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Alfv$'{e}$n acoustic channel for ion energy in high-beta tokamak plasmas revisited with a linear gyrokinetic model (LIGKA)

Bierwage, A.; Lauber, P.*; Aiba, Nobuyuki; Shinohara, Koji; Yagi, Masatoshi

A recently proposed Alfv$'{e}$n acoustic self-heating channel for burning plasmas - where fast-ion-driven shear Alfv$'{e}$n waves transfer energy to sound waves which then heat the bulk ions - is reexamined using a linear gyrokinetic model. A local eigenvalue analysis shows that the ion sound branches required for such a self-heating channel are so strongly damped that they are effectively non-existent when $$T_{rm e} approx 1.7times T_{rm i}$$. However, when $$T_{rm e}$$ is increased by a factor 2.8, low-frequency sound continua in the range of beta-induced Alfv$'{e}$n acoustic eigenmodes (BAAE) are recovered and their excitation becomes feasible. This raises the question whether higher-frequency sound branches in the frequency range of beta-induced Alfv$'{e}$n continuum modes (BACM) and the associated self-heating channels may exist under reactor-relevant conditions. Moreover, it is shown that modifications of the continuous spectra by fast ions may need to be taken into account.



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