  The S-DALINAC is a 130 MeV superconducting recirculating electron accelerator
serving several nuclear and radiation physics experiments as well as driving an
infrared free-electron laser. A system of normal conducting rf resonators for
noninvasive beam position and current measurement was established. For the
measurement of gamma-radiation inside the accelerator cave a system of Compton
diodes has been developed and tested. Detailed investigations of the transverse
phasespace were carried out with a tomographical reconstruction method of
optical transition radiation spots. The method can be applied also to
non-Gaussian phasespace distributions. The results are in good accordance with
simulations. To improve the quality factor of the superconducting 3 GHz
cavities, an external 2K testcryostat was commissioned. The influence of
electro-chemical polishing and magnetic shielding is currently under
investigation. A digital rf-feedback-system for the accelerator cavities is
being developed in order to improve the energy spread of the beam of the
S-DALINAC.
  * Supported by the BMBF under contract no. 06 DA 820, the DFG under contract
no. Ri 242/12-1 and -2 and the DFG Graduiertenkolleg 'Physik und Technik von
Beschleunigern'
