- Email: [email protected]
The European synchrotron radiation facility
Nuclear Instruments and Methods m Physics Research A282 (1989) 375-379 North-Holland, Amsterdam
375
THE EUROPEAN SYNCHROTRON RADIATION FACILITY Ruprecht HAENSEL ESRF, F-38043 Grenoble Cedex, France
This paper reviews the status of the ESRF in Grenoble. The construction has started at the beginning of 1987, the first beam is expected m 1993 1. Historical introduction After many years of preparation initially done by working groups of the European Science Foundation, ESF, continued by the European Synchrotron Radiation Project (ESRP) group working under Buras and Tazzari [1], and finally concluded by the ESRF team in Grenoble, the governments of the countries participating in the ESRF (France, the Federal Republic of Germany, the United Kingdom, Italy, Spain, Switzerland, and the four Nordic Countries Denmark, Finland, Norway and Sweden) * have decided in December 1987 to start the construction of the European Synchrotron Radiation Facility ESRF in Grenoble. The goal of the ESRF is to build, operate and exploit a synchrotron radiation source in the hard X-ray region with characteristics not reached so far with existing synchrotron radiation sources . The ESRF team started its work in April 1986 (with R. Haensel as Director General, J.L. Laclare as Project Director, Gottfried MiAhaupt as Deputy Project Director, and M. Altarelli and A. Miller as Directors of Research) . Growing gradually to 70 persons at the present time, it has made proposals for the selection of the final site, the main parameters of the machine and the beam lines, and for the budget during the construction phase (6.5 years) and the first (4.5) years of the operation phase. The details of this work are published in the Foundation Phase Report [2]. The Foundation Phase Report was submitted to the ESRF Council, who accepted it as the main planning document for the eleven years to come.
* Note added in proof : In the mean time Belgium also joined the ESRF. 0168-9002/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
2. Source parameters 2.1 . Storage ring energy
The storage ring energy was chosen to fulfil the requirement for short-wavelength radiation by undulators. In particular, the production of a high flux in the fundamental of an undulator at 0.86 a.u. (14 .4 keV) was specified . The performance of undulators is, however, very dependent on the magnetic period and consequently on the minimum gap between the magnet poles. A nominal energy of 5 GeV, associated with a 10 mm minimum gap, was originally proposed in the Green Book [1] to meet the same requirements . It was agreed, however, that at 5 GeV such a performance would set critical limits to the beam lifetime and that the tunability would be very small. In fact, the Green Book [1] machine was already designed to reach 6 GeV . It must be pointed out that, in addition, the 10 mm gap option has several consequences that may affect operation of the storage ring: - The beam stay-clear is reduced to 10 mm or less, which is considerably smaller than the aperture defined for the rest of the machine . Therefore, the beam lifetime could be affected . - As a good vacuum is fundamental for the storage ring, it is not desirable to have the undulators under vacuum since they account for 14% of the circumference (about 120 m). This would obviously be detrimental to machine impedance (due to strong electromagnetic interactions between the beam and its environment) and would limit the stored current . - The acceptance of the machine is sensitive to the nonlinear effects introduced by small gap undulators. This could again affect the beam lifetime . In order to overcome these disadvantages and to ease the initial operation of the source, the following strategy has been adopted : - a beam stay-clear of 15 mm; - a rigid vacuum chamber ; and - undulators with a 20 mm minimum gap outside vacuum. I. SOURCES
376
R. Haensel / The European Synchrotron Radiation Facility
As a consequence, nominal machine energy was raised to 6 GeV to reach the requirement at 0.86 a.u . This offers a good safety margin for undulator design and larger overall tunability : for instance, the 1-2 a.u . range can be covered by a single undulator. Once sufficient knowledge of the machine's behaviour has been acquired, it might be possible to decrease the undulator gap to 10 mm and reach the 0.62 a.u . (20 keV) range later on . From a technical point of view, at 6 GeV, the specifications are easier to achieve and this will inevitably lead to a faster commissioning of the machine, followed by smoother operation. The scientific case for a 6 GeV machine, rather than a 5 GeV machine, is that better service can be provided for the majority of users in the range from 5 to 15 keV due to a larger overall tunability of the insertion devices. Increasing the potential machine capability in this way is probably a good investment for the future . The only disadvantage is that dipole sources get harder (20 keV) . To compensate this effect 16 "soft" dipoles radiating at 10 keV will be installed.
