Visible cameras as a tool to study electron beam shape

The characterization of the spatial distribution of particle trajectories, or the respective current distribution, in powerful electron beams is an important scientific and practical task necessary to improve the quality of electron beam technologies. For various applications, a small divergence is required to transport the electron beam over long distances and focus it onto a small spot. Even if one has simultaneous knowledge of accelerating voltage, beam current, focus coil current (or magnetic field), and vacuum level overall, they provide little insight into the properties of the beam itself. In this work, visible cameras are used to study the shape of the electron beam when these parameters are varied. A series of pictures are collected at different camera orientations around the beam. The light emission comes from the argon background gas interacting with the energetic electrons composing the beam. The information is used to reconstruct the two-dimensional shape of the beam using tomographic inversion.