Nuclear Instruments and Methods in Physics Research A 507 (2003) 345–349

The SPARC project: a high-brightness electron beam sourceat LNF to drive a SASE-FEL experiment

D. Alesinia, S. Bertoluccia, M.E. Biaginia, C. Biscaria, R. Bonia, M. Boscoloa,M. Castellanoa, A. Clozzaa, G. Di Pirroa, A. Dragoa, A. Espositoa,

M. Ferrarioa,b,*, V. Fuscoa, A. Galloa, A. Ghigoa, S. Guiduccia, M. Incurvatia,P. Laurellia, C. Ligia, F. Marcellinia, M. Miglioratib, C. Milardia, L. Palumbob,L. Pellegrinoa, M. Pregera, P. Raimondia, R. Riccia, C. Sanellia, F. Sgammaa,B. Spataroa, M. Serioa, A. Stecchia, A. Stellaa, F. Tazziolia, C. Vaccarezzaa,M. Vescovia, C. Vicarioa, M. Zobova, E. Acerbic, F. Alessandriac, D. Barnic,G. Bellomoc, I. Boscoloc, F. Broggic, S. Cialdic, C. DeMartinisc, D. Giovec,C. Marolic, V. Petrilloc, M. Rome’c, L. Serafinic, E. Chiadronid, G. Felicid,

D. Levid, M. Mastruccid, M. Mattiolid, G. Medicid, G.S. Petrarcad, L. Catanie,f,A. Cianchie,f, A. D’Angeloe,f, R. Di Salvoe,f, A. Fantinie,f, D. Moriccianie,f,C. Schaerfe,f, R. Bartolinig, F. Cioccig, G. Dattolig, A. Doriag, F. Florag,G.P. Galleranog, L. Giannessig, E. Giovenaleg, G. Messinag, L. Mezig,

P.L. Ottavianig, L. Picardig, M. Quattrominig, A. Renierig, C. Ronsivalleg,L. Avaldih, C. Carboneh, A. Cricentih, A. Pifferih, P. Perfettih, T. Prosperih,

V. Rossi Albertinih, C. Quaresimah, N. Zemah

a INFN/LNF, via E. Fermi 40, 00044 Frascati (RM), ItalybUniversity of Roma ‘‘La Sapienza’’, Dip. Energetica, via A. Scarpa 14, 00161 Roma, Italy

c INFN/Milano, via Celoria 16, 20133 Milano, Italyd INFN/Roma I, University of Roma ‘‘La Sapienza’’, p.le A. Moro 5, 00185 Roma, Italy

e INFN/Roma II, University of Roma ‘‘Tor Vergata’’, via della Ricerca Scientifica 1, 00133 Roma, ItalyfUniversity of Rome ‘‘Tor Vergata’’, via della Ricerca Scientifica 1, 00133 Roma, Italy

gENEA/FIS, via E. Fermi 45, 00040 Frascati (RM), ItalyhCNR/ISM, Area della Ricerca di Roma-Tor Vergata, via del Fosso del Cavaliere 100, 00133 Roma, Italy

Abstract

The Project Sorgente Pulsata e Amplificata di Radiazione Coerente (SPARC), proposed by a collaboration among

ENEA–INFN–CNR–Universita’ di Tor Vergata–INFM–ST, was recently approved by the Italian Government and

will be built at LNF. The aim of the project is to promote an R&D activity oriented to the development of a coherent

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*Corresponding author. INFN-LNF, Divisione Acceleratori, Via E. Fermi 40, 00044 Frascati (Roma), Italy. Tel.: +39-0694032216;

fax: +39-0694032565.

E-mail address: massimo.ferrario@lnf.infn.it (M. Ferrario).

0168-9002/03/$ - see front matter r 2003 Elsevier B.V. All rights reserved.

doi:10.1016/S0168-9002(03)00943-4

ultra-brilliant X-ray source in Italy. This collaboration has identified a program founded on two main issues: the

generation of ultra-high peak brightness electron beams and of resonant higher harmonics in the SASE-FEL process, as

presented in this paper.

r 2003 Elsevier B.V. All rights reserved.

