Spectral diagnostics of electron density of plasma torch at atmospheric pressure

An atmospheric pressure plasma torch is generated with a hollowneedle-to-plate dielectric barrier discharge and the electron densities in the inside and at the surface of the plasma torch are measured by optical emission spectroscopy (OES). A plasma torch with 1cm long is generated in atmospheric ambient when argon gas is introduced through the hollwneedle. The Stark broadenings of H alpha and Ar I (696. 54 nm) lines, which are decomposed from the experimental profiles by using deconvolution method, are used to estimate the corresponding electron densities. The electron densities are 1.0 x 10(15) cm(-3) and 3.78 x 10(15) cm(-3) corresponding to the Stark broadening of Ha and Ar I (696.54 nm) lines, respectively. The electron density calculated from the Stark broadening of H alpha is the same as that at the surface of the plasma because H alpha line originates from the dissociation and the excitation of H2O at the plasma torch surface where argon can meet with atmosphere. While the electron density calculated from the Stark broadening of Ar I (696. 54 nm) line is the same as that in the insid of plasma.