3.3. Plasma area
Interfacial area was varied by using the gas discharge reactor with grounded plate electrodes of different diameters, as shown in Fig. 5. The leaders (plasma channels) generated in the gas discharge reactor propagate radially out over the liquid surface. As the leaders propagate across the liquid surface, they branch in such a way that the distance between leaders remains relatively constant, due to electrostatic repulsion. The fully propagated plasma occupies a roughly circular region on the liquid surface with visually uniform leader distribution [18–20]. The length of the leaders and therefore the area of this circular region, which will be referred to as the plasma area, increase with the diameter of the grounded plate. Because it is very difficult to define and measure the actual area of the plasma–liquid interface (A in Eq. (4)), plasma area was investigated as a potential surrogate. The plasma area was calculated for each plate size by recording images of the discharges and measuring the average length of the leaders.