As shown in Figure 5, the gradient of the instantaneous voltage is largest at the driving point.

According to the calculation, the largest gradient of the instantaneous voltage in 150 MHz case was approximately 0.45 V/m, while the average electric field across the electrodes was 5,000 V/m. This means that the current flowing in the horizontal direction is small enough compared with that flowing in the vertical direction. Since the difference was even larger in the 13.56 MHz case, the current flowing in the horizontal direction can be neglected. Very different voltage distribution profiles are obtained when radio-frequency power is applied on both ends of the electrode, as shown in Figure 6. The phase of radio frequency was set to be the same. The voltage HCS assay variations INCB024360 order over the electrode are approximately 39% and 11% for 150 and 13.56 MHz, respectively. Therefore, this type of power application would be more advantageous for obtaining more uniform plasma over the electrode. Figure 6 Voltage distributions along the central cross-sectional line on the electrode during plasma generation. Power was applied on both ends of the electrode

with the same phase. (a) 150 MHz and (b) 13.56 MHz. Figure 7 shows the results of the calculations of voltage distribution before plasma ignition. When there is no plasma between the electrodes, the conductance G is zero and the capacitance C is determined by (13) where ϵ0 is the permittivity of vacuum. S and d are the electrode area and the distance between the upper and lower electrodes, respectively. Figure 7 Voltage distribution on the electrode before plasma ignition. Power was applied at the

center of the electrode. (a) 150 MHz and (b) 13.56 MHz. Comparing Figure 7 with Figure 5, a slight difference is seen in the case of 13.56 MHz. When 150 MHz is applied, however, the voltage distribution before plasma ignition is considerably different from that after plasma ignition. From the attenuation coefficient α shown in Table 2, the resistive loss in the 150 MHz case is larger than that in the 13.56 MHz case. However, the resistive loss only causes a monotonic next decay in voltage amplitude from the driving point along the wave-propagation direction. Since Figure 5 does not show a monotonic decay in voltage from the driving point, the drastic change in the voltage pattern in the 150 MHz case is considered to be caused mainly by the standing wave effect. The interference pattern may change sensitively with the changes in various parameters (e.g. electrode shape, setup, and plasma parameters) in the case of 150 MHz. It can be said that in the case of 13.56 MHz, the expected or measured voltage distribution before plasma ignition is useful for designing the electrode setup. However, in the case of 150 MHz, careful design of the electrode setup should be required to obtain stable and uniform plasma generation.