Coherent emission of synchrotron radiation and longitudinal instabilities

At BESSY bursts of coherent synchrotron radiation around 20 cm/sup -1/ have been observed above a certain threshold current. The repetition rate of these bursts depends on the beam current and the thresholds vary strongly with the bunch length. Observed thresholds are in agreement with the theory of beam instability and microbunching due to coherent synchrotron radiation (CSR).