Fig. 20

Achieved horizontal apertures after the straightening of HERA dipoles in mm on the vertical axis versus the identification name of the dipoles according to the chronicle order of the measurements. For comparison the average horizontal aperture before the straightening is shown. For total photon losses below 2·10⁻⁶ an aperture of 45.5 mm is required at the outer ends of the experiment, for infrared light with 1064 nm wavelength used in ALPS II