TY  - JOUR
A1  - Lebiga, O.
A1  - Santos-Lima, Reinaldo
A1  - Yan, Huirong
T1  - Kinetic-MHD simulations of gyroresonance instability driven by CR pressure anisotropy
JF  - Monthly notices of the Royal Astronomical Society
N2  - The transport of cosmic rays (CRs) is crucial for the understanding of almost all high-energy phenomena. Both pre-existing large-scale magnetohydrodynamic (MHD) turbulence and locally generated turbulence through plasma instabilities are important for the CR propagation in astrophysical media. The potential role of the resonant instability triggered by CR pressure anisotropy to regulate the parallel spatial diffusion of low-energy CRs (less than or similar to 100 GeV) in the interstellar and intracluster medium of galaxies has been shown in previous theoretical works. This work aims to study the gyroresonance instability via direct numerical simulations, in order to access quantitatively the wave-particle scattering rates. For this, we employ a 1D PIC-MHD code to follow the growth and saturation of the gyroresonance instability. We extract from the simulations the pitch-angle diffusion coefficient D-mu mu produced by the instability during the linear and saturation phases, and a very good agreement (within a factor of 3) is found with the values predicted by the quasi-linear theory (QLT). Our results support the applicability of the QLT for modelling the scattering of low-energy CRs by the gyroresonance instability in the complex interplay between this instability and the large-scale MHD turbulence.
KW  - MHD
KW  - plasmas
KW  - turbulence
KW  - cosmic rays
Y1  - 2018
U6  - https://doi.org/10.1093/mnras/sty309
SN  - 0035-8711
SN  - 1365-2966
VL  - 476
IS  - 2
SP  - 2779
EP  - 2791
PB  - Oxford Univ. Press
CY  - Oxford
ER  - 
TY  - JOUR
A1  - Santos de Lima, Reinaldo
A1  - Yan, Huirong
A1  - de Gouveia Dal Pino, E. M.
A1  - Lazarian, A.
T1  - Limits on the ion temperature anisotropy in the turbulent intracluster medium
JF  - Monthly notices of the Royal Astronomical Society
N2  - Turbulence in the weakly collisional intracluster medium (ICM) of galaxies is able to generate strong thermal velocity anisotropies in the ions (with respect to the local magnetic field direction), if the magnetic moment of the particles is conserved in the absence of Coulomb collisions. In this scenario, the anisotropic pressure magnetohydrodynamic (AMHD) turbulence shows a very different statistical behaviour from the standard MHD one and is unable to amplify seed magnetic fields. This is in contrast to previous cosmological MHD simulations that are successful in explaining the observed magnetic fields in the ICM. On the other hand, temperature anisotropies can also drive plasma instabilities that can relax the anisotropy. This work aims to compare the relaxation rate with the growth rate of the anisotropies driven by the turbulence. We employ quasi-linear theory to estimate the ion scattering rate resulting from the parallel firehose, mirror and ion-cyclotron instabilities, for a set of plasma parameters resulting from AMHD simulations of the turbulent ICM. We show that the ICM turbulence can sustain only anisotropy levels very close to the instability thresholds. We argue that the AMHD model that bounds the anisotropies at the marginal stability levels can describe the Alfv,nic turbulence cascade in the ICM.
KW  - MHD
KW  - plasmas
KW  - turbulence
KW  - galaxies: clusters: intracluster medium
Y1  - 2016
U6  - https://doi.org/10.1093/mnras/stw1079
SN  - 0035-8711
SN  - 1365-2966
VL  - 460
SP  - 2492
EP  - 2504
PB  - Oxford Univ. Press
CY  - Oxford
ER  -