SIMULTANEOUS PARTICLE SURFACE-TEMPERATURE AND VELOCITY-MEASUREMENTS UNDER PLASMA CONDITIONS

A method is presented for the simultaneous measurement, in flight, of the surface temperature and velocity of individual particles under pla sma conditions. The method is based on the direct measurement of therm al radiation at two wavelengths emitted from the particle surface as t hey cross a well defined measurement volume within the plasma. A detai led description of the data treatment is presented for typical signals obtained. A simple method using each individual particle emission sig nal and the associated photomultiplier noise is used to estimate the m inimum surface temperature that can be measured. Measurements have bee n carried out using alumina powder (d(p) = 49 mu m sigma = 4 mu m) inj ected axially into an inductively coupled radiofrequency (RF) plasma o perated using an Ar/H-2 mixture at 20 kW and 250 Torr. Results of meas urements at a distance of 188 mm from the tip of the injection probe g ive a mean particle surface temperature of 3017 K and a corresponding mean velocity of 23.2 m s(-1). Simultaneous measurement using a laser Doppler anemometer gives a mean velocity of 22.5 m s(-1) Under these c onditions, the minimum particle surface temperature that can be measur ed is estimated to be 1690 K.