In the simulation of streamer discharge propagation, classical integral methods used to calculate the photoionization source term are computationally very expensive. In this work, a new approach based on the direct solution of an approximate radiative transfer equation is developed. Different approximations of the radiative transfer equation are discussed and tested for typical conditions encountered in streamer discharges. An improved Eddington approximation is shown to be very accurate to calculate the photoionization term for a Gaussian emission source term with a half-width length of the order of 0.02 cm when the absorption coefficient of the gas is higher than or equal to 50 cm −1 . For steeper gradients of the source term, good agreement is obtained for higher values of the absorption coefficient. Furthermore, the computation time of the improved Eddington method is four orders of magnitude less than with the usual integral method. For streamer propagation in air at atmospheric pressure, the absorption coefficient is shown to be of the order of 130 cm −1 which validates the use of the improved Eddington approximation to calculate the photoionization term. Finally, two-dimensional calculations of a positive streamer discharge in air at atmospheric pressure in plane-plane geometry with the improved Eddington approximation are presented.

A time-correlated single-photon counting technique was used to verify the formation of a cathode-directed streamer inside the narrow cathode region following the interpulse phase of regular negative corona Trichel pulses in ambient air. A purely experimental approach was used to determine the spatiotemporal development of the electric field during the Trichel pulse rise with an extremely high resolution of 10 μm and tens of picoseconds. The results confirm the positive-streamer mechanism for Trichel pulse formation and provide supportive evidence for the hypothesis that the formation of a primary cathode-directed streamer occurs always in any streamer-initiated breakdown and prebreakdown phenomena associated with cathode spot formation.

The aim of this work was to identify the different diffuse dielectric barrier discharges (DBDs) obtained in the same electrode configuration and in the same gas for an excitation frequency ranging from 50 kHz to 9 MHz. The gas mixture was argon with 133 ppm of NH 3 . This Penning mixture is useful to obtain both low-frequency glow DBDs (GDBDs) and diffuse radio-frequency (RF) discharges. Electrical measurements and short exposure time photographs showed that whatever the frequency, a discharge free of micro-discharge was obtained. In the same configuration, the discharge was a GDBD up to 200 kHz. For frequencies higher than 250 kHz, the discharge behavior was that of a Townsend-like discharge associated with a maximum energy transfer close to the anode and a higher power (about twice that of the GDBD). The cathode fall formation was no longer observed during the discharge current increase because of ion trapping in the gas gap by the rapid electric field oscillations. In the same configuration, the alpha RF mode was observed from 1.3 MHz. Gamma secondary electron emission gave way to electron acceleration by the cathode sheath formation. Bulk ionization was important due to the high electron collision rate at atmospheric pressure. One consequence of the transition from low-frequency to high-frequency discharge was a significant increase in the power (factor ≈30), which reached 35 W cm −3 , while the breakdown voltage decreased from 900 V to less than 200 V.

Several theories have been proposed to explain the current pulse of Trichel, at low pressure, in accordance with experimental results. Nevertheless, these theories failed to explain the very fast rise time (a few nanoseconds) observed at high pressure. The aim of this study is to propose a numerical simulation of the Trichel pulse which explains the typical current shape observed in air at atmospheric pressure in terms of field-effect emission. This theory explains the principal mechanisms responsible for the formation of Trichel pulses and takes into account the cathode material and its surface state. The effects of the field magnification factor on the pulse shape resulting from cathode microprotrusions are discussed. In the same way, the value of the discharge channel's radius is also discussed and compared with the experimental measurements.

Three homogeneous DBD modes have been observed in argon ammonia Penning mixture. The transition from glow to Townsend-like to radiofrequency modes happens when the frequency increases from 50 kHz and 9.6 MHz. The aim of this paper is to characterize these modes based on the study of optical emission spectra. The transition from glow mode to Townsendlike mode is characterized by stronger argon emissions associated to higher energetic electrons. The radio-frequency mode is characterized by a continuum in the UV-vis range. This continuum is attributed to bremsstrahlung emission. Its presence is explained by a high density of less energetic electrons which is consistent with a decrease of argon emissions and an increase of the NH 336 nm system associated with electrons of low energy.