Novel approach for particle velocity and size measurement under plasma conditions

A novel technique is proposed for the simultaneous, in‐flight, measurement of the velocity and size of individual particles under plasma conditions. The method is based on the observation of each particle through its own emission and the analysis, in the time domain, of the waveform of the light burst generated as it crosses an observation window of known dimensions. A theoretical analysis of the parameters affecting the visibility of the particles in an argon plasma showed that depending on the particle diameter and its surface temperature, its thermal visibility factor will drop sharply from 1.0 to almost zero, with the increase of the background plasma temperature. Measurements are carried out using nickel particles (d¯p=78 μm, σ=18.0 μm) injected axially into an inductively coupled rf plasma ( f=3 MHz, P=15 kW) operated using argon as the plasma gas at atmospheric pressure and under soft vacuum conditions (p=760 and 150 Torr). The results are in good agreement with particle velocity data obtained using laser Doppler anemometry. The measured, in‐flight, particle size distribution is consistent with optical microscopic measurement of the particle size distribution of the injected powder.