Needle electrode erosion in water plasma discharge

Various active species are formed by a pulsed electrohydraulic discharge. Analyses of optical emission spectra, hydrogen peroxide production and erosion of needle electrodes in the pulsed discharge in water with a pulse energy of ≈ 10 mJ were investigated in dependence on the type of plasma discharge (unbridged and bridged), the electrode material (tungsten and stainless steel) and the electrical conductivity of the solution (500, 750, 1000 and 1250 μS/cm). It was found that the OH radical emission line intensity was strongly intensified in the case of unbridged discharge mode independently on the electrode material or on solution conductivity. Hydrogen peroxide production did not depend on the electrode material and was not correlated with OH radical emission line intensity. Lower erosion rate was measured for tungsten electrodes with further decrease in the case of unbridged discharge mode of operation. Stainless steel electrodes reveal opposite characteristics. Smooth crater-like morphology was found for stainless steel and finer surface structures with protrusions for the tungsten with a smaller average crater diameter, shorter protrusion size and distribution for unbridged discharge mode of operation.