Method and reactor for processing a gas

A plasma processing method for a gas, the method comprising:

• supplying a gas inside a cavity for plasma processing,
• supplying microwaves having a predetermined frequency and power in order to generate a plasma of the gas,
• propagating the microwaves in the gas by means of a waveguide which communicates directly with the cavity so as to provide a plasma cracking processing operation for the gas inside the cavity, the internal volume with respect to the cavity and the waveguide not having any discontinuities,
• receiving the gas and the microwaves from the waveguide in a processing pipe of the cavity,
• conveying the gas and the microwaves inside an electromagnetic resonator which is arranged along the processing pipe, the electromagnetic resonator being in the form of a widening of the processing pipe and concentrating the microwaves so as to generate a plasma of the gas inside the electromagnetic resonator, wherein the electromagnetic resonator is arranged along the processing pipe downstream of the waveguide in relation to a direction of flow of the gas and propagation of the microwaves by the waveguide towards the processing pipe.