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Experience with diagnostics at FLASH

Experience with diagnostics at FLASH. Holger Schlarb DESY 22607 Hamburg. Current compression scheme Slice measurements Electro-optic techniques Summary Outlook. Longitudinal phase space injector - present design -. < 60 fs. 0. 10. 20. 30. 40. 50. 125-130 MeV.

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Experience with diagnostics at FLASH

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  1. Experience with diagnostics at FLASH Holger Schlarb DESY 22607 Hamburg • Current compression scheme • Slice measurements • Electro-optic techniques • Summary • Outlook Holger Schlarb, DESY

  2. Longitudinal phase space injector- present design - < 60 fs 0 10 20 30 40 50 125-130 MeV Superconducting TESLA module bunch compressor bunch compressor RF gun 12/20 MV/m Laser 4 - 5 MeV Small space charge on cathode sL= 4.4 ± 0.1 ps Time (ps) Holger Schlarb, DESY Courtesy: M. Dohlus

  3. Diagnostics for long. phase space Streak camera Laser phase THz Laser CDR ISR ISR TEO LOLA CDR PP-laser Tosylab CSR/SR Laser EO-container EO/CDR/CTR/TR ACC 1 BC2 ACC 23 ACC 45 BC3 Undulators Diag. Diag. RF gun THz • LOLA: transverse deflecting structure • bunch profile, slice emittance & energy spread EO: electro-optic  bunch profile, timing (TEO) • ISR: incoherent synchrotron radiation •  energy spread & beam energy • CRD: coherent radiation diagnostics (see Oliver Grimm) •  longitudinal spectrum of e-beam (THz radiation, 10GHz-30THz) • CTR : coherent transition radiation • CSR: coherent synchrotron radiation • CDR: coherent diffraction radiation Holger Schlarb, DESY

  4. Transverse deflecting structure Vy(t) S-band Fast hor. kicker ~ z ~ z - - e e z 2 . 4 4 m 2 . 4 4 m D y » D y » 6 0 ° 6 0 ° b b b b c p c p • collaboration between DESY and SLAC • vertical deflecting RF structure (2.856 GHz) operated at zero crossing • vertical size of beam at imaging screen  depends on bunch length • 40 MW klystron power to “streak” the 0.5 GeV at TTF2 (26MV@20MW) • ‘Parasitical’ measurement using hor. kicker and off-axis screens • Resolution: TTF2 ~ 10-50 fs (depending on vertical beam size) 2 3.66 m ~20° Vertical streak Holger Schlarb, DESY TTF2: M. Ross et.al. + MIN DESY

  5. Waveguide Load Beam Direction LOLA IV RF Input Holger Schlarb, DESY Courtesy: M. Nagl, M. Ross et al.

  6. Examples for bunch images LOLA off: LOLA on: • Typical streak strength: 3.5 mm / ps Head • Time resolution: vertical rms beam size (LOLA off) / streak time Tail Holger Schlarb, DESY

  7. First attempts to compare TCAV & simulations Image with LOLA x Simulation with CSR Holger Schlarb, DESY Courtesy: M. Dohlus (DESY)

  8. Projected and slice emittance measurements - early results - Slicing used for meas. Emittance (100%) time Mismatch factor B • Longitudinal Slices of 250um or 154fs • (100%) ~ 7.5um head … 4 um tail • (90%) ~ 6.3 um head … 1.5 um tail • Mismatch phases indicate gradual rotation of the slice rms –ellipses in hor. phase space along the bunch. Most likely caused by chromaticity. Mismatch phase Normal coordinates: Holger Schlarb, DESY Courtesy: M. Röhrs

  9. LOLA in the FLASH beamline Slice emittance and centroid shifts Q9/10ACC4 Q9/10ACC5 Q9/10ACC6 Q9ACC7 ACC4 ACC5 LOLA Horizontal Kicker Off-axis screen Beam direction GUN ACC1 BC2 ACC2/3 BC3 ACC4/5 LOLA Dogleg UND1 … UND6 Keep constant and small y at OTR -> six quads are scanned simultaneous -> check upstream optics (matching!) Holger Schlarb, DESY

