Diagnostic development and process correlation of the plasma spray process for magnetic confinement fusion applications

The need in present and future nuclear fusion reactors for a method of fabricating and repairing plasma facing components has been a significant problem slowing the progress of research in the fusion community. The plasma spraying technique has been proposed for first wall and divertor fabrication and/or repair. However, consistently producing coatings with thermal conductivities suited for fusion applications requires further research and development. Methods for modeling heat transfer through plasma-sprayed coatings and measuring the temperature of plasma-sprayed particles in flight have been developed. The effect of particle temperature, particle velocity, and substrate temperature on the pore structure of plasma-sprayed coatings was also studied.;The effect of pores on the thermal conductivity of plasma-sprayed coatings was investigated. Finite element models of the actual pore structure observed in the coatings gave estimates of the coating thermal conductivity. Comparison of the calculated thermal properties to measured thermal properties of the same coatings show that the pore structure is the major factor decreasing the thermal conductivity of the plasma-sprayed coatings investigated.;The use of optical pyrometry for particle surface temperature measurement has inherent uncertainties due to non-thermal emission signals in the plasma/particle plume. Measurements of the non-thermal signals present have been made. The measurements help to define a method for subtracting the non-thermal signal from the raw data to improve the accuracy of particle temperature calculations.;The effect of particle temperature, velocity, and substrate temperature on the long thin type of porosity in plasma-sprayed coatings was investigated. The particle temperature and velocity were found to change very little over the range investigated leading to the conclusion that they have little effect on the coating pore structure. However, the substrate temperature during spraying was found to decrease the amount of long thin porosity as substrate temperatures increased.;The tools developed for this work can be used for future investigations to increase the fundamental knowledge of plasma spraying and plasma-sprayed coatings. Such future work is critical to the success of plasma-sprayed coatings for use in fusion energy applications.