Discrete Alfvén eigenmodes in the CFETR steady-state scenario

Abstract

In this paper, the stability features of discrete Alfvén eigenmodes (αTAEs) trapped by the α-induced potential wells are explored in CFETR (China Fusion Engineering Test Reactor) advanced steady-state operation, where α denotes a measure of the pressure gradient. For the reversed magnetic shear (RS) H-mode scenario with enhanced internal transport barrier (ITB), the αTAEs are trapped in the electron cyclotron (EC) power deposition region and effects of different pedestals on αTAEs are analysed. For the negative off-axis magnetic shear scenario, the αTAEs are discussed, and the effect of different magnetic shears on the αTAEs is presented. Finally, the effect of beam energies and pitch-angle distributions on αTAE stability is also presented.

An analytical model of how the negative triangularity cuts off the access to the second stable region in tokamak plasmas

“…In addition, it is important to emphasize that incorporating shaping effects in the ideal ballooning mode equation also pertains to modifications of the fluid-like potential energy (as discussed for the αTAE case). This modification can have implications for the vorticity equation governing Alfvén eigenmodes in the presence of energetic particles [18,41,43,44]. Thus, the stability properties of Alfvén eigenmodes resonant with energetic particles can be modified by shaping effects, presenting an intriguing avenue for future research.…”

“…Taken together, in the large α second ballooning stable domain, negative triangularity tends to inhibit the emergence of αTAEs, while positive triangularity has the opposite effect. Based on these findings, it can be speculated that in the presence of energetic particles [43,44], the destabilization of αTAEs will be more difficult with negative triangularity compared to zero and positive triangularity. This is beneficial for sustaining a larger pressure gradient in tokamaks subjected to auxiliary heating or fusion reactions.…”