Abstract
In the field of beam physics, two frontier topics have taken center stage due to their potential to enable new approaches to discovery in a wide swath of science. These areas are: advanced, high gradient acceleration techniques, and x-ray free electron lasers (XFELs). Further, there is intense interest in the marriage of these two fields, with the goal of producing a very compact XFEL. In this context, recent advances in high gradient radio-frequency cryogenic copper structure research have opened the door to the use of surface electric fields between 250 and 500 MV m−1. Such an approach is foreseen to enable a new generation of photoinjectors with six-dimensional beam brightness beyond the current state-of-the-art by well over an order of magnitude. This advance is an essential ingredient enabling an ultra-compact XFEL (UC-XFEL). In addition, one may accelerate these bright beams to GeV scale in less than 10 m. Such an injector, when combined with inverse free electron laser-based bunching techniques can produce multi-kA beams with unprecedented beam quality, quantified by 50 nm-rad normalized emittances. The emittance, we note, is the effective area in transverse phase space (x, p x /m e c) or (y, p y /m e c) occupied by the beam distribution, and it is relevant to achievable beam sizes as well as setting a limit on FEL wavelength. These beams, when injected into innovative, short-period (1–10 mm) undulators uniquely enable UC-XFELs having footprints consistent with university-scale laboratories. We describe the architecture and predicted performance of this novel light source, which promises photon production per pulse of a few percent of existing XFEL sources. We review implementation issues including collective beam effects, compact x-ray optics systems, and other relevant technical challenges. To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine—including the imaging of virus particles—which may profit from this new model of performing XFEL science.
Highlights
The x-ray free electron laser (XFEL) is a transformative instrument, producing coherent x-ray pulses with peak brightness 10 orders of magnitude greater than preceding approaches [1]
To illustrate the potential of such a light source to fundamentally change the current paradigm of XFELs with their limited access, we examine possible applications in biology, chemistry, materials, atomic physics, industry, and medicine – including the imaging of virus particles – which may profit from this new model of performing XFEL science
The principles behind an ultra-compact XFEL have been presented here, as well as the details of how these principles are manifested in the beam and radiation physics involved, and the advanced technologies and methods – such as machine learning – employed
Summary
The x-ray free electron laser (XFEL) is a transformative instrument, producing coherent x-ray pulses with peak brightness 10 orders of magnitude greater than preceding approaches [1]. Given the decade of dedicated research relevant to components of the 5th generation light source, this integrated approach can be crystallized; the concept for an ultra-compact x-ray FEL presented here utilizes a recipe based on dramatic advances in the critical component ingredients of the FEL, with the key aspect being the use of an electron beam with unprecedentedly high six-dimensional brightness. On this basis, we propose here a new class of UC-XFEL sources that can be implemented at the university level, at size and cost diminished more than ten-fold. Through this discussion it is shown that a highly credible path to realizing this paradigm-changing instrument, the ultra-compact x-ray free-electron laser, exists
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