Division of Environmental Physics -
Students Faculty of Mathematics, Physics and Informatics, Comenius University Bratislava
Lenka LEŠTINSKÁ alumni student
PhD. study 2008 - 2012
Supervisor: Zdenko Machala Title:
Abstract: Atmospheric pressure microwave (MW) plasmas present considerable interest for various
industrial or environmental applications. The main advantage of MW plasmas is electrodeless
operation, availability of cheap microwave sources at 2.45 GHz, good microwave to plasma
energy coupling and no need of vacuum devices if operated at atmospheric pressure. MW
torches are sometimes used to preheat gases to high temperatures needed for other
applications or for studying other discharge plasmas in preheated gases. We present
spectroscopic investigations of atmospheric pressure afterglow plasmas generated by MW
torch in nitrogen and air. We employ optical diagnostics: emission spectroscopy to
characterise the plasma jet.
In the first part of this work we analyzed the emission spectra of MW discharge generated in
pure nitrogen and in nitrogen with small oxygen admixture. We also measured the plasma
temperatures and analyzed spatial characteristics of MW discharge at various powers and gas
flow rates. In the second part we examined MW plasma generated in air at atmospheric
pressure. It showed out that the emission or rather the absence of molecular spectra at low
MW powers is the limitation factor for performing the spectroscopic characteristics and direct
temperature measurements of the generated plasma. This is why we developed and tested a
new method for temperature measurements of near-thermal equilibrium air plasmas at
atmospheric pressure. We demonstrated that this so-called corona probe method (where the
corona discharge is placed into the MW plasma) can be generally applied to determine the
temperature of the near-equilibrium plasmas and contrary to the thermocouple it is not limited
to temperatures below 1000 °C or affected by radiative losses and the problems of interaction
with the microwave plasma and electromagnetic fields.
Since there are many applications where large volume plasmas are needed and there is a good
chance of expanding the volume of DC discharges by combining them with MW plasma as
some previous works suggested, in the last part of our work the basic properties and
behaviour of combined MW and glow (or MW and spark) discharges were examined.
Spectroscopic study of these combined discharges, especially the transient spark in the gas
preheated by MW plasma, is also important for the plasma assisted combustion applications.