Many applications of plasma technology at atmospheric pressure use the plasma as a high temperature source. For these thermal plasma jet processes, control and process observation are crucial methods needed to ensure the process stability, reliability and enable new capabilities within the process likewise. Maintaining such a plasma in a steady state of operation and compensate deviations coming from internal disturbances (turbulent flow, inhomogenous axial heat flux, etc.) or due to externally changed conditions (ripple in the current/voltage power supply, erosion of the electrodes) is not an easy task and requires deep insight into the basic physics of the underlying process. Hence, if maintaining a plasma in a stationary state is already a difficult task, to imprint a pulsed pattern, becomes a very demanding job. Designing a efficient feedback control for such a plasma discharge seems to be challenging task, where a solution still has to be found. A lot of the present systems rely on empirical models in order to predict the process behaviour. Yet even works, which are based on physical models, do not consider plasma dynamics. Consequently, there is a need of a thermal arc plasma model, which on one hand considers all the relevant physical phenomena and on the other hand is simple enough to allow an efficient calculation with lower need of computational effort. Also there is a high demand for techniques that analyse the data from measurements of transient phenomena and extract plasma parameters, which are of interest for the regarded process (like particle densities and temperatures). This is most notably relevant for plasma discharges where metal vapour is present. This work pursues a dual approach. At first this work aims to design a flatness based control, able to track a desired plasma temperature trajectory at a relatively high frequency rate. The tracking of this behaviour will be achieved by one physical quantity alone, the cathode temperature. The second idea of this work is to develop a simplified radiation model, which links the emitted radiation of the plasma to the radial plasma temperature and electron density distribution within the thermal arc. Combining both contributions, the model based control and the radiation model, will help to constitute a new tool set to gain and maintain stability of the plasma discharge and observe the process parameter evolution. This novel approach bridges the gap between different scientific disciplines like plasma physics, quantum mechanics, radiation dynamics and control theory by developing a method that enables the control of the plasma discharge through one physical quantity alone, the cathode spot temperature.     «

Many applications of plasma technology at atmospheric pressure use the plasma as a high temperature source. For these thermal plasma jet processes, control and process observation are crucial methods needed to ensure the process stability, reliability and enable new capabilities within the process likewise. Maintaining such a plasma in a steady state of operation and compensate deviations coming from internal disturbances (turbulent flow, inhomogenous axial heat flux, etc.) or due to externally...     »