Optical Transition and Diffraction Radiation Diagnostics for Relativistic Charged Particle Beams

Abstract

Transition radiation (TR) and diffraction radiation (DR) are produced by charged particles passing through or by regions of variable permitivity. The perturbation of the field surrounding the charged particle causes a radiation field to be generated. The radiation eminates from the position of the particle as it crosses through or minimally impacts the boundary. TR’s spatial, angular and frequency distributions have been well characterized both theoretically and experimentally over a wide range of charged particle energies and wavelengths — from x-ray to radio wavelengths. The properties of TR reflect those of the particle(s) producing the radiation, so it is natural that TR has been successfully employed as a diagnostic for the energy, spatial profile, divergence and emittance of charged particle beams. One of the first applications of TR, and still one that is commonly used for high energy and nuclear physics experiments, is as a particle discriminator. This is accomplished utilizing the known dependence of intensity of the radiation in the x-ray regime with energy. In recent years the applications of TR to beam diagnostics, particularly in the optical and near IR portions of the spectrum, have grown tremendously. It is now possible using incoherent and coherent TR to characterize both the transverse and longitudinal phase space of a charged particle beam with high precision. In contrast to TR, diffraction radiation, despite its long theoretical history, has been little studied experimentally and its application to beam diagnostics has only recently been investigated. We review here the diagnostic applications of incoherent optical TR and DR to the measurement of the transverse phase space of relativistic electron beams, a subject in which we have been intimately involved over the last twenty years.