Table 2 The beam dimensions at source locations
2 .2 Storage ring lattice and photon sources
Rms beam size
Wiggler
Undulator
a [mm] a' [inrad] a [mm] a' [mrad]
Bending magnet
0 .069 0 .089 0 .047 0 .013
0 .406 0 .015 0 .084 0 .007
0 .160 0 .137 0 .129 0.005
The potential performance of the storage ring is primarily determined by the lattice design . In line with the Green Book [1] proposal, we retained the same type of magnetic structures : a Chasman-Green lattice with, nevertheless, substantial improvements as far as the beam emittance, sensitivity to errors and flexibility are concerned. At 6 GeV the nominal horizontal emittance is maintained at 7 rim cad. The circumference is increased to 844.39 m. There are thirty-two 6 .34 m long straight sections, identically equipped with triplets at both ends, Phot/s/mm2/mrad2/0 1 1 E+20 , 80 mm
50 mm
Table 1 The proposed parameters for the ESRF storage ring Nominal beam energy Circumference Number of bunches Beam current Horizontal emrttance Vertical emittance Beam lifetime Number of straight sections Length of straight sections Radiation sources
6 GeV 844 39 m 1-992
100 mA multibunch mode 7 .5 mA single-bunch mode 7 rim cad 0.6 rim cad 10 h 32 (29 usable for insertion devices) 6 34 m Undulators (14.4 keV in the fundamental) Wigglers Wavelength shifters Bending magnet (at 10 and 20 keV)
that are tunable over a wide range and can either accommodate wigglers or undulators . Three of these straight sections will be used for machine utilities: one for injection and two for accelerating cavities ; 29 remain available for insertion devices. In addition, 28
35 mm
1 E+18
1 E+16
Undulators gap =20 mm L=5m ( 1 st & 3rd harmonic ) -------------------------- ;_ .__ .__..___ ..____.._ .____.
100
Photon Energy [keV] Fig. 1 Brilliance from bending magnets and insertion devices.
1000
R Haensel / The European Synchrotron Radiation Facihty beam ports will deliver radiation from bending magnets . Twelve ports will be open to the 20 keV radiation from the main dipoles. The remaining 16 beam ports will accept a 10 mrad fan split in two equal parts : 5 mrad from "soft" dipoles at 10 keV, and 5 mrad of harder radiation from the main dipoles at 20 keV . The proposed parameters for the ESRF Storage Ring resulting from the scientific requirements are summarized in table 1 . The beam dimensions at source locations are summarized in table 2 . 2 .3. Strategy for insertion devices and performance In the inventory of insertion devices, the majority (over 2/3) will be undulators using permanent magnets, which are the most effective in achieving the shortest periods for a given peak field . The average requirement is to cover the range from 0.7 to 20 keV . This can be achieved using the first and third harmonics of a 5 cm period undulator (see fig . 1) with a deflection parameter K = 2.6 . In terms of performance, a brilliance of the order of a few times 10 18 photons/ (smm2 mrad 2 %o bw) can be reached with a 6 m long device and 100 mA stored current . The integrated power radiated by this type of 6 m long undulator will be of the order of 3 kW and the power density at a distance of 30 m will be as large as 100 W/mm2 . Thus will be a common feature of radiation from all insertion devices . Beam lines and beam line front ends will have to withstand unprecedented heat loads . A few specific demands could be satisfied by wigglers, e .g . a ten-pole wiggler that could be used for X-ray spectroscopy . This type of device would have the following characteristics : magnetic field : 1 .5 T ; period : 24 cm ; deflection parameter K = 24 ; and a total radiation power of 7 kW . In this case, brilliance is three orders of magnitude less than that of an undulator, but still one order of magnitude larger than that obtained from the bending magnets (see fig . 1) . The strongest insertion device that could be envisaged for the ESRF is probably a wavelength shifter which could be used for high-energy X-ray scattering . It is a 3 .5 T magnet, the radiation spectrum of which is centered around 85 keV, with significant flux up to 400 keV. A 6 mrad fan of radiation can be extracted from this device for a total power of around 2 .5 kW . The ESRF proposes to segment the insertion devices and to compose straight sections with three modules, each about 1 .7 m in effective length . At the start of beam line commissioning, it is suggested to begin with a single module (or with a maximum of two modules) . Once machine behaviour is understood and some experience on heat load problems has been gained on beam lines, the ESRF will proceed to fully equip all the straight sections .
