Observation and analysis of optical transition radiation at the NPS linac and its use for diagnostics of electron beams

Abstract

An experimental technique for observing Optical Transition Radiation, (OTR), that is both simple and effective, is shown. A Macintosh II computer equipped with an image frame grabber board and Image software package allows for extensive analysis of the captured electron beam spot OTR patterns. The equipment is capable of measuring relative intensities to better than 1% for a constant source image. With beam energies of nearly 100 MeV the captured OTR images show an unexpected assymetry in the beam intensity profile. The variations of the beam intensity and shape are shown for nominally steady beam conditions. Using Image, integrated signals of the beam spot OTR patterns for several targets as a function of beam current show a linear relationship, thereby creating a technique for computing electron beam current. Portions of the beam profile with varying percentages of beam spot maximum intensity also show a linear relationship between beam current and OTR image intensity. A radiation cone OTR pattern has been observed for the NPS linac beam. From the pattern, the Lorentz factor for the 100 MeV electrons is observed to be less than the computed value, and probably indicates the non-collinearity of the electron beam.