Patent ID: 7650853

Claim:
A device for applying, in use, electromagnetic microwave radiation in a plasma cavity, said device comprising said plasma cavity present within a housing, the cavity being substantially cylindrically symmetric about a first axis, and which plasma cavity comprises a cylindrical wall provided with a circumferential slit, said plasma cavity being in communication, via said slit, with a first end of an elongated microwave guide having a longitudinally extending second axis, said device being in communication in use with microwave generating means via the other end of said microwave guide, in which the electromagnetic microwave radiation being generated may comprise several modes, wherein the device comprises means which, in use, generate microwave radiation in the slit, which microwave radiation has only one electromagnetic field distribution in only one direction perpendicularly to the propagation direction of the microwave radiation in the microwave guide, wherein the microwave radiation has only one specific electromagnetic field distribution, seen in the direction of rotation relative to the first axis; wherein the two axes form a plane of symmetry for the device such that the microwave radiation is oriented relative to the plane of symmetry; wherein the microwave guide exhibits rectangular cross-section, with the short walls of the microwave guide extending perpendicularly to the plane of symmetry.