2009/03/04 by Peter Bruggeman, Daan Schram, D.C. Schram +6 · 2 citations
Engineering · Medicine · #Electrohydrodynamics and Fluid Dynamics #Plasma Applications and Diagnostics #Plasma Diagnostics and Applications
paper · doi:10.1088/0963-0252/18/2/025017
openalex publication_date 2009/03/04 · openalex created_date 2025/10/10 · openalex updated_date 2026/07/30
Dc-excited discharges generated in water at the tip of a tungsten wire which is located at the orifice of a quartz capillary are investigated by time-averaged optical emission spectroscopy. Two distinctive discharge modes are observed. For small conductivities of the liquid the discharge is a streamer-like discharge in the liquid itself (liquid mode). For conductivities above typically 45 µS cm −1 a large vapour bubble is formed and a streamer discharge in this vapour bubble is observed (bubble mode). Plasma temperatures and electron densities are investigated for both modes. The gas temperature is estimated from the rotational temperature of N 2 ( C – B ) and is 1600 ± 200 K for the bubble mode and 1900 ± 200 K for the liquid mode. The rotational temperature of OH( A – X ) is up to 2 times larger and cannot be used as an estimate for the gas temperature. The rotational population distribution of OH( A ), ν = 0 is also non-Boltzmann with a large overpopulation of high rotational states. This discrepancy in rotational temperatures is discussed in detail. Electron densities are obtained from the Stark broadening of the hydrogen Balmer beta line. The electron densities in the liquid mode are of the order of 10 21 m −3 . In the bubble mode electron densities are significantly smaller: (3–4) × 10 20 m −3 . These values are compared with the Stark broadening of the hydrogen alpha and gamma lines and with electron densities obtained from current density measurements. The chemical reactivities of the bubble and liquid modes are compared by means of the hydrogen peroxide production rate.