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.
