For more than a decade free-electron lasers (FELs) have been in operation, providing scientists from many disciplines with the benefits of ultrashort, nearly transversely coherent radiation pulses with wavelengths down to the Ångstrom range. If no further techniques are applied, the FEL will only amplify radiation from the stochastic distributed electron density in the electron bunch. Contemporary developments aim at producing stable and single-mode radiation by preparing an electron bunch with favorable longitudinal electron density distributions using magnets and conventional laser pulses (seed), hence the name “seeding.” In recent years, short wavelength FELs at high electron beam energies and high repetition rates were proposed and built. At those repetition rates, an external seed with sufficient power to manipulate the electron beam cannot be provided by present state-of-the-art laser systems, thus no external seeding scheme could be applied yet. In this paper, we present ways to seed FELs to generate short wavelength radiation at high repetition rates, making use of tested electron beam manipulation schemes. For our parameter study, we used the parameters of FLASH, the free-electron laser in Hamburg. First simulations are presented, showing the feasibility of the method proposed.

中文翻译：

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从高重复率的自由电子激光器产生稳定辐射的新方法

十多年来，自由电子激光器（FEL）一直在运行，它为许多学科的科学家提供了超短，近乎横向相干的辐射脉冲，其波长低至Ångstrom范围。如果不应用其他技术，则FEL只会放大来自电子束中随机分布的电子密度的辐射。当代的发展旨在通过使用磁体和传统的激光脉冲（种子）制备具有良好纵向电子密度分布的电子束来产生稳定的单模辐射，因此被称为“种子”。近年来，提出并建立了具有高电子束能量和高重复率的短波长FEL。以这些重复率，现有的最新激光系统无法提供具有足够功率来操纵电子束的外部种子，因此尚不能应用外部种子方案。在本文中，我们介绍了使用经过测试的电子束操纵方案为FEL注入种子以产生高重复率的短波长辐射的方法。在参数研究中，我们使用了FLASH（汉堡的自由电子激光器）的参数。首先进行仿真，表明所提出方法的可行性。汉堡的自由电子激光器。首先进行仿真，表明所提出方法的可行性。汉堡的自由电子激光器。首先进行仿真，表明所提出方法的可行性。