37 7
3 . Injector and booster synchrotron Experience gained at existing synchrotron radiation sources shows that when running a storage ring with electrons, under certain circumstances, in particular when running the machine in the multibunch mode, positive ions are trapped and accumulate along the beam trajectory . The electron-ion interactions give rise to uncontrolled transverse instabilities or to excitations of resonances . The net result is a lack of reproducibility of machine performance versus beam current. Consequently, the ESRF has opted for a positron premjector composed of a 200 MeV high-current electron linac, which will be used for commissioning, followed by a converter and a 400 MeV positron linac, which is intended to be installed later on . The booster synchrotron has a circumference of 229 .4 m. Its lattice, based on a simple FODO arrangement of magnets, has a threefold symmetry . It is designed to accelerate the electrons/ positrons from the preinjector to the full energy (6 GeV) of the ESRF storage ring . Full energy injection has been retained as it eases operation, enables the storage ring to run totally do and permits better reproducibility after a refill . The booster and preinjector are run at 10 Hz with charging times varying from a fraction of a minute for 100 mA electrons in the multibunch mode to 15 mm for 7 .5 mA positrons in single-bunch mode . 4 . Site, buildings and infrastructure Several sites to accommodate the ESRF in Grenoble or its vicinity were initially proposed by the French party . Two sites were preselected on the basis that they were near the town and close to other scientific institutes : the Peninsula site on the scientific Polygone, and the Sassenage site on the other side of the river Drac . The inherent requirements for the site of the machine are long- and short-term stability tolerances . A thorough investigation of vibration levels and the underground geophysical properties was carried out on both sites . Vibration levels induced by the environment were found to be well within tolerances . The ESRF Council decided that the site was to be the 27 ha Peninsula site . The development of the building and the infrastructure is, naturally, closely linked to the specificity of the site, and it started immediately after the decision on the final site for the ESRF was made . The building plan contains the tunnel for the storage ring with the experimental hall having an average circumference of 915 m and a width of 22 .5 m . It can house more than 50 beam lines, each with a length up to 75 m between the source point and the detectors . Beam lines from 75 to 500 m in length can be installed outside the storage ring building. I . SOURCES
37 8
R Haensel / The European Synchrotron Radiation Facility
Fig 2 General layout of the facility The big experimental hall is serviced by three 6 ton cranes . The foundations of the storage ring and the experimental areas are well isolated from external vibration sources. User laboratories and offices (1700 m2 ) are distributed along the outer facade of the hall to provide short connections to the experiments . Inside the storage ring building there are buildings for the booster synchrotron and the preinjector, as well as technical buildings . Outside the ring there is a central building for offices, ancillary laboratories, and a computing center. Workshops and technical infrastructure with a strong noise level are placed as far away as possible from the storage ring in order to minimise vibration problems . The total net construction area is 38 500 m2, subdivided as follows : - 25 000 m2 for storage ring and experimental hall ; - 1600 m2 for preinjector plus injector ; - 4400 m2 for technical buildings ; and - 7500 m2 for offices and laboratories . Fig. 2 shows the general layout of the facility . 5. Scientific programme at ESRF The special features of ESRF are that it produces very narrow X-ray beams of especially high brilliance,
