1

FERMI@ELETTRA REPORTFERMI@ELETTRA REPORT

Simone Spampinati

on behalf of the FERMI team

OutlookOutlook

•FEL1 as test facility in the soft x-ray

•Conclusion

•FERMI Presentation and design

•FERMI commisioning

•FERMI@ELETTRA •Linac design

•Commisioning of laser heater, and x-band•Phase space control•Emittance preservation•FEL1 performance in the nominal wavelength range•FEL2 starting commissioning

•Double stage cascade •Harmonic cascade

50 m

Experim. Hall

100 m

Undulator Hall

200 m

Linac Tunnel +

Injector

Extension

SINCROTRONE TRIESTE is a nonprofit shareholder company of national interest, established in 1987 to construct and manage synchrotron light sources as international facilities.

FERMI at the ELETTRA LABORATORYFERMI at the ELETTRA LABORATORY

ELETTRA Synchrotron Light Source:up to 2.4 GeV, top-up mode, ~800 proposals from 40 countries every year

FERMI@Elettra FEL:100 – 4 nm HGHG, fully fundedSponsors:Italian Minister of University and Research (MIUR)Regione Auton. Friuli Venezia GiuliaEuropean Investment Bank (EIB)European Research Council (ERC)European Commission (EC)

FERMI main featuresFERMI main features

• Charge 500-800 pC

• Current 500-800A

• Slice Emittance <1.5 mm mrad

• Energy 1.2-1.5 GeV

Two separate FEL amplifiers to cover the spectral range from 100 nm (12eV) to 4 nm (320 eV)

Radiation feature Electron beam parameter and requirement

• high peak power (0.3 – GW’s range)

• short temporal structure (150-10 fs)

• Good transverse and longitudinal coherhence

• tunable wavelength

• variable polarization (horizontal/circular/vertical)

Restricted list from the scientific case

•High resolution spectroscopy of low density matter •Pump probe spectroscopy •Coherent diffraction imaging

55

FEL1

FEL2I/O mirrors & gas cells

PADReS

EIS

DIPROI

LDM

Photon Beam Lines

slits

experimental hall

FERMI LayoutFERMI Layout

Gun

L1 + XBBC1

SPBC1

L2 L3 L4

linac tunnel

BC2

LH

L0100 MeV,50 A, 0.8 µm

280 MeV,500 A, 1.5 µm

1240 MeV,500 A, 1.5 – 3 µm

COLLIM.SPLH

TLS

DBD

FEL1SPREADER

MBD

undulator hall

COLLIM. COLLIM.

FEL2

66

•FEL-1: seeded FEL single stage high gain harmonic generation (HGHG)

•UV seed laser: 3° of Ti:Sa or OPA

•Energy modulation on the wavelength scale of the seed laser

•Output wavelength from 100 nm down to 20nm.

FEL 1FEL 1 AND AND FEL 2FEL 2

•FEL-2: Double stage of HGHG

•Fresh bunch technique implemented with a magnetic delay line

•UV seed laser: 3° Ti:Sa or OPA

•Output wavelength from 20 nm down to 4nm.

FEL 1FEL 1

FEL 2FEL 2

•Higher harmonic reached by HGHG is limited by energy spread

•120-150keV energy spread is required

•One compressor scheme and laser heater help to contain microbunching and reduce energy spread

•Good region of the electron beam has to be long enough to accommodate seed-electrons time jitter

and slippage. 100 fs jitter and 150 fs seed: 300-400 fs good region of electron beam for FEL1, 500 fs for

FEL2

•Peak current I>500 A (800 nominal) to provide good photon flux and contained gain length :

•C=I×∆T: C>500 pC (800 pC)

•Compression factor CF ~10. Mild compression factor

•Final energy spread vs starting one

Courtesy of M.Venturini Vlasov solver calculations

Design and working point of FERMI@ELETTRA linac (1)Design and working point of FERMI@ELETTRA linac (1)

0E

nE

Design and working point of FERMI@ELETTRA linac (2)Design and working point of FERMI@ELETTRA linac (2)•HGHG is sensible to nonlinearity in electron beam phase space

•E-beam linear energy Chirp + Dispersive Section produces a shift in FEL output fequency and

then a frequency jitter

•E-beam quadratic Chirp + Dispersive Section produces a bandwidth increase

Chirp and modulation

dispersive

e-

quadratic Chirp Bunching and compression

e-

56)(1

1)(

RzhzC

)(znCz s

n

22

2

0)( zdz

Edbz

dz

dEaEzE

• Residual chirp from compression can be compensated with L4 phase•Strong weak in the old ELETTRA linac structure introduce strong quadratic chirp•X can be optimized to compensate quadratic chirp or to linearize current•Start from a particular electron beam current distribution at photocathode (to do)

