SIMULATION OF A LONG STREAMER TAKING INTO ACCOUNT THE CHANNEL EXPANSION DUE TO IONIZATION

A numerical simulation of a long streamer propagating in the air at at mospheric pressure toward the cathode is performed by taking into acco unt the ionization expansion of the channel. The calculation results a re shown to depend weakly on the presumed initial radius of the channe l. The maximum radius of the long channel is found to be greater than the diffusion radius by approximately two orders of magnitude. The spe cific features of the expansion of the ionization channel in dependenc e on the dimensions of the anode and steepness of the voltage pulse fr ont are studied. The calculation results agree well with the measured values of the streamer radius and current, limiting length of the chan nel, and average strength of the electric field in it. An explanation and quantitative description of the experimentally observed secondary ionization wave are presented; this wave starts from the anode and for ms the so-called stem of the pulse corona, in which a leader of the lo ng spark is created.