The beam dynamics of the S-DALINAC is rather complicated. As a recirculation Linac, the machine is neither a single Linac nor a circular accelerator: it combines features of both types of machines in a microtron-like manner. Therefore, investigations of the longitudinal working point are conducted. From a theoretical model, a reduction of the energy spread is predicted and first signs of this existence have been observed many years before- a final prove is one of the major steps lying ahead.
In addition, several machine lattice upgrades are underway, requiring a detailed recalculation of the beam dynamics. One of this is the installation of a third recirculation to boost the accelerator energy, allowing to use the energy gain of the main linac another time, which would lead roughly to 120 MeV in cw operation. The installation of an additional recirculation has become possible recently as the old beam-line to the undulator (as part of the Darmstadt Free Electron Laser facility) has been de-commissioned in 2006. A preliminary design study undertaken so far showed the option to build the new recirculation in between the two existing ones. A considerable advantage of this layout is that most of the existing beam-line and magnets can be used again (even so the energy of the beam changes). Beside the 4 new bending magnets to form the additional recirculation path, only the separation and combining magnets at the beginning and the end of the recirculations have to be replaced.
An other upgrade, involving beam-dynamics issues is the installation of two scraper systems. The injector arc scraper system will remove the low energy tail of the beam injected into the main linac. Currently, the dynamics of the injector bending section is optimized to allow the installation of the recently designed collimator.
After three passes through the linac (housing 8 independently controlled accelerating cavities) a transversal scraping, combined with an additional longitudinal collimation will ensure the highest beam quality by removing any beam halo. The system proposed will be placed in the extraction beam line, the lattice and the dynamics of which has to be adapted. In addition, the longitudinal scraping can further reduce the energy spread of the beam at the cost of beam current. As the dispersion is maximized in this section, a more efficient energy collimation compared to the existing system can be assured, allowing an energy definition of as low as 10 keV being a key figure for several highly demanding experiments proposed within the CRC.