Gas Discharge Atmospheric Pressure Systems for the Biomedical Use

Abstract

The analysis of world literature is carried out, which indicates the intensive development of the scientific and technical field “Plasma in Medicine” based on the use of different gas-discharges for biomedical purposes. The atmospheric pressure plasma discharge systems have the favorite features and are very suitable for medical physiotherapy, bactericide treating and even for sterilization. The systems with non-thermal plasma are in the most use and one of their applications is generation of gas ozone. The given paper is devoted to looking for atmospheric pressure discharge modes, which are more suitable for ozone therapy equipment taking into account the peculiarities of such type of electronic apparatus. As practice shows, for the generation of ozone, discharges with a secondary-emission cathode and non-thermal plasma are most preferable, and of these two types of discharges are discharges with a dielectric barrier and corona discharges with uncoated metal electrodes. The article focuses on the appropriateness of the use of a corona discharge for ozone therapy equipment. This is justified by the fact that the corona discharge ozonizers have certain design advantages over the ozonizers on the discharge with dielectric barriers, namely that the advantages of the ozonizers on the corona discharge are the absence of a expensive barrier and low resistance to the gas flow, so there is no need to significantly increase the pressure at the ozonizer oxygen inlet, and possibility of power supplying the ozonizer with DC voltage. Also, ozonizers on the corona discharge have a lower cost. From the literature and the authors' own practice, there is a wide variety of configurations of electrode systems for creating the corona discharge, but they always have electrodes with a small radius of curvature of the surface: threads, wires, nets, various pointed needles, serrated electrodes. The article considers the physical mechanism of maintaining the corona discharge of a unipolar or bipolar type and notes the role of secondary electron emission of the cathode. All types of corona discharge are capable of generating ozone because discharge electrons have the energy required to dissociate oxygen molecules in a non-thermal gas environment. Then a free oxygen atom attaches to an oxygen molecule to form a metastable ozone molecule. It is noted that the corona discharge and ozone generation were studied in detail mainly in unipolar point-of-plane or wire-in-pipe systems. The data on ozone generation in bipolar discharge is not enough to develop an ozone therapy apparatus, although this form of discharge is interesting because it requires relatively small values of the supply voltage and operates at a direct current. Based on the review of the prospects for the use of bipolar corona discharge in biomedical apparatus and practical considerations of the realistic and expanded future usage of bipolar corona equipment in the ozone therapy, the tasks have been formulated to be solved. It is necessary to thoroughly study the characteristics of the developed equipment and the influence of various external operational factors and physico-chemical processes in the ozonizer electrode system on them. It is necessary to ensure that the parameters of the equipment are maintained during operation, which means that during the eight-hour working day and with the total time between failures of at least 1000 hours. Also, it is necessary to take into account the effect of the decomposition of ozone molecules at elevated temperatures and not to allow excessive heating of the ozonizer. These requirements must be met by choice of the configuration and materials of the electrode system and must be experimentally verified. It is proposed to ensure the linearity of the calibration characteristics of the ozonizer and to formalize it mathematically to simplify the setting and maintenance of stable operating modes of ozone equipment. It is necessary to prove its therapeutic efficacy, including for sterilization treatment, with the participation of medical specialists.