- Email: [email protected]
A French proposal for an innovative accelerators based coherent UV–X-ray source
ARTICLE IN PRESS
Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
A French proposal for an innovative accelerators based coherent UV–X-ray source M.E. Coupriea,b,*, M. Belakhovskyc, B. Gilquind, D. Garzellaa,b, M. Jablonkae, F. Me! ote, P. Monota, A. Mosniere, L. Nahona,b, A. Roussef # 522, 91 191 Gif-sur-Yvette, France Service de Photons, Atomes et Mol!ecules, CEA/DSM/DRECAM, bat. b Universit!e de Paris-Sud, bat. 209 D, BP 34, 91 898 Orsay cedex, France c CEA/DSM/ DRFMC, DRFMC, CEA-Grenoble 17 avenue des Martyrs, 38054, Grenoble Cedex 9, France d CEA-D!epartement d0 Ing!enierie et d0 Etude des Prot!eines, Centre d’Etude de Saclay, Bat 152, 91191 Gif sur Yvette, France e CEA/DSM/DAPNIA/SACM, bat. 701, Orme des Merisiers, 91 191 Gif-sur-Yvette, France f Laboratoire d’Optique Appliqu!ee, LOA - ENSTA, Laboratoire d’Optique Appliqu!ee, Chemin de la Huni"ere, 91761 Palaiseau, France a
Abstract ! At the initiative of the CEA (Commissariat a" l’Energie Atomique), discussions were conducted in France on fourth generation light sources. A new independent accelerator based radiation facility ARC-EN-CIEL (Accelerator Radiation Complex for ENhanced Coherent Intense Extended Light) is proposed, aiming at providing coherent femtosecond light pulses in the UV- to X-ray range for scientific applications. The project is based on a 700 MeV superconducting LINAC, providing low emittance 200 fs RMS electron bunches. They can be injected in undulators used in the Self Amplified Spontaneous Emission mode (SASE), or in the High Gain Harmonic Generation (HGHG), seeded with high harmonics in gases at 20 nm.The SASE source covers the 100–5 nm spectral range, the HGHG goes down to 0.8 nm.Two optional loops, for Energy Recovery or energy enhancement (1.4 GeV), will accommodate fs synchrotron radiation sources in the IR-, VUV- and X-ray ranges, together with a FEL oscillator providing radiation down to 10 nm, taking advantage of the optical development for lithography. The facility also proposes to test plasma acceleration and to provide a Thomson radiation source. Characteristics of the light source will be described. r 2004 Elsevier B.V. All rights reserved. PACS: 41.60.Cr; 41.75.Ht; 41.60.Ap Keywords: FEL; ERL; Synchrotron radiation; Harmonic generation
1. Introduction *Corresponding author. Laboratoire pour 10 utilisation du Rayonnement Electromagnetique, Universite Paris Sud, Bat. 209D, BP 34, Orsay Cedex 91898, France. Tel.: +33-1-64-4680-44; fax: +33-1-64-46-41-48. E-mail address: [email protected] (M.E. Couprie).
Short pulses Free Electron Laser (FEL) in the VUV-soft X-ray spectral range seem very attractive sources for time-resolved studies in various scientific domains [1]. France developed different
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.101
ARTICLE IN PRESS 558
M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
FEL devices, starting with the first storage ring FEL on ACO [2] in 1983, the UV FEL on SuperACO [3] and the Linac based Infra-red FEL user facility CLIO in 1992 [4]. First time-resolved pump–probe two-colour experiments were performed, using the Super-ACO FEL and synchrotron radiation [5]. Starting from a scientific case (condensed matter, chemistry, biology, plasma and molecular physics) that cannot be satisfied by the present synchrotron radiation capabilities, discussions were then conducted for the design of a new accelerator based light source, offering tuneability, adjustable polarisation, high brilliance and fs light pulse for scientific applications in the UV–X-ray range. The scheme of the machine is shown in Fig. 1. Intense electron bunches, delivered by a superconducting 700 MeV accelerator, present a very low transverse emittance and a 200 fs RMS duration. Optional Recirculation loops allow the energy to be enhanced (re-acceleration) or the current to be increased (Energy Recovery Mode), as successfully demonstrated on the Jefferson Laboratory FEL [6]. They will comport undulators for the production of fs synchrotron radiation in the X-ray (keV range) and the VUV ranges, and an infra red bending magnet source [7]. A 120– 10 nm FEL oscillator, with a 15 m long optical cavity, is installed on the first loop. In the LINAC axis, several undulator sections are planned, for Self Amplified Spontaneous Emission (SASE) in the 200–7 nm range and for HGHG [8] in the 100– 0.8 nm range, in particular starting from coherent harmonic generated in gases at 20 nm [9]. A kHz powerful fs laser will be used for the production of
Fig. 1. Layout of the ARC-EN-CIEL proposal. The 72 m LINAC is constituted by 6 modules of 12 m long, 4 m undulator sections are dedicated to SASE and HGHG. Two optional loops will accommodate a FEL oscillator and fs synchrotron radiation sources on undulators and on a dipole.