that the photons emitted have a very broad energy range up to high energies, and that the sources of light (the insertion devices) are independently adjustable to match the requirements of the planned scientific experiments. Each scientific experiment at ESRF requires a "beam line", usually defined as a sequence of source (undulator, wiggler or benging magnet), optical system (mirrors, monochromators, slits, collimator, filters), specimen chamber and detector. The unprecedented properties of the ESRF will demand that a carefully thought-out plan of research and development be started immediately on the problem of building optical systems, detectors and data capture systems can match the precision of the ESRF beam and does not destroy this precision during the experiment . The most outstanding feature about the science which can be done at ESRF is its breadth. ESRF will have important applications in physics, chemistry, biology, medicine and materials science. The special properties of ESRF beams mean that : specimens can be studied with high spatial resolution ; on-going events can be followed with higher time resolution ; reactions, scattering processes and absorption can be probed with higher energy resolution ; and atonuc and molecular structure can be determined to finer detail . The new science that will be possible at ESRF can be pursued by six major
R Haensel / The European Synchrotron Radiation Facility techniques : diffraction, surface science, absorption, imaging, diffuse scattering and inelastic scattering . In diffraction and diffuse scattering, the scattering patterns, because of the small ESRF beam, can be recorded in fine spatial detail . This is not equivalent to producing an image or structure with high spatial resolution . Rather, it means that materials with very long periodicities can be examined . These can be assemblies of biological macromolecules or they can be regular perturbations in large or small structures . It also means that the diffuse scattering from disordered crystals, liquid crystals, true liquids or amorphous solids (alloys, metallic glasses, etc .) may be used to gain information about the nature of the disorder materials . The energy range of ESRF beams also means that more powerful methods will exist for solving crystal structures, and time-resolved studies will be feasible on dynamic molecules such as enzymes. The ability to study tiny specimens does not only apply to small crystals ; diffraction patterns from animal or plant tissues will allow tissue structures to be probed to high spatial resolution, and will lead to more general microprobes. Atoms in very small concentrations (e .g. impurities in semiconductors) will be accessible to selective investigation . The characteristics of the ESRF will allow the opening up of completely new applications, e .g . the very weak signals due to magnetic scattering and inelastic scattering can be detected ; the mechanism of human muscle contraction can be visualised with better time resolution ; a new microscope with unique properties can be developed ; and a much wider range of atomic species can be studied by absorption. A crucial advantage of the higher-energy X-rays is that they penetrate more deeply into matter . Hence it is possible to probe both the surface and the bulk of the same specimen because of the wide energy range available at ESRF .
37 9
6. Time schedule The construction phase, covering the time until the first set of beam lines will be routinely available for users, will last for 6 .5 years, i .e . until mid-1994 . It is dedicated to the sequential construction and running-in of the accelerators and the storage ring (until Summer, 1993). The last year of the construction phase is essentially devoted to tests of the machine and to the commissioning of the first set of beam lines . The operation phase covered by the present planning lasts for 4 .5 years (until 1998) . It corresponds to the completion of the planned experimental facility : installation and running-in of a second set of beam lines, and upgrading the insertion devices. In total, we plan for 28 insertion device beam lines and 2 from bending magnets . After 1998 the ESRF will certainly continue to expand on the experimental side because of the expected request for beam lines which will greatly surpass the number of 30 covered in the Foundation Phase Report . Nevertheless, all personnel and cost estimates have been made assuming that in the year 1998 the machine will be running on a steady-state basis with 30 beam lines, built and funded by ESRF .
References [1] Report of the European Synchrotron Radiation Project, eds . B . Buras and S. Tazzari, Geneva (1984) . [21 ESRF Foundation Phase Report, Grenoble (1987) . Both reports can be obtained from the author.
