This paper deals with the electric and hydrodynamic confinement of negative ions in a point-to-plane corona discharge gap. Radial ion current density profiles have been measured on the earthed planar electrode, drilled in the axis of the point. The experimental setup is first validated by comparison with the Warburg's law without injected gas flow rate. The gas injected in the gap and blown from the discharge gap through the hole located at the centre of the plane affects neither the electric field close to the point nor the subsequent electric wind. However, it leads to the confinement of ions flux towards the central symmetry axis in the low electric field region up to a critical gas velocity, which for no more effect is measurable. Hence, electro hydro-dynamics confinement of ions can be achieved by limiting the outward radial expansion of ions to increase ion current densities on specific locations close to the low field planar electrode.

The influence of aerosol concentration on the charge per particle is investigated in post-DC corona diffusion chargers for particle diameter between 10 nm and 1 µm. Particles are charged as they pass through the charger volume by collection of ions; the ion concentration decreases along the same path due to unipolar space charge repulsion and collection on walls. With crossflow of ions and aerosols, the final mean charge per particle decreases by up to one order of magnitude with increasing aerosol concentration from 10 9 to 10 11 m -3 . The evolution of the ion density profile along particle trajectories with aerosol concentration is shown to be due to the consumption of ions by aerosol charging and to ion dispersion by unipolar space charge repulsion including ions and charged particles. Both are investigated using a simplified 1.5D model with axial symmetry and homogeneous mixing of ions and aerosols. It is shown that, for a given operating condition, the aerosol space charge is responsible for the modification of the spatial ion distribution and the related lower Niand charge per particle reported at higher aerosol concentration. From calculations, we define the maximal aerosol concentration to keep the mean charge per particle unaffected by aerosol space charge in the optimal case of homogeneous mixing of ion and aerosol. Finally, the comparison of different ion-aerosol mixing conditions highlights that an axial symmetry of the charger reduces the influence of aerosol space charge. This effect of aerosol concentration on the particle charge is critical for aerosol chargers devoted to electric mobility selection for size measurements or focused electro-deposition, as well as for concentration measurements as performed using emerging low cost sensors based on corona chargers.