Determination of the beam width in a stellatron accelerator

The UCI (University of California Univ., Irvine) stellatron is a strong-focusing, high-current betatron that accelerates a 1-kA electron beam. To measure the minor dimension of the beam, targets were inserted at different radii from the outer sides of the torus. The beam was swept outward by applying a pulse vertical magnetic field. The time dependence of the X-ray emission from the target was analyzed to determine the expansion velocity and the density distribution of the beam. 50% and 90% of the electrons were found within 4-mm and 7-mm radii, respectively, at 5 MeV