• H. Geng, Y.T. Ding, P. Emma, J.N. Galayda, Z. Huang, Y. Nosochkov
  SLAC, Menlo Park, California

LCLS capabilities can be significantly extended with a second undulator aiming at the soft x-ray spectrum (0.5- 5 nm). To allow for simultaneous hard and soft x-ray operations, 14 GeV beams at the end of the LCLS accelerator can be intermittently switched into the SLAC A-line (the beam transport line to End Station A) where the second undulator may be located. Recently, a new optics has been designed to transport the LCLS beam through the A-Line while preserving the beam brightness. In this paper, we discuss the A-Line Soft X-ray FEL design ─ parameter selections and performance expectations with an energy-chirped LCLS beam as required by the A-Line optics. Start-to-end simulations using realistic LCLS beams show that it is possible to generate ~100 GW FEL power with the pulse duration as short as 1-fs.