harmonics in gases and of fs X-rays by Thomson scattering, for test of plasma electron acceleration, and for time-resolved pump–probe two-colour experiments.
2. The light source 2.1. The accelerator ensemble Energy recovery justifies the choice of the superconducting technology, which offers a more flexible temporal structure for the users. Injector 1, a 40 MV/m RF gun, equipped with a CsTe photocathode [10], operates with macropulses of 200 ms at 50 Hz or 1 ms at 10 Hz, with either 1 nC and 1 MHz for the SASE/GHC mode or 0.1 nC and 10 MHz for the FEL oscillator. Injector 2, in a CW mode, could be based on an electrostatic gun [11], such as the one developed in TJNAF with 5 mA and 320 kV, now aiming at 10 mA and 500 kV, with 1 mm rad and 0.1 nC or 7 mm rad and 1 nC, or with a RF gun powered by a single short RF pulse, with 1 mm rad and 0.1 nC as in the LBNL proposal [12]. A future injector, for high bunch frequency, charge could be based on a RF superconducting gun [13] (see Fig. 2). A preaccelerating structure raises the energy up to 10– 20 MeV.The LINAC (see Table 1) is composed of six TTF like modules, with 8–9 cavities of 9 cells,
Fig. 2. Temporal structure: (a) injector 1: 1 ms, 10 Hz macropulses, with 200 fs RMS, 10 MHz micropulses (b) injector 2: CW 200 fs, 10 kHz micropulses after compression, (c) future injector : CW 200 fs micropulses at 1 MHz
ARTICLE IN PRESS M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
at 1.3 GHz, with 1010 quality factors, powered each by two 100 kW CW klystrons, with 107 external coupling. Efficient extraction of highorder modes excited by the beam in the cavities is one of the main concerns. Two optional loops, one for energy recovery and high average current operation, and one for beam energy enhancement at 1.4 GeV, provide a beam up to 2.1 GeV. Beam stability and collective effects remain a difficult issue. Coherent synchrotron radiation and wakefield effects make crucial the bunch compression down to 200 fs, with emittance conservation. A first stage in the injector uses a magnetic compression in a chicane or the velocity bunching scheme, followed by a chicane in the middle of the LINAC. A more complex scheme, using one complete injector module in a separate loop as in the LUX scheme [14] is also considered. 2.2. Sources in the loops To provide more flexibility for users in terms of light polarisation and spectral range, two 12 m
Table 1 Main Linac beam characteristics Energy RF frequency Gradient Intensity per 1 passage Intensity with ER Bunch charge Bunch frequency Transverse emittance Energy spread
MeV GHz MV/m mA mA nC MHz m rad
700 1.3 15 1 5–10 1 p10 2 106 1 103
559
long planar to helical permanent magnets could be placed. Table 2 gives the main undulator characteristics for different beam energies E: period lo, deflection parameter K, wavelength l1 and energy E1 of the fundamental. They provide typically a few 1012 ph/s/0.1% BW in the VUV and the X-ray for 0.1 mA average current. One order of magnitude would be gained with in emerging vacuum superconducting undulators. An infra-red source, using the central or the edge field of a bending magnet of the loop, could provide 1011 ph/ s mrad2 0.1% BW in the 10 mm–0.01 mm range, for two colour experiments coupling the infra-red with the VUV–X-ray radiation. 2.3. Laser sources A fs Titanium:Sapphire laser source will serve for the seeding of HGHG, Thomson scattering X production, plasma radiation or electron beamplasma interaction studies. A first part will deliver a few mJ at kHz, sufficient for the production of higher order harmonics in gases. An amplification chain will raise the energy up to a few J at 10 Hz, offering 30 TW power and 1020 W/cm2. A FEL oscillator will be installed in the first loop, and undulators, located in the Linac axis, will be used for SASE and HGHG from higher harmonics in gases. The undulators characteristics are given in Table 3. The SASE radiation covers the 200–7 nm spectral range for beam energies ranging between 135 and 700 MeV, with a Pierce parameter of the order of a few 103. The oscillator covers the 120– 10 nm, thanks to recent development multilayer mirrors for lithography, and to SiC in normal