1 . SOURCES
375
THE EUROPEAN SYNCHROTRON RADIATION FACILITY Ruprecht HAENSEL ESRF, F-38043 Grenoble Cedex, France
This paper reviews the status of the ESRF in Grenoble. The construction has started at the beginning of 1987, the first beam is expected m 1993 1. Historical introduction After many years of preparation initially done by working groups of the European Science Foundation, ESF, continued by the European Synchrotron Radiation Project (ESRP) group working under Buras and Tazzari [1], and finally concluded by the ESRF team in Grenoble, the governments of the countries participating in the ESRF (France, the Federal Republic of Germany, the United Kingdom, Italy, Spain, Switzerland, and the four Nordic Countries Denmark, Finland, Norway and Sweden) * have decided in December 1987 to start the construction of the European Synchrotron Radiation Facility ESRF in Grenoble. The goal of the ESRF is to build, operate and exploit a synchrotron radiation source in the hard X-ray region with characteristics not reached so far with existing synchrotron radiation sources . The ESRF team started its work in April 1986 (with R. Haensel as Director General, J.L. Laclare as Project Director, Gottfried MiAhaupt as Deputy Project Director, and M. Altarelli and A. Miller as Directors of Research) . Growing gradually to 70 persons at the present time, it has made proposals for the selection of the final site, the main parameters of the machine and the beam lines, and for the budget during the construction phase (6.5 years) and the first (4.5) years of the operation phase. The details of this work are published in the Foundation Phase Report [2]. The Foundation Phase Report was submitted to the ESRF Council, who accepted it as the main planning document for the eleven years to come.
* Note added in proof : In the mean time Belgium also joined the ESRF. 0168-9002/89/$03.50 © Elsevier Science Publishers B.V. (North-Holland Physics Publishing Division)
2. Source parameters 2.1 . Storage ring energy
The storage ring energy was chosen to fulfil the requirement for short-wavelength radiation by undulators. In particular, the production of a high flux in the fundamental of an undulator at 0.86 a.u. (14 .4 keV) was specified . The performance of undulators is, however, very dependent on the magnetic period and consequently on the minimum gap between the magnet poles. A nominal energy of 5 GeV, associated with a 10 mm minimum gap, was originally proposed in the Green Book [1] to meet the same requirements . It was agreed, however, that at 5 GeV such a performance would set critical limits to the beam lifetime and that the tunability would be very small. In fact, the Green Book [1] machine was already designed to reach 6 GeV . It must be pointed out that, in addition, the 10 mm gap option has several consequences that may affect operation of the storage ring: - The beam stay-clear is reduced to 10 mm or less, which is considerably smaller than the aperture defined for the rest of the machine . Therefore, the beam lifetime could be affected . - As a good vacuum is fundamental for the storage ring, it is not desirable to have the undulators under vacuum since they account for 14% of the circumference (about 120 m). This would obviously be detrimental to machine impedance (due to strong electromagnetic interactions between the beam and its environment) and would limit the stored current . - The acceptance of the machine is sensitive to the nonlinear effects introduced by small gap undulators. This could again affect the beam lifetime . In order to overcome these disadvantages and to ease the initial operation of the source, the following strategy has been adopted : - a beam stay-clear of 15 mm; - a rigid vacuum chamber ; and - undulators with a 20 mm minimum gap outside vacuum. I. SOURCES
376
R. Haensel / The European Synchrotron Radiation Facility
As a consequence, nominal machine energy was raised to 6 GeV to reach the requirement at 0.86 a.u . This offers a good safety margin for undulator design and larger overall tunability : for instance, the 1-2 a.u . range can be covered by a single undulator. Once sufficient knowledge of the machine's behaviour has been acquired, it might be possible to decrease the undulator gap to 10 mm and reach the 0.62 a.u . (20 keV) range later on . From a technical point of view, at 6 GeV, the specifications are easier to achieve and this will inevitably lead to a faster commissioning of the machine, followed by smoother operation. The scientific case for a 6 GeV machine, rather than a 5 GeV machine, is that better service can be provided for the majority of users in the range from 5 to 15 keV due to a larger overall tunability of the insertion devices. Increasing the potential machine capability in this way is probably a good investment for the future . The only disadvantage is that dipole sources get harder (20 keV) . To compensate this effect 16 "soft" dipoles radiating at 10 keV will be installed.
