Electron temperature, ion density and energy influx measurements in a tubular plasma reactor for powder surface modification

The tubular plasma reactor was designed for the continuous surface modification of fine powders in non-equilibrium RF discharges. So far, little has been known about the plasma characteristics of this inductively coupled reactor system. Therefore, moderate pressure argon-oxygen discharges, commonly used for powder processing, are investigated with tailor-made probe techniques. The influence of plasma power, system pressure, gas composition and mean gas velocity on the axial profiles of plasma parameters was studied. Electron temperature and positive ion density profiles were measured with a Langmuir double probe and the energy influx due to the plasma was determined by a new type of calorimetric probe. The limits for the E-H-mode transition are provided and photographs of the discharge are presented to illustrate the relationship between process parameters and plasma characteristics. Both, ion density and energy influx increased with rising plasma power. The axial energy influx profiles were in addition strongly influenced by the mean gas velocity. Based on these profiles the maximum transient particle temperature was calculated as a function of the particle diameter. Particle temperatures in the order of 100 °C were estimated, whereas the thermal load of the substrates rises with increasing plasma power, residence time and pressure.