Speaker
Description
Ion cyclotron resonance heating (ICRH) is an important auxiliary heating method in tokamak devices. It also produces a large number of energetic particles (EPs) with energies up to MeV, which can potentially destabilize variety of instabilities such as Alfvén eigenmodes (AEs) or fishbone. Recently, several modes with frequencies ranging from $50$ to $300 kHz$ have been observed in high $\beta_P$ experiments with ICRF heating on EAST. In order to understand these experimental phenomena, we have carried out simulations of the ICRF heated scenario using the hybrid MHD-kinetic code MEGA.
In the simulations, experimentally measured equilibrium profiles ($q/n_e/T_e/T_i$) are used as input; and EPs are described by an anisotropic slowing-down distribution with $E_{birth}=1MeV,\Lambda_0=0.8,\Delta\Lambda=0.3 (\Lambda\equiv(\mu B_0)⁄E)$; and we focus on AEs with the toroidal mode number $n\le4$. As shown in Fig. 1, the $n=2$ mode is the most unstable during the linear growth stage, with the frequency of $77.5 kHz$ and the growth rate of $\gamma/\omega\approx3.3\%$. According to the poloidal mode structure and the corresponding Alfvén continuum (Fig. 2), we conclude that it is a TAE. The statistics of the value of $|\delta f|$ show that most resonant particles have energies less than $300 keV$, and the proportions of the trapped, co-current passing and counter-current passing particles are about $50\%$, $35\%$ and $15\%$, respectively. During the nonlinear saturation stage, the $n=1$ mode saturates with the largest amplitude, and the Fourier decomposition shows that it has three frequency components: $55 kHz$, $73 kHz$, and $86 kHz$. Its magnetic field perturbation amplitude is about $|\delta B⁄B_0 |\approx2×10^{-4}$, and it induces a very small radial transport of EPs. By scanning the parameters, it is found that, the saturation amplitude of AEs increased significantly with the initial beta of EPs, leading to a significant transport of EPs. It is also found that, changing the radial profile of $\beta_{EP}$ will lead to consequent changes of the mode frequency and radial position.
| Presentation type | Oral |
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