Authors: Yifan Huang (LANL)

We study the anisotropy of the interstellar pick-up ions (PUIs) in the solar wind (SW) by simulating pitch angle scattering using the MHD-PIC method, in which the electrons and solar wind ions are treated as fluid and the PUIs are treated as particles. We show the evolution of self-generated waves and the interstellar PUI pitch angles in cases with different PUI densities, and in cases with different angles between solar wind velocity and magnetic field direction. We study the waves generated due to the ring-beam instability and streaming instability and their effects on the PUI pitch angle scattering. We show that the PUIs can be scattered more quickly with larger PUI density. We also show that the PUIs at low latitude can be scattered more quickly than at high latitude, which is consistent with the observations that the anisotropy of PUIs is smaller at low latitude.