THE RESPONSE OF THE INDUCTIVELY-COUPLED ARGON PLASMA TO SOLVENT PLASMA LOAD - SPATIALLY-RESOLVED MAPS OF ELECTRON-DENSITY OBTAINED FROM THE INTENSITY OF ONE ARGON LINE

A survey of spatially resolved electron number density (n(e)) in the tail cone of the inductively coupled argon plasma (ICAP) is presented: all of the results of the survey have been radially inverted by numerical, asymmetric Abel inversion. The survey extends over the entire volume of the plasma beyond the exit of the ICAP torch; It extends over distances of z = 5-25 mm downstream from the induction coil, and over radial distances of +/- 8 mm from the discharge axis. The survey also explores a range of inner argon flow rates (Q(IN)), solvent plasma load (Q(SPL)) and r.f. power: moreover, it explores loading by water, methanol and chloroform. Throughout the survey, n(e) was determined from the intensity of one, optically thin argon line, by a method which assumes that the atomic state distribution function (ASDF) for argon lies close to local thermal equilibrium (LTE). The validity of this assumption is reviewed. Also examined are the discrepancies between n(e) from this method and n(e) from Stark broadening measurements. With the error taken into account, the results of the survey reveal how time averaged values of n(e) in the ICAP respond over an extensive, previously unexplored range of experimental parameters. Moreover, the spatial information lends insight into how the thermal conditions and the transport of energy respond. Overall, the response may be described in terms of energy consumption along the axial channel and thermal pinch within the induction region. The predominating effect depends on the solvent plasma load, the solvent composition, the robustness of the discharge, and the distribution of solvent material over the argon stream.