## 3 Results and Discussion
### Length and Width of the Jet  
Measurement of the length and width of the jet of argon and oxygen/argon admixture discharges, for different flow rates and different discharge plasma powers of the emerging jet, can be performed by photo-imaging the plasma jet. Figure 4a represents eight photo images of an argon discharge as a function of flow rate (from 0.2 to 4 slm). Figure 4b represents four photo images of an oxygen/argon discharge as a function of oxygen ratio (from 0.25% to 1.5%). The images were taken in a darkened laboratory. All the photo images, depending on the calibrated length and width of the ground electrode (10 and 3 mm, respectively), as shown in Figure 1c, were taken as a reference for measuring the length and the width of the emerging jet. As shown in Figure 4, the jet is tilted and not vertical, which may be due to the sheath around the jet besides the edge effect of the jet. Figure 3: Influence of different flow rates on discharge plasma power (**a**) for pure argon, (**b**) for different oxygen ratios. Figure 5a shows the plasma jet length for an argon discharge as a function of flow rate from 0.2 to 4 slm. The plasma jet length decreases from 20.6 to 10.7 mm with increasing flow rate from 0.2 to 2 slm and begins to stabilize at an average jet length of 9.8 mm when the flow rate increases from 2.2 to 4 slm. Figure 5b shows the plasma jet length of an oxygen/argon discharge as a function of the oxygen ratio admixture with 1 slm of Ar; with increasing oxygen concentration using oxygen ratios from 0.25% to 1.5%, the plasma length decreases from 17.9 to 15.6 mm. This may be because of an electronegative property of oxygen, to attract electrons, meaning that the effects on the discharge intensity diminish, as does the plasma jet length [28]. The width of the jet is an active and interesting parameter that depends on plasma jet length and the applied flow rates of argon and oxygen. The width is a guideline for the maximum area of irradiance emerging from the jet and reaching the exposed sample. Figure 4: (**a**) Photo-imaging of the plasma jet lengths for argon discharge as a function of flow rate from 0.2 slm to 4 slm, and (**b**) Photo-imaging of the plasma jet lengths for oxygen ratio from 0.25% to 1.5%. For the argon discharge, Figure 6a shows that in group I\({}_{\text{Ar}}\), as the flow rate increases from 1.2 to 2 slm, the jet width increases axially to a maximum of 1.39 to 2.07 mm, for a plasma jet length of 13.2 mm; the jet length then begins to decrease recognizably to between 0.56 and 1.5 mm, for a plasma jet length of 15.4 mm. Figure 6b shows that in group II\({}_{\text{Ar}}\), as the flow rate increases from 2.8 slm to 4 slm, the jet width increases axially to a maximum of 1.88 to 1.1 mm, for a plasma jet length of 8.8 mm; the jet width begins to decrease recognizably to between 1.4 and 0.6 mm, for a plasma jet length of 11 mm. Figure 6a,b show that the best flow rates of dry argon, which obtain maximal irradiance that emerges from the jet and reaches the exposed samples, are moderate flow rates (2-2.8 slm). These moderate flow rates represent the maximum transition region from the laminar flow mode to the turbulent flow mode to obtain the largest widths, help to cover the largest exposure area of sample and accelerate the antibacterial process by dry argon, as discussed and applied in our previous work [29]. Figure 7a,b show the influence of the flow rate ratio of oxygen on the width and the length of the jet, from 0.25%, 0.5%, and 1% to 1.5% admixture with 1 slm of Ar, where two phases will be observed as follows:  
1. Figure 7a shows the jet width for wet argon as a function of plasma jet length less than 10 mm, at different applied flow rate ratios of oxygen, ranging from 0.25% to 1.5%. As the flow rate ratio of oxygen increases, the jet width recognizably decreases axially to a minimum of 0.609 to 0.366 mm, for a plasma jet length of 8.8 mm. 2.