Straightening of Superconducting HERA Dipoles for the Any-Light-Particle-Search Experiment ALPS II

At DESY the ALPS II experiment is being installed in the HERA tunnel to search for axion like particles (ALPs). A laser beam will be injected into a string of superconducting HERA dipole magnets, to produce ALPs. After passing a light tight wall, the ALPs can reconvert into photons in a second string of HERA dipoles.The sensitivity of the experiment will be increased by two mode-matched optical cavities before and behind the wall. The curvature of the magnets limits the performance of the optical resonators, Therefore the aperture for the optical resonators inside the HERA dipoles was increased by straightening the curved magnet yoke. The procedure of straightening the HERA dipoles is described in this report.