Abstract: In the process of carrying out high temperature, chemical reactions including reductions for producing elemental metal powders, especially refractory metals; chlorinations for producing halogens and for chemical synthesis in general using a plasma generator, the reactant or reactants feed material is introduced into the reaction zone of the apparatus and the effluent from the reaction zone is directed into a quenching zone through a selectively variable passageway or orifice in a manner that permits in the reduction process separation of the desired reaction product from the effluent hot gas stream and the continuous collection of the reaction product in a collection zone wherein in some instances, the reaction product is of a selected characteristic, controlled by the maintenance of certain operational parameters, including a selected differential fluid pressure in the reaction and collection zone as well as reaction and collection zone temperatures.