An improved microwave interferometer technique for plasma density measurements

An improved technique has been developed for microwave interferometer measurements of plasma density, where the most useful features of previously described techniques are combined. Phase angles from a few degrees to several times 360 degrees can be measured without ambiguity, and there are no phase angles with zero phase shift sensitivity. Reductions of the microwave power (e.g. due to absorption in the plasma) with up to a factor 100 can be taken into account in the evaluation of the measurements. With low power in the test beam, a polar display of the test beam phasor is possible. The minimisation of errors due to imperfect components, and due to uncertainties in the measured quantities, is investigated theoretically and experimentally. The method of evaluation eliminates the influence also of rather large imperfections of the components. The construction and testing of an interferometer based on this technique is described.