Speaker
Dirk Luggenhölscher
(Ruhr-University Bochum)
Description
The electric field strength is a basic parameter of non-thermal plasmas since it determines the energy that electrons gain. On timescales which are of interest in high pressure plasmas, the ions are at rest and the discharge dynamic is determined by the electrons. If the electric field strength and its temporal develeopment are known and additional diagnostics are applied, many other quantities of interest e.g. displacement and conduction current, dissipated power, and electron density can be inferred.
Two laser beams (pump and Stokes) are focussed into the plasma and together with the quasi-static electric field a fourth IR signal wave is generated. The signal intensity is proportional to the square of the local electric field. A high temporal (5 ns) and spatial (0.1 mm) resolution can be achieved, which is ideal for the investigation of atmospheric pressure plasmas. The method can be applied in pure hydrogen or nitrogen discharges or by an admixture of about 100 mbar partial pressure of one of these as a tracer gas. Since the signal strength depends of the molecular gas density, the sensitivity is determined by the partial pressure and Raman cross section of the applied gas. Typical values are 100-1000 V/mm.
The method is used to investigate several kinds of atmospheric pressure discharges: ns-pulsed discharges between two parallel electrodes (jet-like geometry) [1], single streamer dielectric barrier discharges (DBD) [2], plasma bullets [3], and inside a fast ionization wave discharge [4]. In all cases the temporal development of the elctric field is measured, mostly spatially resolved. In case of the ionization-wave discharge even the direction of the electric vector has been determined. The field measurements are complemented by streak camera measurements in which spectral lines or the total emission is determined with the same temporal resolution like the laser method.
[1] S. Müller et. al., J. Phys. D.: Appl. Phys. 44 (2011) 165202
[2] P. Böhm, et. al., Plasma Sources Sci. Technol. 25 (2016) 054002
[3] M. Van der Schans, et. al., submitted to Plasma Sources Sci. Technol.
[4] B. Goldberg, et. al., Plasma Sources Sci. 24 (2015) 055017
Primary authors
Dirk Luggenhölscher
(Ruhr-University Bochum)
Uwe Czarnetzki
(Ruhr-University Bochum)
