A microphysical view of heating processes in the intracluster medium

Author / Creator

Ley, Francisco, Ph.D. author

Available as

Online

Physical

Summary

Turbulent heating from active galactic nuclei (AGN) is a promising channel to dissipate energy into the intracluster medium (ICM) plasma to counteract the rapid radiative cooling inferred from X-ra...

Turbulent heating from active galactic nuclei (AGN) is a promising channel to dissipate energy into the intracluster medium (ICM) plasma to counteract the rapid radiative cooling inferred from X-ray observations, and giving a plausible solution to the well known Cooling Flow Problem. However, it is not yet clear how AGN outflows thermalize and deposit their energy in the ICM. The study of ICM turbulent dissipation demands an understanding of the plasma at small scales, and therefore its study at a kinetic level becomes a necessity. In the first part of this thesis, we use theory and particle-in-cell simulations to propose a heating mechanism for the ICM based on magnetic pumping, where the plasma is heated directly by large-scale turbulent fluctuations. We show that a net energy gain is attained when the magnetic field is periodically varied and there is an effective scattering in the plasma, given by kinetic instabilities (mirror, firehose, ion-cyclotron, and whistler). The efficiency of the heating depends on the frequency of the large-scale turbulent fluctuations. In the second part of this thesis, we study the serendipitous discovery of secondary instabilities observed in the nonlinear evolution of the primary mirror instability. We identify the instabilities as ion and electron cyclotron waves, grown from the pressure anisotropy of ions and electrons generated by the trapping process that primary mirror modes produce. These secondary instabilities are a concomitant feature of the mirror instability, from the Earth's magnetosphere to galaxy clusters, and their presence has a profound impact on the magnetic pumping heating mechanism studied in this thesis.

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