  A Dielectric Barrier Discharge (DBD) plasma jet in a four electrodes
configuration was investigated in order to improve the discharge parameters,
such as, plasma power and rotational and vibrational temperatures of molecular
species in the plasma plume. The improvement attempts were made by introducing
an auxiliary floating electrode in a form of a metallic pin inside the DBD
device. That piece was placed near the bottom of the main device, centered in
relation to the four powered electrodes, which were covered with a dielectric
material. By using metallic pins with different lengths, it was observed that
there were considerable variations of the plasma parameters as a function of
the pin length. Two carrier gases were tested: argon and helium. With helium as
the working gas, it was found that there is an optimal pin length that
maximizes the plasma power and its vibrational temperature. In addition, it was
verified that for the pin of optimum length the relative intensity of light
emissions from OH and NO species achieved higher values than in other
conditions studied.
