[Spectroscopic study of atmospheric pressure argon DC microdischarge]

Microhollow cathode discharge or microdischarge is an efficient method to generate plasma in a high pressure gas. In the present work, the emission spectra were observed in an atmospheric pressure argon direct current microdischarge apparatus, using a stainless steel capillary as the cathode, and a stainless steel mesh as the anode. It was shown that all of the seventeen argon spectral lines arose from electronically excited argon atom 4p-4s transition in the wavelength range of 690-860 nm. The dependences of emission intensity on the discharge current, gas pressure and argon flow rate were investigated. The experimental results show that the emission intensity increased with discharge current from 1 to 6 mA and argon flow rate from 100 to 700 mL x min(-1). The dependence of emission intensity on gas pressure exhibited different characteristics, i.e., spectral signal increased with the gas pressure, but reached the intensity maximum at 13.3 kPa, and decreased afterwards. The argon atom spectral lines 763.51 and 772.42 nm were chosen to measure the electron excitation temperature by the intensity ratio of two spectral lines. The electron excitation temperature was determined to be in the range of 2000 to 2800 K in the atmospheric pressure argon microdischarge. The changes in electron excitation temperature with discharge current, gas pressure and argon flow rate were explored, indicating that the electron excited temperature increased with the discharge current, but decreased when gas flow rate or argon pressure increased.