Barrier Discharge Excilamp Research Articles

Optical characteristics of the two-band barrier discharge excilamp on mercury monoiodide and mercury monobromide molecules

Introduction: An important direction in the development of excilamps is the study of working media emitting simultaneously several molecular bands of various exciplex molecules and or excimer molecules in the visible and ultraviolet spectral ranges in connection with possible applications in biotechnologies, medicine, and others. Purpose : The aim of the research was to determine the optical characteristics of a two-band excilamp on mercury monoiodide and monobromide molecules, the working media of which is a barrier discharge plasma on a mixture of mercury diiodide vapor and mercury dibromide vapor with helium and a small admixture of molecular nitrogen. . Methods: The development of a gas-discharge plasma and excitation of the components of the working mixture was carried out by a pulse-periodic barrier discharge with a pulse repetition rate of 1-20 kHz, pulse duration was 150 ns. Results : The ratio of the partial pressures of the components that give the maximum radiation yield at the wavelengths l max == 502 nm and l max = = 444 nm, namely: HgI 2 :HgBr 2 :N 2 :He = 0.1 kPa: 0.5 kPa: 2 kPa: 180 kPa are revealed. The following are achieved: the specific average and pulsed radiation power of 12 mW / cm 3 and 15.9 W / cm 3 , respectively, at a pulse repetition rate of 18 kHz, the efficiency of excilamp is ~ 15%. The long-term operation of the excilampi was detected (~ 10 7 pulses). Additional processes were found, that increase the population of the upper -state of mercury monohalides in the gas-discharge plasma, which are: additional processes of excitation of mercury monobromide molecules (-state)- the process of transfer of the population from the nitrogen molecule in metastable states of N 2 (), as well as the excitation of radicals by electrons in B 2 Σ + 1/2 -state of mercury monoiodide and mercury monobromide molecules. Conclusion : The optical characteristics of a two-band barrier discharge excilamp on a mixture of mercury diiodide and mercury dibromide with helium and a small addition of molecular nitrogen are established. The radiation spectrum consists of the predominant radiation of two spectral bands of mercury monoiodide and mercury monobromide exciplex molecules, and low-intensity spectral bands of molecular nitrogen, lines of helium atoms and mercury. It is established the regularities in the change of the dependence in optical characteristics of plasma on repetition rate of the pump pulses of the discharge and quantitative composition of mixtures. These studies are of interest for the production of exciplex gas-discharge sources (excilamps) that simultaneously radiate two bands in a visible spectral range.

Determining the energy balance in barrier-discharge Xe2 excilamp by the pressure jump method

The energy redistribution in barrier-discharge Xe2 excilamp in various excitation regimes is investigated using the pressure jump method. Analytic expressions are derived for calculating power W dissipated in the excilamp discharge plasma in the form of heat and for calculating total discharge heat power PT spent on heating the excilamp. It is shown that the mechanism of the thermal energy dissipation gradually changes upon an increase in the xenon pressure in the excilamp. The conditions for generating the maximal radiation power of the excilamp are determined. It is shown that the maximum of the average radiation power is attained for an excitation pulse duration of 500 ns and the maximal pulse power is attained for a pulse duration of 100 ns. It is found that the optimal operation regime for the excilamp corresponds to the maximal values of the PT–W difference.

Effects of the Operating Conditions on the UV-B (308 nm) Power and Efficiency of the XeCl* Barrier Discharge Excilamp

A dielectric barrier discharge in Xe-Cl <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> mixtures has been investigated numerically in a wide range of operating conditions with the purpose to study their effects on the XeCl* excimer radiation by means of a 1-D fluid model. First, a simplified chemical kinetics scheme is proposed and validated by benchmarking with the long chemical kinetics. These results show a limited loss of accuracy of discharge properties, while it is two times faster in computational time as compared with the complete version. The simulated results demonstrate that the discharges are typically Glow-like. During the breakdown, the cathode fall region is contracted to 85 μm. At that instant, the number density of XeCl* molecules in the sheath is maximum, and the principal channel of the XeCl* generation is harpoon reactions. The UV-B radiation dependence on the total gas pressure, voltage amplitude, and frequency of power supply and gap width has been analyzed. It was shown that the maximal radiative efficiency of UV-B emission is obtained at low gas pressure, high alternating voltage frequency, and high gap width. The radiative efficiency slowly depends on amplitude of the source alternating voltage. In addition, the emission power of the B→X band of XeCl* molecules grows when frequency or amplitude of the source voltage increases as well as when pressure decreases, but the emission power depends weakly on the gap width. Furthermore, the most part of the power deposited in the gas goes into heating electrons and lesser part goes into heating ions in the cathode fall.

