Properties of microwave-generated, atmospheric pressure plasmas

The chief advantage of atmospheric-pressure plasmas for technological applications is the much greater flexibility afforded by the absence of a vacuum vessel. In principle this allows large-scale, continuous processing instead of the small-scale, batch processing associated with low pressure plasmas. The price to be paid for lack of control over the pressure is a restriction in the range of parameters which can be achieved, thus reducing the degree to which conditions can be optimised for particular purposes. As will become clearer, it may be possible to offset some of these restrictions by careful attention to plasma source design, operating frequency, power density, etc. This report will focus on the properties of plasmas produced by 2.45 GHz microwaves in a high-Q cavity of the kind used in microwave ovens; a method of production which was discovered and patented by EA Technology. But first we consider some general properties of atmospheric pressure plasmas.