Experimental Investigation of the Velocity Distribution in the Tail Flame of an Inductively- Coupled-Plasma

Abstract

To achieve an accurate description of an Inductively Coupled Plasma (ICP) source, numerous two-dimensional and three-dimensional numerical models have been developed. However, experimental validation of these models remains a major challenge. Compared with plasma temperature and electron number density, the measured gas flow velocity distribution is more direct and reliable, and can serve as an important criterion for assessing model validity. In this work, the experimental method was improved by optimizing the observation parameters of a high-speed camera, effectively suppressing the interference from the intense emission spectra in the normal analytical zone. For the first time, ion clouds formed by injected particles were directly observed. Five types of suspended particles were sequentially introduced, including Er₂O₃, Y₂O₃, and borosilicate glass particles with diameters of 10, 5, and 2 μm. The particle-flow following behavior was comparatively evaluated. Using a tracer method, the gas flow velocity distribution in the ICP tail plume was measured. Furthermore, with Y₂O₃ as the tracer, the axial gas velocity distribution in the central channel was systematically measured under different radio-frequency (RF) powers and carrier gas flow rates. The results show that within the range of 2.5 mm < z < 12.5 mm, the axial gas velocity in the central channel of the tail plume exhibits a distinct plateau region. The axial gas velocity increases with increasing RF power, while showing weak sensitivity to variations in carrier gas flow rate. The present study provides experimental data on the axial gas velocity distribution, offering essential validation and correction benchmarks for numerical ICP models.