Table 2 Undulators in the loops E (GeV)
lo (mm)
Gap (mm)
XUV undulator in the second loop 0.7 30 40–10 1.4 20 40–10 VUV undulator in the first loop 0.25 30 10–40 Possible future in vaccum superconducting undulator 0.7 4 1.4 4
K
l1 (nm)
E1 (eV)
0.01–2 0.01–0.9
8–25 1–2
2.1–0.1
200–63
6–20
0.1–2 0.1–2
1.1–3.2 0.3–0.8
1100–400 4000–1550
155–50 1200–600
ARTICLE IN PRESS 560
M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
Table 3 Undulators for FELs SASE Period (mm) Gap (mm) Magnetic field (T) Length (m) Section number Wavelength (nm) Photon energy (eV)
30 10–30 0.1–0.75 4 1–2 200–8 6–150
Oscillator 20 10–20 0.1–0.5 4 4 60–6 20–200
25 10–24 0.1–1.05 5 1 120–13 10–90
spectral range, delivering 2mJ–0.2 nJ/ pulse (5 1011–2 107 ph/pulse). For the SASE undulators, it leads to 25 MW at 7 nm (FEL harmonics n 3), 1 MW at B4 nm.The cascade scheme, with one or two sections optimised for 21 nm at 700 MeV and 4 sections designed for 7 nm, will allow the radiation to be extended down to 0.8 nm (1.5 keV, on the 9th harmonics) with a few MW peak power and a flux of 1014 ph/s/0.1% BW, with 0.1–1% bandwidth. Harmonics can also be produced from the FEL oscillator, with 500 MW at 4.5 nm and 10 MW at 2.7 nm. Besides, using the beam at 1.4 GeV from the loop will allow to shorten further the radiation wavelength down to 0.4 nm with an additional undulator section. A second cascade module could also be considered. In addition, an 8–10 keV X-ray source, produced by Thomson scattering, will be implemented. Fig. 3 shows the brilliance performances of this light source project.
3. Scientific prospects
Fig. 3. Peak and average brilliance of ARC-EN-CIEL. High Harm in gas jet stands for the higher harmonics produced in a Xenon gas jet. U20 and U30 refer to the undulators in the loops, respectively, with 20 and 30 mm period.
incidence, offers 0.1-1 kW average power, a 0.1– 1% bandwidth. One could also produce mutually coherent FEL sources. For coherent harmonic generation, the seeding will be provided either by the harmonics 2 and 4 of the Ti:Sa laser (1 kHz repetition rate, 5 W, 5 mJ/pulse at 400 nm and 1 W, 1 mJ/pulse at 200 nm) or the harmonics in the gases (n 11 to 31 in the plateau) in the 70–21 nm
This facility proposes a variety of different fs coherent light sources from the infra-red to the Xrays, with an adjustable polarisation, allowing different scientific topics to be investigated. In gas phase, femtochemistry on free species or adsorbates can be studied by photoemission (electronic states) or EXAFS (structure). Photoionisation and alignment dynamics (valence or internal band), spectroscopy on extremely dilute species (radicals, ions), and non-linear physics in the XUV on isolated systems such as clusters can be investigated. In condensed matter, it offers higher resolutions due to high brilliance, new coherence possibilities in imagery, microscopy, holography, especially for nanostructures (spintronics, integrated devices), and the extension of absorption X diffraction, diffusion techniques towards ultimate temporal resolutions for the study of transitory systems out of equilibrium and in situ analysis of ultrafast processes under an external constraint (such as a pulse of magnetic field) due to the fs pulse duration. Optical phonons role in phase transitions, spin polarisation dynamics, identification of complex intermediates in
ARTICLE IN PRESS M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
biochemical reactions, study of plasma generation and dynamical behaviour can be analysed. The flux hungry ‘‘photon in-photon out’’ techniques, such as time resolved magnetic holography and resonant inelastic scattering will be developed. In the UV–X domain, protein folding and cell studies using microscopy will benefit from the high brilliance of the source. Exploitation of non-linear techniques opens new prospects for structure and magnetism at interfaces.
