• C.-X. Wang
  ANL, Argonne

Funding: This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

Low-frequency normal-conducting photoinjectors have the potential to generate CW beam due to low frequency and relatively low field. They can provide a much higher accelerating field at the cathode than envisioned DC injectors but without the complexity involved in superconducting rf injectors. Low frequency allows a relatively long bunch near the cathode to reduce space-charge effects, which is detrimental for generating demandingly high-brightness beams. However, low frequency means higher bunch charge for a given average current, counteracting the potential benefits of low-frequency rf injectors. Furthermore, significant bunch length reduction in the injectors is often needed, which may degrade transverse brightness. To explore the potential of a normal-conducting injector for the envisioned ERL upgrade of the Advanced Photon Source, we made a preliminary design and searched for a suitable solution using genetic optimization. Simulation results are presented.

• C.-X. Wang
  ANL, Argonne

Funding: This work was supported by U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.

The envisioned next-generation ERL-based x-ray light sources demand costly CW superconducting linacs and high-brightness high-current photoinjectors that are beyond the state of the art. To overcome the fiscal challenge of a multi-GeV CW superconducting ERL and the physical challenge of high-brightness high-current CW photoinjectors, we explore a new scheme using multi-beam injection into a quasi-CW ERL. Multi-beam injection lowers the burden on individual rf injectors at subharmonics of the linac frequency. Lower injector frequency allows higher bunch charge, which permits lower duty factor of the linac with significant reduction in construction and operation costs. Preliminary studies foresee many benefits and no obvious physical showstoppers, despite potential technical challenges. Here we provide a simulation study of a preliminary design.