• A.H. Lumpkin, A.S. Johnson, J. Ruan, J.K. Santucci, R. Thurman-Keup
  Fermilab, Batavia

Optical transition radiation (OTR) imaging for transverse beam-size characterization is a well-established technique at many accelerators including the Fermilab A0 photoinjector (A0PI) facility. However, there is empirical evidence for gamma greater than 10⁰⁰ beams that the utilization of the polarization component orthogonal to the dimension of interest resulted in a smaller projected image profile. Generally, at the A0PI low beam energies of 14-15 MeV and emittances of 3 mm mrad, one encounters beam sizes of 0.8 to 1.5 mm (σ). However, the use of 50-micron wide slits to sample the beam’s transverse phase spaces significantly alters the required resolution of the converter screen and imaging system. In this case, we dealt with slit-image sizes of about σ 10⁰ microns and less, depending on drift distance and beam divergence. In the course of our study of the slit images, we have found that the OTR polarized component orthogonal to the narrow beam dimension of interest systematically gave us ~20-micron smaller projected image sizes than with the total OTR intensity. This is one of the first reports of this polarization effect at such a low-gamma regime (~30).