Monochromatic imaging technique used to study dc arc plasma under the influence of a transverse magnetic field

The monochromatic imaging technique was used for diagnosing atmospheric pressure direct-current (dc) arc plasma with continuous aerosol analyte supply. The arc plasma was subjected to transverse sine wave variable magnetic fields of strengths up to 12 mT (peak-to-peak) and a frequency of 50 Hz. Spatially resolved spectral emission redistributions, coupled with intensity enhancements, are characterized in steady state and plasma exposed to the magnetic field. By a magnetic field oriented transversally to the electric field of the plasma column, fast lateral oscillatory swings of the current carrying plasma core are induced, which is followed by enhancement of the analyte emission. Depending on the strength of the applied magnetic field, appropriate elongations of the plasma core were generated. A digital camera, in conjunction with a slit-less monochromator, was used to capture unsaturated monochromatic images of the whole plasma volume during such oscillations. From the intensity emission patterns at different axial positions in the plasma, obtained for a series of magnetic field strengths, it was found that the magnitude of analyte emission enhancement depends primarily on the amplitude/velocity of the plasma core motion. However, it was clearly shown that the magnitude of the analyte emission enhancement at different axial positions is affected not only by the velocity of the plasma core motion but also by the discharge electric field orientation. This was confirmed when the electrode polarity was reversed. Regardless of the electric field orientation the bulk of the intensity enhancement occurs in the closer-to-cathode plasma region.