Speaker
Description
The potential for ICRF accelerated energetic ions to drive vertical modes with toroidal mode number equal to zero ($𝑛_{\phi} = 0$) in tokamaks is explored. In particular, two effects are considered: (i) drive due to the highly anisotropic nature of the distribution function of ICRF accelerated ions; and (ii) pure “bump on tail” in the energy direction of the distribution function following sawtooth redistribution of the ICRF accelerated ions. The latter case can arise transiently if highly energetic trapped ions are less redistributed than lower energy ions as suggested in [Ya.I. Kolesnichenko et al 2000 Nucl. Fusion 40 1325]. Numerical simulations of the ICRF accelerated ions, including a sawtooth redistribution model, are used as input to linear calculations of the instability drive. A semi-analytical approach is also employed to gain insight into the effect the anisotropy of the distribution function on the drive of the modes. The analysis shows that ICRF resonance layers (i.e. where the ion cyclotron frequency of the heated species is equal to a harmonic of the ICRF wave frequency), placed somewhat on the high field side of the tokamak provides the most conducive conditions for driving $𝑛_{\phi} = 0$ modes.
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