Free standing plasma in a bifocal microwave concentrator

Summary form only given. Low pressure plasma reactors usually suffer from contamination of their plasma generating device. We designed a "remote", electrode less, free standing plasma source which is linearly extendable. Using a bifocal geometry for the microwave cavity we disconnect the plasma treatment area from the plasma generator location. This bifocal geometry has a big influence on the microwave field distribution and plasma homogeneity as demonstrated in a large (3 m) reactor. The homogeneous field distribution can be reached in a "microwave concentrator stack" concept. Over a wide range of gas pressure a homogeneous free standing plasma can be sustained. Technical add-ons in the microwave power supply, like phase locking, allows an easy extension of this linear plasma source.