Spatio-temporal characterization of the multiple current pulse regime of diffuse barrier discharges in helium with nitrogen admixtures

Abstract

This work reports on the spatio-temporal characterization of the multiple current pulse regime of diffuse barrier discharges driven by sine-wave feeding voltage at a frequency of 2 kHz in helium with small nitrogen admixtures. The discharge gap of 3 mm is bounded by glass plates on both plane electrodes. Priority is given to the lateral discharge inhomogeneities, underlying volume-and surface-memory effects, and the breakdown mechanism. Therefore, relevant processes in the discharge volume and on the dielectric surfaces were investigated by ICCD camera imaging and optical emission spectroscopy in combination with electrical measurements and surface charge diagnostics using the electro-optic Pockels effect of a bismuth silicon oxide crystal. The number of current pulses per half-cycle of the sine-wave voltage rises with increasing nitrogen admixture to helium due to the predominant role of the Penning ionization. Here, the transition from the first glow-like breakdown to the last Townsend-like breakdown is favored by residual species from the former breakdowns which enhance the secondary electron emission during the pre-phase of the later breakdowns. Moreover, the surface charge measurements reveal that the consecutive breakdowns occur alternately at central and peripheral regions on the electrode surface. These spatial inhomogeneities are conserved by the surface charge memory effect as pointed out by the recalculated spatio-temporal development of the gap voltage.

Review of surface transient charge measurement on solid insulating materials via the Pockels technique

“…The critical function of these two algorithms is to establish a transformation between surface charge density on dielectrics and induced electric field in Pockels crystals. It should be noted that the directly calculated surface charge density is not equal to the actual one in most cases unless the phase retardation induced by the applied voltage between two electrodes is subtracted [45,54]. A common practice is to deduct a virtual surface charge distribution numerically calculated by surface electric field distribution under the boundary condition of measured applied voltage on electrodes.…”

“…Minimum shutter duration of cameras √ Equip ultra-fast imaging technologies [41] Narrowest pulse width of light sources √ Adopt ultra-short pulse LED or laser sources [53] Charge resolution Thickness of tested samples √ Prepare thinner film or plate samples [54] Half-wave voltage of Pockels cells √ Utilise frequency-domain 2D Flourier transform inversion algorithm [46] Anti-noise surface charge inversion algorithms Effective area Maximum area of Pockels crystals √ Replace with needle or transparent electrodes [55] Blockage in light path by electrodes √ Control induced electric field at 45°to light path [50] √ Operate in reflection-type measurement systems [56] Charge range Wavelength of light sources √ Use lasers or LED sources with larger wavelengths [27] Electro-optic coefficient of Pockels crystals…”

“…Pockels crystals, acting as the dielectric barriers, were inserted into DBD reactors to hold and detect the transferred charge. Usually, the optical reflecting measurement system is constructed as shown in Figure 9, with a metal mirror as the ground electrode and a transparent ITO layer as the high-voltage electrode [54,56,60,61,67,81]. Various dielectrics, such as borosilicate glass, mono-crystalline alumina, magnesia and PE film were attached on Pockels crystals to investigate influence of material properties on transient behaviour of surface charge in different modes [27,59].…”

On the chronological understanding of the homogeneous dielectric barrier discharge

“…The key effect of the additional nitrogen is regarded to stimulate Penning ionisation, thereby facilitating volume ionisation and the consequent MCP discharge. In 2017, Bogaczyk et al [111] also presented a thorough experimental study on the spatio-temporal characterisation of the MCP regime of diffuse DBD in helium with small nitrogen admixtures. They also observed that the number of current pulses per half cycle rises with the increase of nitrogen admixture due to the predominant role of Penning ionisation.…”

Very large-scale gap distances of atmospheric pressure dielectric barrier glow discharge using semiconductor materials

“…2(b)-(d). The multiple discharge phenomenon can be explained through the evolution of the gas voltage induced by both the accumulated charge and the applied voltage [38]. While d increases and exceeds 40 mm, it is difficult to generate the discharges.…”