Magnetic field generation in a jet-sheath plasma via the kinetic Kelvin-Helmholtz instability

摘要

We have investigated the generation of magnetic fields associated withvelocity shear between an unmagnetized relativistic jet and an unmagnetizedsheath plasma. We have examined the strong magnetic fields generated bykinetic shear (Kelvin–Helmholtz) instabilities. Compared to the previousstudies using counter-streaming performed by Alves et al. (2012), thestructure of the kinetic Kelvin–Helmholtz instability (KKHI) of ourjet-sheath configuration is slightly different, even for the global evolutionof the strong transverse magnetic field. In our simulations the majorcomponents of growing modes are the electric field , perpendicular to the flow boundary, and the magneticfield , transverse to the flow direction. After the component is excited, an induced electricfield , parallel to the flow direction, becomes significant. However, other field components remainsmall. We find that the structure and growth rate of KKHI with mass ratios/ = 1836 and / = 20 aresimilar. In our simulations saturation in the nonlinear stage is not as clearas in counter-streaming cases. The growth rate for a mildly-relativistic jetcase (γ = 1.5) is larger than for a relativistic jet case(γ = 15).