Future applications of science with synchrotron radiation and free-electron lasers in Europe

Abstract

On 16±17 March 2001, many scientists from synchrotron and freeelectron laser (FEL) facilities met at the ESRF site in Grenoble for a workshop on `Future Applications of Science with Synchrotron Radiation and Free-Electron Lasers in Europe'. The workshop was organized following several suggestions that emerged during the 2000 meeting of the European Round Table (RT) for Synchrotron Radiation and Free Electron Lasers in Karlsruhe. The main purpose was an open and broad discussion on the development of this ®eld in Europe over the next 10±20 years. The objectives were a clari®cation of the possible development lines after the recent approval of the Soleil and Diamond projects, and, if possible, a consensus on priorities. The participants included experts on accelerators and X-ray sources from Europe and the USA, and a limited number of X-ray users. A school on the same theme at Les Houches preceded the workshop in Grenoble. Two days of presentations and discussions were extremely helpful in clarifying the foreseeable technical development avenues. They also revealed several important points of broad consensus that could provide the basis for a realistic and effective long-term strategy in Europe. The most relevant facts emerging from the workshops were the following: (i) Synchrotron radiation and FEL facilities have been exceedingly successful in the previous 15 years, both in Europe and worldwide: (a) The development of many major facilities did not encounter any failure; (b) On the contrary, all projects signi®cantly exceeded the promised performances with no additional cost; (c) The number of users is still rapidly growing; all facilities are largely oversubscribed, in many cases to unacceptable levels; (d) The users spectrum is much broader and more diversi®ed than 15 years ago, with a strong and rapidly expanding life-science component; (e) The domain has produced its ®rst Nobel prize and many other top-level awards. Although the symposium was focused on X-ray and UV sources, one should note that FEL facilities operating in the IR are extremely successful and serve a large and active community of users. This remark applies, in particular, to the CLIO and FELIX facilities in Europe. (ii) The present leading source technology based on storage rings has not yet reached its limits. Substantial improvements are still possible as far as stability, brightness, ux, coherence and polarization are concerned. (iii) Novel technologies are emerging thanks to intense R&D, primarily in Europe and the USA. All of them are based on LINACs rather than on storage rings. LINAC-based X-ray emission techniques can be divided into two broad subsets: (a) Energy-recover LINACs (ERLs). This has been de®ned as an `evolutionary' technology, which could potentially extend the performances of storage-ring-based sources. (b) X-ray free-electron lasers (X-FELs) based on the SASE (selfampli®ed spontaneous emission) mechanism. This is a `revolutionary' rather than evolutionary technology, whose main objective is to produce ultrashort (100±200 fs) X-ray pulses with extremely high peak brightness and ux and very high coherence. The R&D for ERLs is primarily centred in the USA, with an important contribution from Russia. The R&D for X-FELs is shared between Europe (primarily HASYLAB in Germany) and the USA (primarily Argonne and Stanford). The workshop stressed, in general, the scienti®c relevance of the new X-ray production technologies: (i) The scienti®c case for pushing the storage-ring technology to the limit is well established, touching diverse domains of physics, chemistry, materials science, biology and other areas. (ii) Similar considerations provide a strong scienti®c case for ERLs, that would constitute to some extent a continuation of the storage-ring technology. (iii) A strong scienti®c case is also emerging for X-FELs, primarily based on the concentration of unprecedented X-ray ux into very short pulses. The X-FELs applications are largely complem