Studies on Excitation and Rotational Temperatures of an Oxygen-shielded Argon Microwave Plasma Torch Source

Excitation（ Texc ） and rotation（ Trot ） temperatures were determined under different conditions for an oxygen-shielded argon microwave plasmsa torch source（OS-Ar-MPT）. The Texc value, which was shown to be between 4300 and 5250 K under different operating conditions, was calculated from the slope of the Boltzmann plot with Fe as the thermometric species. The Trot value, which was in the range of 2100-2500 K, was measured with OH molecular spectra. The influences of microwave power, flow rates of the support gas, cartier gas, and shielding gas, as well as the observation height on Texc and Trot were investigated and discussed. The detailed results of Texc and Trot provided a better understanding of the performance of an OS-ArMPT as a source for atomic emission spectrometry.

Diagnosis of Electron,Vibrational and Rotational Temperatures in an Ar/N2 Shock Plasma Jet Produced by a Low Pressure DC Cascade Arc Discharge

In this paper, a low pressure Ar/N2 shock plasma jet with clearly multicycle al- ternating zones produced by a DC cascade arc discharge has been investigated by an emission spectral method combined with Abel inversion analysis. Plasma emission intensity, electron, vi- brational and rotational temperatures of the shock plasma have been measured in the expansion and compression zones. The results indicate that the ranges of the measured electron temperature, vibrational temperature and rotational temperature are 1.1 eV to 1.6 eV, 0.2 eV to 0.7 eV and 0.19 eV to 0.22 eV, respectively, and it is found for the first time that the vibrational and rota- tional temperatures increase while the electron temperature decreases in the compression zones. The electron temperature departs from the vibrational and the rotational temperatures due to non-equilibrium plasma effects. Electrons and heavy particles could not completely exchange energy via collisions in the shock plasma jet under the low pressure of 620 Pa or so.

Measurements of non-equilibrium and equilibrium temperature behind a strong shock wave in simulated martian atmosphere

Non-equilibrium radiation measurements behind strong shock wave for simulated Martian atmosphere are presented in this paper. The shock wave is established in a hydrogen oxygen combustion driven shock tube. Time- resolved spectra of the Av = 0 sequence of the B^2∑^＋ → X^2∑^＋ electronic transition of CN have been observed through optical emission spectroscopy （OES）. A new method, which is based on fitting high resolution spectrum for rotational and vibrational temperatures measurement, is proposed to diag- nose temperature distribution behind the shock wave. It is estimated that the current scheme has the maximum deviation less than 8% （lσ） for vibrational temperature measurement through detailed analysis of the influence of the uncertainties of spectroscopic constants and spectral resolution. Radiation structure of the shock layer, including induction, relaxation and equilibrium process, and corresponding rotational and vibrational temperatures are obtained through time gating OES diagnostics with sub-microsecond temporal resolution. The present extensive results will strongly benefit the reaction rate estimation and computational fluid dynamics （CFD） code validation in high enthalpy Mars reentry chemistry.

Generation of atmospheric pressure air diffuse discharge plasma in oxygen enriched working gas with floating electrode

In this work,a floating electrode is employed to generate a stable large-area diffuse discharge plasma under an open oxygen-rich environment.The discharge image and the optical emission spectra of the N2(C-B),N2+(B-X),N2(B-A),and O(3p–3s,777 nm)are measured to analyze the morphological and optical characteristics of the discharge.The effects of applied voltage,gas flow rate,and electrode gap on the reactive species,vibrational temperature and rotational temperature are investigated,and the discharge mode is discussed by simulating the electrostatic field before the breakdown.It is found that the changes of applied voltage and electrode gap causes the transition of the discharge modes among corona mode,diffuse discharge mode and spark mode.It is shown that the floating electrode can inhibit the transition from discharge to spark mode to a certain extent,which is conducive to maintaining the stability of discharge.As is vividly illustrated in this study,the increase of applied voltage or the decrease of electrode gap contributes to the generation of more active particles,such as N2(C)andN+2(B).Furthermore,the Joule heating effect becomes more evident with the increased applied voltage when the electrode gap is 15 and 20 mm.Moreover,as the applied voltage increases,the vibrational temperature increases at the electrode gap of 25 mm.

