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Weakly collisional plasmas, such as the solar wind, hot accretion flows and the intracluster medium of galaxy clusters, have dynamically strong magnetic fields. In collisional plasmas, which can be approximated in the magnetohydrodynamical (MHD) limit, the turbulent dynamo mechanism can amplify seed magnetic fields of much weaker strength of astrophysical or primordial origin to strong dynamical levels efficiently by converting turbulent kinetic energy into magnetic energy. However, the viability of this mechanism in weakly collisional or completely collisionless plasma is much less understood. In this talk, I will discuss the properties of the collisionless turbulent dynamo using three-dimensional hybrid-kinetic particle-in-cell simulations with the "AHKASH" code. I will describe "AHKASH" - a new Hybrid particle-in-cell (PIC) code developed within the framework of the multi-physics code FLASH. Our new second-order accurate hybrid PIC method uses the Boris particle integrator and a predictor-predictor-corrector algorithm for advancing the Hybrid-kinetic equations. We introduce turbulence driving, modelled using the Ornstein-Uhlenbeck process, in the new Hybrid PIC code. To investigate steady-state turbulence with a fixed Mach number, it is important to maintain isothermal conditions, and we introduce a novel cooling method for PIC codes to achieve this. I will describe the properties of the collisionless turbulent dynamo in the kinematic regime for different values of the magnetic Reynolds number, initial magnetic-to-kinetic energy ratio, and initial Larmor ratio, i.e. the ratio of the Larmor radius to the size of the turbulent system. I will also discuss the distribution and evolution of the pressure anisotropy in the collisionless plasma and compare our results with the MHD turbulent dynamo. The nature of the collisional turbulent dynamo in the subsonic and supersonic regimes can differ significantly, as demonstrated by numerical MHD studies. I will discuss the features of turbulence and magnetic field amplification from the collisionless turbulent dynamo in both the subsonic and supersonic regime. |
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