EFFECT OF ELECTRIC FIELD ON THE NON-EQUILIBRIUM IN AN INDUCTIVELY COUPLED PLASMA

A simple way to predict the temperature difference between electrons and heavy particles due to the electric field in Joule effect heated plasmas has been studied. The temperature difference is calculated from the electrical conductivity as a function of the electric field. A LTE based numerical model of ICP has been modified in order to take into account, in a simplified approach, this temperature difference. This model has been coupled with the simulation of the plasma spectroscopic emission to compare predicted and measured temperature values. The maximum electric field increases from 12 Vm⁻¹ in a low power torch up to 50 Vm⁻¹ in a high power torches. The temperature difference between electrons and atoms reaches 450 K in the 27 MHz, 600 W ICP, and 6500 K in the 3.4 MHz, 7 kW plasma torch. The difference between predicted and measured excitation temperatures assuming the excitation due to the electronic collisions is very low, less than 200 K.