As part of the ongoing upgrade of the accelerator complex, the ID23 straight section has been lengthened from 5 m to 7 m, with no disruption to the operation of beamline ID23. The magnets at both ends of the straight section have been replaced by shorter and stronger ones. The two undulators presently in operation have been moved to either end of the straight section, leaving free space in the centre for installation of the new RF HOM-damped cavities (Figure 161). The 7 m straight section, which broke the symmetry of the storage ring, has not caused any deterioration of the beam parameters – in fact they are now even better thanks to improved optic tuning techniques.

Layout of the lengthened ID23 straight section

Fig. 161: Layout of the lengthened ID23 straight section.

In addition to the new magnets and corresponding power supplies installed in the straight section, the modification required a change of magnet coils and new power supplies, providing individual control of the quadrupoles over a full cell, rather than over a whole magnet family, as in the past. These modifications were completed with the installation of the new straight section girders and new magnets during the winter 2012-2013 shutdown.

The first 7 m straight section during installation at ID23 in January 2013

Fig. 162: The first 7 m straight section during installation at ID23 in January 2013.

During the first half of 2013, before the installation of the RF cavities, an additional quadrupole was installed at their location and powered during machine dedicated studies only. The aim was to test the possibility of splitting a long straight section into two halves with a small vertical b of 1.5 m in the middle of each half. This configuration could allow a further reduction of the undulator gaps, possibly down to 4 mm. The tests provided the opportunity to check the impact on the machine performance of such a significant modification to the optics, in particular on injection efficiency and lifetime. The experiments have indicated that the effects are rather limited. This extensive project, which included the reconstruction of part of a cell arc, as well as the whole straight section, was also an excellent exercise in view of future works towards a new storage ring lattice (Figure 162).