Table 2 The beam dimensions at source locations
2 .2 Storage ring lattice and photon sources
Rms beam size
Wiggler
Undulator
a [mm] a' [inrad] a [mm] a' [mrad]
Bending magnet
0 .069 0 .089 0 .047 0 .013
0 .406 0 .015 0 .084 0 .007
0 .160 0 .137 0 .129 0.005
The potential performance of the storage ring is primarily determined by the lattice design . In line with the Green Book [1] proposal, we retained the same type of magnetic structures : a Chasman-Green lattice with, nevertheless, substantial improvements as far as the beam emittance, sensitivity to errors and flexibility are concerned. At 6 GeV the nominal horizontal emittance is maintained at 7 rim cad. The circumference is increased to 844.39 m. There are thirty-two 6 .34 m long straight sections, identically equipped with triplets at both ends, Phot/s/mm2/mrad2/0 1 1 E+20 , 80 mm
50 mm
Table 1 The proposed parameters for the ESRF storage ring Nominal beam energy Circumference Number of bunches Beam current Horizontal emrttance Vertical emittance Beam lifetime Number of straight sections Length of straight sections Radiation sources
6 GeV 844 39 m 1-992
100 mA multibunch mode 7 .5 mA single-bunch mode 7 rim cad 0.6 rim cad 10 h 32 (29 usable for insertion devices) 6 34 m Undulators (14.4 keV in the fundamental) Wigglers Wavelength shifters Bending magnet (at 10 and 20 keV)
that are tunable over a wide range and can either accommodate wigglers or undulators . Three of these straight sections will be used for machine utilities: one for injection and two for accelerating cavities ; 29 remain available for insertion devices. In addition, 28
35 mm
1 E+18
1 E+16
Undulators gap =20 mm L=5m ( 1 st & 3rd harmonic ) -------------------------- ;_ .__ .__..___ ..____.._ .____.
100
Photon Energy [keV] Fig. 1 Brilliance from bending magnets and insertion devices.
1000
R Haensel / The European Synchrotron Radiation Facihty beam ports will deliver radiation from bending magnets . Twelve ports will be open to the 20 keV radiation from the main dipoles. The remaining 16 beam ports will accept a 10 mrad fan split in two equal parts : 5 mrad from "soft" dipoles at 10 keV, and 5 mrad of harder radiation from the main dipoles at 20 keV . The proposed parameters for the ESRF Storage Ring resulting from the scientific requirements are summarized in table 1 . The beam dimensions at source locations are summarized in table 2 . 2 .3. Strategy for insertion devices and performance In the inventory of insertion devices, the majority (over 2/3) will be undulators using permanent magnets, which are the most effective in achieving the shortest periods for a given peak field . The average requirement is to cover the range from 0.7 to 20 keV . This can be achieved using the first and third harmonics of a 5 cm period undulator (see fig . 1) with a deflection parameter K = 2.6 . In terms of performance, a brilliance of the order of a few times 10 18 photons/ (smm2 mrad 2 %o bw) can be reached with a 6 m long device and 100 mA stored current . The integrated power radiated by this type of 6 m long undulator will be of the order of 3 kW and the power density at a distance of 30 m will be as large as 100 W/mm2 . Thus will be a common feature of radiation from all insertion devices . Beam lines and beam line front ends will have to withstand unprecedented heat loads . A few specific demands could be satisfied by wigglers, e .g . a ten-pole wiggler that could be used for X-ray spectroscopy . This type of device would have the following characteristics : magnetic field : 1 .5 T ; period : 24 cm ; deflection parameter K = 24 ; and a total radiation power of 7 kW . In this case, brilliance is three orders of magnitude less than that of an undulator, but still one order of magnitude larger than that obtained from the bending magnets (see fig . 1) . The strongest insertion device that could be envisaged for the ESRF is probably a wavelength shifter which could be used for high-energy X-ray scattering . It is a 3 .5 T magnet, the radiation spectrum of which is centered around 85 keV, with significant flux up to 400 keV. A 6 mrad fan of radiation can be extracted from this device for a total power of around 2 .5 kW . The ESRF proposes to segment the insertion devices and to compose straight sections with three modules, each about 1 .7 m in effective length . At the start of beam line commissioning, it is suggested to begin with a single module (or with a maximum of two modules) . Once machine behaviour is understood and some experience on heat load problems has been gained on beam lines, the ESRF will proceed to fully equip all the straight sections .
