Abstract. This paper presents simulations of an air plasma discharge at atmospheric pressure initiated by a needle anode set inside a dielectric capillary tube. We have studied the influence of the tube inner radius and its relative permittivity ε r on the discharge structure and dynamics. As a reference, we have used a relative permittivity ε r = 1 to study only the influence of the cylindrical constraint of the tube on the discharge. For a tube radius of 100 µm and ε r = 1, we have shown that the discharge fills the tube during its propagation and is rather homogeneous behind the discharge front. When the radius of the tube is in the range 300 to 600 µm, the discharge structure is tubular with peak values of electric field and electron density close to the dielectric surface. When the radius of the tube is larger than 700 µm, the tube has no influence on the discharge which propagates axially. For a tube radius of 100 µm, when ε r increases from 1 to 10, the discharge structure becomes tubular. We have noted that the velocity of propagation of the discharge in the tube increases when the front is more homogeneous and then, the discharge velocity increases with the decrease of the tube radius and ε r . Then, we have compared the relative influence of the value of tube radius and ε r on the discharge characteristics. Our simulations indicate that the geometrical constraint of the cylindrical tube has more influence than the value of ε r on the discharge structure and dynamics. Finally, we have studied the influence of photoemission processes on the discharge structure by varying the photoemission coefficient. As expected, we have shown that photoemission, as it increases the number of secondary electrons close to the dielectric surface, promotes the tubular structure of the discharge.

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This paper presents simulations of the dynamics of nanosecond repetitively pulsed discharges between two point electrodes in atmospheric pressure air at 300 and 1000 K. At 300 K, the preionization left by successive discharges at the end of interpulses mainly consists of positive and negative ions with a density of about 10 9 cm −3 for a repetition frequency of 10 kHz. When photoionization is taken into account with a level of seed charges of about 10 9 cm −3 , the dynamics and the characteristics of the discharge during a voltage pulse are shown to depend only weakly on the nature of negative seed charges (electrons or ions). At 1000 K, the preionization left by successive discharges at the end of interpulses consists of positive and negative ions and electrons with a density of about 10 10 cm −3 for a repetition frequency of 10 kHz. Simulation results show that the dynamics and the characteristics of the discharge during a voltage pulse remain rather close whatever the preionization level considered in the range 10 9 -10 11 cm −3 , corresponding to nanosecond repetitively pulsed discharges in the frequency range 1-100 kHz. The simulation of several consecutive nanosecond voltage pulses at a frequency of 10 kHz shows that, at 1000 K, the discharge can reach in a few voltage pulses a stable 'quasi-periodic' glow regime in agreement with experiments. Finally, the influence of an external air flow aligned with the electrode axis on the conditions to obtain a stable 'quasi-periodic' glow regime is discussed.