标题： 硬X射线区域欧洲XFEL的CW和LP运行前景 显示英文标题

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

摘要： 欧洲XFEL将在SP（短脉冲）模式下以17.5 GeV的额定能量运行，具有0.65 ms长的束团序列和10 Hz的重复率。 多年来一直在讨论将直线加速器升级为CW（连续波）或LP（长脉冲）模式的可能性，相应的电子束能量会降低。 最近在专门的研发计划中取得的成功使我们能够预测这种升级在可预见的未来在技术上的可行性。 其中一个挑战是在CW和LP模式下实现亚埃级的FEL运行。 在本文中，我们对欧洲XFEL在CW和LP模式下在硬X射线区域的可能运行进行了初步分析，分别对应7 GeV和10 GeV的能量。 我们考虑了基线XFEL波荡器以及一个周期减小的新波荡器中的激光作用。 我们表明，在合理的电子束质量要求下，在亚埃级范围内实现基频激光是可能的。 作为在短波长下产生高亮度光子束的一种选择，我们还考虑了最近引起广泛关注的谐波激光。 显示英文摘要

摘要： The European XFEL will operate nominally at 17.5 GeV in SP (short pulse) mode with 0.65 ms long bunch train and 10 Hz 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 since 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-Angstrom 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 the energies of 7 GeV and 10 GeV, 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 sub-Angstrom regime. As an option for generation of brilliant photon beams at short wavelengths we also consider harmonic lasing that has recently attracted a significant attention.