Gas temperature measurements in a high pressure argon pulsed dielectric barrier discharge using diode laser absorption spectroscopy

摘要

A tunable diode laser absorption spectroscopic technique has been used to quantify the high-pressure (p= 100–500 Torr) scaling of gas temperature in an argon dielectric barrier discharge (DBD) excited using two different applied unipolar voltage pulses from 1.7-6.0 kV and <800μJ/pulse maximum deposited energy. The diode laser tuning range was sufficient to capture both collision-broadened "wings" of the 1s3-2p2 (772.42 nm) and 1s5-2p7 transitions simultaneously in a single scan. The diagnostic technique is based upon Lindholm-Foley theory¹ which is particularly applicable for highly nonequilibrium discharge conditions in which the Lorentzian line shape dominates over the Doppler component. Along with the ideal gas law, Lindholm-Foley theory can be used to express both "shift" and "collision width" temperatures as Ts=To(βop/β)^10/7 and Tc=To(2Γop/2Γ)^10/7, respectively, where Ts =300 K, βo, and 2Γo are the reduced shift and broadening coefficients for a specified transition. In order to use this method to measure small gas temperature changes, it is important to obtain accurate values of βo and 2Γo for each transition. Measurements of 2Γo were not found in literature², while βo was found to be systematically biased². Estimates of these coefficients were performed using a self-consistent in situ cross-calibration incorporating both transitions, (i) low pressure measurements of 2Γo and (ii) high pressure measurements of the absolute shifts and line widths. Low pressure (p=5-50 Torr) measurements gave 2Γo(1s<--inf>3-2p2)=22.8±1.0 MHz/Torr and 2Γo(1s5-2p7)=21.6±0.3 MHz/Torr. Frequency shift measurements were performed by comparing absorption peaks obtained simultaneously from the DBD and a 1 Torr argon dc discharge. The 2Γ measurements were obtained from Voigt profile fitting. Lindholm-Foley theory predicts that β/2Γ=βo/2Γo ≈ -0.3627. Our measurements indicate that βo2Γo=-0.333±0.025 for both transitions so that within the specified uncertainties, βo(1s3-2p2)≈-7.6±0.7 MHz/Torr and βo(1s5-2p7)≈-7.2±0.5 MHz/Torr. Over the range of pressure and voltages, the measured gas temperature was nearly constant at 330±30 K.