During the last two decades atmospheric (or high) pressure non-thermal plasmas in and in contact with liquids have received a lot of attention in view of their considerable environmental and medical applications. The simultaneous generation of intense UV radiation, shock waves and active radicals makes these discharges particularly suitable for decontamination, sterilization and purification purposes. This paper reviews the current status of research on atmospheric pressure non-thermal discharges in and in contact with liquids. The emphasis is on their generation mechanisms and their physical characteristics.

http://iopscience.iop.org/article/10.1088/0022-3727/42/5/053001/pdf

Non-thermal plasmas in and in contact with liquids

A stable discharge was produced in atmospheric air using water as a cathode. Spectral lines of elements dissolved in tap water could be observed. It is demonstrated that the appearance of these spectral lines is a consequence of cathode sputtering of water during the discharge. The intensity of the lines was found to depend strongly on the acidity of the water. This kind of discharge gives a possibility for continuous analysis of water and waste water solutions.

https://iopscience.iop.org/article/10.1088/0022-3727/26/12/015/pdf

Emission studies on a glow discharge in atmospheric pressure air using water as a cathode

The pseudospark, an axially symmetric gas discharge at low pressures of typically 10 to 100 Pa and high voltages (of some hundred volts up to several hundreds of kilovolts), has become of interest in fast high-power switching, in producing well-pinched high intensity electron or ion beams, and as an X-ray source. The essential features of this type of discharge are described. The results of fast time-resolved spectroscopic investigations and breakdown delay statistics of the pseudospark are discussed. >

The fundamentals of the pseudospark and its applications

A glow discharge using a solution as the cathode was investigated to add to the understanding of the operating mechanism and characteristics of such systems. The intensities and vertical distributions of emission from several analytes and background species were observed and compared with the vertical distribution of Fe excitation and OH rotational temperatures, as well as to electrical characteristics. The effects of the discharge gap size, the pH and conductivity of the solution, the applied current and the solution flow rate on these distributions were also studied. Detection limits for this system were found to be comparable to those of similar systems and mostly in range of tens of parts per billion.

Spectroscopic and electrical studies of a solution-cathode glow discharge

The electrolyte cathode atmospheric glow discharge (ELCAD) invented in 1992 is a new optical emission source with upcoming application in the field of environmental protection as an outstanding instrument for monitoring the toxic heavy metal content of waters and wastewaters. The main operating parameters, mechanisms (secondary electron emission from the electrolyte cathode, self‐sustaining processes in the cathode dark space, dependence of the emitted line intensities on the discharge parameters, temperatures), and the analytical performance of this special discharge are presented through a critical review using the papers related to the ELCAD published from 1993 to 2006.

Electrolyte Cathode Atmospheric Glow Discharges for Direct Solution Analysis

The pressure dependence of the cathodic current density in the case of an electrolyte and a metal cathode glow discharge operating in air and helium atmospheres was investigated. In all cases, at pressures above 100-200 mbar, violation of the similarity law was observed, which was attributed to the occurrence of the dissociative recombination of molecular ions of the applied gases (O, and ). Taking into consideration this process, the relation was deducted, which was found to be in accordance with experimental data. In the case of an electrolyte cathode this relation was found to be valid also at low pressures.

https://iopscience.iop.org/article/10.1088/0022-3727/31/20/016/pdf

Similarity laws for glow discharges with cathodes of metal and an electrolyte

Near infrared CW laser oscillation in Cu II

Noble gas mixture CW hollow cathode laser with internal anode system

CW Cu II laser in a hollow anode-cathode discharge

The gas temperature was calculated in the cathode surface - dark space boundary layer in the case of the electrolyte cathode atmospheric glow discharge (ELCAD), taking into account the symmetrical charge transfer as a dominant collision. The gas temperature was found to be approximately 7000 K, which is in accordance with experimental results.

https://iopscience.iop.org/article/10.1088/0022-3727/31/11/001/pdf

M. Jánossy

Papers

Similarity laws for glow discharges with cathodes of metal and an electrolyte

Near infrared CW laser oscillation in Cu II

Noble gas mixture CW hollow cathode laser with internal anode system

CW Cu II laser in a hollow anode-cathode discharge

The gas temperature in the cathode surface - dark space boundary layer of an electrolyte cathode atmospheric glow discharge (ELCAD)