Dual Magnetic Probe System for Phase Measurements in Thermal Induction Plasmas

Abstract

Previously reported measurements of rf magnetic field distributions in thermal induction plasmas by a water-cooled coil probe have been extended to phase measurements through the use of a second identical probe placed at a fixed position near the plasma boundary. From measurements of the vector sum and/or difference in addition to the individual signals from both probes, data for the variation of the phase angle with radius were obtained. The reliability of the method was checked with an electrolyte of known conductivity. Tests conducted at 2.6 MHz in a 14-cm-wide argon-plasma column at ambient pressure yielded a change in phase angle of 285 deg over the radius. The variations in phase and magnitude of the magnetic field were used to derive those of the induced electric field, the current density, the electrical conductivity, and the real part of the Poynting vector. From the latter a specific power input of about 1500 W/cm was obtained. A correlation of the conductivity data with temperatures derived from absolute line and continuum intensities is in good agreement with predictions from an equilibrium theory.