Investigation of the electrical properties of standard and low-gas-flow ICPs using novel probes for the direct measurements of RF voltage and current in the load coil and the corresponding calculation of the ICP power

Abstract

New probes for the direct measurement of high radio-frequency (RF) voltage and current in the load coil of an inductively coupled plasma (ICP) are presented. Based on these measurements, a method for the calculation of power in the ICP is developed. Electrical parameters of the ICP are measured for a wide range of operational conditions in a standard ICP torch with wet aerosol introduction. Further, changes of the electrical parameters are monitored when operating the ICP with a very low argon flow rate of only 0.6 L min−1 using a so-called “Static High-Sensitivity ICP” (SHIP) torch. Direct measurements with the new RF probes allow following the evolution of plasma properties as a function of time. Noteworthy, it is found that there is a strong correlation between the plasma power and temperature changes in the RF generator itself. Depending on the plasma parameters, the measured plasma power was shown to differ significantly from the applied power (in the vendor software settings).