1. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Diagnostics in the LCLS LCLS Injector Commissioning Workshop October 9-11, 2006 Henrik Loos Diagnostics overview Beam profile monitors Longitudinal diagnostics

2. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 LCLS Diagnostics Tasks Charge Toroids (Gun, Inj, BC, Und) Faraday cups (Gun & Inj) Trajectory & energy Stripline BPMs (Gun, Inj, Linac) Cavity BPMs (Und) Profile monitors (Inj), compare position with alignment laser Transverse emittance & energy spread Wire scanners YAG screen (Gun, Inj) OTR screens (Inj, Linac) Bunch length Cherenkov radiators + streak camera (Gun) Transverse cavity + OTR (Inj, Linac) Coherent radiation power (BC) Zero-phasing with L0b or L1 Slice measurements Horizontal emittance T-cavity + quad + OTR Vertical Emittance OTR in dispersive beam line + quad Energy spread T-cavity + OTR in dispersive beam line

3. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Diagnostics Requirements ParameterMethodUnitResolution CurrentToroid, FC%2 PositionStripline BPMμm5 - 20 Cavity BPMμm1 Beam SizeWire Scannerμm5 YAGμm15 – 30 OTRμm5 – 30 Bunch LengthStreak Camerafs300 Transverse CavitySlices10 BLM%5

4. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 LCLS Injector Diagnostics Wire Scanner YAG, FC Cherenkov OTR YAG T-Cavity YAG Phase Monitor Toroid

5. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 LCLS Linac Diagnostics SLAC linac tunnel research yard Linac-0 L =6 m Linac-1 L  9 m Linac-2 L  330 m Linac-3 L  550 m BC-1 L  6 m BC-2 L  22 m LTU L =275 m undulator 135 MeV 250 MeV 4.30 GeV13.6 GeV Linac-X L =0.6 m 21-3b24-6d25-1a30-8c 6 MeV L0-A,B rf gun X T-Cav T-Cav Dump 21-1b21-1d Spect. OTR BLM WS OTR WS BLM - Bunch Length Monitor WS - Wire Scanner

6. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Requirements for YAG & OTR Monitors NameLocationHor. Beam Size (mm) Ver. Beam Size (mm) Resol. (µm) YAG01GTL1.400 [7.0] 1.400 [6.0] 15 YAG02GTL0.460 15 YAG03L00.410 15 YAGG1GTL3.340 [45.0] 1.500 [8.0] 30 YAGS1SAB0.0300.06015 YAGS2SAB0.030 [10.0] 0.100 [12.0] 15 OTRH1DL10.1800.38040 OTRH2DL10.2000.28040 OTR1,3DL10.1250.13030 OTR2DL10.065 [8.0] 15 OTR4DL10.160 [1.5] 0.120 [14.0] 25 OTRS1SAB0.030 [10.0] 0.100 [12.0] 7 NameLocationHor. Beam Size (mm) Ver. Beam Size (mm) Resol. (µm) OTR11BC13.8000.10030 OTR12BC10.0401.00013 OTR21BC22.6000.05016 OTRTCAVL30.0500.070 [1.0] 16 OTR30DL20.010 [0.2] 0.0253 OTR33DL20.0401.00013 OTRDMPDump0.0750.060 [0.6] 20 Large 50mm crystal required for gun spectrometer. Zoom lens needed. Requires foil with and angle of 5 deg to the beam and a likewise tilted camera to keep the entire screen in focus. Very high resolution required. Special optics design needs to be developed.

7. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Beam Profile Monitor Specifications YAG screens High yield at low energy 10 8 Photons at 5pC 100µm to meet resolution Saturation at high charge densities Combined with Faraday cup in GTL -> camera shielding Thin mirror (1mm) at higher energies OTR screens Small yield Aluminum foil 1µm Mitigates radiation issue Foil damage is concern Limited z-space Foil at 45 degree Depth of field ~1mm Match reflection direction with TCAV or dispersion direction OTR yield for 100mrad angular acceptance Energy (MeV)QE (%), 450-650 nm 1350.44 43000.98 135001.17

8. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Optics Layout Used for all standard YAG/OTR screens Telecentric lens 55mm focal length >100 line pairs/mm Magnification up to 1:1 Stack of 2 insertable neutral density filters Beam splitter and reticule for in situ calibration Megapixel CCD with 12bit and 4.6µm pixel size Radiation shielding in gun region Vacuum Filters Lens CCD OTR e-beam Reticule YAG Beam splitter Illumination

9. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 OTR/YAG Optics Design Filters CCD Lens Beam Splitter Reticle Optics BoxActuator Screen Courtesy V. Srinivasan

10. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 OTR Imager for Spectrometer Need wide field of view in focus for measurements in spectrometer beam line Tilt OTR screen and CCD by 5 degrees in 1:1 imaging 10um resolution B.X. Wang et al. PAC05

11. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Simulation of OTR Beam Size Measurement Simulation of CCD image Include 0.5% TR yield, photon shot noise, and typical CCD parameters for quantum efficiency, read out noise, pixel size, digitizer gain Calculation of beam size Generate beam profile with 10σ bounding box Compare rms width of profile with original Gaussian beam size Simulation agrees well with OTR measurement at GTF Error of 5% in beam size for beam of 0.1nC, 260µm at 10µm resolution Q = 0.1nC E = 135 MeV

12. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 YAG Efficiency N φ = 14µm -1 l sin 2 (θ/2) l = 0.1mm, θ = 70mrad, N φ = 1.7/e - 1nC: N φ = 1*10 10 200pC: N φ = 2*10 9 5pC: N φ = 5*10 7 YAGG1 beam image at 5 pC

13. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 CCD Camera and Lens Test Resolution: B/W transition < 20um TECM55 lens with ruler (scale 1/64”)Uniq Vision CCD Dark Image Test Periodic BG structure removed with background subtraction

14. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 OTR Diagnostics Behind Bend Non-uniform background from synchrotron (SR) and edge (ER) radiation. Affects horizontal and vertical beam profiles. Simulation of SR, ER, and TR distribution on OTR screen as seen by camera. Polarization filter Removes hor. SR Reduces TR by 50% Image processing Cut vertical lobes of SR & ER in software Fit Gaussian to vertical beam profile Simulation for BC1 hor. pol.vert. pol. — TR+SR+ER — TR — Vertical cut, ± 5σ Beam profile Energy 250 MeV

15. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Profile Monitor Controls Rate limit electron beam Single bunch & burst mode Prevent foil damage and limit camera irradiation Camera control Cameralink and EPICS IOC Buffered acquisition@10Hz Screen update @1Hz Image processing Flip image to match image coordinates with beam Background subtraction Beam size calculation Different algorithms Gaussian fit Baseline cut, etc. Mock-up x CCD Image YAG Crystal Rows y

16. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Profile Monitor Commissioning Tasks Verify correct image polarity and calibration. Compare with alignment laser, BPMs and wire scanners. Find proper attenuation filter for YAG profile monitors. Determine beam center with alignment laser.

17. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Longitudinal Diagnostics Gun region Cherenkov radiator & streak camera Bunch length and slice emittance Transverse cavity, absolute single shot bunch length measurement Longitudinal feedback Integrated coherent radiation, relative single shot measurement Incoherent radiation fluctuation, can be absolute measurement More in J. Frisch’s presentation

18. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Cherenkov Radiators Located in gun region for temporal diagnostics of 6 MeV beam from gun Convert electron beam time structure into light pulse for streak camera measurement Cherenkov light suitable at low beam energies Design requirements Match time resolution of radiator to streak camera (Hamamatsu FESCA-200, < 300fs) Generate and transport a sufficient # of photons for 200pC beam to streak camera in laser room (10m away)

19. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Cherenkov Radiator Selection Fused silica n = 1.458, θ CR = 46.7° Total internal reflection Frosting of back surface N Φ = 7.5/e/mm/50nm @400nm Temporal and spatial resolution Thickness of 100µm Δt = 375fs Δx = 190μm Courtesy D. Dowell

20. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Optical Transport Layout 1:1 relay imaging from radiator to streak camera Efficiency of frosted surface very low Long transport tube has small acceptance for diffuse light source “Best case” 10 5 photons on slit of streak camera at 200 pC Streak Camera 10m long optics tube 50 mm clear aperture Laser Room mirror reflectivity 75% 20 surfaces with 95% transmission/surface 100 micron thick radiator Courtesy D. Dowell

21. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Transverse Cavity Bunch Length Measurement TCAV in injector @ 135 MeV Low field of 1.4 MV sufficient Invasive measurements on OTR2, 4, S1, YAGS2 TCAV in Sector 25 at 5.9 GeV Max field of 25 MV Parasitic measurement with horizontal kicker and off-axis OTR Horizontal Kicker Vertical Deflecting Cavity Off-axis Screen Electron Beam

22. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Transverse Cavity Calibration Temporal resolution limited by beta function, RF power, screen size Calibration with TCAV phase scan Calibration accuracy limited by phase jitter TCAV injector: >>20 slices possible TCAV linac: <5 slices due to limited RF, non- dedicated optics, screen resolution Mock-up

23. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 TCAV in LCLS after BC2 Short 70fs bunch length requires full 25MV/m RF of cavity Parasitic measurement with beam optics optimized for SASE Resolution 20fs sufficient for length measurement

24. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Bunch Length Monitor Relative bunch length measurement used for longitudinal feedback Non-intercepting, calibrated with interceptive TCAV measurement Based on integrated power from coherent radiation source (C*R) Single electron radiation spectrum W 1 (ω) depends on radiation source Bunch length determined by long wavelengths λ » 2πσ rms BC1: 1cm – 1mm BC2: 1mm -.1mm BC1BC2

25. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Radiation Sources Wide range of bunch lengths from 25um to 300um Diode detectors work well below 300GHz Pyroelectric detectors work well above 300GHz Long bunches Couple radiation from ceramic gap in beam pipe into waveguides with different diode detectors Short bunches Extract coherent radiation from bend magnet with hole mirror and send to a pyroelectric detector

26. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 CER Detector Layout Edge rad. dominates over synchrotron and diffraction Near field calculation necessary for radiation spectrum at detector Pyro-Detector Lenses, f = 350mm 200mm 50mm 15mm 8mm Bend e-Beam 200mm Window DR SR ER

27. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 CER Monitor Layout Electron beam Edge radiation Courtesy T. McCullough

28. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Bunch Length Sensitivity of Detector Signal Detection efficiency includes diffraction, vacuum window, water absorption, pyroelectric detector response, and bunch form factor. Introduce high and low pass filters at 10cm -1 and 20cm -1.

29. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 M ~ 10 Photon radiation by charged particles is a stochastic process. (synchrotron radiation, transition radiation, Cherenkov radiation, …) LCLS Injector Commissioning Workshop – SLAC, October 9-11, 2006 Bunch Length by Incoherent Radiation Fluctuation Measurement Proposed for LCLS-BC1 by F. Sannibale and M. Zolotorev and based on the method described in Zolotorev, Stupakov, SLAC-PUB 7132 (1996) The number of photons per pulse radiated by a single mode follows the Poisson distribution with 100% fluctuation. The fluctuation of the total number of photons radiated per pulse becomes ( M combined Poisson processes): ( M combined Poisson processes): By fixing a bandwidth  , we define a mode with coherence length: In a bunch of length   there are M =   /  tc independent modes radiating simultaneously.

30. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 LCLS Injector Commissioning Workshop – SLAC, October 9-11, 2006 LCLS-BC1 Implementation T. Borden, P. Emma, H. LoosF. Sannibale, G. Stupakov, M. Zolotorev. T. Borden, P. Emma, H. Loos, F. Sannibale, G. Stupakov, M. Zolotorev.

31. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Summary Electron beam diagnostics based on proven methods Redundancy in diagnostics, independent methods to determine the most important beam parameters Before commissioning check-out of each device by physicist to verify proper functioning and correct assignment in control system

32. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006

33. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Laser Diagnostics Energy Joule meter on launch table Position CCD cameras for position feedback Transverse shape Virtual cathode image Longitudinal profile Streak camera Single shot and multi shot

34. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Laser Temporal Diagnostics DiagnosticsResolution (fs)Single shotInvasive Streak camera900YesNo TG-FROG500Yes Cross Correlator, scanning200No Cross Correlator, single shot200YesNo

35. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 Streak Camera

36. Henrik Loos LCLS ICW 2006 loos@slac.stanford.edu 10 October 2006 UV Cross Correlator 1” R 1.125” L 2.125” L 1.125” 1.25” f=100 f=150 L=36” L=32.5” 2.375” 2.2” 1.19”/1.44” Delay IRUV Diode BBO 100um Blue