Bulfone, D

Cargnello, F

Castellano, M G

Cevenini, F

Ciocci, F

Cutolo, A

D'Auria, G

Daclon, F

Dattoli, Giuseppe

De Angelis, A

Dipace, A

Doria, A

Ferianis, M

Gallerano, G P

Garosi, F

Giannessi, L

Giannini, M M

Giovenale, E

Margaritondo, G

Massarotti, A

Mezi, L

Ottaviani, P L

Patteri, P

Renieri, A

Rindi, A

Rosei, R

Rubbia, Carlo

Sabia, Elio

Segreto, A

Tazzari, S

Tazzioli, F

Torre, A D

Visintini, R

Walker, R P

Wrulich, A F

Zangrando, D

R.P. Walker

D. Bulfone

F. Cargnello

M. Castellano

F. Cevenini

F. Ciocci

A. Cutolo

G. D'Auria

F. Daclon

G. Dattoli

A. De Angelis

A. Dipace

A. Doria

M. Ferianis

G.P. Gallerano

F. Garosi

L. Giannessi

M. Giannini

E. Giovenale

G. Margaritondo

A. Massarotti

L. Mezi

P.L. Ottaviani

P. Patteri

A. Renieri

A. Rindi

R. Rosei

C. Rubbia

E. Sabia

A. Segreto

S. Tazzari

F. Tazzioli

A. Torre

R. Visintini

A. Wrulich

D. Zangrando

Crossref

Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment

The FERMI FEL project at Trieste

CERN Document Server

THE FERMI FEL PROJECT AT TRIESTED. Bulfone, F. Cargnello, G. D'Auria, F. Daclon, M. Ferianis, M. Giannini,G. Margaritondo§, A. Massarotti, A. Rindi, R. Rosei, C. Rubbia¥, R. Visintini,R.P. Walker†, A. Wrulich, D. Zangrando,  Sincrotrone Trieste S.c.p.A.F. Ciocci, G. Dattoli, A. De Angelis¶, A. Dipace,  A. Doria, G. P. Gallerano, F. Garosi, L. Giannessi,E. Giovenale, L. Mezi, P. L. Ottaviani, A. Renieri, E. Sabia, A. Segreto‡, A. Torre,  ENEA-FrascatiM. Castellano, P. Patteri, S. Tazzari, F. Tazzioli,  INFN-FrascatiF. Cevenini,  INFN-Naples and Univ. Naples, Dept. of PhysicsA. Cutolo,  Univ. Naples, Dept. of Electronic Engineering† corresponding author; ¶ guest; ‡ study grant holder§ also at EPFL, Lausanne, Switzerland; ¥ also at CERN, Geneva, SwitzerlandThe main features of the FERMI project are described,including beam transport design and FEL performancecalculations.I. INTRODUCTIONThe FERMI (Free Electron Radiation and MatchingInstrumentation) project aims to construct an Infra-Red FELuser facility covering a broad spectral range (2-250 m m) tocomplement the high brightness radiation from the ELETTRAsynchrotron radiation facility at Trieste [1]. A unique featureof the project will be the possibility of carrying out "pump-probe" experiments using synchronized radiation beams fromFERMI and ELETTRA on the same sample.The project was launched at a meeting of Italian FELexperts held in Trieste on the 18th November 1994, chaired byC. Rubbia, as a collaboration between Sincrotrone Trieste,ENEA (Frascati), INFN (Frascati) and the University ofNaples (Department of Electronic Engineering).The facility will make use of an existing linac, that formspart of the ELETTRA injection system, and a hall into whichthe beam can be extracted.  In addition, for the first phase ofthe project equipment will be used from the suspendedINFN/ENEA "SURF" FEL experiment [2], including theundulator, beam transport magnets and optical  cavity.Development of the facility is foreseen in three phases.Phase 1 will consist of setting up the first FEL (FEL-1) tocover the range 5-20 m m. Initially, the existing optical cavitywill be used to demonstrate laser operation at a fixedwavelength of 16 m m. Later, new mirrors will be installedallowing tuneability over the range 5-20 m m with a higheroutput coupling, permitting a first user experiment to becarried out. In Phase 2 a second FEL (FEL-2) will be set upfor the 15-250 m m region. To allow a full support for userexperiments a new building will be constructed (Phase 3)hosting several experimental stations. As part of this phase anew linac gun will also be implemented to reduce theemittance, which is necessary to reach the shortestwavelengths on FEL-1 (2-5 m m).II. LAYOUTFigure 1 shows the layout of the facility adjacent to theELETTRA storage ring. The beam from the first 100 MeVpart of the 1.5 GeV injector linac will be transported into anexisting hall adjacent to the linac tunnel, sufficiently large(32 m x 10 m) to accommodate both FELs as well as space forpower supplies etc. and an area for optical diagnostics andpilot experiments. In the final phase the FEL beams will beFig. 1 Layout of the FERMI FEL facility.186© 1996 IEEE. Personal use of this material is permitted. However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to serversor lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.transported along the klystron gallery (above the linac tunnel)and into a new FEL experimental area (~ 21 m x 17 m) whichwill host a number of experimental hutches. The location ofthe new building will allow the possibility of easilytransporting synchrotron radiation beams into the FELexperimental area, or FEL radiation into the ELETTRAexperimental hall.III. LINACThe low energy part of the linac has been designed tooperate in a FEL mode in the 20-75 MeV range with a 10 m spulse length. First tests in this mode of operation are reportedelsewhere in these Proceedings [3]. Table 1 summarises theexpected linac parameters, on which the FEL performancecalculations were based. It will be seen that the