4. Conclusion The short wavelength FEL oscillator and the seeding with harmonics in gas provides a spectral range extension towards short wavelengths, in a much more compact device as compared to a simple SASE scheme, and will offer better source quality (Fourier limit) for users. Moreover, SASE, oscillator and harmonics properties can be compared on the same facility, allowing a step forward in the FEL physics understanding. This project
561
relies also on a strong synergy between the accelerator, the FEL and the laser community. It can help to gather a user community exploiting fs X-ray sources.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
H. Wabnitz, et al., Nature 420 (2002) 482. M. Billardon, et al., Phys. Rev. Lett. 51 (1983) 1652. M.E. Couprie, et al., Phys. Rev. A. 44 (1991) 1301. R. Prazeres, et al., Phys. Rev. Lett. 78 (1997) 2124. M. Marsi, et al., Appl. Phys. Lett. 70 (1997) 895. G. Neil, Phys. Ev. Lett. 84 (2000) 662. Workshop IRSR, Proceedings ed. LURE, 1998. L.-H. Yu, et al., Science 289 (2000) 932. P. Sali"eres, et al., Adv. At. Mol. Opt. Phys. 41 (1999) 83. D. Dwersteg, et al., Nucl. Instr. and Meth. A 393 (1997) 93. B.C. Yunn, PAC 2001, p. 2254. R.A. Rimmer, et al., PAC 2001, p. 1801. V.N. Volkov, et al., PAC 2001, p. 2218; T. Schultheiss, et al., PAC 2001, p. 2287. J.N. Corlett, et. al., PAC 2003.
Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
A French proposal for an innovative accelerators based coherent UV–X-ray source M.E. Coupriea,b,*, M. Belakhovskyc, B. Gilquind, D. Garzellaa,b, M. Jablonkae, F. Me! ote, P. Monota, A. Mosniere, L. Nahona,b, A. Roussef # 522, 91 191 Gif-sur-Yvette, France Service de Photons, Atomes et Mol!ecules, CEA/DSM/DRECAM, bat. b Universit!e de Paris-Sud, bat. 209 D, BP 34, 91 898 Orsay cedex, France c CEA/DSM/ DRFMC, DRFMC, CEA-Grenoble 17 avenue des Martyrs, 38054, Grenoble Cedex 9, France d CEA-D!epartement d0 Ing!enierie et d0 Etude des Prot!eines, Centre d’Etude de Saclay, Bat 152, 91191 Gif sur Yvette, France e CEA/DSM/DAPNIA/SACM, bat. 701, Orme des Merisiers, 91 191 Gif-sur-Yvette, France f Laboratoire d’Optique Appliqu!ee, LOA - ENSTA, Laboratoire d’Optique Appliqu!ee, Chemin de la Huni"ere, 91761 Palaiseau, France a
Abstract ! At the initiative of the CEA (Commissariat a" l’Energie Atomique), discussions were conducted in France on fourth generation light sources. A new independent accelerator based radiation facility ARC-EN-CIEL (Accelerator Radiation Complex for ENhanced Coherent Intense Extended Light) is proposed, aiming at providing coherent femtosecond light pulses in the UV- to X-ray range for scientific applications. The project is based on a 700 MeV superconducting LINAC, providing low emittance 200 fs RMS electron bunches. They can be injected in undulators used in the Self Amplified Spontaneous Emission mode (SASE), or in the High Gain Harmonic Generation (HGHG), seeded with high harmonics in gases at 20 nm.The SASE source covers the 100–5 nm spectral range, the HGHG goes down to 0.8 nm.Two optional loops, for Energy Recovery or energy enhancement (1.4 GeV), will accommodate fs synchrotron radiation sources in the IR-, VUV- and X-ray ranges, together with a FEL oscillator providing radiation down to 10 nm, taking advantage of the optical development for lithography. The facility also proposes to test plasma acceleration and to provide a Thomson radiation source. Characteristics of the light source will be described. r 2004 Elsevier B.V. All rights reserved. PACS: 41.60.Cr; 41.75.Ht; 41.60.Ap Keywords: FEL; ERL; Synchrotron radiation; Harmonic generation
1. Introduction *Corresponding author. Laboratoire pour 10 utilisation du Rayonnement Electromagnetique, Universite Paris Sud, Bat. 209D, BP 34, Orsay Cedex 91898, France. Tel.: +33-1-64-4680-44; fax: +33-1-64-46-41-48. E-mail address: [email protected] (M.E. Couprie).
