A processing reactor includes a microwave energy source and a field-enhancing waveguide. The field-enhancing waveguide has a field-enhancing zone between a first cross-sectional area and a second cross-sectional area of the waveguide, and also has a plasma zone and a reaction zone. The second cross-sectional area is smaller than the first cross-sectional area, is farther away from the microwave energy source than the first cross-sectional area, and extends along a reaction length of the field-enhancing waveguide. The supply gas inlet is upstream of the reaction zone. In the reaction zone, a majority of the supply gas flow is parallel to the direction of the microwave energy propagation. A supply gas is used to generate a plasma in the plasma zone to convert a process input material into separated components in the reaction zone at a pressure of at least 0.1 atmosphere.