Open Microwave Resonators for Ionized Wake Measurement

A method is described for measuring changing ionization levels by observing the phase shift of a microwave signal which has passed through an open resonator while the resonator is being perturbed by the ionization. The measurement range is 10
⁹
to 10
¹¹
e/cm
³
with a time resolution of 1 μs and a spatial resolution of 2.5 cm. Methods of measuring the phase shift and converting the phase information to useful results are detailed. Sources of error are also considered.