Pascal Elleaume

Review of third and next generation synchrotron light sources

Synchrotron radiation (SR) is having a very large impact on interdisciplinary science and has been tremendously successful with the arrival of third generation synchrotron x-ray sources. But the revolution in x-ray science is still gaining momentum. Even though new storage rings are currently under construction, even more advanced rings are under design (PETRA III and the ultra high energy x-ray source) and the uses of linacs (energy recovery linac, x-ray free electron laser) can take us further into the future, to provide the unique synchrotron light that is so highly prized for todays studies in science in such fields as materials science, physics, chemistry and biology, for example. All these machines are highly reliant upon the consequences of Einsteins special theory of relativity. The consequences of relativity account for the small opening angle of synchrotron radiation in the forward direction and the increasing mass an electron gains as it is accelerated to high energy. These are familiar results to every synchrotron scientist. In this paper we outline not only the origins of SR but discuss how Einsteins strong character and his intuition and excellence have not only marked the physics of the 20th century but provide the foundation for continuing accelerator developments into the 21st century.

A three-dimensional magnetostatics computer code for insertion devices.

RADIA is a three-dimensional magnetostatics computer code optimized for the design of undulators and wigglers. It solves boundary magnetostatics problems with magnetized and current-carrying volumes using the boundary integral approach. The magnetized volumes can be arbitrary polyhedrons with non-linear (iron) or linear anisotropic (permanent magnet) characteristics. The current-carrying elements can be straight or curved blocks with rectangular cross sections. Boundary conditions are simulated by the technique of mirroring. Analytical formulae used for the computation of the field produced by a magnetized volume of a polyhedron shape are detailed. The RADIA code is written in object-oriented C++ and interfaced to Mathematica [Mathematica is a registered trademark of Wolfram Research, Inc.]. The code outperforms currently available finite-element packages with respect to the CPU time of the solver and accuracy of the field integral estimations. An application of the code to the case of a wedge-pole undulator is presented.

Computing 3D magnetic fields from insertion devices

A 3D magnetostatics computer code optimized for Undulators and Wigglers is described. The code uses a boundary integral method and makes extensive use of analytical expressions for the field and field integrals along a straight line. The code outperforms currently available finite element packages in the area of simple data input, CPU time of the solver and accuracy reached for the estimation of field integrals. It is written in C++ and takes advantage of object-oriented programming. The code is interfaced to Mathematica. Pre- and post-processing of the field data is done in the Mathematica Language. It has been extensively benchmarked with respect to a commercial finite element code. All ESRF Insertion Devices built during the last 4 years have been designed using this code or an older version.

A flexible planar/helical undulator design for synchrotron sources

Abstract This paper presents a new design for a helical permanent-magnet undulator. It can be easily implemented on a synchrotron source without engineering difficulty. The effect on the electron beam is discussed and found to be acceptable. Flux and brilliance are similar to those from conventional planar undulators. Heat load can be considerably reduced which makes it a very attractive device for the new generation of 6–8 GeV light sources. On the ESRF, very brilliant helical radiation is expected in the 0.5 to 10 keV photon energy range.

Phase analysis and focusing of synchrotron radiation

Abstract High accuracy calculations of synchrotron radiation (SR) emitted by a relativistic electron show that the phase of the frequency domain electric field of SR differs from the phase of radiation of a virtual point source. These differences may result in the reduction of focusing efficiency of diffraction-limited SR, if the focusing is performed by conventional optical components optimised for point sources. We show that by applying a phase correction locally, one may transform the phase of SR electric field at a desired polarisation to that of a point source. Such corrections are computed for undulator radiation (planar and helical) and bending magnet radiation (central part and edges). The focusing of the corrected SR wavefront can result in the increase of peak intensity in the focused spot up to several times compared to the focusing without correction. For non-diffraction-limited radiation, the effect of the phase corrections is reduced. Due to this reason, the use of the proposed phase corrections in existing electron storage rings is essentially of interest in the photon energy range from infrared to VUV. All numerical calculations discussed in the paper were performed by means of the computer code SRW.

Generation of various polarization states from insertion devices: A review

Most insertion devices (IDs) which have been built so far are planar with the field in the vertical plane. They are the easiest to design, and they fit well to the narrow vertical aperture available on storage rings. As bending magnets, these IDs generate essentially horizontally polarized radiation. Recently, several new proposals and prototypes have been produced in order to generate different polarization states. The Stokes decomposition of the radiation from these devices is given versus photo energy. This discussion is illustrated by taking the European Synchrotron Radiation Facility (ESRF) conditions in the hard x‐ray range.

End field structures for linear/helical insertion devices

The field integral tolerances required on third generation synchrotron sources are of the order of 10-20 Gcm in the whole gap range of an insertion device. This can be achieved without electromagnet correction by a proper magnetic design of the field termination. The paper describes several such end field terminations to be used for planar undulators. A new termination valid for an APPLE II undulator is presented which produces a field integral variation smaller than 20 Gcm for any useful setting of the magnetic gap and phase. It compares quite favorably with other known type of terminations.

A high-resolution silicon drift chamber for X-ray spectroscopy

Abstract Silicon drift chambers are very attractive detectors for X-ray fluorescence excitation spectroscopy (between 1 and 15 keV) due to their ultra low capacitance (typically 200 fF) which is also independent of the detector active area. High-energy resolution can be obtained while preserving a large solid detection angle. We have designed a new silicon drift chamber for X-ray spectroscopy. The active area is 1 cm 2 , the measured energy resolution is 143 eV FWHM for the Kα line of Mn (5.89 keV). This detector has also been used to characterize the spectral line shape of the emission of a standard planar undulator installed on the ESRF 6 GeV storage ring.

Refractive lenses for high-energy x-ray focusing

Focusing of hard X-rays by refraction has been a long time been considered as unfeasible due to strong absorption and weak refraction of X-rays in matter. Recently it has been shown that compound refractive lenses can overcome the problem. It was demonstrated that the best candidates for lenses are low Z, high density materials. Linear and 2D lenses from aluminum, boron carbide, beryllium, pyrographite and Teflon were produced and tested. Focusing of 2 - 3 microns was achieved at an energy range from 9 to 30 keV. Compound refractive lenses have low sensitivity to heatload and are extremely well suited for focusing of undulator radiation. Two-plane focusing lenses have been optimized, built and installed in the white beam of the undulator on the machine diagnostic beamline of the ESRF to be used as an X-ray emittance diagnostic. The future potentials of the refractive lenses will be discussed as well.

Insertion devices for the new generation of synchrotron sources : a review (invited)

A review is made of the principal characteristics of the undulators and wigglers for the new generation of synchrotron sources. The main characteristics of the radiation are summarized followed by the effect on the stored electron beam. The technology of IDs is presented. Finally exotic IDs designed to produce circularly polarized radiation are discussed.