RADIAL MEASUREMENTS OF GAS DISCHARGE PARAMETERS OF ATMOSPHERIC PRESSURE MICROPLASMA

In this work Abel inversion technique was used for radial measurements of the microplasma in Ar-2% H-2 flow at open atmosphere. The gas discharge parameters were investigated using spatially resolved high resolution optical emission spectroscopy (OES) to allow acquisition of OH (A (2)Sigma(+), v = 0 -> X-2 Pi, v' = 0) rotational bands at 306.357 nm, Ar I 603.213 nm line and N-2 (C-3 Pi(u), v = 0 -> B-3 Pi(g), v' = 0) second positive system with the band head at 337.13 nm. The nonthermal plasma was generated between microhollow anode (similar to 500 mu m inner diameter) and a cathode copper foil, fed by direct current source for a current ranging from 20 mA to 100 mA (Townsend discharge from 20 mA to 30 mA, normal glow discharge from 30 mA to 80 mA at 210 V and abnormal discharge beyond 90 mA). The 1.5 mm length cylindrical-shape plasma has an outspread bright disk (negative glow region) near the cathode surface. Besides the gas temperature, the excitation temperature was measured radially for a current ranging from 20 mA to 100 mA, either from Boltzmann-plot of Ar I 4p - 4s and 5p - 4s transitions of excited argon or from Cu I two lines method of excited cuprum atoms released from the cathode surface. The measurements showed a nearly bell-shaped distribution of these temperatures, peaked at 120 mu m from the center with the minimum at the plasma border. The average excitation temperature was about similar to 8000 K (maximum similar to 10, 000 K) and the average rotational temperature was about 650 K (maximum similar to 800 K) from 20 K to 100 K. For the N-2 second positive system with Delta v = -2 it was estimated the vibrational temperature for the bright disk (1500 K to 5000 K). H-beta line Stark broadening was employed to define the electron number density of the negative glow (10(15) cm(-3)).