Tools to control longitudinal phase spaceTools to control longitudinal phase space

High energy deflector

Laser Heater

X-band

•Control of linac microbunhing•Short scale length homogeneity•Reduction of COTR and CSR•Control of slice energy spread

•Linearization of compression•Flat top current profile•Longer green region (slide 7)•Highr compression possible

•Phase space imaging @Llinac end

From May

From May

From February

Laser Heater Laser Heater Laser heater system in the linac tunnel a) input laser tableb) chicane magnetc) multiscreen station LH01.02

(CROMOX)d) laser heater undulatore) multiscreen station LH01.03f) bpm LH01.03 (CROMOX)g) output laser table.

•Beam heated deflected and sent in a spectrometer with ~0.58m dispersion•Spectrometer located after BC1 @320 MeV•Chicane and all cavity on creast (X-BAND in off)•Slice energy spread measured without heater 40 KeV ( optic +deflector)•Maximum energy spread with heater on is 100KeV (160µJ laser energy). •Laser spot size 200µm electron beam 140µm

Heater on Heater off

Energy spread versus laser energyEnergy spread for no heating is removed in quadrature from dataRed points are data of the energy spread added by the heaterGreen error bar from statistic errorsBlue line for theoretical behaviorMagenta points (on the bottom) Theory (only laser modulation without LSC)-Measurements

Laser Spot 200 µm

160µJ

•Energy spread added by heater versus undulator gap•Energy spread for no heating is removed in quadrature from data•Green points are data of the energy spread added by the heater•Best gap 27.67mm. Predicted 27.3mm →97.2MeV instead of 97.7MeV

•Slice energy spread added by the heater along the bunch•Green curve: Energy spread with heater in off•Red curve: Measured with heater on (160µJ)•Blue curve energy spread added

Heating measurementHeating measurement

Beam profile (ps)

Microbunching suppression Microbunching suppression •500 pC, no X-band cavity, CF=5.6•Residual chirp from compression•Beam energy spectrum measured in DBDfor several setting of laser heater •Reduction and suppression of beam modulation

•Suppression of COTR after spreader (screen sfel01.02)•350 pC, X-BAND,CF=10•>1µJ laser energy to suppress COTR (>10KeV). •~1% of further reduction inserting an OTR before this one

20µJ Laser

20µJ Laser+sfel01.01

X-bandX-band•4° harmonic cavity of S band installed in L1

• to linearize the energy chirp with L1 off crest

• linearize compression

• Nominal working point on decelerating crest (-20MeV):near flat current

Linearize phase space

Linearize compression to obtain flat current

H deflector V deflector

Not installed

•Horizontal deflecting cavity installed in the linac to spreader transfer line

•High dispersion spectrometer: ~1.8m

•spectrometer energy spread resolution by twiss function, dispersion and screen resolution 60keV

•Optical functions have same variation along the bunch than resolution too. Energy spread from deflector

•Longitudinal resolution >30fs

High energy deflector for phase space and current profileHigh energy deflector for phase space and current profile

500 pC CF=1 X-band off

Courtesy of G.Penco

Longitudinal Phase space without laser heater and x bandLongitudinal Phase space without laser heater and x band•500 pc CF=5.6 •L4 @+30deg

•Linear chirp•Microbunching

•Ramped current distribution

Courtesy of G.Penco

Longitudinal Phase space with laser heater and x-bandLongitudinal Phase space with laser heater and x-band•500pc CF~10-12•X-band@270deg -20MeV•L4@+30deg to compensate linear chirp

•Linear chirp<1MeV/ps•Quadratic term 1MeV/ps²•Small energy variation along the bunch•Is it possible compensate the quadratic termwith X-band@265deg

•Flat current •Small core energy spread•Is it possible reduce energy spread with X-band@265deg (residual slope on the current and lower current and lower photon flux)

Courtesy of G.Penco

18

Wavelength= 35.4 nmPhoton energy= 35.0 eV

Lambda jitter = 0.016 nm0.046 (%)

Bandwidth(rms) = 0.022 (nm)22.0 meV6.2e-04

Bandwidth jitter = 0.0065 (nm)29 (%)

Pulse energy= 200µJ

FEL1 performancesFEL1 performancesFEL stability and performance over 400 shots

Courtesy of E. Allaria

•Data taken in a user shift Timex•CF~10-12•C=500pC•X-band@270 deg -20MeV•L4@+30 deg to compensate linear chirp•248nm/7

