Optical emission spectroscopy of high voltage cold atmospheric plasma generated using dielectric barrier discharges
While numerous experiments have demonstrated the efficacy of high voltage cold atmospheric pressure plasmas for extending food shelf-life and sterilizing medical instrumentation in sealed packages, the influence of the packaging material and gas composition on the reactive gas species generated by the high voltage atmospheric cold plasma is poorly understood. This study elucidates the impact of these parameters on plasma generation in sealed packages for four gases (ambient air, commercial grade compressed air, and high purity helium and nitrogen) placed in commercially available transparent plastic containers and bags. After adequate gas flushing, we observed that the container and bag individually reduced signal intensity by 63% and 45% across the measured wavelengths of 200 nm to 1100 nm, demonstrating that they acted as broadband absorbers. Neither the container nor bag influenced the wavelengths of the peak emissions, only the amplitude, indicating no significant effect on the types of species generated. Lissajous diagrams showed that the power dissipated by the nitrogen and ambient air plasma generated at 72 ± 3.7 kV RMS were comparable to the compressed dry air discharge generated at 80 ± 3.7 kV RMS.^ The helium discharge at 37 ± 3.7 kV RMS absorbed approximately 92% more power than these gases. We observed translational temperatures ranging from 1088 K for nitrogen to 1421 K for compressed air and rotational temperatures ranging from 285 K for helium to 479 K for compressed air. These results indicate that packaging materials have minimal effect on the most dominant peaks although further studies are required to elucidate the impact on less intense peaks observed.^ We next assessed the effect of voltage on species generation using a helium air plasma generated using the Phenix system with applied voltages of 36.4, 44.8, 58.1, and 71.0 kV. The light from the plasma was collected using a fiber optic cable that was provided with the SP2500 spectrometer. The N2 Second Positive system of a helium air plasma generated at 36.4 kV was observed using the 1800 g/mm grating of a spectrometer. SPECAIR fits for the spectra show no real correlation to voltage. Higher voltage did not necessarily translate to higher plasma temperature although the relative intensities for the observed peaks increased with increasing voltage. This clearly showed that the increased voltage did not directly correlate to increased temperature of the bulk gas.^
Allen L. Garner, Purdue University.
Nuclear engineering|Plasma physics
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