## 3 Results
### Temporal Evolution of the Plasma Parameters  
The circuitry described in Section 2.3 allows triggering the laser scattering setup at different points of time of a current pulse. By doing so, the temporal evolution of the plasma parameters is assessed. The parameters are examined at four trigger timeframes stretching across a current pulse, as depicted in the upper left diagram in Figure 3. No exact trigger time points can be defined, since the plasma system operates without a control loop, which implies fluctuations in plasma and thus in the tapped electrical signals. Accordingly, the width of the timeframes in Figure 3 illustrates approximately the small jitter of the trigger time point. Figure 4: Spatial distribution of the heavy particle temperature estimated based on Rayleigh scattering for a pulse frequency of 60 kHz and power setting of 100% (corresponding to a current amplitude of \(\sim\)1 A). Figure 3: Temporal distribution of the mean plasma parameters for both considered frequencies of 60 kHz and 43 kHz at a power setting of 100% and axial distance \(d=1\) mm. The upper left diagram shows a typical current trace and the timeframes at which the scattering setup was triggered in relation to a current pulse. The temporal distribution is analyzed for both operating frequencies at an axial distance of 1 mm from nozzle exit and a pulse current amplitude of \(\sim\)1 A. Similarly to the analysis of the axial distribution in the previous section, the results presented in Figure 3 are averages calculated from the full radial range of several measurements. For a pulse frequency of 60 kHz, the amplitudes of the plasma parameters follow the current trajectory, i.e., the maximum value of \(1.7\times 10^{21}\) m\({}^{-3}\) is reached for the peak current timeframe \(I_{peak}\). From there, the electron density follows the current trajectory with an almost linear decrease from the current peak towards the rising edge of the next current pulse. Here, an almost 24% reduction is observed compared to the maximal \(\overline{n}_{e}\) value. A similar behavior is observed for the mean electron temperature \(\overline{T}_{e}\) at 60 kHz, although the values remain unchanged at the current minimum (\(I_{valley}\)) after an initial reduction of 5% for the falling edge. Again, the lowest mean temperature, which is about 15% lower than at \(I_{peak}\), is estimated for the rising current edge. Looking at the mean heavy particle temperature \(\overline{T}_{h}\), an almost linear decrease is observed from \(I_{peak}\) towards the current minimum, where the temperature is reduced by about 15%. The lowest temperature of approx. 4800 K is estimated for the rising edge of the following current edge, giving a reduction of 18% when compared to the highest value at \(I_{peak}\). The behavior of the plasma parameters estimated for the lower operating frequency of 43 kHz does not correlate so well with the current trace as before. According to the results in Figure 3, only the mean electron number density follows the current progression with a maximal value of \(2.0\times 10^{21}\) m\({}^{-3}\) reached at the current peak when the process is pulsed with 43 kHz. Thereafter, the electron density decreases about 10% while the current is falling towards the minimal current value \(I_{valley}\). The \(\overline{n}_{e}\) values recorded for the rising edge are almost identical to those estimated for \(I_{valley}\) and almost 15% lower than for peak current. The mean electron temperature on the other hand behaves differently with the highest value of 53,000 K registered for the rising edge of the current pulse, about 10% higher than for peak current. The temperature decreases by a further 10% for the remaining two timeframes. In addition, the \(\overline{T}_{h}\) values progress differently than at 60 kHz. The highest heavy particle temperature of almost 5900 K registered for the falling current edge, over 10% higher than at \(I_{peak}\).