37 7
3 . Injector and booster synchrotron Experience gained at existing synchrotron radiation sources shows that when running a storage ring with electrons, under certain circumstances, in particular when running the machine in the multibunch mode, positive ions are trapped and accumulate along the beam trajectory . The electron-ion interactions give rise to uncontrolled transverse instabilities or to excitations of resonances . The net result is a lack of reproducibility of machine performance versus beam current. Consequently, the ESRF has opted for a positron premjector composed of a 200 MeV high-current electron linac, which will be used for commissioning, followed by a converter and a 400 MeV positron linac, which is intended to be installed later on . The booster synchrotron has a circumference of 229 .4 m. Its lattice, based on a simple FODO arrangement of magnets, has a threefold symmetry . It is designed to accelerate the electrons/ positrons from the preinjector to the full energy (6 GeV) of the ESRF storage ring . Full energy injection has been retained as it eases operation, enables the storage ring to run totally do and permits better reproducibility after a refill . The booster and preinjector are run at 10 Hz with charging times varying from a fraction of a minute for 100 mA electrons in the multibunch mode to 15 mm for 7 .5 mA positrons in single-bunch mode . 4 . Site, buildings and infrastructure Several sites to accommodate the ESRF in Grenoble or its vicinity were initially proposed by the French party . Two sites were preselected on the basis that they were near the town and close to other scientific institutes : the Peninsula site on the scientific Polygone, and the Sassenage site on the other side of the river Drac . The inherent requirements for the site of the machine are long- and short-term stability tolerances . A thorough investigation of vibration levels and the underground geophysical properties was carried out on both sites . Vibration levels induced by the environment were found to be well within tolerances . The ESRF Council decided that the site was to be the 27 ha Peninsula site . The development of the building and the infrastructure is, naturally, closely linked to the specificity of the site, and it started immediately after the decision on the final site for the ESRF was made . The building plan contains the tunnel for the storage ring with the experimental hall having an average circumference of 915 m and a width of 22 .5 m . It can house more than 50 beam lines, each with a length up to 75 m between the source point and the detectors . Beam lines from 75 to 500 m in length can be installed outside the storage ring building. I . SOURCES
37 8
R Haensel / The European Synchrotron Radiation Facility
Fig 2 General layout of the facility The big experimental hall is serviced by three 6 ton cranes . The foundations of the storage ring and the experimental areas are well isolated from external vibration sources. User laboratories and offices (1700 m2 ) are distributed along the outer facade of the hall to provide short connections to the experiments . Inside the storage ring building there are buildings for the booster synchrotron and the preinjector, as well as technical buildings . Outside the ring there is a central building for offices, ancillary laboratories, and a computing center. Workshops and technical infrastructure with a strong noise level are placed as far away as possible from the storage ring in order to minimise vibration problems . The total net construction area is 38 500 m2, subdivided as follows : - 25 000 m2 for storage ring and experimental hall ; - 1600 m2 for preinjector plus injector ; - 4400 m2 for technical buildings ; and - 7500 m2 for offices and laboratories . Fig. 2 shows the general layout of the facility . 5. Scientific programme at ESRF The special features of ESRF are that it produces very narrow X-ray beams of especially high brilliance,
