On 14 October 2016 at 14.15 Rasmus Talviste will defend his doctoral thesis titled "Atmospheric pressure He plasma jet: effect of dielectric tube diameter" in the Faculty of Science and Technology of the University of Tartu, in Physicum (W. Ostwaldi 1-B103).
Indrek Jõgi, Institute of Physics, University of Tartu
Karol Hensel, Comenius University (Slovakia)
Atmospheric pressure plasma jet working in noble gas flow is a promising plasma source that has been actively investigated during the past decade. A plasma jet ignited by high voltages in the kHz frequency range appears continuous to the eye but actually consists of discrete highly luminous travelling plasma fronts which have also been referred to as “plasma bullets” or “ionization waves” propagating with velocities up to 103 km/s. The motivation behind the intensive research of plasma jets is the “cold” nature of these devices which enables a vast variety of applications where the gas temperature has to remain close to room temperature. Most important applications for plasma jets are in the field of biomedicine. The application of plasma jets in medicine requires precise control over plasma parameters. It has been shown that the propagation velocity of the ionization wave and several plasma parameters are influenced by externally controllable parameters such as the voltage, gas type and the electrode configuration of the plasma jet device. The dielectric tube diameter might offer an alternative approach to control the key plasma parameters. However, the possible effect of the dielectric tube has received little attention. In the PhD thesis the effect of dielectric tube in a He APPJ in the kHz frequency range was studied. Quartz tubes with inner diameters between 80 to 500 µm were used in the experiments. As an alternative Yttria stabilized ZrO2 microtubes were also tested. It was determined that reducing the microtube diameter has the following effects:
• Plasma ignition and sustaining voltage increases
• Several plasma parameters are affected: electron density and He excitation temperature increase while gas temperature decreases
• The ionization wave velocity increases
As a conclusion, it was demonstrated that several key parameters can be altered by changing the dielectric tube diameter which can thus prove an alternative method for controlling the plasma parameters.