Propagation and detection of RF-modulated electron and X-ray beams in air

Electron beams produced in RF linear accelerators will naturally be modulated at the RF frequency. Here we report measurements of the RF harmonic content of a 21.6 MeV electron beam coasting in air, as well as the RF harmonic content of x-rays produced from that electron beam, and the effects of these modulated electron and x-ray beams on several fast detection systems. The RF fundamental and its higher harmonics were found to be impressed onto the x-rays generated from the electron beam, and the response of an RF waveguide to passage of the modulated x-ray signal indicated that this harmonic content was also impressed onto the secondary electrons produced by the passage of the x-rays through the waveguide. An unexpected, interference-like effect was observed, which was particularly prominent in the case of the waveguide when struck by the modulated x-rays. The participation of secondary electrons produced by passage of the x-rays through the x-ray converter upstream of the waveguide was ruled out as a si...