A Monte Carlo Simulation of Coulomb Collisions and Wave-Particle Interactions in Space Plasma at High Latitudes

Four studies were considered to simulate the ion behavior in the auroral region and the polar wind. In study I, a Monte Carlo simulation was used to investigate the behavior of O+ ions that are E x B-drifting through a background of neutral O, with the effect of O+(Coulomb) self-collisions included. Wide ranges of the ion-to-neutral density ratio ni|nn and electrostatic field E were considered in order to investigate the change of ion behavior with respect to the solar cycle and altitude. For low altitudes and/or solar minimum (ni|nn≤10-5), the effect of self-collisions is negligible. For higher values of ni|nn, the effect of self-collisions becomes significant and, hence, the non-Maxwellian features of the O+ distributions are reduced. In study II, the steady-state flow of the polar wind protons through a background of O+ ions was studied. Special attention was given to using an accurate collision model. The Fokker-Planck expression was used to represent H+-O+ Coulomb collisions. The transition layer between the collision-dominated and the collision less regions plays a pivotal role in the behavior of the H+ flow. In the transition region, the shape of H+ distribution changes in a complicated manner from Maxwellian to kidney bean . The flow also changes from subsonic to supersonic within the transition region. The heat fluxes of parallel and perpendicular energies change rapidly from their maximum (positive) to their minimum (negative) values within the same transition region. In study III, a Monte Carlo simulation was developed in order to study the effect of the wave-particle interactions (WPI) on O+ and H+ ions outflow in the polar wind. The simulation also considered the other mechanisms included in the classical polar wind studies such as gravity, polarization electrostatic field, and divergence of geomagnetic field lines. Also, an altitude dependent wave spectral density was adopted. The main conclusions are (I) the o+ velocity distribution develops conic features at high altitudes; (2) the O+ ions are preferentially energized; (3) the escape flux of O+ increased by a factor of 40, while the escape flux of H+ remained constant; (4) including the effect of a finite ion Larmor radius produced toroidal features for o+ and H+ distributions at higher altitudes. In study IV, a comparison between the effect of WPI on H+ and O+ ion outflow in the polar wind and in the auroral regions was studied. It was concluded that: (I) O+ is preferentially energized in both regions; (2) both ions (H+ and O+) are more energetic in the auroral region at most altitudes; (3) in the auroral region, the ion conics formed at lower altitudes, at 1.6 R, for O+ and 2.5 R, for H+, while in the polar wind H+ did not form conics and O+ formed conics at high altitudes; (4) the effects of body forces are more important in the polar wind than in the auroral region, and for O+ than H+

Transport coefficients for drifting Maxwellian plasmas: The effect of Coulomb collisions

We derive the collisional momentum and energy transport coefficients in Maxwellian plasmas with a general drift velocity with respect to the ambient magnetic field by using two approaches, the Fokker-Planck approximation and Boltzmann collision integral. We find the transport coefficients obtained from Fokker-Planck representation are similar to those obtained by using Boltzmann collision integral approach, and both results are presented in a closed form in terms of hypergeometric functions. This has been done for drifting Maxwellian plasmas with special emphasis on Coulomb collision, i.e. inverse-square force. Also, we calculate the transport coefficients for two special cases, firstly, when the drift velocity is parallel to the ambient magnetic field (i.e. u = u∥, and zero perpendicular drift velocity), and secondly, when the drift velocity is perpendicular to the ambient magnetic field (i.e. u = u⊥, and zero parallel drift velocity). It is worthy to mention that, up to our knowledge, none of the derived transport coefficients for the above mentioned case are presented in closed form and in terms of hypergeometric function