## 3 Results and Discussion
### Basic Safety Properties  
When considering dissipated power values of up to 5 W in the system, the range of safety relevant parameters should be considered to qualify potential application relevant settings. The results on patient leakage current and temperature of a treated copper surface are shown in Figure 7. According to DIN SPEC 91315 [45] and the norms within the leakage current, the safety threshold is set to 0.1 mA in AC and 0.01 mA in DC mode. Temperature should not cross 40 \({}^{\circ}\)C to avoid denaturation of proteins. Results within a certain range of these thresholds can be adjusted by further adjustment of system parameters, while significant overvalues cast doubts on a direct medical application. In addition, these values are correlated with efficacy parameters, so that a device is always both safe and effective and not just either. Here, that value is accessed via reactive oxygen and nitrogen species (ROS and RNS) measurements. While intuitively a higher power value implies an improved effectivity, the present system will show for the first time that this correlation is not that simple. Concerning the AC patient leakage current at different voltage amplitudes, the overall range for helium and argon are comparable, with no DC leakage current detectable in either He-CAP and Ar-CAP. While the He-CAP delivers AC leakage current values of 10 \(\mu\)A at 7 kV\({}_{pp}\), the Ar-CAP delivers 80 \(\mu\)A at identical settings. In the Ar-CAP, the values rise continuously with increased voltage up to 250 \(\mu\)A. In contrast, the He-CAP provides a constant leakage current up to 11 kV\({}_{pp}\) and a jump with a further on increase up to 200 \(\mu\)A. The surface temperature rises in dependence on the leakage current curve for He-CAP with values from 35 \({}^{\circ}\)C up to 130 \({}^{\circ}\)C. For Ar-CAP, the temperature ranges between 40 \({}^{\circ}\)C and 60 \({}^{\circ}\)C. In case of Ar-CAP, the temperature could be reduced by increasing the gas flow to optimize for a potential medical setting with compliant leakage current values at lower amplitudes. For the He-CAP, the range  
Figure 6: Dissipated power as a function of (**a,b**) distance and (**c**) applied voltage (at d = 5 mm) for helium and argon operation. G1 and G2 describe the measurement position of either grounded ring electrode at the capillary (G1) and ground surface (G2). Figure 7: Measured values of patient leakage current and temperature for different voltage and distance settings in helium and argon. (**a**) shows the AC-leakage current for various applied voltages and the temperature for d = 5 mm to a copper surface (the DC-leakage current is below the detection limit of 1 \(\mu\)A for all conditions); (**b**) shows the temperature as a function of distance for two applied voltages (8 and 14 kV\({}_{pp}\)); (**c**) shows the AC-leakage current for different distances for two investigated voltages (8 and 14 kV\({}_{pp}\)). of operation voltage with a compliant set of leakage current and temperature is increased with a more pronounced threshold transgression. A variation of the distance for these measurements considers application relevant uncertainties since a fixed treatment distance in complex geometries is neither possible in hand-held operation nor in case of complex geometries with robotic operation. For the temperature values in He-CAP, a drop is observed for longer distance of over 10 mm, while prior to it a mostly constant value is detected (Figure 7b). In Ar-CAP, interestingly, the value rises slightly over the whole distance for both investigated voltages. On the contrary, for Ar-CAP, the cooling effect of the working gas is reduced the further away the treated surface is moved. Hence, here again an adjustment of gas flow range could impact the temperature amplitude. For He-CAP, it seems that most of the heat is produced inside the capillary with a volume discharge while outside mainly diffusion and buoyancy cools the output gas from the capillary [72; 73].