Doppler frequency conversion of microwaves by reflection from a relativistic beam front in a gas filled waveguide

Microwave reflection is observed on a relativistic electron beam front propagating into a gas filled waveguide. The frequency conversion from the incident X band electromagnetic waves and the reflected Ksub(a) band signal is consistent with the value of the beam front velocity measured from time-of-flight using Bsub(theta) probes. The reflection is found to occur during the current rise tim