Effect of field-aligned beam on upstream wave excitation and particle scattering in the earth’s foreshock: One-dimensional PIC simulation

Abstract

The Earth's foreshock extends to a large domain of upstream quasi-parallel bow shock, and is characterized by a presence of field-aligned beams (FABs), diffuse ions, ultra-low frequency (ULF) waves, high frequency whistler waves, shocklets, and so on. Kinetic self-consistent numerical simulation is one of the key tools to analyze detailed physics of the foreshock which has not been clearly understood. Because of the necessity of the large simulation domain, a full particle-in-cell (PIC) simulation of quasi-parallel shock has seldom been performed. In this paper we show preliminary results of a long-term and large-scale one-dimensional full PIC simulation of the quasi-parallel collisionless shock with the Alfven Mach number 6.6 and shock angle $20$ degrees. The FAB component is observed far upstream with the beam velocity of 10.5 times the Alfven velocity and the beam density of 0.5 % of the background plasma. This FAB generates right-handed Alfven waves in the plasma rest frame via resonant mode instability, and the excited waves are amplified as approaching the shock during the plasma convection. The number densities of energetic particles for both electrons and ions also increase as approaching the shock.