New marker for determining the degree of inhomogeneity of capacitive and barrier discharges

A new thermodynamic approach to estimating the degree of nonuniformity of filling of the excimer lamp bulb with the discharge plasma is proposed for refining the results of numerical simulation of generation of radiation in the excilamp plasmas. It is shown that the thermal power of the discharge in a capacitive-discharge XeCl excilamp is proportional to the discharge filling factor. For a barrier-discharge XeCl excilamp, it is shown that the discrepancy between the efficiencies obtained by numerical simulation of an “ideal” discharge system and in the experiment can be explained taking into account the discharge filling factor of the cuvette.

Estimation of the Light Output Power and Efficiency of a XeCl Dielectric Barrier Discharge Exciplex Lamp Using One-Dimensional Drift–Diffusion Model for Various Voltage Waveforms

A XeCl dielectric barrier discharge (DBD) excilamp applied by pulsed and sinusoidal voltage waveforms is simulated using a 1-D drift-diffusion model. In both waveforms, the light output power depends not only on the gas mixture composition but also on the electrical parameters of each voltage waveform such as the frequency, the duty cycle, etc. At the same amplitude of the applied voltage and frequency, the light ultraviolet output efficiency of a pulsed voltage is higher than that of a sine voltage. These results obtained in this paper permit us to find out an appropriate power supply for a DBD excilamp.

Acoustic characteristics of a barrier-discharge XeCl excilamp

The generation of an acoustic signal by means of voltage pulses (f = 15 kHz) applied to the electrodes of a barrier-discharge excilamp based on a Xe/Cl2 = (50–500)/1 mixture kept at a pressure of 5–500 Torr is studied. It is shown that, from the time variation of the acoustic signal intensity, one can judge the time instant the excilamp starts operating in a steady mode. Optimal (in power and efficiency) operating conditions of the excilamp are found (Xe/Cl2 = 240/1, p = 98 Torr, η ≈ 9.5%). It is experimentally demonstrated that the discharge energy at a low pressure is spent largely on heating the gas. This is indicative of the volume heat release and volume glow discharge (as the pressure grows, the efficiency of this source of energy consumption drops and more and more energy is spent on acoustic vibration excitation). Under higher pressures, the Fourier spectrum of the acoustic signal becomes richer, the intensity of the spectrum rises, and the dispersion of the signal grows. At very high pressures, the intensity of the acoustic signal drops to a level corresponding to the natural vibrations of the excilamp envelope without the discharge (when the discharge is quenched, the Fourier spectrum of the signal becomes depleted and contains only harmonics corresponding to the carrier frequency of voltage pulses from the power source).

Control of the UV flux of a XeCl dielectric barrier discharge excilamp through its current variation**Reported at the IX International Conference on Atomic and Molecular Pulsed Lasers (Tomsk, 2009).

The efficiency of the electrical power transfer to the gas mixture of a XeCl dielectric barrier discharge (DBD) exciplex lamp is analysed. An equivalent circuit model of the DBD is considered. It is shown that the excilamp power can be controlled by applying current to the lamp. This highly desired property isensured by means of a specific power supply topology, whose concepts and design are discussed. The experimental prototype of a current-mode converter operating in the pulsed regime at pulse repetitionrate of 50 kHz is presented and its capability to control the amount of energy transferred during each current pulse is demonstrated. The capability of this power supply to maintain specific operating conditions for the DBD lamp, with a very stable behaviour (even at a very low current, in the regime of a single discharge channel), is illustrated. The experimental results of a combined use of this converter and a XeCl excilamp are presented. The influence of the supply parameters on the 308-nm XeCl excilamp is analysed.The shape of the UV pulse of the lamp is experimentally shown to be similar to that of the current, which actually flows into the gas mixture. The UV radiation power is demonstrated to be tightly correlated to the current injected into the gas and controlled by the available degrees of freedom offered by the power supply. The measured UV output characteristics and performance of the system are discussed. Time resolved UV imaging of a XeCl DBD excilamp is used to analyse the mechanisms involved in the production of exciplexes at various power supply regimes. It is shown that a pulsed voltage source leads to formation of short high intensity UV peaks, while current pulses lead to formation of sustained discharge filaments. Based on the results of modelling of the above-mentioned operation conditions, the two power supply regimes are compared and analysed from the point of view of the UV power and radiative control.

