X radiation sources based on accelerators

Abstract

Light sources based on accelerators aim at producing very high brilliance coherent radiation, tuneable from the infrared to X-ray range, with picosecond or femtosecond light pulses.The first synchrotron light sources were built around storage rings in which a large number of relativistic electrons produce "synchrotron radiation" when their trajectory is subjected to a magnetic field, either in bending magnets or in specific insertion devices (undulators), made of an alternating series of magnets, allowing the number of curvatures to be increased and the radiation to be reinforced.These "synchrotron radiation" storage rings are now used worldwide (there are more than thirty), and they simultaneously distribute their radiation to several tens of users around the storage ring.The most effective installations in term of brilliance are the so-called 3rd generation synchrotron radiation light sources. The radiation produced presents pulse durations of the order of a few tens of ps, at a high rate (of the order of MHz); it is tuneable over a large range, depending on the magnetic field and the electron beam energy and its polarisation is adjustable (in the VUV-soft-X range). Generally, a very precise spectral selection is made by the users with a monochromator.The single pass linear accelerators can produce very short electron bunches (∼ 100 femtosecond). The beam of very high electronic density is sent into successive undulator modules, reinforcing the radiation's longitudinal coherence, produced according to a Free Electron Laser (FEL) scheme by the interaction between the electron bunch and a light wave. The very high peak brilliance justifies their designation as 4th generation sources. The number of users is smaller because an electron pulse produces a radiation burst towards only one beamline. Energy Recovery Linacs (ERL) let the beam pass several times in the accelerator structures either to recover the energy or to accelerate the electrons during several turns, and thus provide subpicosecond beams for a greater number of users.A state-of-the-art of X sources using conventional (and not laser plasma based) accelerators is given here, underlying the performance already reached or forecast and the essential challenges.

Synchrotron ultrafast techniques for photoactive transition metal complexes

“…The availability in the near future of hard X-ray FEL facilities [220][221][222][223][224][225][226][227][228][229] will represent an impressive improvement in the potentialities of both TR-XSS and TR-XAS techniques, both in terms of photon flux (moving from 10 6 to 10 12 photons per electron bunch) and ultimate time resolution (the typical bunch width moving from 10 −10 down to 10 −14 s). The development of adequate measurement techniques and data-acquisition schemes for measuring X-ray scattering/absorption data at FELs will be essential to derive full benefit from these new-generation photon sources.…”

“…However, for the time being, this apparently simple solution is not feasible since, for q > 7 Å −1 , the experimental q I(q) data are dominated by noise and the interval 4 Å −1 < q < 7 Å −1 is too limited for extracting any reliable structural information. This situation will change in the future, with the availability of hard X-ray free electron lasers (FELs) [220][221][222][223][224][225][226][227][228][229], where the number of photons per electron pulse will reach values as high as 10 12 , compared with 10 6 for third-generation synchrotron radiation sources.…”

Strategies towards a compact XUV free electron laser adopted for the LUNEX5 project

“…In a FEL, synchrotron radiation is emitted by the relativistic charged particles submitted to the periodic permanent magnetic field (amplitude B o , period λ o ) generated by an undulator [7,8]. The radiation from a planar undulator creating a vertical sinusoidal field is emitted at the wavelength λ, so-called resonance wavelength, and its odd harmonics of order n, with a linear horizontal polarisation λ, = λ o (1 + K 2 /2)/ 2nγ 2 with the deflexion parameter K = 0.94 λ o (cm) B o (T) and γ the relativistic factor of the electrons.…”

“…Fifty years after the discovery of laser [1,2] and nearly 40 years after the first free electron laser (FEL) [3] in the infra-red, X-ray FELs [4][5][6][7] appear as a unique tuneable intense coherent elements in the landscape of short wavelength light sources (among synchrotron radiation [8], high order harmonic generation in gas (HHG) [9,10] or on solid targets [11], X-ray laser [12]). …”

Development of a 2 m Pr2Fe14B Cryogenic Permanent Magnet Undulator at SOLEIL

“…Short period and small gap undulators are used to produce hard X rays in intermediate energy storage rings of synchrotron radiation facilities [1]. Short period undulators enable short wavelength FEL at low beam energy, with decreased gain length, thus allowing much more compact and less costly FEL systems [2].…”