An improved microwave interferometer technique for plasma density measurements: II

A 4 mm microwave interferometer is described, together with a working system for numerical evaluation of the recorded signals. The interferometer signals are processed in a computer to provide an immediate display of the plasma column density. The numerical evaluation makes it possible to eliminate the influence of rather large imperfections in the components, and also to take into account large and rapid variations in the strength of the transmitted microwave signal. The limits of performance of the system are tested in a pulsed plasma source. Column plasma densities are measured from 1015 m-2 to 3*1018 m-2, corresponding to phase swings from less than one degree up to several times 360 degrees .