Air entrainment in an inductively coupled plasma measured with Raman and Rayleigh scattering

Summary form only given, as follows. The inductively coupled plasma is well known from its spectrochemical application. The argon plasma operates at atmospheric pressure and flows out into the open air. The observation zone is usually taken in the plasma part above the end of the quartz torch where the argon plasma is surrounded by air so that it might be expected that this plasma part will be influenced by air entrainment. To study this we combined two techniques namely vibrational Raman scattering and Rayleigh scattering. In this way it was possible to measure absolute densities of air and argon. At an axial position of 2 mm above the end of the quartz torch and at 90% of the plasma radius it is found that 55% of the particles originate from air. By exponential extrapolation towards 70% of the radius it is predicted that about 1% of the particles originates from air entrainment. The same diagnostical techniques were effectuated on a cold argon flow (no plasma). By comparing the results it is found that the entrainment in the cold argon flow is larger than in the plasma case. So apparently the high temperature (and thus high viscosity) avoids the air entrainment.