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 - TY - JOUR A1 - Nishikawa, Ken-Ichi A1 - Frederiksen, J. T. A1 - Nordlund, A. A1 - Mizuno, Y. A1 - Hardee, P. E. A1 - Niemiec, J. A1 - Gomez, J. L. A1 - Dutan, I. A1 - Meli, A. A1 - Sol, H. A1 - Pohl, Martin A1 - Hartmann, D. H. T1 - EVOLUTION OF GLOBAL RELATIVISTIC JETS: COLLIMATIONS AND EXPANSION WITH kKHI AND THE WEIBEL INSTABILITY JF - The astrophysical journal : an international review of spectroscopy and astronomical physics N2 - In the study of relativistic jets one of the key open questions is their interaction with the environment. Here. we study the initial evolution of both electron-proton (e(-) - p(+)) and electron-positron (e(+/-)) relativistic jets, focusing on their lateral interaction with ambient plasma. We follow the evolution of toroidal magnetic fields generated by both the kinetic Kelvin-Helmholtz and Mushroom instabilities. For an e(-) - p(+) jet, the induced magnetic field collimates the jet and electrons are perpendicularly accelerated. As the instabilities saturate and subsequently weaken, the magnetic polarity switches from clockwise to counterclockwise in the middle of the jet. For an e(+/-) jet, we find strong mixing of electrons and positrons with the ambient plasma, resulting in the creation of a bow shock. The merging of current filaments generates density inhomogeneities that. initiate a forward shock. Strong jet-ambient plasma mixing prevents a full development of the jet (on the scale studied), revealing evidence for both jet collimation and particle acceleration in the forming bow shock. Differences in the magnetic field structure generated by e(-) - p(+) and e(+/-) jets may contribute to the polarization properties of the observed emission in AGN jets and gamma-ray bursts. KW - acceleration of particles KW - plasmas KW - radiation mechanisms: non-thermal KW - relativistic processes KW - stars: jets KW - Sun: magnetic fields Y1 - 2016 U6 - https://doi.org/10.3847/0004-637X/820/2/94 SN - 0004-637X SN - 1538-4357 VL - 820 PB - IOP Publ. Ltd. CY - Bristol ER - TY - JOUR A1 - Dzhanoev, Arsen R. A1 - Schmidt, J. A1 - Liu, X. A1 - Spahn, Frank T1 - Charging of small grains in a space plasma: Application to Jovian stream particles JF - International psychogeriatrics N2 - Context. Most theoretical investigations of dust charging processes in space have treated the current balance condition as independent of grain size. However, for small grains, since they are often observed in space environments, a dependence on grain size is expected owing to secondary electron emission (SEE). Here, by the term "small" we mean a particle size comparable to the typical penetration depth for given primary electron energy. The results are relevant for the dynamics of small, charged dust particles emitted by the volcanic moon Io, which forms the Jovian dust streams. Aims. We revise the theory of charging of small (submicron sized) micrometeoroids to take into account a high production of secondary electrons for small grains immersed in an isotropic flux of electrons. We apply our model to obtain an improved estimate for the charge of the dust streams leaving the Jovian system, detected by several spacecraft. Methods. We apply a continuum model to describe the penetration of primary electrons in a grain and the emission of secondary electrons along the path. Averaging over an isotropic flux of primaries, we derive a new expression for the secondary electron yield, which can be used to express the secondary electron current on a grain. Results. For the Jupiter plasma environment we derive the surface potential of grains composed of NaCl (believed to be the major constituent of Jovian dust stream particles) or silicates. For small particles, the potential depends on grain size and the secondary electron current induces a sensitivity to material properties. As a result of the small particle effect, the estimates for the charging times and for the fractional charge fluctuations of NaCl grains obtained using our general approach to SEE give results qualitatively different from the analogous estimates derived from the traditional approach to SEE. We find that for the charging environment considered in this paper field emission does not limit the charging of NaCl grains. KW - plasmas KW - planets and satellites: individual: Jupiter Y1 - 2016 U6 - https://doi.org/10.1051/0004-6361/201527891 SN - 1432-0746 VL - 591 SP - 647 EP - 684 PB - EDP Sciences CY - Les Ulis ER -