In this paper we use a hydrodynamic minimal streamer model to study negative
corona discharge. By reformulating the model in terms of a quantity called
shielding factor, we deduce laws for the evolution in time of both the radius
and the intensity of ionization fronts. We also compute the evolution of the
front thickness under the conditions for which it diffuses due to the geometry
of the problem and show its self-similar character.Comment: 4 pages, 4 figure