Research on the characteristics of atmospheric air dielectric barrier discharge under different square wave pulse polarities

Energy efficiency limits the application of atmospheric pressure dielectric barrier discharge(DBD),such as air purification,water treatment and material surface modification.This article focuses on the electrical and optical effects of the DBD under three square wave pulses polarities-positive,negative and bipolar.The result shows that under the same voltage with the quartz glass medium,the discharge efficiency of bipolar polarity pulse is the highest due to the influence of deposited charge.With the increase of air gap distance from 0.5 to 1.5 mm,average power consumed by the discharge air gap and discharge efficiency decrease obviously under alumina,and increase,and then decrease under quartz glass and polymethyl methacrylate(PMMA).Through spectrum diagnosis,in the quartz glass medium,the vibration temperature is the highest under negative polarity pulse excitation.Under bipolar pulse,the vibration temperature does not change significantly with the change of air gap distance.For the three dielectric materials of quartz glass,alumina and PMMA,the molecular vibration temperature is the highest under the quartz glass medium with the same voltage.When the gap spacing,pulse polarity or dielectric material are changed,the rotational temperature does not change significantly.

The investigation of OH radicals produced in a DC glow discharge by laser-induced fluorescence spectrometry

In this paper the OH radicals produced by a needle-plate negative DC discharge in water vapor,N_(2)+H_(2)O mixture gas and He+H_(2)O mixture gas are investigated by a laser-induced fluorescence(LIF)system.With a ballast resistor in the circuit,the discharge current is limited and the discharges remain in glow.The OH rotation temperature is obtained from fluorescence rotational branch fitting,and is about 350 K in pure water vapor.The effects of the discharge current and gas pressure on the production and quenching processes of OH radicals are investigated.The results show that in water vapor and He+H_(2)O mixture gas the fluorescence intensity of OH stays nearly constant with increasing discharge current,and in N_(2)+H_(2)O mixture gas the fluorescence intensity of OH increases with increasing discharge current.In water vapor and N_(2)+H_(2)O mixture gas the fluorescence intensity of OH decreases with increasing gas pressure in the studied pressure range,and in He+H_(2)O mixture gas the fluorescence intensity of OH shows a maximum value within the studied gas pressure range.The physicochemical reactions between electrons,radicals,ground and metastable molecules are discussed.The results in this work contribute to the optimization of plasma reactivity and the establishment of a molecule reaction dynamics model.

Characteristics of Low Power CH_4/Air Atmospheric Pressure Plasma Jet

A low power atmospheric pressure plasma jet driven by a 24 kHz AC power source and operated with a CH4/air gas mixture has been investigated by optical emission spectrometer. The plasma parameters including the electron excitation temperature, vibrational temperature and rotational temperature of the plasma jet at different discharge powers are diagnosed based on the assumption that the kinetic energy of the species obeys the Boltzmann distribution. The electron density at different power is also investigated by HS Stark broadening. The results show that the plasma source works under non-equilibrium conditions. It is also found that the vibrational temperature and rotational temperat;ure increase with discharge power, whereas the electron excitation temperature seems to have a downward trend. The electron density increases from 0.8×10^21 m^-3 to 1.1×10^21 m^-3 when the discharge power increases from 53 W to 94 W.

Contrasting Behaviours of AC and DC Excited Plasmas in Contact with Liquid

A comparative study of the needle-to-liquid plasma in the continuous mode with DC and AC excitations is detailed in this paper. All plasmas studied here are shown to be glow discharges. This study is based on measurements of several key parameters, including electrical energy, optical emission intensities of active species, rotational and vibrational temperatures, and temperatures of the needle and liquid electrodes. AC plasmas can produce 1.2～5 times higher excited state active species than DC plasmas under the same dissipated power. AC excited liquid plasmas have the highest energy utilization efficiency among the three systems （AC excited plasmas, DC excited plasmas with water anode and DC excited plasmas with water cathode）; most of the energy is used to produce useful species rather than to heat the electrodes and plasmas.

Spatio-temporal evolution characteristics and pattern formation of a gas–liquid interfacial AC current argon discharge plasma with a deionized water electrode

A discharge ignited by an AC power source in contact with deionized water as one of the electrodes is investigated.Immediately after initiation,the discharge exhibits a unique phenomenon:the gas-phase discharge is extended into the liquid.Later,a cone-like structure is observed at the liquid surface.Synchronous monitoring of current–voltage characteristics and liquid properties versus time suggests that the discharge shapes are functions of the liquid properties.The spatio-temporal profiles indicate the potential effects of water,ambient air impurities,and metastable argon on the discharge chemistry.This becomes more obvious near the liquid surface due to increasing production of various transient reactive species such as centerdot OH and NO centerdot.Moreover,it is revealed that thermalization of the rotational population distributions of the rotational states(N′⩽6,J′⩽13/2)in the Q1 branch of the OH(A2Σ+,υ′=0→X2Π3/2,υ′′=0)band ro-vibrational system is influenced by the humid environment near the liquid surface.In addition,the transient behaviors of instantaneous concentrations of long-lived reactive species(LRS)such as H2O2,NO−2,and NO−3 are observed with lengthening the discharge time.The production of multiple transient and LRS proposes AC excited gas–liquid argon discharge as a potential applicant in industrial wastewater cleaning,clinical medicine,and agriculture.