Abstract
We present the experimental results of femtosecond slicing an ultrarelativistic, high brightness electron beam with a collimator. In contrast to some qualitative considerations reported in Phys. Rev. Lett. 92, 074801 (2004), we first demonstrate that the collimation process preserves the slice beam quality, in agreement with our theoretical expectations, and that the collimation is compatible with the operation of a linear accelerator in terms of beam transport, radiation dose, and collimator heating. Accordingly, the collimated beam can be used for the generation of stable femtosecond soft x-ray pulses of tunable duration, from either a self-amplified spontaneous emission or an externally seeded free electron laser. The proposed method also turns out to be a more compact and cheaper solution for electron slice diagnostics than the commonly used radio frequency deflecting cavities and has minimal impact on the machine design.
Highlights
In response to the interest of the community of synchrotron radiation and free electron laser (FEL) users in ever shorter x-ray pulses [1,2] and flexible parameters of the output photon beam [3,4], we propose an electron beam collimation system for the generation of femtosecond soft x-ray pulses with tunable duration from a free electron laser
We demonstrate that the beam collimation is compatible with the machine operation both in terms of radiation dose production and beam diagnostics, i.e. trajectory control in the beam delivery system
Measurements of the beam slice optical parameters supported by an analytical evaluation, demonstrate that the collimator transverse wakefield does not degrade the emittance of the collimated beam, which can be devoted to FEL production as well as to slice diagnostics
Summary
In response to the interest of the community of synchrotron radiation and free electron laser (FEL) users in ever shorter x-ray pulses [1,2] and flexible parameters of the output photon beam [3,4], we propose an electron beam collimation system for the generation of femtosecond soft x-ray pulses with tunable duration from a free electron laser. To the work presented in [5], the method relies on the linear correlation between the particle energy and its longitudinal coordinate along the bunch established via upstream off-crest radio frequency (rf) acceleration. Such a beam manipulation is regularly implemented in modern linac-based FELs for bunch length compression in a magnetic chicane, in order to increase the electron bunch peak current and eventually enhance the FEL process [6,7,8]. In Eq (1) we used the following notation: ÁtFWHM is the full-width-half-maximum (FWHM) duration of the collimated beam, Áx is the collimator halfaperture, x is the rms beam size at the collimator that includes the particle chromatic motion, and t;f is the final rms bunch duration after the chicane, if the collimator were removed
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