The present work is devoted to the comparison between numerical and experimental determination of the velocity profile of an ionizing front (primary streamer) in a DC positive point-to-plane corona discharge in dry air at atmospheric pressure. The inception and propagation of the ionizing front is simulated by a one-dimensional model, using finite differences in a flux-corrected transport numerical scheme, including gamma -effects, and using experimental results concerning the swarm parameters. This model provides the spatio-temporal local field and charge density variations as well as the ionization front velocity. An optical measurement of the velocity is performed with the same discharge parameters, using a photomultiplier and a single-slit device. The technique is based on the experimental fact that, for a 1 cm gap in the 7-9 kV voltage range, the successive primary streamers corresponding to a given gap voltage display identical velocity profiles. As a result of the comparison, it appears that a precise coupling between simulation and experiment is possible. There is a voltage range (8-9 kV) within which good agreement is observed. The front velocity in most of the gap is about 2*107 cm s-1 and the profile presents an increase when the streamer leaves the point electrode and when it reaches the cathode. The possible mechanisms of these accelerations are discussed. The model may be applied to a large variation range for various parameters such as the nature of the gas, pressure, inter-electrode gap and curvature radius of the active electrode.

The role of positive ions and field emission in the negative corona triggering is discussed, in room air, at atmospheric pressure. First, an artificial positive space charge is created in a point-to-plane gap by focusing a pulsed ultraviolet laser beam at a determined distance from the point. The triggered corona current pulse is compared with the natural one. Numerical simulations which are presented take into account the insulating layers charging by positive ions on the cathode surface. The theory of electron emission is based upon a conduction mechanism in the bulk of insulating layers. Second, the role of field emission is enhanced by covering the point with a graphite coating. Field emission is modeled by introducing a field enhancement factor and current instabilities are attributed to the switch-off of emission sites on the cathode surface.

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Using a DC pulsed plasma for the polymer surface treatment allows the attainment of macroscopic modifications of the surface such as an important increase of the wettability. In the same time microscopic variations of the surface structure are mainly linked to low depth chemical modifications even if very weak roughness changes appear.As a consequence this technique presents two major interests. The first one is an economical interest because of the low power consumption compared to other techniques like radiofrequency or microwaves plasmas. The second one is the very significant treatment (macroscopic) realized in soft conditions without degradation of the polymer.These results composed of macroscopic and microscopic studies on polystyrene surfaces may allow to establish a macroscopic interpretation of the interaction between polymer and the DC pulsed plasma.