Atmospheric microwave-induced plasmas in Ar/H2 mixtures studied with a combination of passive and active spectroscopic methods

Several active and passive diagnostic methods have been used to study atmospheric microwave-induced plasmas created by a surfatron operating at a frequency of 2.45 GHz and with power values between 57 and 88 W. By comparing the results with each other, insight is obtained into essential plasma quantities, their radial distributions and the reliability of the diagnostic methods. Two laser techniques have been used, namely Thomson scattering for the determination of the electron density, ne, and temperature, Te, and Rayleigh scattering for the determination of the heavy particle temperature, Tg. In combination, three passive spectroscopic techniques are applied, the line broadening of the Hβ line to determine ne, and two methods of absolute intensity measurements to obtain ne and Te. The active techniques provide spatial resolution in small plasmas with sizes in the order of 0.5 mm. The results of ne measured with three different methods show good agreement, independent of the plasma settings. The Te values obtained with two techniques are in good agreement for the condition of a pure argon plasma, but they show deviations when H2 is introduced. The introduction of a small amount (0.3%) of H2 into an argon plasma induces contraction, reduces ne, increases Te, enhances the departure from equilibrium and leads to conditions that are close to those found in cool atmospheric plasmas.