Dynamo in the Intra-Cluster Medium: Simulation of CGL-MHD Turbulent Dynamo

TL;DR

This paper investigates magnetic field amplification in the intra-cluster medium using 3D simulations of kinetic MHD with CGL closure, revealing similar growth rates to MHD but lower saturation levels, emphasizing the role of pressure anisotropy.

Contribution

It introduces a novel simulation study of turbulent dynamo in collisionless plasma using CGL-closure kinetic MHD, highlighting the effects of pressure anisotropy on magnetic field growth.

Findings

Magnetic energy growth rate similar to MHD dynamo.

Magnetic energy saturates at lower levels than MHD.

Pressure anisotropy limits are necessary for dynamo operation.

Abstract

The standard magnetohydrodynamic (MHD) description of the plasma in the hot, magnetized gas of the intra-cluster (ICM) medium is not adequate because it is weakly collisional. In such collisionless magnetized gas, the microscopic velocity distribution of the particles is not isotropic, giving rise to kinetic effects on the dynamical scales. These kinetic effects could be important in understanding the turbulence, as so as the amplification and maintenance of the magnetic fields in the ICM. It is possible to formulate fluid models for collisonless or weakly collisional gas by introducing modifications in the MHD equations. These models are often referred as kinetic MHD (KMHD). Using a KMHD model based on the CGL-closure, which allows the adiabatic evolution of the two components of the pressure tensor (the parallel and perpendicular components with respect to the local magnetic field), we performed 3D numerical simulations of forced turbulence in order to study the amplification of an initially weak seed magnetic field. We found that the growth rate of the magnetic energy is comparable to that of the ordinary MHD turbulent dynamo, but the magnetic energy saturates in a level smaller than of the MHD case. We also found that a necessary condition for the dynamo works is to impose limits to the anisotropy of the pressure.