that the photons emitted have a very broad energy range up to high energies, and that the sources of light (the insertion devices) are independently adjustable to match the requirements of the planned scientific experiments. Each scientific experiment at ESRF requires a "beam line", usually defined as a sequence of source (undulator, wiggler or benging magnet), optical system (mirrors, monochromators, slits, collimator, filters), specimen chamber and detector. The unprecedented properties of the ESRF will demand that a carefully thought-out plan of research and development be started immediately on the problem of building optical systems, detectors and data capture systems can match the precision of the ESRF beam and does not destroy this precision during the experiment . The most outstanding feature about the science which can be done at ESRF is its breadth. ESRF will have important applications in physics, chemistry, biology, medicine and materials science. The special properties of ESRF beams mean that : specimens can be studied with high spatial resolution ; on-going events can be followed with higher time resolution ; reactions, scattering processes and absorption can be probed with higher energy resolution ; and atonuc and molecular structure can be determined to finer detail . The new science that will be possible at ESRF can be pursued by six major
R Haensel / The European Synchrotron Radiation Facility techniques : diffraction, surface science, absorption, imaging, diffuse scattering and inelastic scattering . In diffraction and diffuse scattering, the scattering patterns, because of the small ESRF beam, can be recorded in fine spatial detail . This is not equivalent to producing an image or structure with high spatial resolution . Rather, it means that materials with very long periodicities can be examined . These can be assemblies of biological macromolecules or they can be regular perturbations in large or small structures . It also means that the diffuse scattering from disordered crystals, liquid crystals, true liquids or amorphous solids (alloys, metallic glasses, etc .) may be used to gain information about the nature of the disorder materials . The energy range of ESRF beams also means that more powerful methods will exist for solving crystal structures, and time-resolved studies will be feasible on dynamic molecules such as enzymes. The ability to study tiny specimens does not only apply to small crystals ; diffraction patterns from animal or plant tissues will allow tissue structures to be probed to high spatial resolution, and will lead to more general microprobes. Atoms in very small concentrations (e .g. impurities in semiconductors) will be accessible to selective investigation . The characteristics of the ESRF will allow the opening up of completely new applications, e .g . the very weak signals due to magnetic scattering and inelastic scattering can be detected ; the mechanism of human muscle contraction can be visualised with better time resolution ; a new microscope with unique properties can be developed ; and a much wider range of atomic species can be studied by absorption. A crucial advantage of the higher-energy X-rays is that they penetrate more deeply into matter . Hence it is possible to probe both the surface and the bulk of the same specimen because of the wide energy range available at ESRF .
37 9
6. Time schedule The construction phase, covering the time until the first set of beam lines will be routinely available for users, will last for 6 .5 years, i .e . until mid-1994 . It is dedicated to the sequential construction and running-in of the accelerators and the storage ring (until Summer, 1993). The last year of the construction phase is essentially devoted to tests of the machine and to the commissioning of the first set of beam lines . The operation phase covered by the present planning lasts for 4 .5 years (until 1998) . It corresponds to the completion of the planned experimental facility : installation and running-in of a second set of beam lines, and upgrading the insertion devices. In total, we plan for 28 insertion device beam lines and 2 from bending magnets . After 1998 the ESRF will certainly continue to expand on the experimental side because of the expected request for beam lines which will greatly surpass the number of 30 covered in the Foundation Phase Report . Nevertheless, all personnel and cost estimates have been made assuming that in the year 1998 the machine will be running on a steady-state basis with 30 beam lines, built and funded by ESRF .
References [1] Report of the European Synchrotron Radiation Project, eds . B . Buras and S. Tazzari, Geneva (1984) . [21 ESRF Foundation Phase Report, Grenoble (1987) . Both reports can be obtained from the author.
1 . SOURCES