1. 1 FERMI@ELETTRA REPORT Simone Spampinati on behalf of the FERMI team

2. Outlook 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

3.  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 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 funded  Sponsors: Italian Minister of University and Research (MIUR) Regione Auton. Friuli Venezia Giulia European Investment Bank (EIB) European Research Council (ERC) European Commission (EC)

4. FERMI 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

5. 5 FEL1 FEL2 I/O mirrors & gas cells PADReS EIS DIPROI LDM Photon Beam Lines slits experimental hall FERMI Layout

6. 6 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 1 AND FEL 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 1 FEL 2

7. 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)

8. 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 ChirpBunching and compression e- 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)

9. Tools 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 February

10. Laser Heater Laser heater system in the linac tunnel a)input laser table b) chicane magnet c) multiscreen station LH01.02 (CROMOX) d) laser heater undulator e) multiscreen station LH01.03 f) 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

11. Energy spread versus laser energy  Energy spread for no heating is removed in quadrature from data  Red points are data of the energy spread added by the heater  Green error bar from statistic errors  Blue line for theoretical behavior  Magenta points (on the bottom) Theory (only laser modulation without LSC)-Measurements Laser Spot 200 µm 160µJ

12. 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 measurement Beam profile (ps)

13. Microbunching suppression 500 pC, no X-band cavity, CF=5.6 Residual chirp from compression Beam energy spectrum measured in DBD for 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

14. X-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

15. H deflectorV 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 profile 500 pC CF=1 X-band off Courtesy of G.Penco

16. Longitudinal 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

17. Longitudinal 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 term with 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. 18 Wavelength= 35.4 nm Photon energy= 35.0 eV Lambda jitter = 0.016 nm 0.046 (%) Bandwidth(rms) =0.022 (nm) 22.0 meV 6.2e-04 Bandwidth jitter = 0.0065 (nm) 29 (%) Pulse energy= 200µJ FEL1 performances FEL 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

19. Laser 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

20. Laser 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

21. Higher 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

22. FEL2 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 synchronization calibration 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

23. Double cascade test with FEL 1 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 x7 Coherent emission on fundamental Coherent emission on the fundamental Too high energy modulation is requested to have bunching. Longer gain length in the second undulator. only coherent radiation in the radiator

24. 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 1

25. Double 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 current in the previous stage h1 h2 off axis Coherent emission on the fundamental Coherent emission on the second harmonic 4nmh65

26. Conclusions 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

27. END