SYNCHROTRON RADIATION IN 2003

Sandra Biedron, Argonne National Laboratory and MAX-Laboratory
Patrick O’Shea, University of Maryland
Alan Todd, Advanced Energy Systems, Princeton, New Jersey

Accelerator-based synchrotron radiation light sources have become indispensable tools for an extraordinarily wide spectrum of user research and development. New projects under construction promise to greatly expand the brightness and shorten the radiation pulse length for the users.

The synchrotron radiation community presently employs many so-called “third-generation” light sources, including hard x-ray sources like the Advanced Photon Source (APS) [1] at Argonne National Laboratory (ANL), USA, the European Synchrotron Radiation Facility (ESRF) [2] in Grenoble, France, SPring-8 [3] in Harima Science Garden City, Japan, and the Swiss Light Source [4] in Villigen. There are also a number of operational VUV and soft x-ray light sources that include MAX-Laboratory [5] in Sweden, BESSY II [6] in Berlin, and the National Synchrotron Light Source (NSLS) [7] at Brookhaven National Laboratory (BNL). Such sources are currently capable of producing photons with energies up to 100 keV at peak spectral brightnesses of 1 x 10²³ photons.s-1 (0.1% bandwidth)-1 x mm-2 x mrad^-2. In the figure below, the peak and average spectral brightness versus wavelength are shown for all generations of synchrotron light sources, including the new “fourth-generation” sources, DESY-TTF and the SLAC-LCLS.

Average and Peak Spectral Brightness as a Function of Wavelength for all Generations of Synchrotron Light Sources [8]

These International light sources produce high-brilliance photon beams that are used by scientists and engineers from diverse research and development communities — for instance: biology, chemistry, physics, material science, environmental science, medicine, geophysical, and planetary science. These “user” communities utilize light sources to explore the structure and dynamics of materials. Recent highlights of this research can be found at the following sites:

www.aps.anl.gov/apsimage/cobrafrnt.html
www.aps.anl.gov/
www.esrf.fr/News/FrontNews/ PressRelease_23-06-2003/
www-als.lbl.gov/als/science/sci_archive/ zinc.html
nslweb.nsls.bnl.gov/nsls/sci&tech/

First-generation light sources were electron synchrotrons and storage rings that were built for other purposes (e.g., high-energy and nuclear physics), but whose bending magnet radiation was parasitically used by synchrotron radiation “users.” This radiation covered many wavelength regimes due to the nature of the bending magnet emission and had rather large photon source size because the electron beam emittance in such older machines was large. Further, the devices were neither originally intended nor ideal for synchrotron radiation applications. Second-generation machines that employ bending magnets as the primary source of synchrotron radiation are specifically dedicated to synchrotron radiation users. Beam emittance levels were designed to be smaller in order to provide users with smaller source size and thus higher brilliance. Third-generation machines, the current standard, are also dedicated to synchrotron radiation users, but were additionally designed to accommodate many so-called “insertion devices” such as wiggler and undulator magnets. Since these ‘insertion devices” wiggle/undulate the electron beam back and forth through multiple bending magnet fields, these magnets generate a higher brightness photon beam than bending magnets alone. Undulator magnets have the additional feature that they generate narrow spectral lines and this enhances the overall photon brilliance of the machine. Today, there are 43 operational second and third-generation synchrotron light sources with more than 15 third-generation facilities presently under construction.

Although all of these short-wavelength, high-brightness machines have proven successful in discovering previously inaccessible structural information in a variety of scientific disciplines, the ability to obtain dynamical (temporal) information on the subpicosecond time scale, particularly in relation to the biological sciences, is not presently possible. This is because the current machines are limited to time scales longer than ~10 ps. To obtain dynamical information at shorter time scales one must produce and utilize x-rays in the 1-C-wavelength regime that have pulse lengths on the order of a few tens of femtoseconds. It is also preferable that these pulses are fully coherent longitudinally in order to insure the delivery of a narrow spectral bandwidth, and that the source is diffraction-limited with full transverse coherence. Finally, there is great interest in the generation of peak intensity and peak brightness that is many orders of magnitude higher than is available today from existing machines. This will enhance spatial resolution and may even lead to the possibility of determining single molecule structures. This promise has spawned a number of international construction projects [9] and numerous proposals. Two of the largest projects, based upon self-amplified spontaneous emission (SASE) free-electron laser (FEL) technology, are the Linac Coherent Light Source [10] that will operate at 1.5 C at the Stanford Linear Accelerator Center, and the DESY FEL [11] in Hamburg, Germany, that is designed to operate at 1 C.

Other complimentary “light source” development includes Energy Recovery Linacs (ERL) [12, 13, 14], x-ray laser development [15] and high-harmonic generation using traditional lasers [16]. The ERL concept in particular has recently generated tremendous community excitement and spawned a plethora of projects and proposal all around the world.

The number of synchrotron radiation “users” is constantly on the rise and the number of machines proposed and under construction is increasing year by year. Synchrotron radiation is one of the most robust and evolving analytical tools in the world and it has continued to benefit society. Examples that demonstrate this enormous social value are new designer drugs that have been brought to market by the pharmaceutical industry due to protein crystallography research, and computer development including semiconductor performance and patterning and giant magnetoresistance for storage media.

[1] www.aps.anl.gov
[2] www.esrf.fr
[3] www.spring8.jp
[4] sls.web.psi.ch/view.php/about/index.html
[5] www.maxlab.lu.se
[6] www.bessy.de
[7] nslsweb.nsls.bnl.gov/nsls/Default.htm
[8] Courtesy of the Advanced Photon Source.
[9] See, for example, the Proceedings of the 2002 Free-Electron Laser      Conference, Elsevier.
[10] www-ssrl.slac.stanford.edu/lcls/
[11] xfel.desy.de/
[12] www.jlab.org/FEL/
[13] erl.chess.cornell.edu
[14] www.4gls.ac.uk/
[15] See, for example, the proceedings of the 8th International Conference
       on X-ray Lasers Aspen, Colorado, 2002 AIP conference
       Proceedings, 641.
[16] See, for example, Proceedings of the Workshop on the Generation
       and Uses of Soft X-ray Coherent Pulses, MAX-Laboratory 2001.

Sandra Biedron can be reached at the Argonne National Laboratory, 9700 S. Cass Ave., Bldg. B4208, Lemont, IL 60439-4803; Phone: +1 630 252-1162; E-mail: biedron@aps.anl.gov. Patrick O'Shea can be reached at the University of Maryland, College Park, MD 20742-3511; Phone: +1 301 405 4952; Fax: +1 301 314 9437; E-mail: poshea@umd.edu. Alan Todd can be reached at Advanced Energy Systems, P.O. Box 7455, 501 Forrestal Road, Suite 316, Princeton, NJ 08543-7455; Phone: +1 609 514-0316; Fax: +1 609 514-0318; E-mail: alan_todd@mail.aesys.net.