Discharge Ignition Near a Dielectric

Abstract

Electrical breakdown in noble gas near a dielectric is an important issue in lighting industry. In order to investigate the influence of the dielectric on the ignition process, we perform measurements in argon, with pressure varying from 0.1 to 1 bar, using a pin-pin electrode geometry. Here, we present timeresolved images of ignition process for two different distances from electrodes to the dielectric.Index Terms-Electric breakdown, gas discharges.M ODERN lighting depends mainly on plasma radiation.Still, the process of discharge ignition is not yet fully understood, and a significant question in the ignition process of a standard lamp is the role of the dielectric wall. Using a highspeed camera and a versatile reactor, breakdown in the presence of a dielectric can now be systematically studied. In this paper, we present time-resolved images of electrical breakdown near a flat dielectric wall.We modified the setup that has already been described [1] in a way that is more suitable for this investigation. We used a pin-pin geometry, instead of pin-plate, and added a flat wall made of BK7, which is a material with ε r = 2.28. The distance between the tips of the two pins was 30 mm, and the distance between pins and the dielectric varied between 6 and 16 mm. The 2-D (x − y) schematic representation of the geometry is shown in Fig. 1, along with the equipotential lines. For discharge ignition, we used 5-25-kV positive voltage pulses with rise times between 100 and 200 ns. Measurements were done in argon at pressures from 0.1 to 1 bar. The photographs were taken with a 4QuickE intensified charge-coupled device camera. For photographs presented in this paper, we used exposure times of 5-10 ns.The top electrode is the anode, and the bottom one is grounded. The dielectric is positioned left from the electrodes, as shown in Fig. 1. As shown in Figs. 2 and 3, the discharge always starts at the anode and travels toward the grounded electrode. At one point, light starts emitting near the grounded electrode, and subsequently, the channel between the two electrodes is formed. However, there is an obvious difference between the discharges shown in Figs. 2 and 3. Fig. 2 shows the evolution of the discharge in 400 mbar of argon, with the dielectric wall being 6 mm away from the electrodes. The discharge starts at the anode, reaches the dielectric, and rapidly propagates along its surface. After the channel is formed, it becomes brighter as it Manuscript Fig. 1. Electric field strength shortly after the voltage pulse starts, when there is 1.25 kV across the anode, plotted against the 2-D projection of the geometry in the experiment. The color bar represents the electric field strength (in volts per meter). The left photograph shows the electric field strength in the case when the dielectric is 6 mm away from the electrodes; the electric field strength for 16-mm distance is on the right. Electric field was calculated using the Plasimo code [2]. The tip radius used in the calculation was 0.2 mm, whereas the real tip radius was 15 µ...

Reconnection and merging of positive streamers in air

“…in lamp ignition [6,7] as well as in the counter leaders stretching from tall structures upwards towards an approaching lightning leader [8].…”

The Role of Metastables in the Formation of an Argon Discharge in a Two-Pin Geometry

“…Our model, being 2-D cylindrically symmetric, cannot simulate the branching of the discharge, or its erratic path, as observed in the experiments [17], [30]. We do, however, show the propagation of a thin channel along the direction of the electric field.…”

“…The experimentally observed breakdown process in nearatmospheric pressure argon has been documented and described before [3], [17], [18], [30]. It features bright constricted channels propagating through the gas volume at high velocities.…”

“…The experiments have shown that the discharge in 700-mbar argon forms thin channels that propagate from the anode to the cathode at high velocities [17], [18], [30]. The breakdown voltage for the conditions that we simulated was measured at 14 kV [20].…”

“…These modeling efforts have described the ignition process in noble gas pressures ranging from 10 to 90 torr (13-120 mbar), where the discharge is glowlike and not constricted. Research in the field of high pressures of noble gases has been mainly experimental [4], [17]- [19], and it has been shown that, due to high voltages, the criterion for glow-tostreamer transition is fulfilled and that the discharges forming under these conditions are filamentary streamerlike ionizing channels. The experiments have also shown that the breakdown voltage rises with pressure and that the speed of propagation of the discharge rises with applied voltage and decreases with the increase in pressure.…”