Chemical treatment plasma apparatus for forming a ribbon-like plasma

Chemical treatment plasma apparatus having a high frequency electromagnetic wave source, a sealed plasma enclosure equipped with gas supply means for forming the plasma, means for coupling the source to the plasma enclosure, means for pumping the plasma enclosure and at least one sample holder, wherein the plasma enclosure is of a non-radiating nature and is shaped like a rectangular parallelepiped with first and second dielectric material faces parallel to a first direction and a third face provided with a rectangular opening oriented in the first direction in order to form a ribbon-like plasma, said opening linking the plasma enclosure and a treatment enclosure in which is housed the sample holder, the coupling means comprising a first rectangular linear waveguide oriented in a second direction perpendicular to the first and second faces, a horn for coupling the first guide to the plasma enclosure via the first face and whose rectangular cross-section widens in the first direction from the first guide towards the plasma enclosure, and a second rectangular linear waveguide oriented in the second direction and located on the side of the plasma enclosure opposite to that of the first guide, said second guide being provided with a short-circuit for said electromagnetic waves.