Spatial and Temporal Analysis of Microplasma Light Emission
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Spatial and Temporal Analysis of Microplasma Light Emission M. Blajan, H. Fukunaga and K. Shimizu Innovation and Joint Research Center, Shizuoka University, 3-5-1 Jyohoku, Nakaku, 432-8561 Hamamatsu, Japan
ABSTRACT Emission spectroscopy analysis was used to study the microplasma phenomena. The microplasma discharge in Ar, N2/Ar and O2/Ar was analyzed in the discharge gap area and spatial distribution of active species was measured also outside the electrodes. Spatial and temporal distribution showed the propagation of light emission from anode towards cathode within a time period of 190 ns. The measurement of OH peak at 308.9 nm proved the existence of this excited species 1 mm outside the electrodes area. INTRODUCTION Microplasma proved to be an efficient and economical solution for a series of applications such as NOx removal, indoor air treatment, sterilization of bacteria or surface treatment of polymers [1-4]. Moreover among nonthermal plasma technologies microplasma has advantages due to its small size of reactor and power supply. Our microplasma is a dielectric barrier discharge at atmospheric pressure [5]. It is still necessary that some of the fundamental aspect of microplasma physics to be studied in order to develop and optimize the application processes. Emission spectroscopy is one of the methods for plasma analysis [6-11]. Due to the particularities of microplasma such as narrow discharge gap, the analysis can be performed only by this non invasive technique. EXPERIMENTAL SETUP Emission spectra were measured by an ICCD camera (Ryoushi-giken, SMCP–ICCD 1024 HAM-NDS/UV), and a spectrometer to which was attached a fiber optic (Fig. 1). Photos of microdischarges were taken using a high speed ICCD camera (Princeton Instruments, PI-MAX 3). A fiber optic with diameter of about 100 µm was used in order to have an accurate measurement of a small part of the microplasma discharge. A negative pulse Marx Generator was used to energize the electrodes [7]. Emission spectroscopy experiments were carried out at atmospheric pressure in Ar, N2/Ar and O2/Ar mixtures. Discharge voltage was negative pulse, rise time 100 ns, width 1 µs at 1 kHz (Fig. 2). Due to small discharge gaps (0~100 μm) and to the assumed specific dielectric constant of εr = 104, a high intensity electric field (107 ~108 V/m) could be obtained with relatively low discharge voltages around 1 kV [1]. The electrode size was 20 mm versus 40 mm. They have holes to flow the gas, with a diameter of Ø 3mm and an aperture ratio of 36%. The discharge gap was set at 100 μm using a spacer. Microplasma was measured in different points along X axis by
varying the position of the electrodes as shown in Fig. 3 (a). Also the spatial distribution was measured outside the electrode area as shown in Fig. 3(b).
Fig. 1 Experimental setup for emission spectroscopy measurements .
Fig. 2. Waveforms of discharge voltage, discharge current and gate signal for ICCD camera. Microplasma electrodes are perforated metallic plates covered with a dielectric layer. (a)
(b)
Fig.
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