A system for converting a carbon-containing feedstock into one or more useful materials, comprising: a thermal reactor in fluid communication having a feedstock inlet and a gas and waste char output, said thermal reactor including, a polygonal internal microwave cavity having exterior sides; a cylindrical outer shell surrounding and encasing said polygonal internal microwave shell on said exterior sides, said outer shell having a closed top with a feedstock inlet at the input end and a closed bottom with a gas and waste char outlet at the gas output end; a plurality of microwave generators disposed outside of, and coupled to, said outer shell, one each of said microwave generators for each side of said polygonal internal microwave cavity, said microwave generators including waveguides disposed through said outer shell and said internal microwave cavity to direct and deliver microwave energy to the interior of said internal microwave cavity; an inert gas source in fluid communication with said internal microwave cavity; a plurality of heating elements disposed around said internal microwave cavity; a vertically oriented microwave transparent ceramic sleeve generally centered in said internal microwave cavity and spanning between an inner side of said top and said bottom of said outer shell; a mixing auger rotatingly and axially disposed in said ceramic sleeve; a plurality of microwave-absorbing spheres contained within said ceramic sleeve and surrounding said mixing auger; an outlet grate through which vaporized gases and waste char pass after processing in said thermal reactor; a feedstock feed assembly in fluid communication with said feedstock inlet; and a cooling and condensation system in fluid communication with said gas and waste char outlet. a polygonal internal microwave cavity having exterior sides; a cylindrical outer shell surrounding and encasing said polygonal internal microwave shell on said exterior sides, said outer shell having a closed top with a feedstock inlet at the input end and a closed bottom with a gas and waste char outlet at the gas output end; a plurality of microwave generators disposed outside of, and coupled to, said outer shell, one each of said microwave generators for each side of said polygonal internal microwave cavity, said microwave generators including waveguides disposed through said outer shell and said internal microwave cavity to direct and deliver microwave energy to the interior of said internal microwave cavity; an inert gas source in fluid communication with said internal microwave cavity; a plurality of heating elements disposed around said internal microwave cavity; a vertically oriented microwave transparent ceramic sleeve generally centered in said internal microwave cavity and spanning between an inner side of said top and said bottom of said outer shell; a mixing auger rotatingly and axially disposed in said ceramic sleeve; a plurality of microwave-absorbing spheres contained within said ceramic sleeve and surrounding said mixing auger; an outlet grate through which vaporized gases and waste char pass after processing in said thermal reactor; a feedstock feed assembly in fluid communication with said feedstock inlet; and a cooling and condensation system in fluid communication with said gas and waste char outlet.