A reaction vessel and a method for efficiently producing and collecting nanoparticles in the reaction vessel using cyclonic gas flow. Gas is injected through an inlet tangentially positioned relative to the axis of the vessel to cause the gas to form an outer helical vortex flow and an inner helical vortex flow within the vessel. A reaction synthesizer is operated within the inner helical vortex to produce nanoparticles and larger byproduct particles from precursor materials. The double helical vortex conveys the byproduct particles to an outlet for collection responsive to the cyclonic flow and gravity and an outlet downstream of the inner helical vortex collects the nanoparticles. The vortices formed in the reaction vessel minimize buildup on walls of the reaction vessel and provide a way to rapidly move the synthesized nanoparticles out of the reaction vessel.