Abstract
At the SASE-FEL user facilities FLASH and European XFEL, superconducting TESLA type cavities are used for acceleration of the driving electron bunches. The high achievable duty cycle allows for operating with long bunch trains, hence considerably increasing the efficiency of the machine. However, multibunch free electron lasers (FEL) operation requires longitudinal and transverse stability within the bunch train. The purpose of this work is to investigate the intra-bunch-train transverse dynamics at FLASH and European XFEL. Key relationships of superconducting rf cavity operation and the resulting impact on the intrabunch-train trajectory variation are described. The observed trajectory variation during multibunch user runs at FLASH is analyzed and related to both, intrabunch-train variations of the rf and the following impact on the multibunch FEL performance.
Highlights
Single pass free electron lasers (FEL) are state-of-the-art technology to generate high brilliance self-amplified spontaneous emission (SASE) radiation [1], which is a powerful tool used for fundamental and applied research in many different fields of science
At the FEL user facilities FLASH (Free-Electron Laser in Hamburg) [2,3] and European XFEL (European X-Ray Free-Electron Laser) [4,5,6], the driving electron bunches are accelerated in superconducting radiofrequency resonators based on the TESLA (TeV-Energy Superconducting Linear Accelerator) [7] technology
Please note that all analyzed data is taken from user runs with stable machine operation, after deliberate SASE tuning
Summary
Single pass free electron lasers (FEL) are state-of-the-art technology to generate high brilliance self-amplified spontaneous emission (SASE) radiation [1], which is a powerful tool used for fundamental and applied research in many different fields of science. At the FEL user facilities FLASH (Free-Electron Laser in Hamburg) [2,3] and European XFEL (European X-Ray Free-Electron Laser) [4,5,6], the driving electron bunches are accelerated in superconducting radiofrequency (rf) resonators based on the TESLA (TeV-Energy Superconducting Linear Accelerator) [7] technology. Their main advantage over normal conducting cavities are the low Ohmic losses resulting in the possibility to combine high accelerating gradients with a high duty cycle, long rf pulse structure.
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