Photoinactivation of theEscherichia coliby the Pulsed Dielectric Barrier Discharge Excilamp Krypton Chlorine Emitted at 222 nm

The photoinactivation of the Escherichia coli bacteria with the pulsed dielectric barrier discharge excilamp krypton chorine (KrCl) emitted at 222 nm is presented. The Escherichia coli, with the initial density of 34.106 colony forming units (CFU)/?L, has been irradiated in the aqueous and on the surface medias, respectively. A high reduction rate in the survival density of E. coli has been reached by the photoinactivation in both media during the first 30 s. The photoinactivation resulted in the logarithmic reduction factor of 5.6 log and 5.1 log within irradiation time of 30 s on the surface and in the aqueous medias, respectively. At the high dose of 2880 mJ/cm2 , the logarithmic reduction factor reached 6.1 log and 5.5 log on the surface and in the aqueous medias, respectively. The first tailing plateau was appeared on the surface and in the aqueous medias at 60 and 300 s of irradiation time, respectively.

Photodecomposition of hexachlorobiphenyl by radiation of a KrCl (222 nm) barrier-discharge excilamp

The process of dechlorination of 2,2′,4,4′,5,5′-hexachlorobiphenyl (PCB 153) under the action of UV radiation of a KrCl* (222 nm) barrier-discharge excilamp has been studied. The photolysis was performed in PCB 153 solutions in hexane with concentrations of 10 μg/ml (sample 1) and 1 μg/ml (sample 2) and in a PCB 153 film on a silica plate (sample 3). The degree of PCB 153 decomposition was determined using the optical transmission spectra measured in a 185–350 nm wavelength range. An analysis of these spectra showed that chlorine atoms in ortho 2,2′-positions are detached first. At a UV radiation intensity of 3 mW/cm2 on the sample surface, the residual PCB 153 content in samples 1–3 was below 2% (60-min exposure), below 3% (25-min exposure), and below 20% (60-min exposure), respectively.

Investigation of the conditions of efficient I*2 (342 nm) luminescence in a barrier discharge in a Kr-I2 mixture

The energy and spectral characteristics of a barrier discharge in a mixture of iodine vapor with krypton have been investigated theoretically and experimentally. The emission spectrum consists of the single I*2 molecular band D′ → A′ peaking at 342 nm, the iodine resonance line at 206.2 nm, and the group of bands corresponding to iodine emission. The highest intensity of the I*2 (342 nm) band was obtained at a mixture pressure near 450 Torr. A mean output power and an efficiency of 550 mW and 1.6%, respectively, have been achieved. It is shown that, for the I2 barrier-discharge excilamp, the homogeneous, rather than filamentary form of discharge glow is optimal from the viewpoint of the highest mean output power. The maximal calculated value of the emission efficiency for the 342-nm band was 5%. The main processes determining energy losses in plasma have been found, and ways to increase the efficiency of emission in the D′ → A′ band of the I*2 molecule have been proposed.

Barrier-discharge excilamp on a mixture of krypton and molecular bromine and chlorine

Spectral and energy characteristics of a barrier-discharge excilamp on a mixture of krypton with bromine and chlorine molecules that emits in the range 200–300 nm are presented. The radiation spectrum contains the bands of the B → X transitions of the KrCl* (222 nm) and KrBr* (207 nm) molecules and the band of the D′ → A′ transition of the Br*2 molecule (291 nm). It is demonstrated that the bromine content must be higher than the chlorine content in the triple (Kr−Cl2−Br2) mixtures that are optimal with respect to the radiant power. A radiant power of 0.7 W and an efficiency of 3% are realized. A multiband barrier-discharge excilamp based on the triple mixture exhibits a potentially long lifetime.