PhD Thesis
UNIVERSITY OF BELGRADE
Faculty of Physics
Nikola Škoro
 
Electrical breakdown and forming of discharges from standard to microscopic dimesions
 
Supervisors: Dr D Marić and Dr Z Lj Petrović
 
Abstract
In this PhD thesis subjects of investigation are low temperature nonequilibrium DC discharges with standard (cm) dimensions and microdischarges with electrode gap around 100 mm. By analysis of breakdown conditions and temporal development of discharges in Argon in both centimeter and micrometer size we want to examine the validity of scaling laws, i.e. what are the similarities between well known processes in standard size discharges and microdischarges as well as the appearance of new processes in microdischarges. We want to compare Paschen curves (breakdown voltage vs. pressure times electrode gap dependence) and current-voltage characteristics of cm and micrometer size discharges.
 
Another aim of this research is to investigate breakdown and discharge development in molecular gases CF4 and water vapour at low pressure. Both gases are significant concerning plasma applications. Investigation of discharge properties in CF4 is important for plasma processing industry and obtained results could be used in computer simulations of such applications. On the other hand, water vapour is present in all low temperature nonequilibrium discharges at atmospheric pressure that are also present in industrial applications of plasma. Apart from measurements of Paschen curve and current-voltage characteristics, temporal development of several distinctive discharge regimes is obtained. The results are acquired using special electrical circuit synchronized with an ICCD camera. In that way, both electrical and optical properties of the discharge can be recorded at the same time.
 
Further on, we widen the research from simple geometry, parallel plate electrodes, to a complex geometry of hollow cathode. In this part, electrical and spatial properties of steady state discharge regimes and transients are investigated using aforementioned experimental diagnostics. Obtained results can provide possibility of comparison to micro hollow cathode discharges which are widely spread in microplasma research.