Short pulses Free Electron Laser (FEL) in the VUV-soft X-ray spectral range seem very attractive sources for time-resolved studies in various scientific domains [1]. France developed different
0168-9002/$ - see front matter r 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.nima.2004.04.101
ARTICLE IN PRESS 558
M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
FEL devices, starting with the first storage ring FEL on ACO [2] in 1983, the UV FEL on SuperACO [3] and the Linac based Infra-red FEL user facility CLIO in 1992 [4]. First time-resolved pump–probe two-colour experiments were performed, using the Super-ACO FEL and synchrotron radiation [5]. Starting from a scientific case (condensed matter, chemistry, biology, plasma and molecular physics) that cannot be satisfied by the present synchrotron radiation capabilities, discussions were then conducted for the design of a new accelerator based light source, offering tuneability, adjustable polarisation, high brilliance and fs light pulse for scientific applications in the UV–X-ray range. The scheme of the machine is shown in Fig. 1. Intense electron bunches, delivered by a superconducting 700 MeV accelerator, present a very low transverse emittance and a 200 fs RMS duration. Optional Recirculation loops allow the energy to be enhanced (re-acceleration) or the current to be increased (Energy Recovery Mode), as successfully demonstrated on the Jefferson Laboratory FEL [6]. They will comport undulators for the production of fs synchrotron radiation in the X-ray (keV range) and the VUV ranges, and an infra red bending magnet source [7]. A 120– 10 nm FEL oscillator, with a 15 m long optical cavity, is installed on the first loop. In the LINAC axis, several undulator sections are planned, for Self Amplified Spontaneous Emission (SASE) in the 200–7 nm range and for HGHG [8] in the 100– 0.8 nm range, in particular starting from coherent harmonic generated in gases at 20 nm [9]. A kHz powerful fs laser will be used for the production of
Fig. 1. Layout of the ARC-EN-CIEL proposal. The 72 m LINAC is constituted by 6 modules of 12 m long, 4 m undulator sections are dedicated to SASE and HGHG. Two optional loops will accommodate a FEL oscillator and fs synchrotron radiation sources on undulators and on a dipole.
harmonics in gases and of fs X-rays by Thomson scattering, for test of plasma electron acceleration, and for time-resolved pump–probe two-colour experiments.