PACS: 41.60.Cr

Keywords: High-brightness electron beams; SASE-FEL

1. The SPARC project

The overall SPARC project consists of fourmain lines of activity aiming at several goals: theircommon denominator is to explore the scientificand technological issues that set up the mostcrucial challenges on the way to the realisation of aSASE-FEL based X-ray source, the SPARXproposal [1]. These are:(1) 150Mev advanced photo-injector: Since the

performances of X-ray SASE-FELs are criticallydependent on the peak brightness of the electronbeam delivered at the undulator entrance, we wantto investigate two main issues—generation of theelectron beam and bunch compression via mag-netic and/or RF velocity bunching—by means ofan advanced system delivering 150MeV electrons,the minimum energy to avoid further emittancedilutions due to time-dependent space chargeeffects.(2) SASE-FEL visible-VUV experiment: In order

to investigate the problems related to matching thebeam into an undulator and keeping it well alignedto the radiation beam, as well as the generation ofnon-linear coherent higher harmonics, we want toperform a SASE-FEL experiment with the150MeV beam, using a segmented undulator withadditional strong focusing, to observe FEL radia-tion at 530 nm [2] and below.(3) X-ray optics/monochromators: The X-ray

FEL radiation will provide unique radiationbeams to users in terms of peak brightness andpulse time duration (100 fs), posing at the sametime severe challenges to the optics necessary toguide and handle such radiation. This project willpursue also a vigorous R&D activity on theanalysis of radiation–matter interactions in thespectral range typical of SASE X-ray FELs (from

0.1 to 10 nm), as well as the design of new opticsand monochromators compatible with thesebeams.(4) Soft X-ray table-top source: In order to test

these optics and to start the R&D on applications,the project will undertake an upgrade of thepresently operated table-top source of X-rays atINFM-Politecnico Milano, delivering 107 softX-ray photons in 10–20 fs pulses by means of highharmonic generation in a gas.In the following, the layout and planned

activities for items (1) and (2) will be presentedin more detail.

2. Advanced photo-injector

The main goals of this activity are acquiring anexpertise in the construction, commissioning andcharacterisation of an advanced photo-injectorsystem and performing an experimental investiga-tion of two theoretical predictions that have beenrecently conceived and presented by members ofthis study group. These are the new working point[3] for high brightness RF photo-injectors and thevelocity bunching technique to apply RF bunchcompression through the photo-injector, withemittance preservation [4]. The 150MeV injectorwill be built inside an available bunker of theFrascati INFN National Laboratories: the generallayout of the system is shown in Fig. 1.

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Fig. 1. Layout of SPARC R&D project.

D. Alesini et al. / Nuclear Instruments and Methods in Physics Research A 507 (2003) 345–349346

The proposed system to be built consists of a 1.6cell RF gun operated at S-band (2.856GHz, of theBNL/UCLA/SLAC type [5]) and high peak fieldon the cathode (120–140MeV/m) with incorpo-rated metallic photo-cathode (Copper or Mg),generating a 6MeV beam which is properlyfocused and matched into two accelerating sec-tions of the SLAC type (S-band, travelling wave)the third section is foreseen for the rectilinearcompressor experiment, as explained later.The laser system driving the photocathode will

use the radiation from a Ti:Sa laser with theoscillator pulse train locked to the RF (see Fig. 2).Ti:Sa mode locked oscillator and amplifiers able toproduce the requested energy per pulse (500 mJ at266 nm) are commercially available. To obtain thetime pulse shape we are going to test themanipulation of frequency lines in the largebandwidth of Ti:Sa, in order to produce the10 ps long flat top shape. We can use a liquidcrystals mask in the Fourier plane of the non-dispersive optic arrangement or a collinear acusto-optic modulator for line frequency manipulation.Liquid crystals act as pixels that introduce a

controlled phase delay on different parts of thespatially dispersed spectrum. The acusto-opticmodulator performs a continuos frequency mod-ulation and can operate on a bandwidth up to200 nm, one order of magnitude larger than the

capability of liquid crystals. The transverse homo-geneity is produced with a pinhole and a positiondependent transmission filter. The time and energystability can be achieved by proper feedback loopsand by the control of the laser environment. Laserpulse shaping technique has been recently demon-strated to be a useful tool for the reduction of non-linear space charge forces, achieving an emittanceof 1.2 mm with a 1 nC, 9 ps long bunch [6].The first experiment with the electron beam we

have planned to do is the verification of the beamemittance compensation process predicted by thenew working point described in Ref. [3] incombination with the laser pulse shaping. Thekey point is the measurement of the emittanceoscillation in the drift after the gun where a doubleminima behaviour is expected. Since the optimumbeam matching to the booster is predicted on therelative emittance maximum, see Fig. 3, a dedi-cated movable emittance measurement station hasbeen designed, as shown in Fig. 4.A pepperpot and a screen are connected with

three long bellows in order to scan the emittancealong a 1m long drift and to find experimentallythe optimum location of the first TW structure.The chromatic origin of the double emittance

minima behaviour [7], due to the solenoid energy-dependent focal length, and the charge and gunpeak field scaling will also be investigated at thebeginning of the experimental program.Our PARMELA [8] simulations show an rms

normalised emittance as low as 0.6 mm (1.2 mm) for

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Fig. 2. Layout of the photocathode Laser system.

