Sustaining long linear uniform plasmas with microwaves using a leaky-wave (troughguide) field applicator

Linear, uniform, high density plasma sources can be realized using linear microwave field applicators. Such systems can be applied to process large surfaces of materials that can be made to move transversely across the plasma source. This paper details the design and operating characteristics of appropriate linear applicators that are of the leaky-wave type. A general analysis of longitudinally uniform leaky-wave-sustained discharges provides us with the generic features of the corresponding field applicators. On practical ground, we turn to troughguide structures which are well known in the field of antenna engineering; we consider periodically asymmetric troughguides terminated with a matched load and show experimentally that they can be designed to achieve the required linear uniform discharge. To assure the operation of the applicator at microwave powers of the order of one kW or more, we have devised and tested a new kind of ridge-waveguide mode transformers allowing one to feed microwave power to the applicator directly from a standard rectangular waveguide. The main advantages of the leaky-wave applicators are their relative simplicity of design and operation (no tuning elements), a good power match with the microwave generator and a good longitudinal uniformity of the sustained plasma.<
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