Simulation of Gas Discharge in a Needle-to-Plane Geometry With Hundreds of Micrometers Gap and Its Enlightenment for Direct Charging of Aerosol Particles

It is necessary to recognize the spatial distribution of ion density and temperature in some practical applications. While numerical modeling is a useful method to fulfill this task, a self-consistent numerical model based on the first few moments of the Boltzmann transport equation coupled to Poisson’s equation was built using COMSOL Multiphysics to simulate the dc discharge of a needle-to-plane geometry in atmospheric pressure. Simulation of the discharge was carried out for an actual geometry in aerosol sensors when only the main compositions of air and the main collisional populating and depopulating processes were considered. The simulation results demonstrated that the space occupied by the positive ions with a density of sufficiently charging aerosol particles was very limited. In the meanwhile, the electron temperature in the vicinity of the entire plane electrode was higher than the melting point of most metals. Experiments of measuring the current inducted by charged particles with a diameter of 95 nm using devices with narrowed channels showed that the specific current increased to nearly five times when the width of the channel in the charging stage decreases from 5 to 2 mm. Furthermore, the ablation of the plane electrode used in the experiments occurred on almost the entire surface, which was agreed with the prediction by simulation.