[email protected] report

*[email protected] REPORTSimone Spampinati

on behalf of the FERMI team

Outlook

FEL1 as test facility in the soft x-ray

Conclusion

FERMI Presentation and designFERMI [email protected] Linac design

Commisioning of laser heater, and x-bandPhase space controlEmittance preservationFEL1 performance in the nominal wavelength rangeFEL2 starting commissioningDouble stage cascade Harmonic cascade

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 LABORATORY

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FERMI main features Charge 500-800 pC Current 500-800A Slice Emittance

*FERMI Layout

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*FEL-1: seeded FEL single stage high gain harmonic generation (HGHG)UV seed laser: 3 of Ti:Sa or OPAEnergy modulation on the wavelength scale of the seed laserOutput wavelength from 100 nm down to 20nm.FEL 1 AND FEL 2FEL-2: Double stage of HGHGFresh bunch technique implemented with a magnetic delay lineUV seed laser: 3 Ti:Sa or OPAOutput wavelength from 20 nm down to 4nm.FEL 1FEL 2

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Higher harmonic reached by HGHG is limited by energy spread120-150keV energy spread is requiredOne 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=IT: C>500 pC (800 pC) Compression factor CF ~10. Mild compression factorFinal energy spread vs starting oneCourtesy of M.Venturini Vlasov solver calculations Design and working point of [email protected] linac (1)

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Design and working point of [email protected] 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 jitterE-beam quadratic Chirp + Dispersive Section produces a bandwidth increase

Chirp and modulation

dispersive e-quadratic ChirpBunching and compression e- Residual chirp from compression can be compensated with L4 phaseStrong weak in the old ELETTRA linac structure introduce strong quadratic chirpX can be optimized to compensate quadratic chirp or to linearize currentStart from a particular electron beam current distribution at photocathode (to do)

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Tools to control longitudinal phase spaceHigh energy deflector

Laser HeaterX-bandControl of linac microbunhingShort scale length homogeneityReduction of COTR and CSRControl of slice energy spreadLinearization of compressionFlat top current profileLonger green region (slide 7)Highr compression possible

Phase space imaging @Llinac end

From MayFrom MayFrom February

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Laser Heater Laser heater system in the linac tunnel input laser table chicane magnet multiscreen station LH01.02 (CROMOX) laser heater undulator multiscreen station LH01.03 bpm LH01.03 (CROMOX)output laser table.Beam heated deflected and sent in a spectrometer with ~0.58m dispersionSpectrometer located after BC1 @320 MeVChicane 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 (160J laser energy). Laser spot size 200m electron beam 140mHeater on Heater off

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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 m160J

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Energy spread added by heater versus undulator gapEnergy spread for no heating is removed in quadrature from dataGreen points are data of the energy spread added by the heaterBest gap 27.67mm. Predicted 27.3mm 97.2MeV instead of 97.7MeV Slice energy spread added by the heater along the bunchGreen curve: Energy spread with heater in offRed curve: Measured with heater on (160J)Blue curve energy spread added

Heating measurementBeam profile (ps)

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Microbunching suppression

500 pC, no X-band cavity, CF=5.6Residual chirp from compressionBeam energy spectrum measured in DBDfor several setting of laser heater Reduction and suppression of beam modulationSuppression of COTR after spreader (screen sfel01.02)350 pC, X-BAND,CF=10>1J laser energy to suppress COTR (>10KeV). ~1% of further reduction inserting an OTR before this one

20J Laser20J Laser+sfel01.01

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X-band4 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 spaceLinearize compression to obtain flat current

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H deflectorV deflectorNot installedHorizontal deflecting cavity installed in the linac to spreader transfer lineHigh dispersion spectrometer: ~1.8mspectrometer energy spread resolution by twiss function, dispersion and screen resolution 60keVOptical functions have same variation along the bunch than resolution too. Energy spread from deflector Longitudinal resolution >30fsHigh energy deflector for phase space and current profile500 pC CF=1 X-band offCourtesy of G.Penco

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Longitudinal Phase space without laser heater and x band500 pc CF=5.6 L4 @+30deg

Linear chirpMicrobunching

Ramped current distribution

Courtesy of G.Penco

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Longitudinal Phase space with laser heater and x-band

500pc [email protected] [email protected]+30deg to compensate linear chirp

Linear chirp

*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= 200JFEL1 performancesFEL stability and performance over 400 shotsCourtesy of E. AllariaData taken in a user shift [email protected] deg [email protected]+30 deg to compensate linear chirp248nm/7

Laser heater effect on FEL1100 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 140m Black lines are the main spectrum.Laser heater clean the spectrum

Gaussian likeNoisy and spiky

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Laser heater effect on FEL1FEL intensity on ionization gas monitor vs seed laser energy for different laser heater settingsCircular polarizationData of 13 July 2012 LDM shift500 pc CF=10 in BC1. X-band on. Laser transverse dimensions 140m

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Higher harmonic testFEL1 nominal range of operation is down to 20nm 13 harmonic of the seedThe electron beam was so good in July to reach a pulse energy of 200 J at 20 nmTests with higher harmonic

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

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FEL2 commisioningTested first stage of FEL2Used the only diagnostics availableSynchronization between seed laser and electron found by looking on the electron beam dump. Footprint of laser energy modulation Emission on first radiator observedVerified laser transport and initial synchronizationcalibration of three undulator (of 10)At least 1J 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 hereObserved hereInstalled nowSpace for 2 sections

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Double cascade test with FEL 1We tune the last two radiator undulator on a harmonic of the first fourThe bunching is propagated from one stage to the other In this configuration every stage is resonant on one harmonic of the previous stageCoherent emission on the fundamental Less energy modulation by seedShorter gain length in the second undulator Coherent emission on the fundamental FEL gain and exponential growthStrong harmonic bunching near satBunching could be enhanced by slippageBetter bunching in the last stageConfiguration with 3/3 and 5/1 worstx7 Coherent emission on fundamentalCoherent emission on the fundamentalToo high energy modulation is requestedto have bunching. Longer gain length in the second undulator. only coherent radiation in the radiator

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h39Double stage can go higher in harmonic up conversion In this case we dont know the limit: we where limited by undulator calibration available

Double cascade test with FEL 1

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

h1h2 off axisCoherent emission on the fundamentalCoherent emission on the second harmonic4nmh65

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ConclusionsSome activities of the last three months of FERMI commissioning have been presentedLaser heater and x-band have been commissionedElectron phase space closer to nominal oneFERMI1 near specs in the nominal wavelength rangeFEL2 s first stage has been testedFERMI electron beam is bright enough to reach the water windowHarmonic cascade done for the first timewater window reachedOther activity have been performed in the meanwhileImproved matching in the undulator regionImproved alignment in the spreader (BBA of quads)Studies on the trajectory in linac are ongoingCommissioning of FEL diagnostic and FEL beam lineWorks on other system (BPM, current monitor, EOS )Other FEL studies

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END

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