OPTICAL EMISSION CHARACTERISTICS OF GUIDED STREAMERS GENERATED IN HELIUM AND ARGON MIXTURES WITH N 2 AND O 2 K. GAZELI 1, 2 , P. SVARNAS 2 AND F. CLEMENT 1 * 1 IPREM, LCABIE, Plasmas et Applications, Université de Pau et des Pays de l’Adour, 64000, Pau, France 2 Electrical and Computer Engineering Department, High Voltage Laboratory, University of Patras, 26504, Rion-Patras, Greece *Corresponding author: franck.clement@univ-pau.fr ABSTRACT The optical emission characteristics of Atmospheric Pressure Guided Streamers (APGSs) generated in He and Ar mixtures with N 2 and O 2 , are herein reported. The reactor employed is based on a DBD geometry and driven by high voltage microsecond positive pulses. For fixed values of the main operating parameters, the influence of the gas composition on the formation of principal emissive species as well as on the rotational temperature of probe molecules is investigated. In addition, the vibrational temperature is estimated for both He and Ar mixtures. Optimal gas compositions for enhanced plasma chemistry are found. This is of great importance in various applications and especially biomedical ones. In the latter case the temperature must be maintained close to the room one. 1. INTRODUCTION Atmospheric pressure cold plasma devices operating with noble gases and driven by sinusoidal or pulsed high voltage, have gained great interest in many fields of research such as biomedicine [1]. Up to today, numerous topologies have been suggested for plasma production at atmospheric pressure. As regards the nature of the plasma produced, it is found that it consists of fast travelling streamer-like ionizing waves (APGSs) guided by a dielectric surface and a channel formed by the gas [2,3]. Concerning plasma-surface interactions, the role of reactive oxygen and nitrogen species (ROS and RNS) appears to be dominant. However the contribution of other factors such as plasma- induced heating effects, UV radiation, electric field and charged species must not be disregarded. On the other hand, to achieve enhanced plasma chemistry, small controllable amounts of molecular gases such as N 2 and O 2 can be mixed uniformly with the main gas (usually He, Ar, Ne, etc.). The present work is devoted to the investigation of optical emission features of APGS generated in mixtures of He and Ar with N 2 and O 2 . The rotational temperature of probe molecules is measured and the gas temperature as a function of the gas composition remains close to the room one. Additionally, the measurement of the vibrational temperature for He and Ar mixtures provides information on the absorbed energy. These results contribute to the better understanding of the formation and propagation mechanisms of reactive plasma species, and operational windows oriented to biomedical applications are determined. 2. EXPERIMENTAL SETUP Fig. 1 depicts the configuration of the material used in this study. The reactor employed consists of a quartz tube into which a tungsten micro-wire is inserted. A cylindrical hollow electrode is tightly attached on the outer surface of the tube and grounded directly. The micro-wire is biased by positive HV pulses (kHz range) of steep slopes. Herein the amplitude (V) of the voltage is fixed at 7.5 kV, the frequency (f) at 10 kHz, and the pulse duty cycle (d) at 1%. The applied