Fig. 3. PARMELA simulation of emittance evolution along

the injector (gun+2 TW structures).

D. Alesini et al. / Nuclear Instruments and Methods in Physics Research A 507 (2003) 345–349 347

a 1 nC (1.6 nC) bunch. We can generate with thissystem a beam like that needed by the FELexperiment at 150MeV. The rms correlated energyspread over the bunch is 0.14% with a rmsnormalised emittance of 1.2 mm (at 1.6 nC bunchcharge, 150A peak current), but the slice energyspread and the slice normalised emittance, calcu-lated over a 300 mm slice length (comparable to theanticipated cooperation length), are well below0.05% and 0.5 mm, respectively, all over the bunch.

3. The FEL SASE source

The FEL SASE experiment will be conductedusing a permanent magnet undulator made of 6sections, each 2.5m long, separated by 0.3m gapshosting single quadrupoles which focus in thehorizontal plane. The undulator period is set at3.3 cm, with an undulator parameter kw ¼ 1:88:A simulation performed with GENESIS [9] is

reported in Fig. 5, showing the exponential growthof the radiation power at 530 nm along theundulator: almost 108W can be reached after14m of total undulator length. Preliminary eva-

luations of the radiation power generated into thenon-linear coherent odd higher harmonics showthat 107 and 7� 105W can be reached on the thirdand fifth harmonics, respectively.

4. Further experiments

As shown in Fig. 1, the SPARC layout displaystwo main upgrades that will be implemented in asecond phase of the project: a third acceleratingsection which will be inserted downstream the RFgun and a parallel beam line containing a magneticcompressor.The new section will be designed to study RF

compression: it will support travelling waves at anadjustable phase velocity (from v ¼ c down tov ¼ 0:999c) in order to exploit the full potential-ities of the velocity bunching technique [3]. Itsdesign and construction will proceed in parallel tothe commissioning of the SPARC injector system(RF gun+2 standard SLAC-type 3m sections).These tests of RF compression assume greatrelevance in our R&D program [1] since thegeneral lay-out for SPARX foresees the use of amixed compression scheme, RF compression inthe photoinjector up to 700A and one single stageof magnetic compression at 1GeV up to the finalpeak current of 2.5 kA.The second beam line will allow us to conduct

experiments on magnetic compression. We alsoplan to investigate experimentally CSR inducedeffects on emittance degradation and surfaceroughness wake-field effects, without interferingwith the ongoing FEL experiment.

Acknowledgements

We would like to thank D.T. Palmer (SLAC)and J.B. Rosenzweig (UCLA) for the many helpfuldiscussions and suggestions.

References

[1] D. Alesini, et al., Nucl. Instr. and Meth. A 507 (2003) 503.

[2] S. Milton, et al., Science 292 (2001) 2037.

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Fig. 4. Movable emittance measurement station.

Fig. 5. Radiation power at 530 nm growth along the undulator.

D. Alesini et al. / Nuclear Instruments and Methods in Physics Research A 507 (2003) 345–349348

[3] M. Ferrario, et al., Homdyn study for the LCLS RF

photoinjector, SLAC-PUB 8400.

[4] L. Serafini, M. Ferrario, AIP Conf. Proc. 581 (2001) 87.

[5] D.T. Palmer, The next generation photoinjector, Ph.D.

Thesis, Stanford University.

[6] J. Yang, et al., J. Appl. Phys. 92 (3) (2002).

[7] M. Ferrario, et al., in: J. Rosenzweig, L. Serafini, (Eds.),

The Physics & Applications of High Brightness Electron

Beams, World Scientific, Singapore, to be published.

[8] L.M. Young, J.H. Billen, PARMELA, LA-UR-96-1835,

2000.

[9] S. Reiche, Nucl. Instr. and Meth. A 429 (1999) 243.

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