Effects of inner electrode diameter on discharge characteristics of atmosphere pressure plasma jet in ar

We experimentally investigated the discharge characteristics of Ar atmosphere pressure plasma jet (APPJ) with inner electrodes of different radii by means of electrical measurements (including voltage-current waveforms and Lissajous figures) and optical diagnosis (including emission spectra and light-emission pictures) to understand the effect of electrode arrangement on the characteristics. With inner electrode of 0.5 mm, 0.95 mm and 1.6 mm in diameter, we observed the changing of APPJ in Ar, obtained some main discharge parameters including discharge power, transported charges, electronic excitation temperature, molecular vibrational temperature and molecular rotational temperature through further calculation, and explained the experimental results through analyzing the discharge mechanism. The results show that the discharge process of APPJ in Ar can be divided into three phases, namely corona, dielectric barrier discharge (DBD) and plasma jet, which can be distinguished obviously by electrical characteristics and light-emission pictures. The influence of inner electrode's diameter on APPJ in Ar mainly shows in plasma jet stage: Ar volume in tube increases with decreasing inner electrode diameter; this increases discharge area and enhances discharge, and accordingly the pulsed current peak, discharge power and transported charges all become larger. For the APPJ in Ar, smaller inner electrode corresponds to lower rotational temperature and vibrational temperature of molecular and lower excitation temperature of electrons, while the rotational temperature and vibrational temperature of molecular increase with applied voltage.