Resonant Cavity Measurements of Ionized Wakes

A transmission resonant cavity technique, which is suitable for making measurements of electron line densities and collision frequencies in the ionized wakes of hypervelocity projectiles, is described. With this method electron density measurements can be made over six orders of magnitude. Resonant cavity design requirements and limitations of the method are discussed. Typical data from measurements behind projectiles traveling at speeds up to 6.5 km/s are given.