###### Abstract  
Non-equilibrium conditions in plasma are often achieved by pulsed power delivery, where the pulse shape and repetition rate determine the properties of the plasma constituents and thus its chemical reactivity. The evaluation of the latter is becoming increasingly important to understand the observed effects, especially when new application fields are targeted. The composition of the plasma and the occurring chemical reactions can be calculated using various models. Thereby, the temperature of the electrons, the electron number density, as well as the heavy particle temperature are usually required as the basis of such calculations. In this work, the influence of pulse amplitude and repetition rate on these plasma parameters is determined by laser scattering for a low-current, high-voltage discharge operated with nitrogen at atmospheric pressure. In particular, the characteristic parameters regarding the plasma free electrons in such discharges have not yet been experimentally determined to this extent. The results are validated by spectroscopic measurements, i.e., the electron density is estimated from the Stark broadening of the hydrogen beta line and the heavy particle temperature is estimated by fitting the spectrum of nitrogen molecular transitions. Depending on the operating frequency, a pure nitrogen discharge with an input power of about 650 W displays an electron density between \(1.7\times 10^{21}\) m\({}^{-3}\) and \(2.0\times 10^{21}\) m\({}^{-3}\) with electron temperatures in the range of 40,000 K and heavy particle temperatures of about 6000 K in the core of the discharge channel. Furthermore, a relatively slow electron recombination rate in the range of 20 us is observed. plasma jet; low-current discharge; atmospheric pressure; laser scattering; emission spectroscopy; electron density; electron temperature +
Footnote †: journal: Applied Sciences  
Article Influence of Pulse Amplitude and Frequency on Plasma Properties of a Pulsed Low-Current High-Voltage Discharge Operated at Atmospheric Pressure  
[PERSON], [PERSON], [PERSON], [PERSON] Influence of Pulse Amplitude and Frequency on Plasma Properties of a Pulsed Low-Current High-Voltage Discharge Operated at Atmospheric Pressure
The energy distribution in a plasma and the associated energy transfer to the treated surface is important [23], as it can affect the treated surface by etching or thermal modification [9] or influence the efficiency of thin film deposition [10,11] or the antibacterial effects of a plasma [4,24,25]. As pointed out by [PERSON] et al., who deposited and analysed acrylic acid thin films using a pulsed low-current high-voltage discharge [10], an increase in plasma temperature achieved by increasing the operating frequency can be compensated by faster lateral movement of the generator to achieve similar coating efficiencies. Nevertheless, the analysis of the deposited layers revealed different chemical properties when the frequency was varied, suggesting a temperature dependence of the plasma reactivity [10]. [PERSON] et al. reported similar effects and indicated that the steep axial temperature gradient plays an important role in the chemical composition of a coating [11]. The correlation between the plasma properties, i.e., chemical composition and characteristic temperatures, and the effects observed after a treatment become observable when considering different hydrodynamic models. Usually, a two-temperature model is assumed for a non-equilibrium plasma, where the kinetic energy of electrons is described by electron temperature \(T_{e}\), and consequently, the kinetic energy of heavy particles, i.e., ions, atoms, molecules, and neutrals, is described by the heavy particle temperature \(T_{h}\), assumed to be much lower than \(T_{e}\) for such plasmas. [PERSON] and [PERSON] developed a detailed model for plasma modification of polypropylene, emphasizing the variety of reactions occurring in the plasma and the temperature dependence of the corresponding reaction rate coefficients [26].