Undulator Considerations in the Baseline Design of the MAX IV Soft X-Ray Laser

We examine the optimal parameter space for an x-ray free-electron laser (FEL) in the operation mode of self-amplified spontaneous emission (SASE). The study focuses on FEL operation with a shorter undulator period and higher undulator strength made available through recent developments in in-vacuum, cryogenic and superconducting undulators. We survey the progress on short-period undulator technologies and compute the FEL output characteristics versus the undulator parameters. We perform the study on a case of the planned soft-x-ray FEL at the MAX IV Laboratory in Sweden. An extension of the SASE mode into the harmonic lasing self-seeded mode is also analysed