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Understanding whether Helium can sediment to the core of galaxy clusters isimportant for a number of problems in cosmology and astrophysics. All currentmodels addressing this question are one-dimensional and do not account for thefact that magnetic fields can effectively channel ions and electrons, leadingto anisotropic transport of momentum, heat, and particle diffusion in theweakly collisional intracluster medium (ICM). This anisotropy can lead to awide variety of instabilities, which could be relevant for understanding thedynamics of heterogeneous media. In this paper, we consider the radialtemperature and composition profiles as obtained from a state-of-the-art Heliumsedimentation model and analyze its stability properties. We find that theassociated radial profiles are unstable, to different kinds of instabilitiesdepending on the magnetic field orientation, at all radii. The fastest growingmodes are usually related to generalizations of the Magnetothermal Instability(MTI) and the Heat-flux-driven Buoyancy Instability (HBI) which operate inheterogeneous media. We find that the effect of sedimentation is to increase(decrease) the predicted growth rates in the inner (outer) cluster region. Theunstable modes grow fast compared to the sedimentation timescale. This suggeststhat the composition gradients as inferred from sedimentation models, which donot fully account for the anisotropic character of the weakly collisionalenvironment, might not be very robust. Our results emphasize the subtletiesinvolved in understanding the gas dynamics of the ICM and argue for the need ofa comprehensive approach to address the issue of Helium sedimentation beyondcurrent models.

Plasma Instabilities in the Context of Current Helium Sedimentation Models: Dynamical Implications for the ICM in Galaxy Clusters