A reactor (12, 128, 198) and method for the conversion of hydrocarbon gases utilizes a reactor (12, 128, 198) having a unique feed assembly (58, 136, 200) with an original vortex disk-like inlet flow spaces (72, 74, 76, 80, 146, 148, 150, 152, 208, 216, 218), a converging-diverging vortex mixing chamber (116), and a cylindrical reactor chamber (40). This design creates a small combustion zone and an inwardly swirling fluid flow pattern of the feed gases that passes through a converging conduit (48) with a constricted neck portion (54). This provides conditions suitable for efficient cracking of hydrocarbons, such as ethane, to form olefins.