TU Darmstadt, Darmstadt, Germany
IKP, Mainz, Germany
Since 1991 the superconducting recirculating electron accelerator S-DALINAC is running at TU Darmstadt. Its designated design energy of 130 MeV wasn't reached yet due to a lower quality factor of the 3 GHz cavities and thus a higher dissipated power to the helium bath. To increase the maximum achievable energy in cw operation from approx. 85 MeV to the design value of 130 MeV the main accelerator will be passed a fourth time. In this configuration the accelerating gradients of the cavities can be lowered, so that the resulting dissipated power will match the available cooling power of the cryo plant. To realize an additional main linac pass a new recirculation beam line is needed. The most crucial points are the design of the separation dipole and its mirrored version as well as a properly calculated lattice. For the implementation of a new recirculation beam line the existing sections must be adapted to fit the new boundary conditions. This contribution will present some aspects of the design and will report on the actual status of this project.
Cornell University (CLASSE), Cornell Laboratory for Accelerator-Based Sciences and Education, Ithaca, New York, USA
TU Darmstadt, Darmstadt, Germany
IKP, Mainz, Germany
Linear accelerators, in particular those with a recirculating design and superconducting cavities, have to deal with the problem of Beam Break-Up (BBU). This instability can limit the maximum beam current in such accelerators. Knowing the effectiveness of prevention strategies is of great interest especially for future accelerators like energy recovery linacs (ERL) which aim for high beam currents. One option is to optimize the cavities and higher order mode couplers of those machines. In addition one may adapt the beam line lattice for further suppressing BBU. The superconducting recirculating accelerator S-DALINAC at the Technische Universität Darmstadt provides electron beams in c.w. for nuclear physics experiments since 1991. As the SRF components were never optimized for higher order mode suppression the S-DALINAC suffers from BBU at relatively low beam currents of a few μA. While those currents are sufficient for most nuclear physics experiments we can investigate BBU with respect to the beam optics. We will report on first measurements of threshold currents at different beam energies of the S-DALINAC. The results of a first test to increase the BBU limit by using skew quadrupoles will be presented.
