Fig. 21

Horizontal apertures of the dipoles installed in the HERA tunnel. Large apertures are at the outer ends of the magnet strings, smaller apertures close to the middle of the experimental setup. Near the ends of the strings for ALPS II, magnets with large quench currents (>6400 A) were selected, to compensate for potential additional heat loads from the neighboring boxes or the cryogenic bypass in the middle of the experimental setup. The positions of dipoles with a pumping port are marked by red circles. The vertical bar in the middle of the experiment indicates the position of the light tight wall