A gas processing system, comprising: a waveguide (205, 305, 605, 705, 805) having a first gas inlet (302, 602, 702), a second gas inlet (310, 610, 710) downstream of the first gas inlet (302, 602, 702), and a length, wherein the first gas inlet (302, 602, 702) is configured to provide a flow of a supply gas into the waveguide (205, 305, 605, 705, 805), and the second gas inlet (310, 610, 710) is configured to add a flow of a process gas into the waveguide (205, 305, 605, 705, 805); and a pulsed microwave radiation source (204, 304, 604, 704, 804) coupled to the waveguide (205, 305, 605, 705, 805) to provide microwave radiation and to generate a plasma in the supply gas, such that, in use, the microwave radiation propagates in a direction along the length of the waveguide (205, 305, 605, 705, 805) and reacts with the process gas within the waveguide (205, 305, 605, 705, 805) which serves as a reaction chamber, wherein the pulsed microwave radiation source (204, 304, 604, 704, 804) is configured to pulse the microwave radiation on and off at a frequency from 500 Hz to 1000 kHz and with a duty cycle less than 90%; wherein the first gas inlet (302, 602, 702), the second gas inlet (310, 610, 710) and the waveguide (205, 305, 605, 705, 805) are configured so that, in use, a majority of the flow of the supply gas and a majority of the flow of the process gas are parallel to the direction of the microwave radiation propagation; wherein the second gas inlet (310, 610, 710) and the waveguide (205, 305, 605, 705, 805) are further configured so that, in use, said majority of the flow of the process gas is greater than 5 slm, standard liter per minute; and wherein the waveguide (205, 305, 605, 705, 805) is configured to accommodate pressures of at least 0.1 atmosphere. a waveguide (205, 305, 605, 705, 805) having a first gas inlet (302, 602, 702), a second gas inlet (310, 610, 710) downstream of the first gas inlet (302, 602, 702), and a length, wherein the first gas inlet (302, 602, 702) is configured to provide a flow of a supply gas into the waveguide (205, 305, 605, 705, 805), and the second gas inlet (310, 610, 710) is configured to add a flow of a process gas into the waveguide (205, 305, 605, 705, 805); and a pulsed microwave radiation source (204, 304, 604, 704, 804) coupled to the waveguide (205, 305, 605, 705, 805) to provide microwave radiation and to generate a plasma in the supply gas, such that, in use, the microwave radiation propagates in a direction along the length of the waveguide (205, 305, 605, 705, 805) and reacts with the process gas within the waveguide (205, 305, 605, 705, 805) which serves as a reaction chamber, wherein the pulsed microwave radiation source (204, 304, 604, 704, 804) is configured to pulse the microwave radiation on and off at a frequency from 500 Hz to 1000 kHz and with a duty cycle less than 90%; wherein the first gas inlet (302, 602, 702), the second gas inlet (310, 610, 710) and the waveguide (205, 305, 605, 705, 805) are configured so that, in use, a majority of the flow of the supply gas and a majority of the flow of the process gas are parallel to the direction of the microwave radiation propagation; wherein the second gas inlet (310, 610, 710) and the waveguide (205, 305, 605, 705, 805) are further configured so that, in use, said majority of the flow of the process gas is greater than 5 slm, standard liter per minute; and wherein the waveguide (205, 305, 605, 705, 805) is configured to accommodate pressures of at least 0.1 atmosphere.