Generation of picosecond electron bunches in storage rings

Approaches to generating short X-ray pulses in synchrotron light sources are discussed. In particular, the method of using a superconducting harmonic cavity to generate simultaneously long and short bunches in storage rings and the approach of injecting short bunches from a linac injector into a storage ring for multi-turn circulation are emphasized. If multi-cell superconducting RF (SRF) cavities with frequencies of ∼1.5 GHz can be employed in storage rings, it would be possible to generate stable, high-flux, short-pulse X-ray beams with pulse lengths of 1–10 ps (FWHM) in present or future storage rings. However, substantial challenges exist in adapting today's high-gradient SRF cavities for high-current storage ring operation. Another approach to generating short X-ray pulses in a storage ring is injecting short-pulse electron bunches from a high-repetition-rate linac injector for circulation. Its performance is limited by the microbunching instability due to coherent synchrotron radiation. Tracking studies are carried out to evaluate its performance. Challenges and operational considerations for this mode are considered.