  10. Optics for slice emittance measurements • Scan of horizontal phase advance (~210 deg range) using the 6 quadrupoles Q9ACC4 – Q10ACC6 upstream of LOLA • Streak at the screen is held constant (y = const) • Values of the beta functions at the screen: ~5m - 10m Q9ACC4 LOLA OTR small large Courtesy: M. Röhrs Holger Schlarb, DESY

  11. LOLA in the FLASH beamline Slice emittance and centroid shifts Q9/10ACC4 Q9/10ACC5 Q9/10ACC6 Q9ACC7 ACC4 ACC5 LOLA Horizontal Kicker Off-axis screen Slice energy spread & energy correlation C1 C2 C3 C4 Beam direction GUN ACC1 BC2 ACC2/3 BC3 ACC4/5 LOLA Dogleg UND1 … UND6 Keep constant and small y at OTR -> six quads are scanned simultaneous -> check upstream optics (matching!) Large dispersion + small spot at OTR -> change of optics, open collimators -> check dispersion & streak calibration Holger Schlarb, DESY

  12. Optics for energy-time correlation measurements Standard optics`: Optics for the measurements: Objectives: small beta function values (~ 3m) , maximum streak, large dispersion at the screen (~290mm), LOLA OTR Holger Schlarb, DESY Courtesy: M. Röhrs

  13. Screen Calibration Time axis (vertical): Measurement of the vertical beam position for different phases Energy axis (OTR 5ECOL): Measurement of the horizontal dispersion by variation of the current in the dipole Holger Schlarb, DESY Courtesy: M. Röhrs

  14. On-crest operation: Longitudinal density profile 4.8 ps (BCs off) Head Tail rms-lengths: 3.8 ps (BCs on) Charge: 1 nC, Energy: 650 MeV Holger Schlarb, DESY Courtesy: M. Röhrs

  15. On-crest operation:Longitudinal phase space Bunch compressors on, Charge: 1 nC, Energy: 650 MeV 130 keV rms • Dispersion at the screen: 290 mm • Total rms energy spread: 0.09% (585 keV) • rms slice spread < 0.02% (130 keV) limited by transverse beam size Holger Schlarb, DESY Courtesy: M. Röhrs

  16. On-crest operation:Slice emittance 1σ-emittance, 100% of particles • Systematic rms error of absolute values ~ 30% due to quadrupole gradient end energy errors. But: ratios not affected! • Projected emittance upstream of BC3: 4.3 mm mrad Bunch compressors on, Charge: 1 nC, Energy: 650 MeV Holger Schlarb, DESY Courtesy: M. Röhrs

  17. SASE at 13.7 nm (5µJ): Longitudinal profile Parameter: Charge: 0.5 nC Energy: 677 MeV ACC1-phase: -9˚ ACC23-phase: -25˚ ACC45-phase: 0˚ Spike width: ~75 fs (FWHM) Resolution: ~20 fs Charge in spike: ~0.12 nC (23%) spike current: ~1.7 kA Holger Schlarb, DESY Courtesy: M. Röhrs

  18. SASE at 13.7 nm:Longitudinal phase space • Energy spread in the spike: ~0.23% (1.6 MeV) • Result for SASE operation at 31.4 nm (450 MeV): 0.4% peak energy spread, similar shape of energy-time correlation Dispersion: 233 mm; Time resolution: ~ 50 fs; Energy spread resolution: ~ 0.06% (380 keV) Holger Schlarb, DESY Courtesy: M. Röhrs

  19. SASE at 13.7 nm: Slice emittance • Vertical rms width during the scan: < 220 µm(60 fs resolution) • Projected emittance: 13.5 mm mrad • Similar result for SASE operation at 31.4nm Holger Schlarb, DESY Courtesy: M. Röhrs

  20. Tomography: one slice Region used for tomography (duration: 50 fs) Holger Schlarb, DESY Courtesy: M. Röhrs

  21. Tomography: one slice Holger Schlarb, DESY Courtesy: M. Röhrs

  22. Overview on EO-techniques Electro-optic Sampling : + simple (laser) system + arbitrary time window + high resolution - no single bunch Spectral Decoding: + simple (laser) system + high repetition rate - limited resolution (500fs) - distorted signal for e-bunches < 200fs Temporal Decoding: + large time window + high resolution (120fs, GaP) - mJ laser pulse energy - low repetition rate Spatial Decoding: + simple laser system + high repetition rate + high resolution (170fs, ZnTe) - more complex imaging optics Courtesy: B. Steffen et al

