Investigation Of Frequency Dependence Of Temperatures In Atmospheric Pressure Low-temperature Plasma Produced By Dielectric Barrier Discharge

This thesis investigates the dependence of the temperatures of the cold plasma produced by dielectric barrier discharge(DBD)on the frequency of the applied AC voltage in various gases under conditions of atmospheric pressure.In literature review the main scopes of investigation of low-temperature plasma applications are introduced.Plasma sources operating in the surrounding air have many advantages,for example,they don't need complex and expensive vacuum equipment,therefore they have already found wide applications in industry and became promising healing technology in medicine.However,for medical purposes gas temperature in plasma should be low and not exceed 42~??,and plasma itself should be very chemically active.Therefore factors that can influence temperatures that are used to describe plasma(such as electron temperature and translational temperature of gas,hereinafter are referred to as plasma temperatures)should be fully investigated.However,analysis of the literature showed that at the moment,the dependence of the cold DBD plasma temperatures on the applied AC frequency has not been sufficiently investigated and to our knowledge there are practically no reported studies on the frequency dependences of the plasma temperatures under atmospheric pressure conditions.This study applies the method of the optical emission spectroscopy in order to implement system diagnostics of electron and gas temperatures in the plasma produced by dielectric barrier discharge generators.The object of a given study is the plasma generated by atmospheric pressure air dielectric barrier discharge and by atmospheric pressure dielectric barrier discharge plasma jet with Ar,Ar-Air mixture and air as working gases.Plasma was produced by AC power supply in applied voltage range from 4.4 kV to 7.5 kV.Influence of AC frequency on the electron,rotational and gas temperatures of the atmospheric pressure Ar and Ar/Air plasma jets was investigated.Plasma emission intensity,gas temperature,electron temperature,and rotational temperature of plasma jet have been measured under the different applied AC frequency conditions,the frequency range was chosen as 9.7 kHz to 13.5 kHz.The results indicate that the ranges of the measured electron temperature,rotational temperature and gas temperature are 1460 K to 1750 K,360 K to 430K and 310 K to 323 K,respectively,for argon as working gas.For argon-air mixture as working gas,measured electron temperature,rotational temperature and gas temperature ranges are 2620 K to 3110 K,435 K to 490 K and 335 K to 359 K.It is found that all temperatures tend to rise with increasing of AC frequency.Also,in this thesis possibility of obtaining low-temperature plasma in atmospheric air has been investigated.This was achieved by lowering the high voltage frequency applied to dielectric barrier discharge down to 9.7 kHz and natural cooling of plasma area in the main by means of convective air streams.Applied method allowed reducing gas temperature in DBD virtually to air temperature in the laboratory.In this case stable barrier discharge along with ozone formation occurred.We suggest to apply the obtained result for cosmetic and therapeutic purposes as part of the ozone therapy for the human skin improvement.The thesis concludes that it is necessary to conduct further studies on the dependence of the temperatures of cold plasma produced by atmospheric pressure dielectric barrier discharge on the AC frequency in various gases in order to apply low-temperature plasma in practice,including for medical purposes.