In this study, the bed temperature profile of a conical/plasma fluidized bed without a distributor was studied. The same reactor was also used for growing diamond by chemical vapour deposition. It was found that the fluidized bed quenches the plasma gas quite significantly. The bed temperature increases with both the plasma gas flow rate and the plasma input power. A lateral temperature difference from the centre of the bed to the wall exists due to heat loss through the wall. The temperature profiles obtained are suitable for controlling of bed quenching conditions in particle processing and synthesis. The conical/plasma fluidized bed with a distributor on top of the plasma was then applied to diamond synthesis from a gas phase using a distributor between the bed and the plasma. The deposition mainly occurred in the plasma tail flame. Both the scanning electron micrographs and Raman spectra show the existence of diamond on seed particle surfaces, but with a rather low nucleation density. The limitations of the d.c. plasma fluidized bed system are discussed and modifications to the reactor are recommended.