  23. Results on temporal decoding- cross-check of theory - < 200 fs Typical measurement at medium compression EO signals seen: typical 150 fs-200 fs (FWHM) with GaP, corresponds to 220-290 fs for e-bunch due to crossed polarizer setup. Courtesy: B. Steffen et al (DESY) G. Berden (FELIX) S. Jamison et al (Dundee) Holger Schlarb, DESY

  24. Time jitter measured by EO-SD • Time jitter: • here 270 fs (rms) over 5 min incl. slow drifts • without slow drifts typically <200 fs (rms) Courtesy: B. Steffen et al (DESY) Holger Schlarb, DESY

  25. EO measurement and LOLA Shortest pulse observed LOLA EO Longitudinal profile for two different compression scenario red: temporal decoding blue: squared signal from a transverse deflecting cavity Reasonable good agreement, cross-check for resolution! needs further analysis … Courtesy: B. Steffen et al (DESY) G. Berden (FELIX) S. Jamison et al (Dundee) Holger Schlarb, DESY

  26. Timing between pump-probe laser & FEL TEO t= 130 fs 100 shots Time [sec] Time • Transport of laser pulse critical in Tunnel Pulse in fiber will be broadened (50 fs to 0,4 ns) and distorted due to high order dispersion (~100 pulses seen) 150m Courtesy: Armin Azima DESY D. Fritz/A. Cavalieri Michigan Holger Schlarb, DESY

  27. Summary • Operation with highly non-uniform compression causes significant difficulties for the standard diagnostic tool such as • BPM • Beam imaging screens • Wire scanner • Only access to relevant phase space volume possible with transverse deflecting structure • but current setup requires tomographic quadrupole scans • incompatible with SASE operation (on-line diagnostics) • still time consuming • Electro-Optical techniques • come to there theoretical limits for GaP (~120fs FWHM) • need still to be improved to provide operations tool (e.g. FB) • TEO ready for Pump-probe experiments (timing!) Holger Schlarb, DESY

  28. Outlook and future developments Tarrial, A/ ACC1 incoming orbit exiting orbit energy compression time Fast FB A/ ACC1 • 2007 installation of optical replica synthesizer (< 5fs resolution) • in cooperation with Uppsala & Uni. Stockholm • preparation of longitudinal feedback system (mainly new monitor systems) • allow for laser based beam manipulation and external seeding option: • requires ~ 30-60 fs rms arrival time stability Holger Schlarb, DESY

  29. Principle of the Arrival Time Detection sampling time of ADC The timing information of the electron bunch is transferred into an amplitude modulation. This modulation is measured with a photo detector and sampled by a fast ADC. 40.625 MHz (54 MHz) Holger Schlarb, DESY Courtesy: F. Löhl

  30. Beam Pick-up Output signal measured in EOS hutch • Isolated impedance-matched ring electrode installed in a „thick Flange“ • Broadband signal with more than 5 GHz bandwidth • Sampled at zero-crossing with laser pulse Holger Schlarb, DESY

  31. Electro-Optical-Modulator (EOM) RF signal bias voltage Commercially available with bandwidths up to 40 GHz (we use a 12 GHz version) Lithium Niobate Holger Schlarb, DESY

  32. Test Bench for the Arrival-time Monitor System Holger Schlarb, DESY Courtesy: F. Löhl

  33. Measurement of Bunch Arrival Time over Bunch Train Bunch to bunch time jitter rms(tn – t(n+1)) ~ 30fs dA/A ~ 0.2% ACC1 Beam loading compensation off ~ 3 ps difference over bunch train ~ 3 ps difference over bunch train Beam loading compensation on (not optimized) ~ 1 ps difference over bunch train Holger Schlarb, DESY Courtesy: F. Löhl

  34. Same method used for chicane bpm EOM1 ADC Large transverse dynamic range (5-15cm), but high resolution ~ <10 um Strip-line Left pickup Flat chicane chamber Right pickup beam EOM2 - ADC • compare time of flight across stipline • centering of measurement is perform by optical delay line Holger Schlarb, DESY Courtesy: K. Hacker

  35. End

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