1. Field of the Invention
The invention relates to an arrangement for microwave transmission between wave guide regions having different internal gas pressures and/or different fill-gas compositions, that is to say, for coupling or outcoupling microwaves of such a wave guide region into another region.
2. Description of the Related Art
In German Patent Application No. DE-OS 36 22 614 which corresponds to commonly owned U.S. Pat. No. 4,877,642, is disclosed a method of manufacturing electrically conductive moulded bodies by a plasma-activated chemical deposition from a gaseous phase. With such methods the coupling of high-power microwaves is effected through a hermetically sealed insulating microwave aperture of dielectric material in a microwave resonator used as a reaction chamber, in which a plasma is formed and electrically conductive layers are chemically deposited. During this process the problem arises that an electrically conductive film generally covers the surface of the microwave aperture arranged at the coupling place, that is, its inside surface facing the reaction chamber, as a result of which the coupling is stopped. This problem is solved according to DE-OS 36 22 614 either by having the inside of the microwave aperture rinsed by an inertial gas, or selecting for the microwave aperture a dielectric material which is kept free from growth of electrically conductive film as a result of an etching reaction with one of its reaction partners.
A cognate problem occurs when high-power microwaves from gyrotrons are outcoupled during transition from high-vacuum to air. With microwave powers of the order of 0.1 to 1 MW the thermal load of the known materials used for microwave apertures becomes too large, as a result of which the output power is restricted. With maximum power levels of 0.3 MW one manages by enlarging the wave guide and additionally cooling the aperture consisting of, for example, Al.sub.2 O.sub.3.
Evacuation of a wave guide through non-radiating or non-coupling slots is known from British Patent Specification No. GB-PS 644,749.