THE ELECTROMAGNETIC PERFORMANCE OF A SURFATRON-BASED COAXIAL MICROWAVE PLASMA TORCH

Low power microwave plasma torches are of particular interest to analy tical chemists. The torch design investigated herein, called TPS, is b ased on the known surfatron structure to which a coaxial section is ad ded consisting of an impedance transformer followed by the metallic no zzle at the tip of which the discharge occurs. A series of experiments illustrate the main electromagnetic features and performance of this novel coaxial microwave plasma torch operating at 2.45 GHz and with in put power in the range 10-180 W. A specially devised slotted coaxial l ine with a movable probe arrangement can be inserted into the torch in place of the transformer section to provide in situ measurements of t he plasma impedance. Analyzing these results, we show that the shape o f the torch tuning characteristics can be controlled to improve the po wer transfer to the plasma and stability of operation with respect to changes in discharge conditions; under these conditions, the design of the device can be simplified. The procedures presented have a general character and can be applied to various torch configurations.