2. The light source 2.1. The accelerator ensemble Energy recovery justifies the choice of the superconducting technology, which offers a more flexible temporal structure for the users. Injector 1, a 40 MV/m RF gun, equipped with a CsTe photocathode [10], operates with macropulses of 200 ms at 50 Hz or 1 ms at 10 Hz, with either 1 nC and 1 MHz for the SASE/GHC mode or 0.1 nC and 10 MHz for the FEL oscillator. Injector 2, in a CW mode, could be based on an electrostatic gun [11], such as the one developed in TJNAF with 5 mA and 320 kV, now aiming at 10 mA and 500 kV, with 1 mm rad and 0.1 nC or 7 mm rad and 1 nC, or with a RF gun powered by a single short RF pulse, with 1 mm rad and 0.1 nC as in the LBNL proposal [12]. A future injector, for high bunch frequency, charge could be based on a RF superconducting gun [13] (see Fig. 2). A preaccelerating structure raises the energy up to 10– 20 MeV.The LINAC (see Table 1) is composed of six TTF like modules, with 8–9 cavities of 9 cells,
Fig. 2. Temporal structure: (a) injector 1: 1 ms, 10 Hz macropulses, with 200 fs RMS, 10 MHz micropulses (b) injector 2: CW 200 fs, 10 kHz micropulses after compression, (c) future injector : CW 200 fs micropulses at 1 MHz
ARTICLE IN PRESS M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
at 1.3 GHz, with 1010 quality factors, powered each by two 100 kW CW klystrons, with 107 external coupling. Efficient extraction of highorder modes excited by the beam in the cavities is one of the main concerns. Two optional loops, one for energy recovery and high average current operation, and one for beam energy enhancement at 1.4 GeV, provide a beam up to 2.1 GeV. Beam stability and collective effects remain a difficult issue. Coherent synchrotron radiation and wakefield effects make crucial the bunch compression down to 200 fs, with emittance conservation. A first stage in the injector uses a magnetic compression in a chicane or the velocity bunching scheme, followed by a chicane in the middle of the LINAC. A more complex scheme, using one complete injector module in a separate loop as in the LUX scheme [14] is also considered. 2.2. Sources in the loops To provide more flexibility for users in terms of light polarisation and spectral range, two 12 m
Table 1 Main Linac beam characteristics Energy RF frequency Gradient Intensity per 1 passage Intensity with ER Bunch charge Bunch frequency Transverse emittance Energy spread
MeV GHz MV/m mA mA nC MHz m rad
700 1.3 15 1 5–10 1 p10 2 106 1 103
559
long planar to helical permanent magnets could be placed. Table 2 gives the main undulator characteristics for different beam energies E: period lo, deflection parameter K, wavelength l1 and energy E1 of the fundamental. They provide typically a few 1012 ph/s/0.1% BW in the VUV and the X-ray for 0.1 mA average current. One order of magnitude would be gained with in emerging vacuum superconducting undulators. An infra-red source, using the central or the edge field of a bending magnet of the loop, could provide 1011 ph/ s mrad2 0.1% BW in the 10 mm–0.01 mm range, for two colour experiments coupling the infra-red with the VUV–X-ray radiation. 2.3. Laser sources A fs Titanium:Sapphire laser source will serve for the seeding of HGHG, Thomson scattering X production, plasma radiation or electron beamplasma interaction studies. A first part will deliver a few mJ at kHz, sufficient for the production of higher order harmonics in gases. An amplification chain will raise the energy up to a few J at 10 Hz, offering 30 TW power and 1020 W/cm2. A FEL oscillator will be installed in the first loop, and undulators, located in the Linac axis, will be used for SASE and HGHG from higher harmonics in gases. The undulators characteristics are given in Table 3. The SASE radiation covers the 200–7 nm spectral range for beam energies ranging between 135 and 700 MeV, with a Pierce parameter of the order of a few 103. The oscillator covers the 120– 10 nm, thanks to recent development multilayer mirrors for lithography, and to SiC in normal
Table 2 Undulators in the loops E (GeV)
lo (mm)
Gap (mm)
XUV undulator in the second loop 0.7 30 40–10 1.4 20 40–10 VUV undulator in the first loop 0.25 30 10–40 Possible future in vaccum superconducting undulator 0.7 4 1.4 4
K
l1 (nm)
E1 (eV)
0.01–2 0.01–0.9
8–25 1–2
2.1–0.1
200–63
6–20
0.1–2 0.1–2
1.1–3.2 0.3–0.8
1100–400 4000–1550
155–50 1200–600
ARTICLE IN PRESS 560
M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
Table 3 Undulators for FELs SASE Period (mm) Gap (mm) Magnetic field (T) Length (m) Section number Wavelength (nm) Photon energy (eV)
30 10–30 0.1–0.75 4 1–2 200–8 6–150
Oscillator 20 10–20 0.1–0.5 4 4 60–6 20–200
25 10–24 0.1–1.05 5 1 120–13 10–90
spectral range, delivering 2mJ–0.2 nJ/ pulse (5 1011–2 107 ph/pulse). For the SASE undulators, it leads to 25 MW at 7 nm (FEL harmonics n 3), 1 MW at B4 nm.The cascade scheme, with one or two sections optimised for 21 nm at 700 MeV and 4 sections designed for 7 nm, will allow the radiation to be extended down to 0.8 nm (1.5 keV, on the 9th harmonics) with a few MW peak power and a flux of 1014 ph/s/0.1% BW, with 0.1–1% bandwidth. Harmonics can also be produced from the FEL oscillator, with 500 MW at 4.5 nm and 10 MW at 2.7 nm. Besides, using the beam at 1.4 GeV from the loop will allow to shorten further the radiation wavelength down to 0.4 nm with an additional undulator section. A second cascade module could also be considered. In addition, an 8–10 keV X-ray source, produced by Thomson scattering, will be implemented. Fig. 3 shows the brilliance performances of this light source project.
