Cosmic-ray Streaming Instabilities using MHD-Particle-in-Cell Method

Cosmic-rays are an important constituent of the Galaxy. Their origin, propagation and escape have been subjects of active research. Moreover, they likely play a dynamically significant role in providing pressure support and driving galactic winds. Better understandings of these cosmic-ray physics require detailed knowledge on the kinetic effects of cosmic-rays interacting with background thermal plasma, especially the resonant and non-resonant (Bell) streaming instabilities when cosmic-rays drift faster than the Alfven speed of the background gas. We have developed a magnetohydrodynamic (MHD)-particle-in-cell (PIC) method, which retains the full kinetic nature of the CRs while bypassing the microscopic scales that conventional PIC methods must resolve, and hence is dramatically more computationally efficient. Using this method, I will discuss our initial studies of particle acceleration in non-relativistic shocks, where the Bell instability mediates the upstream turbulence to provides the source of scattering in the Fermi process. I will then discuss preliminary studies of the resonant streaming instability, which forms the basis for the picture of cosmic-ray self-confinement and cosmic-ray-driven wind.