Lecher wire microwave interferometer for measurements of electron density and electron temperature in a flowing transient plasma

A microwave diagnostic system for measurement of electron density and temperature in a transient plasma flow, generated by a laser pulse focused on a solid target, has been constructed using a twin conductor (Lecher wire) probing element coupled to X-band waveguide components by tapered parallel planes. The analysis of the operation of the probing section has required the solution of a symmetric seven layer dielectric problem, which models the transmission, reflection, and attenuation of the microwave signal by plasma located around Lecher wires. Simultaneous measurements of the phase and amplitude of the transmitted signal, together with an experimental configuration which accurately defines the interaction of the plasma with the Lecher wire section, have made possible the reliable determination of plasma properties with a spatial resolution of ∼0.5 cm and a temporal resolution of ∼5×10−8 sec.