Characterization and Multi-Physical Analysis of RF-Driven Microwave Plasma Applications from 1.3 GHz to 3.5 GHz

Doctoral thesis (2018)

This thesis presents the analysis of microwave plasma frequency-dependence based on the investigation of multi-physical parameters. Fundamentals of a microwave plasma and high-frequency technology are ... [more ▼]

This thesis presents the analysis of microwave plasma frequency-dependence based on the investigation of multi-physical parameters. Fundamentals of a microwave plasma and high-frequency technology are explained. Frequency-dependent effects on the base point impedance are presented in combination with the description of the used measuring hardware. Development of a bi-static network for the main plasma states (ignition and operation) is presented on the example of two high-pressure lamps at 2.45 GHz. Networks of both lamps are custom-built during the course of this thesis. An efficacy of 135 lm/W is achieved exceeding the efficacy of most LEDs. Frequency-dependent electrical properties are analyzed by reflection measurements of three different prototypes (argon plasma jet, phosphor-coated lamp and hollow glass cylinder filled with xenon) for the first time. A novel and simple lumped element and 3D-model are developed for the fitting of the plasma. A series resonance circuit substitutes the frequency-dependency of the capacitive plasma. The models are extended for S21 measurements by a novel developed transmission prototype. A simple frequency-dependent capacitor lumped element model fits the transmission parameters of the plasma. The novel core/cone3D-model is capable of fitting the plasma in an FEM simulator by only using the conductivity. A significant influence of the frequency on the spatial properties of all prototypes is measured for the first time by a simple CMOS camera and a custom image registration routine. The spatial extension is inversely proportional to the frequency. Optical measurements identify the participating ion species. Influence of the frequency on single spectral bands are presented in an in-depth analysis using optical emission spectroscopy. A proportionality of the frequency and the energy density in the microwave plasma is revealed. This is supported by the thermal measurements. The plasma jet rotational temperature is determined by the hydroxyl band at 310nm and shows a maximum values of 1350 K at only 15 W. [less ▲]