Open Access Version

Abstract:
The interaction of a short bunch of electrons with its own coherent synchrotron radiation, CSR, leads to low longitudinal instability thresholds. According to Bane, et al. [1] these thresholds follow a quite simple scaling law. More detailed theoretical calculations for the underlying shielded CSR-impedance have been performed for BESSY II and the Metrology Light Source, MLS. It is found that there are additional parameter regions where the instability is weak and thus the thresholds depend on the longitudinal damping time, Tlong, and the synchrotron tune, 1/Tsyn. Most of the observed longitudinal instability features [2, 3] are in surprisingly good agreement with the theoretical findings.