Michał Szulc

The plasma bulk velocity is one of the key parameters describing the behavior of a plasma jet and is relevant for applications such as plasma spraying or electric propulsion. Therefore, different measurement techniques to determine the velocity were developed in the past. This paper presents a novel, non-invasive method for spatially resolved velocity measurements. The method is based on tracking of characteristic features in tomographic reconstructions of the plasma plume. A high-speed image recording system combined with tomographic acquisition is therefore the backbone of this method. The proposed setup captures the object under study from six different directions at a frame rate up to one million frames per second, providing high spatial and temporal resolution. The tomographic reconstructions are then calculated using the ART algorithm to track features in the plasma fluctuations, from which the bulk velocity is determined. The setup was tested with a DC plasma torch operated at reduced pressures in the range of tens of millibars. For the analyzed parameters, the axial velocity reached a maximum of 1061 m/s at a distance of three centimeters from the plasma torch exit and decreased to 919 m/s further downstream at a distance of seven centimeters, which is in good accordance with previous work. Therefore, the proposed diagnostic method can serve as a non-invasive alternative to velocity measurements, providing additional information in the form of a 3D model of the plasma bulk.

In this work the design and development of a power processing unit for a vacuum arc thruster is presented. The thruster is part of the Seamless Radio Access Networks for Internet of Space (SeRANIS) mission of the University of the Bundeswehr Munich, which will work as first multifunctional laboratory in orbit with public access. In addition to the basic functionality of generating a voltage peak for igniting the thruster, the power processing unit is equipped with techniques for controlling the ignition sequence and monitoring desired key values. The ignition procedure starts with generating the first trigger signal up to the point where a full-blown plasma is established. The PPU guarantees reliable performance by blocking every additional incoming signal while the ignition sequence is under way and the separation of the satellite’s power bus before the thruster discharges. The status of the power processing unit is constantly controlled and information is provided whether ignition was successful or not. The functionality of this circuit is based on simulation before assembly and testing. In addition, the presented system was designed to pass a test cycle of mechanical, thermal and electrical tests before being declared ready for the space mission.

Recent research trends show an increasing interest in non-equilibrium plasmas operated at atmospheric pressure, which are often used to tackle several environmental and health issues. Nevertheless, due to the complexity of the applications, these trends also show the need for a comprehensive characterization of such plasmas for a deeper understanding of the observed effects. One of the diagnostic methods for experimental determination of key parameters which affect the reactivity of a plasma, i.e., electron temperature, electron density and heavy particle temperature, is laser scattering. In this work, an approach based on a simple and compact laser scattering setup is proposed, which allows an estimation of the above parameters without any additional changes in the acquisition settings. Thus, the experimental effort and possible sources of error can be reduced. The proposed setup is tested experimentally with a commercially available pulsed plasma system, and the results are compared to available data. From this comparison, it is found that the plasma parameters estimated with the proposed scattering setup are plausible.

The advantages of pulsed low-current high-voltage discharges operated at atmospheric pressure and the ease with which such discharges can be implemented industrially contributed to their popularity. However, the high reactivity of a pulsed plasma implies that thorough diagnostics are needed to fully understand the interactions inside these plasmas. Some of the key parameters determining plasma properties of low-current discharges are the electron number density and the temperature of heavy particles. Both parameters can be determined experimentally with spectroscopic techniques, for example by investigating the broadening of spectral lines due to the Stark effect and by fitting synthetic spectra to molecular transitions. To the authors’ knowledge, experimentally determined electron densities for pulsed low-current discharges operated in a power range between 300 W and 1000 W have not been performed in previous works. Thus, in this work, the electron number density and temperature of heavy particles of one of several commercially available plasma systems are determined by means of emission spectroscopy.