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The agglomeration of the matter in plasma, from the atomic level up to millimetre size particles, is here considered. In general we identify a continuous growth, due to deposition, and two agglomeration steps, the first at the level of tens of nanometres and the second above the micron. The agglomeration of nano‐particles is attributed to electrostatic forces in presence of charge polarity fluctuations. Here we present a model based on discrete currents. With increasing grain size the positive charge permanence decreases, tending to zero. This effect is only important in the range of nanometre for dust of highly dispersed size. When the inter‐particle distance is of the order of the screening length another agglomeration mechanism dominates. It is based on attractive forces, shadow forces or dipole‐dipole interaction, overcoming the electrostatic repulsion. In bright plasma radiation pressure also plays a role.

International audience; Kinetic simulations of collisionless shocks have provided a wealth of information on injection and acceleration of thermal ions into a diffusive acceleration process. At quasi-parallel shocks upstream diffuse ions and the induced upstream turbulence are an integral part of the collisionless shock structure. Before injected into a diffusive acceleration process thermal ions are trapped near the shock and are accelerated to higher energies. The injection and acceleration process for thermal ions at quasi-perpendicular shocks depends on the possibility of these ions to recross the shock many times. A viable mechanism for injection is cross-field diffusion of the specularly reflected ions after they have crossed the shock into the downstream region. Determination of the cross-field diffusion coefficient in strong turbulence suggests that specularly reflected ions can recross the quasi-perpendicular shock and can get further accelerated. At more oblique shocks the same injection process as at quasi-parallel shocks can work: particles gain high enough velocities during their first shock encounter so that they can escape the shock along the magnetic field in the upstream direction. Because of the form of the pickup ion distribution in velocity space there seems to be no problem for accelerating these ions at either quasi-parallel, quasi-perpendicular, or perpendicular shocks.