Transition Radiation Monitors at the Canadian Light Source

Abstract

Diagnostic monitors are required to perform electron beam diagnostic tests at select points along the beam line of the Canadian Light Source (CLS) synchrotron. The decision has been made to equip the specified facility locations with Transition Radiation Monitors (TRM) for diagnostic purposes. TRM systems use Optical Transition Radiation (OTR), the physical phenomenon by which a charged particle crossing the boundary between two media emits electromagnetic radiation in the optical region of the spectrum. For the CLS TRM systems, the electrons traveling through a vacuum impinge upon aluminum surfaces that serve as the Transition Radiation (TR) foils. If the TR-emitting foils are made extremely thin, the infrequent encounters with material atoms causes only negligible acceleration of the charge, and the process is relatively non-destructive. The foils are mounted on a driving mechanism, which enable the beam operator to control the placement and removal of the individual foils in the beam line. The emitted radiation from each TR foil is focused by a pair of achromatic lenses, and is then imaged by a Charge Coupled Device (CCD) camera. The image captured by the camera is subsequently sent to a remote PC for image analysis of the beam cross-section profile and centroid. This report discusses the theoretical underpinnings of OTR, the prototype design of the TRM system and tests undergone by the prototype, as well as describing the possible changes to be made for the subsequent final design of the TRM system.