Time-resolved characterization of plasma properties in a CH₄/He nanosecond-pulsed dielectric barrier discharge

Abstract

Non-equilibrium plasmas for plasma-assisted combustion, pollutant remediation, fuel reforming, and catalysis rely on the production of energetic electrons that ionize, dissociate, and excite the fuel and oxidizer molecules. Experimental characterization of the electron temperature, electron density, and vibrational temperature are necessary to validate and improve plasma kinetic models. An experimental apparatus capable of Thomson scattering and vibrational Raman scattering measurements in the same discharge with molecular admixtures was developed. Both diagnostics are necessary to study the induced vibrational non-equilibrium from electron impact. Thomson scattering spectra were resolved by placing a physical mask at the output of a single grating spectrometer. The electron temperature and density and the impact of hydrocarbon addition was measured for a 60 Torr CH 4 /He nanosecond pulsed plane-to-plane dielectric barrier discharge with 0%-2% CH 4 addition. Electron densities as low as 1 × 10 12 cm −3 and electron temperatures ranging from 0.5 eV to 9 eV were observed. A decrease in the electron temperature and density was observed even with 1% CH 4 addition. Moreover, the addition of N 2 to the discharge enabled vibrational Raman scattering and quantification of the first level vibrational temperature starting from 75 ns after the voltage pulse. The electron temperature and density were also measured in this CH 4 /N 2 /He mixture by Thomson scattering. Addition of N 2 led to a faster electron temperature decay than in the original CH 4 /He mixture. The advantages and disadvantages of this detection scheme for Thomson scattering over the triple grating spectrometer and the volume Bragg grating notch filter is discussed.

Plasma-Catalytic Partial Oxidation of Methane on Pt(111): A Microkinetic Study on the Role of Different Plasma Species

“…We simultaneously vary the vibrational temperatures of CH 4 and O 2 between 500 and 1500 K and assume both vibrational temperatures to have the same value. Chen et al 62 measured the vibrational temperature in a CH 4 / N 2 /He DBD plasma at 60 Torr based on the ν = 1 peak of N 2 and observed a maximal vibrational temperature of 1350 K. We here choose an upper limit of 1500 K, which is still in the uncertainty range of the results from Chen et al 62 We choose this value to be an upper limit since the vibrational temperature measured by Chen et al was based on the ν = 1 peak of N 2 and the vibrational temperature of CH 4 is likely to be lower. As a comparison, Butterworth et al 63 studied the vibrational excitation of CH 4 in low-pressure pulsed microwave plasma and found that the vibrational and gas temperatures equilibrate around 900 K. In any case, varying the vibrational temperature in this wide range is interesting from a theoretical point of view as well.…”

Investigation on the electron density and temperature in a nanosecond pulsed helium plasma jet with Thomson scattering

“…The method introduced in this paper was implemented for low‐pressure discharge [ 23,24 ] and then was applied in moderate pressure conditions. [ 22 ] By adjusting the micrometer‐driven translation stages, a more precise alignment can be achieved for the mask placement. Compared with a triple grating spectrometer, the current setup requires fewer optics, which can increase transmission efficiency and reduce complexity.…”

“…Then, the recorded spectra can be corrected for the various transmission curves of the optical components such as the ICCD camera and the diffraction grating. [ 22 ] Besides, the transmission efficiency ratio of the polarizer to the longpass filter is determined by measuring the power of a DPSS laser (MGL‐III‐532) with the polarizer parallel to the laser polarization.…”

“…A volume Bragg notch filter with single grating can also be used to get rid of Rayleigh scattering signal, [ 19,21 ] but the alignment of the optical path is difficult to achieve. Recently, a new setup has been developed by Chen et al [ 22 ] for middle‐pressure discharges, which is implemented in low‐pressure discharges. [ 23,24 ]…”

Numerical Study of Stream-wise and Span-wise Nanosecond DBD Plasma Actuators Effects on Supersonic Flow Separation

“…They concluded that rapid localized heating in the boundary layer produced a microwave, similar to the experiment performed by Roupassov et al (2009). Some kinetic methods have been suggested to model the NS-DBD actuator effects (Orr et al 2021;Chen et al 2019). The kinetic approach requires computational cost and time; thus, simpler models have been suggested.…”