Experience with diagnostics at FLASH Holger Schlarb DESY 22607 Hamburg Current compression scheme Slice measurements Electro-optic techniques Summary Outlook LCLS ICW2006 10/10 Holger Schlarb, DESY

Longitudinal phase space injector - present design - 125-130 MeV Superconducting TESLA module bunch compressor bunch compressor RF gun 12/20 MV/m < 60 fs Laser 4 - 5 MeV Small space charge on cathode sL= 4.4 ± 0.1 ps 10 20 30 40 50 Time (ps) LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Dohlus

Diagnostics for long. phase space Laser THz Laser EO-container EO/CDR/CTR/TR Streak camera Laser phase CDR ACC 1 BC2 ACC 23 BC3 ACC 45 ISR Diag. Undulators TEO PP-laser Tosylab CSR/SR CDR LOLA ISR 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 LCLS ICW2006 10/10 Holger Schlarb, DESY

Transverse deflecting structure 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) Fast hor. kicker ~ z Vy(t) S-band 2 ~ z e - z 2 . 4 m 3.66 m b c p D y » 6 ° ~20° Vertical streak LCLS ICW2006 10/10 Holger Schlarb, DESY TTF2: M. Ross et.al. + MIN DESY

Waveguide Beam Direction Load RF Input LOLA IV LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Nagl, M. Ross et al.

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 LCLS ICW2006 10/10 Holger Schlarb, DESY

First attempts to compare TCAV & simulations Image with LOLA x Simulation with CSR LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Dohlus (DESY)

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: LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

LOLA in the FLASH beamline Beam direction GUN ACC1 BC2 ACC2/3 BC3 ACC4/5 LOLA Dogleg UND1 … UND6 Q9ACC7 Q9/10ACC6 Q9/10ACC5 Q9/10ACC4 Horizontal Kicker Off-axis screen ACC5 ACC4 LOLA Slice emittance and centroid shifts Keep constant and small y at OTR -> six quads are scanned simultaneous -> check upstream optics (matching!) LCLS ICW2006 10/10 Holger Schlarb, DESY

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 LCLS ICW2006 10/10 Holger Schlarb, DESY

LOLA in the FLASH beamline Beam direction GUN ACC1 BC2 ACC2/3 BC3 ACC4/5 LOLA Dogleg UND1 … UND6 Q9ACC7 Q9/10ACC6 Q9/10ACC5 Q9/10ACC4 Horizontal Kicker Off-axis screen ACC5 ACC4 LOLA Slice emittance and centroid shifts C1 C2 C3 C4 Slice energy spread & energy correlation 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 LCLS ICW2006 10/10 Holger Schlarb, DESY

Optics for energy-time correlation measurements Objectives: small beta function values (~ 3m) , maximum streak, large dispersion at the screen (~290mm), Standard optics`: Optics for the measurements: LOLA OTR LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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 LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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 LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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 LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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 LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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 LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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) LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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 LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

Tomography: one slice Region used for tomography (duration: 50 fs) LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

Tomography: one slice Courtesy: M. Röhrs LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: M. Röhrs

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

Results on temporal decoding - cross-check of theory - Typical measurement at medium compression < 200 fs 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) LCLS ICW2006 10/10 Holger Schlarb, DESY

Time jitter measured by EO-SD here 270 fs (rms) over 5 min incl. slow drifts without slow drifts typically <200 fs (rms) Courtesy: B. Steffen et al (DESY) LCLS ICW2006 10/10 Holger Schlarb, DESY

EO measurement and LOLA Longitudinal profile for two different compression scenario LOLA EO Shortest pulse observed 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) LCLS ICW2006 10/10 Holger Schlarb, DESY

Timing between pump-probe laser & FEL Transport of laser pulse critical TEO 100 shots Time [sec] t= 130 fs Time 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 LCLS ICW2006 10/10 Holger Schlarb, DESY

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!) LCLS ICW2006 10/10 Holger Schlarb, DESY

Outlook and future developments 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 incoming orbit energy exiting orbit time compression Fast FB A/ ACC1 Tarrial, A/ ACC1 LCLS ICW2006 10/10 Holger Schlarb, DESY

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) LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: F. Löhl

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 LCLS ICW2006 10/10 Holger Schlarb, DESY

Electro-Optical-Modulator (EOM) RF signal bias voltage Commercially available with bandwidths up to 40 GHz (we use a 12 GHz version) Lithium Niobate LCLS ICW2006 10/10 Holger Schlarb, DESY

Test Bench for the Arrival-time Monitor System LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: F. Löhl

Measurement of Bunch Arrival Time over Bunch Train Beam loading compensation off ~ 3 ps difference over bunch train ~ 3 ps difference over bunch train Beam loading compensation on (not optimized) dA/A ~ 0.2% ACC1 Bunch to bunch time jitter rms(tn – t(n+1)) ~ 30fs ~ 1 ps difference over bunch train LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: F. Löhl

Same method used for chicane bpm Large transverse dynamic range (5-15cm), but high resolution ~ <10 um Strip-line Left pickup Flat chicane chamber Right pickup beam ADC EOM1 - ADC EOM2 compare time of flight across stipline centering of measurement is perform by optical delay line LCLS ICW2006 10/10 Holger Schlarb, DESY Courtesy: K. Hacker

End