Microwave radiation from interactions of modulated electron beams with solid matter

Abstract

RF-modulated electron beams, such as those produced by an RF linear accelerator, propagating through vacuum, air, and solid matter are well known to drive signals in microwave cavities and waveguides via interactions with these structures. Past experiments with a microwave waveguide in a radiation-shielded vault indicated the presence of a multipath propagation phenomenon, hypothesized to be a result of reflections of RF-modulated x rays. In this work, we study the signals induced in a microwave coaxial cable from nearby beam interactions with materials commonly found in accelerator facilities in order to better understand RF production and propagation in these environments. Our results show that (1) when an RF-modulated electron beam is incident on a block of aluminum, lead, or concrete, the frequency content of the induced microwave signals is strongly dependent on the orientation of the block and the relative position of the detector, (2) at least some of the detected signals are consistent with reflections off of the blocks, and (3) beam interactions with the blocks can induce appreciable microwave signals in detectors located tens of cm from the block.