linacperformance is not sufficient to allow saturation to be reachedbelow about 5 m m, and therefore possible schemes forupgrading the gun are being evaluated.Table 1. Main linac parameters in the FEL-modeEnergy, MeV 20-75Macropulse repetition rate, Hz 10Macropulse length, m s 10Charge per micropulse, nC 0.4Micropulse length (FWHM), ps 10Peak current, A 37.5Micropulse repetition rate, MHz 20.8-31.3Normalized emittance (rms), mm mrad 62.5Energy spread at 75 MeV, % –  0.3Fig. 2 Layout of the transport line and two FELsIV. BEAM TRANSPORTA particular requirement of the transport line is to providea variable path length dependence with energy, in order tomaintain high peak currents or to allow bunch lengthmanipulations in conjunction with linac phase adjustments.Fig. 2 shows a suitably flexible design using four bends foreach FEL line. Fig. 3 shows the optical functions for FEL-1 inthe isochronous case. The design is compatible with operationover the full 20-75 MeV range using the existing  magnets.Fig. 3 FEL-1 transport line optics in the isochronous case.V. UNDULATORS AND OPTICAL CAVITIESTable 2 summarises the undulator parameters. Theundulator for FEL-1 was built by Ansaldo in collaborationwith ENEA, Frascati  [4]. The minimum gap of 20 mm allowsa vacuum aperture of 15 mm which gives minimal diffractionlosses at 20 m m. The FEL-2 undulator is designed to have theshortest period allowing 250 m m to be reached at the lowestenvisaged energy of 20 MeV, compatible with a vacuumaperture of 40 mm for minimal diffraction losses.Table 2. Main parameters of the FEL undulators.FEL-1 FEL-2Length, m 2.20 2.28Period, m 0.044 0.095Number of periods 50 24Minimum gap, mm 20 45Peak field, T 0.35 0.43K parameter, max. 1.44 3.79The optical cavity length has been chosen to be 5.4 m,which allows the same bunch separation to be obtained inELETTRA with a regular filling pattern with 24 bunches. ForFEL-1 the mirror adjustment system for the SURF project willbe used which has combined PZT and motorized adjustmentof mirror tilt and longitudinal position [5]. Mirrors areavailable for the first demonstration experiment at 16 m m.Thereafter other mirrors will be substituted to cover the5-20 m m range. No decision has yet been taken about theFEL-2 optical cavity that could employ metal mesh mirrorsand a waveguide cavity.187VI. PERFORMANCE CALCULATIONSFig. 4. Small signal gain for FEL-1 and FEL-2.The estimated small signal gain (Gmax.) , including theeffects of emittance, energy spread and slippage is shown infig. 4 as a function of undulator K value for various electronbeam energies. Table 3 presents a summary of the optimizedparameters at various wavelengths, assuming 5 % outputcoupling and 1 % losses. It can be seen that the gain issufficient above about 5 m m to reach saturation in asufficiently small time ( t r) with respect to the macropulseduration. The results indicate that high micropulse energies(Emicro.) and power (Pmicro.) can be produced, with lowaverage power (Pav.) due to the low duty cycle.Table 3. Results of FEL performance calculations.FEL-1 FEL-2l , m m 5 10 16 20 20 50 100 250E, MeV 48 34 27 24 46 30 23 20Gmax. (%) 18.3 27.3 31.2 31.4 24.0 33.1 33.6 25.0t r, m s 6.3 3.8 3.2 3.2 4.3 3.0 2.9 4.1Emicro., m J 27 24 20 18 96 62 40 23Pmicro., MW 2.2 2.0 1.6 1.4 9.0 5.8 3.8 2.2Pmacro., kW 0.80 0.67 0.56 0.49 2.7 1.7 1.1 0.64Pav., mW 30 42 38 34 152 120 79 38Fig. 5  Results of pulse propagation analysis (see text).  A more accurate numerical analysis of pulse propagationeffects has been made, using a code developed by the ENEAgroup based on the solution of the FEL integral equationincluding saturation effects. Figure 5 shows the output poweraveraged over the macropulse and the optical pulse length,near the beginning of the macropulse (small signal value) andat the end (saturated value), as a function of cavity lengthdetuning (d L) for 2 cases : FEL-1 at 16 m m (upper) and FEL-2at 250 m m (lower). In general the results confirm thatsaturation is reached in the 5-250 m m range, and that the pulseenergy and power is in agreement with the previouscalculations. It can also be seen that the pulse length at smalldetuning is smaller than the electron pulse length (rms = 4.2ps), but increases with detuning and due to saturation,particularly in the case of large  slippage (e.g. at 250 m m).VII. PRESENT STATUSThe work presented here is a summary of a more detailedConceptual Design Report that has recently been completed.The present phase of activity concerns the identification ofpotential users and possible collaborators, as well as sourcesof funding. A formal collaborative agreement between theItalian partners is also being prepared.VIII. REFERENCES[1] C.J. Bocchetta et al., this Conference.[2] M. Castellano et al., Proc. 3rd European ParticleAccelerator Conference, Editions Frontières (1992) p. 611[3] G. D'Auria et al., this Conference.[4] F. Rosatelli et al., Proc. 1991 US Particle AcceleratorConference, p. 2760.[5] M. Castellano et al., Nucl. Instr. Meth. A304 (1991) 204.188

The FERMI FEL project at Trieste

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