Prospects for CW and LP operation of the European XFEL in hard X-ray regime

• Published in: Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment Accelerators, spectrometers, detectors and associated equipment, 2014-12, Vol.768, p.20-25
• Main Authors: Brinkmann, R., Schneidmiller, E.A., Sekutowicz, J., Yurkov, M.V.
• Format: Article
• Language: English
• Subjects: Accelerators; Continuous wave; Electron beams; Free electron laser; Lasing; Photon beams; Superconducting accelerator; Trains; Wavelengths; X-ray laser; X-rays
• ISSN: 0168-9002; 1872-9576
• DOI: 10.1016/j.nima.2014.09.039

The European XFEL will operate nominally at 17.5GeV in SP (short pulse) mode with 0.65ms long bunch train and 10Hz repetition rate. A possible upgrade of the linac to CW (continuous wave) or LP (long pulse) modes with a corresponding reduction of electron beam energy is under discussion for many years. Recent successes in the dedicated R&D program allow to forecast a technical feasibility of such an upgrade in the foreseeable future. One of the challenges is to provide sub-Ångström FEL operation in CW and LP modes. In this paper we perform a preliminary analysis of a possible operation of the European XFEL in the hard X-ray regime in CW and LP modes with electron energies of 7GeV and 10GeV, respectively. We consider lasing in the baseline XFEL undulator as well as in a new undulator with a reduced period. We show that, with reasonable requirements on electron beam quality, lasing on the fundamental will be possible in the sub-Ångström regime. As an option for generating brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.