Synchrotron Radiation Profile Monitor for the HERA Positron Beam

For the measurement of the positron beam emittance at the e-p storage ring HERA at DESY a monitor is used which is based on the direct imaging of visible synchrotron radiation from a bending magnet. While the resolution of profile measurements by synchrotron radiation is already strictly limited by inherent effects, the observation in off-axis geometry modifies the measured vertical angular intensity distribution additionally. As a result the beam image is broadened due to the increased contribution of the diffraction limited resolution. In the present article detailed calculations concerning the image resolution especially in view of off-axis observation are presented. Furthermore the calculations indicate that the influence of resolution broadening effects may be overestimated by the standard formulas used as rule of thumb