Abstract
Output stability of an XFEL setup is naturally linked to the stability of the linac rf system through the bunch compression process. This fact leads to very tight tolerances for rf amplitudes and phases. We propose a feedback scheme using an optically modulated electron beam where the compression factor is self-stabilized due to the action of longitudinal space charge fields. Our scheme allows loosening rf tolerances by an order of magnitude. Alternatively, for the same variations of rf parameters, stability of the FEL pulse energy could be improved by an order of magnitude.
Highlights
Free-electron lasing at wavelengths shorter than the ultraviolet can be achieved with a single-pass, high-gain FEL amplifier
Because of lack of powerful, coherent seeding sources, short-wavelength FEL amplifiers work in the so-called self-amplified spontaneous emission (SASE) mode, where the amplification process starts from shot noise in the electron beam [1,2,3]
Intrinsic fluctuations are due to the start-up from shot pnoffiffiiffiffisffiffieffiffi.ffiffiffiffiIffiffinffi the exponential gain regime they scale as lcoh=z, where lcoh is the FEL coherence length and z is rms bunch length
Summary
Free-electron lasing at wavelengths shorter than the ultraviolet can be achieved with a single-pass, high-gain FEL amplifier. Slow drifts can be compensated by a beam-based slow feedback, as it is done at FLASH, a precursor of the European XFEL, where coherent diffraction radiation produced by compressed bunches is used to regulate the phase of accelerating module upstream of the bunch compressor. In this paper we propose a scheme that allows one to dramatically reduce the sensitivity of the FEL pulse energy on the rf parameters variation by developing, in practice, a single-bunch feedback. Such feedback can only be based on collective fields of each individual bunch. The concept has some similarities with a current-enhanced SASE scheme [12], there are essential differences
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