Laser heater effect on FEL1Laser heater effect on FEL1•100 spectra taken with the laser heater switched, figure on the top •100 spectra taken with the laser heater off, figure on the bottom• 500 pc CF=10 in BC1. X-band on. Laser transverse dimensions 140µm• Black lines are the main spectrum.•Laser heater clean the spectrum

Gaussian like

Noisy and spiky

Laser heater effect on FEL1Laser heater effect on FEL1•FEL intensity on ionization gas monitor vs seed laser energy for different laser heater settings•Circular polarization•Data of 13 July 2012 LDM shift•500 pc CF=10 in BC1. X-band on. Laser transverse dimensions 140µm

h28

h21 h23

h29

h26

λ =12.38 nmλ = 8.96 nm

h25

h27

We could not measure intensities because of the interference of longer wavelength radiation mainly emitted off axis

Higher harmonic testHigher harmonic test•FEL1 nominal range of operation is down to 20nm 13° harmonic of the seed•The electron beam was so good in July to reach a pulse energy of 200 µJ at 20 nm•Tests with higher harmonic

•Whit this beam 28° seems to be the limit of the single stage)

2exp(

2

056

560

ERkn

RkE

EnJb

E

rnn

FEL2 commisioningFEL2 commisioning•Tested first stage of FEL2•Used the only diagnostics available•Synchronization between seed laser and electron found by looking on the electron beam dump. Footprint of laser energy modulation • Emission on first radiator observed•Verified laser transport and initial synchronizationcalibration of three undulator (of 10)•At least 1µJ has been obtained from the two radiator of the first stage (tens of nJ were obtained from 6 radiators in the first light of FEL1)

Done here

Observed here

Installed now Space for 2 sections

Double cascade test with FEL 1Double cascade test with FEL 1

10 nm

Seed λ=10 nm (h2)λ= 20 nm (h13)λ=260nmDisp

•We tune the last two radiator undulator on a harmonic of the first four•The bunching is propagated from one stage to the other• In this configuration every stage is resonant on one harmonic of the previous stage•Coherent emission on the fundamental

•Less energy modulation by seed•Shorter gain length in the second undulator •Coherent emission on the fundamental• FEL gain and exponential growth•Strong harmonic bunching near sat•Bunching could be enhanced by slippage•Better bunching in the last stage•Configuration with 3/3 and 5/1 worst

nmSEED 260 nmSEEDresonance 2013/ nmSEEDresonance 1026/

1b2b

3b...

1b

2b

3b...

13b

Seed λ= 10 nm (h26)λ=260nmDisp

nmSEED 260

1b...

26b...

nmSEEDresonance 1026/

x7 •Coherent emission on fundamental

•Coherent emission on the fundamental•Too high energy modulation is requestedto have bunching. Longer gain length in the second undulator.• only coherent radiation in the radiator

Seed λ=10 nm (h2)λ= 20 nm (h13)λ=260nmDisp

260SEED 2013/ SEEDresonance 7.639/ SEEDresonance

1b

2b

3b...

1b

2b

3b...

13b

h39

•Double stage can go higher in harmonic up conversion •In this case we don’t know the limit: we where limited by undulator calibration available

Double cascade test with FEL 1Double cascade test with FEL 1

Double stage harmonic cascade test with FEL 1Double stage harmonic cascade test with FEL 1•Keep going with harmonic up-conversion•We try with an harmonic cascade as second stage•One of the harmonic of the last stage is in resonance with one of the harmonic of beam currentin the previous stage

Seed λ = 6.67nm (h3) λ = 20 nm (h13)λ=260nmDisp

nmSEEDresonance 2013/ nmSEEDresonance 85.32/ nmSEED 260

2b1b

... h1h2 off axis5b

...

•Coherent emission on the fundamental

•Coherent emission on the second harmonic

4nm h65

ConclusionsConclusions•Some activities of the last three months of FERMI commissioning have been presented•Laser heater and x-band have been commissioned•Electron phase space closer to nominal one•FERMI1 near specs in the nominal wavelength range•FEL2’ s first stage has been tested•FERMI electron beam is bright enough to reach the water window•Harmonic cascade done for the first time•water window reached

•Other activity have been performed in the meanwhile•Improved matching in the undulator region•Improved alignment in the spreader (BBA of quads)•Studies on the trajectory in linac are ongoing•Commissioning of FEL diagnostic and FEL beam line•Works on other system (BPM, current monitor, EOS… )•Other FEL studies

END