3. Scientific prospects
Fig. 3. Peak and average brilliance of ARC-EN-CIEL. High Harm in gas jet stands for the higher harmonics produced in a Xenon gas jet. U20 and U30 refer to the undulators in the loops, respectively, with 20 and 30 mm period.
incidence, offers 0.1-1 kW average power, a 0.1– 1% bandwidth. One could also produce mutually coherent FEL sources. For coherent harmonic generation, the seeding will be provided either by the harmonics 2 and 4 of the Ti:Sa laser (1 kHz repetition rate, 5 W, 5 mJ/pulse at 400 nm and 1 W, 1 mJ/pulse at 200 nm) or the harmonics in the gases (n 11 to 31 in the plateau) in the 70–21 nm
This facility proposes a variety of different fs coherent light sources from the infra-red to the Xrays, with an adjustable polarisation, allowing different scientific topics to be investigated. In gas phase, femtochemistry on free species or adsorbates can be studied by photoemission (electronic states) or EXAFS (structure). Photoionisation and alignment dynamics (valence or internal band), spectroscopy on extremely dilute species (radicals, ions), and non-linear physics in the XUV on isolated systems such as clusters can be investigated. In condensed matter, it offers higher resolutions due to high brilliance, new coherence possibilities in imagery, microscopy, holography, especially for nanostructures (spintronics, integrated devices), and the extension of absorption X diffraction, diffusion techniques towards ultimate temporal resolutions for the study of transitory systems out of equilibrium and in situ analysis of ultrafast processes under an external constraint (such as a pulse of magnetic field) due to the fs pulse duration. Optical phonons role in phase transitions, spin polarisation dynamics, identification of complex intermediates in
ARTICLE IN PRESS M.E. Couprie et al. / Nuclear Instruments and Methods in Physics Research A 528 (2004) 557–561
biochemical reactions, study of plasma generation and dynamical behaviour can be analysed. The flux hungry ‘‘photon in-photon out’’ techniques, such as time resolved magnetic holography and resonant inelastic scattering will be developed. In the UV–X domain, protein folding and cell studies using microscopy will benefit from the high brilliance of the source. Exploitation of non-linear techniques opens new prospects for structure and magnetism at interfaces.
4. Conclusion The short wavelength FEL oscillator and the seeding with harmonics in gas provides a spectral range extension towards short wavelengths, in a much more compact device as compared to a simple SASE scheme, and will offer better source quality (Fourier limit) for users. Moreover, SASE, oscillator and harmonics properties can be compared on the same facility, allowing a step forward in the FEL physics understanding. This project
561
relies also on a strong synergy between the accelerator, the FEL and the laser community. It can help to gather a user community exploiting fs X-ray sources.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14]
H. Wabnitz, et al., Nature 420 (2002) 482. M. Billardon, et al., Phys. Rev. Lett. 51 (1983) 1652. M.E. Couprie, et al., Phys. Rev. A. 44 (1991) 1301. R. Prazeres, et al., Phys. Rev. Lett. 78 (1997) 2124. M. Marsi, et al., Appl. Phys. Lett. 70 (1997) 895. G. Neil, Phys. Ev. Lett. 84 (2000) 662. Workshop IRSR, Proceedings ed. LURE, 1998. L.-H. Yu, et al., Science 289 (2000) 932. P. Sali"eres, et al., Adv. At. Mol. Opt. Phys. 41 (1999) 83. D. Dwersteg, et al., Nucl. Instr. and Meth. A 393 (1997) 93. B.C. Yunn, PAC 2001, p. 2254. R.A. Rimmer, et al., PAC 2001, p. 1801. V.N. Volkov, et al., PAC 2001, p. 2218; T. Schultheiss, et al., PAC 2001, p. 2287. J.N. Corlett, et. al., PAC 2003.