Molecular dynamics simulations of wake structures behind a microparticle in a magnetized ion flow. I. Collisionless limit with cold ion beam

The potential and density structure behind a spherical microparticle in a magnetized ion flow are studied by means of molecular dynamics simulations. It is shown that, with increasing magnetization of the flow, the ion accumulation in the wake diminishes. Instead, ion depleted regions (shadows) form and ions accumulate at the edge of the shadows. The change of the ion density distribution also affects the force on other microparticles in the downstream region. For weak magnetization and a short distance, these interparticle forces can be attractive and non-reciprocal, as in the unmagnetized case. For large magnetization and further downstream, the force becomes repulsive. The mechanism of shadow formation is shown to involve a fast Coulomb scattering during a short fraction of the gyro-period and subsequent trapping of the ions on large-radius gyro-orbits. Published by AIP Publishing.