n being the toroidal mode number). The hybrid reduced O(ϵ0 3) MHD gyrokinetic code HMGC is used ( being the inverse aspect ratio of the torus, with a and R 0 the minor and major radius, respectively), retaining both fluid (wave-wave) and energetic particle nonlinearities. The code HMGC retains self-consistently, in the time evolution, the wave spatial structures as modified by the energetic particle (EP) term. Simulations with toroidal mode numbers 1 < n < 15 have been considered. For the specific energetic particle drive considered, single-n simulations are either stable (n = 1), or weakly unstable (n = 2,3,13,14,15), or strongly unstable (4 < n < 12), with 4 < n < 12 modes exhibiting similar growth-rates, while n = 4 the largest saturated amplitude. A variety of modes are observed (TAEs, upper and lower KTAEs, EPMs). Nevertheless, no appreciable global modification of the EP density profile is observed at saturation. On the contrary, a multi-n, fully nonlinear simulation exhibits an appreciable broadening of the EP radial density profile at saturation, thus demonstrating an enhanced radial transport w.r.t. the single-n simulations. Moreover, the sub-dominant modes are strongly modified by nonlinear coupling which results both from the MHD and from the EP terms. © EURATOM 2018.
Single-n versus multiple-n simulations of Alfvénic modes
Zonca, F.;Giovannozzi, E.;Di Troia, C.;Fusco, V.;Fogaccia, G.;Briguglio, S.;Vlad, G.
2018-01-01
Abstract
The results of a set of simulations of Alfvén modes driven by an energetic particle population are presented, with the specific aim of comparing single-n and multiple-n simulations (n being the toroidal mode number). The hybrid reduced O(ϵ0 3) MHD gyrokinetic code HMGC is used ( being the inverse aspect ratio of the torus, with a and R 0 the minor and major radius, respectively), retaining both fluid (wave-wave) and energetic particle nonlinearities. The code HMGC retains self-consistently, in the time evolution, the wave spatial structures as modified by the energetic particle (EP) term. Simulations with toroidal mode numbers 1 < n < 15 have been considered. For the specific energetic particle drive considered, single-n simulations are either stable (n = 1), or weakly unstable (n = 2,3,13,14,15), or strongly unstable (4 < n < 12), with 4 < n < 12 modes exhibiting similar growth-rates, while n = 4 the largest saturated amplitude. A variety of modes are observed (TAEs, upper and lower KTAEs, EPMs). Nevertheless, no appreciable global modification of the EP density profile is observed at saturation. On the contrary, a multi-n, fully nonlinear simulation exhibits an appreciable broadening of the EP radial density profile at saturation, thus demonstrating an enhanced radial transport w.r.t. the single-n simulations. Moreover, the sub-dominant modes are strongly modified by nonlinear coupling which results both from the MHD and from the EP terms. © EURATOM 2018.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
