Photographic plasma images and electron number density as well as electrontemperature mappings of a plasma sustained with a modified argon microwaveplasma torch (MPT) measured by spatially resolved Thomson scattering

In this work the determination of electron number densities and electron te mperatures for the case of a modified microwave plasma torch (MPT) operated at 100 W with argon by means of spatially resolved Thomson scattering meas urements and photographic records of the MPT at different working condition s are reported. With an internal gas flow of 500 ml min(-l) and an outer ga s flow of 200 ml min(-1) electron number densities and electron temperature s are in the range of 10(20) m(-3) to 10(21) m(-3) and of 16000-18000 K, re spectively. When increasing the internal gas flow from 500 to 900 ml min(-l ) the plasma becomes longer and the maximum electron number density increas es by a factor of 2. An increase of the outer gas flow from 200 to 700 ml m in(-l) leads to a lifting of the whole plasma from the burner edge with the maximum electron number density remaining unchanged. An increase of the po wer from 80 to 180 W was found to lead to higher electron number densities whereas the electron temperatures remain unchanged. The addition of 1.2 mg min(-1) of water vapor to the internal gas flow leads to a decrease of the electron number density from 4.7 x 10(20) m(-3) to 2 x 10(20) m(-3) and to an increase of the electron temperature from 16000 to 22000 K. In order to document the influence of the internal gas flow rate, water introduction an d introducing easily ionized elements on the visible plasma shape digitally recorded photos of the plasma are presented. (C) 1999 Elsevier Science B.V . All rights reserved.