Abstract
The stability of the n = m = 1 alpha-fishbone kinetic-MHD mode on the ITER 15 MA baseline scenario (ITER Physics Expert Group on Energe Drive and ITER Physics Basis 1999 Nucl. Fusion 39 2471–95) is analyzed using the non-linear hybrid kinetic-MHD code XTOR-K. Quantitative agreement is found between the complex frequencies ω + iγ computed with the linear model in (Brochard G. et al 2018 J. Phys.: Conf. Series 1125 012003) 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 , whereas the expected beta ratio on ITER is (ITER Physics Expert Group on Energe Drive and ITER Physics Basis 1999 Nucl. Fusion 39 2471–95).
Highlights
The stability of a hot magnetized plasma against macroscopic modes in fusion devices can generally be predicted by the MagnetoHydroDynamics fluid theory (MHD), provided several assumptions are verified
The fluid equations solved by XTOR-K are an extension of XTOR-2F’s [3], that take into account different moments of the kinetic populations distributions function, depending on the physical model considered
The complex frequencies obtained with XTOR-K and the fishbone linear model for the described Kinetic-MHD equilibrium are displayed in Figure 7, as functions of the on-axis kinetic density nh,0
Summary
The stability of a hot magnetized plasma against macroscopic modes in fusion devices can generally be predicted by the MagnetoHydroDynamics fluid theory (MHD), provided several assumptions are verified. The stability of the so-called ”fishbone” mode driven by alpha particles is studied on the ITER tokamak, with the nonlinear Kinetic-MHD code XTOR-K [3][4]. The main kinetic drive of this instability is brought by the trapped particles, through the precessional resonance ω = ωd This mode was first discovered on the PDX tokamak [5] when fast particles were injected mostly perpendicular to the magnetic field with neutral beam injectors. During the nonlinear phase of the fishbone instability, resonant particles inside the q = 1 surface tend on average to give away their kinetic energy to the n = m = 1 mode, which leads to their transport beyond the q = 1 surface This instability is potentially detrimental to the burning plasmas that will be generated in the ITER tokamak.
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