The foreshock region is the first signature of the interaction of the solar wind with a planet's plasma environment when approaching its collisionless bow shock. Part of its structure and dynamic is determined by instabilities, which are created by the interaction of the solar wind with backstreaming ion populations. The interaction of the reflected ions with the solar wind drives ion/ion beam instabilities, which generate waves that are then convected towards the shock by the solar wind. Subsequently they may mediate the shock structure and its reflection properties. The most well-know examples are the field aligned ion beams (FABs), produced by reflection processes in the quasi-perpendicular and oblique regions of the shock. Other prominent examples are the gyrating ions with well-defined pitch-angle and gyrophase organization around the local magnetic field observed downstream of the FABs region. These gyrophase-bunched ions are always associated with large amplitude quasi-monochromatic right-hand mode low-frequency waves. Different mechanisms have been put forward to explain these ion features. This paper will discuss recent advances on this topic from multi-spacecraft observations (Cluster) as well as theoretical considerations.
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