Luminescence of argon in a spatially stabilized mono-filamentary dielectric barrier micro-discharge: spectroscopic and kinetic analysis

Abstract

The experimental work reported here is devoted to the temporal behaviour of a mono-filamentary dielectric barrier discharge in pure argon, from 100 to 700 Torr. A sinusoidal voltage supply is used, its frequency ranging from 10 to 90 kHz. An anode avalanche followed by a cathode streamer as well as the spatial stability of the micro-discharge is clearly seen in successive 3-ns snapshots in the visible range. Near the cathode, its diameter is about 0.2 mm, at 400 Torr. The electrical characteristics of the discharge are also evaluated, in particular the breakdown voltage and the energy deposited in the micro-discharge. The light output in the vacuum ultraviolet range is essentially due to the second continuum of argon, centred at 130 nm. The kinetic study of this continuum shows that primary excitation of the lowest argon atomic 4s and 4s′ states is practically achieved after 120 ns since beyond that time the luminescence decay of the second continuum is fairly described by only two exponential terms. So collisions between excited states, electronic collisions, and recombination of ionic species do not contribute significantly to this luminescence, after 120 ns. Surprisingly, we do not observe the contribution of the Ar(3P1) resonant state in the production of the argon excimers. The radiative lifetime of the Ar2[1u(3P2)]low v excimer ((3.18 ± 0.03) µs) and the three-body rate constant relative to the decay of the Ar(3P2) metastable state ((13.2 ± 0.9) Torr−2 s−1) leading to the formation of Ar2[1u(3P2)], are estimated. These results are consistent with those found from the literature. A simple kinetic scheme is proposed for times later than 120 ns.

Electric and spectroscopic analysis of a pure nitrogen mono-filamentary dielectric barrier discharge (MF-DBD) at 760 Torr

“…Each electrode is a 4-mm diameter cylindrical aluminium rod, covered with a d die = 0.5 mm thick insulating MAKOR on its flat front-end (relative electrical permittivity: ε R = 4.0). Such small plate-to-plate double barrier configuration electrodes ensures establishment of a unique filamentary barrier discharge for every half-cycle of the driving sinusoidal voltage u sup (t) [Merbahi N et al 2004] and was previously used to investigate rare gas DBDs. The gap distance was maintained at d =1 mm, so as to achieve stable MF-DBDs in pure nitrogen at a pressure of P N2 = 760 Torr, with our electric supply at a frequency of f = 7.8 kHz.…”

“…The measured supply current i sup (t) is then a fast-rising pulsed current superimposed on a slow displacement current [Merbahi N et al 2004]. The current i cell (t) flowing through the DBD cell can be evaluated:…”

“…The gas ignites (i dis starts) when the space charge is high enough to accelerate "seed electrons" present in the gas. In other gases like argon and xenon this phase is generally skipped [Merbahi N et al 2004] [ Merbahi et al 2007]. So it seems that, in nitrogen based DBDs ignition processes followed by When the ionization wave reaches the cathode, the discharge current rise slows down because of the additional charge deposited on the cathode layer.…”

“…Operating in xenon or neon, they produce VUV or EUV (10 nm < λ < 100 nm) emissions with an efficiency as high as 50 to 60% [Vollkommer F and Hitzschke L 1996, Hitzschke L and Vollkommer F 2001, Mildren R P and Carman R J 2001, Carman R J and Mildren R P 2003, Carman R J et al 2004, Merbahi N et al 2007, Carman R J et al 2010. In order to understand their behaviour, stable MF-DBDs were must be achieved at frequencies around tens of kilohertz [Adler F and Muller S 2000, Sewraj N et al 2009, Merbahi N et al 2004, Merbahi N et al 2010. In such circumstances, for each half-period all the observed emissions can be unambiguously attributed to a single filament whose time-origin is well defined by the fast rising supply current.…”

Axial and radial development of microdischarges of barrier discharges in N2/O2mixtures at atmospheric pressure

“…Besides streak photography [16,17], an ICCD-camera is the only diagnostic tool for the investigation of individual MDs [18]. But under the conditions being considered the MDs occurs statistically.…”