Linear stability of the ITER 15 MA scenario against the alpha fishbone

Abstract

The stability of the $n=m=1$ alpha-fishbone kinetic-MHD mode on the ITER 15 MA baseline scenario \cite{ITERB} is analyzed using the nonlinear hybrid Kinetic-MHD code XTOR-K. Quantitative agreement is found between the complex frequencies $\omega +i\gamma$ computed with the linear model in \cite{Brochard2018} and XTOR-K's linear simulations. Identical precessional resonance positions in phase space are also found between the linear model and XTOR-K. Linear hybrid simulations performed with XTOR-K on the ITER 15 MA scenario reveal that this configuration is likely to be unstable against the alpha fishbone mode. The fishbone thresholds for kinetic-MHD equilibria with flat q profiles with on-axis safety factor just below unity lies between ${\beta }_{\alpha ,thres}/{\beta }_{tot}=6-10\%$, whereas the expected beta ratio on ITER is ${\beta }_{\alpha }/{\beta }_{tot}=15-20\%$ \cite{ITERB}.

22 pages, 12 figures, submitted to Nuclear Fusion