LCLS Injector Diagnostics

1. LCLS Injector Diagnostics Henrik Loos Diagnostics overview Transverse Beam Properties Longitudinal Beam Properties

2. 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 Transverse cavity + OTR (Inj, Linac) Coherent radiation power (BC) 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 LCLS Diagnostics Tasks

3. LCLS Injector Diagnostics YAG, FC YAG Toroid T-Cavity Phase Monitor Wire Scanner Toroid OTR Toroid OTR YAG

4. Diagnostics Through BC1 RF Gun & Solenoid L0a&L0b S-Band Linacs T-Cav Sec 29 Transverse RF Cavity Bunch-Compressor-1 (BPM, OTR, collimator) OTR & Wire Scanners Gun Spectrometer L1 S-Band Linac Wire Scanners + OTR 135 MeV 250 MeV TD-11 stopper X-Band RF Straight Ahead Spectrometer Bunch Length Diagnostics 40 m

5. Transverse Diagnostics • YAG scintillator • OTR • Wire Scanners

6. Requirements for YAG & OTR Monitors 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.

7. Yellow scintillator crystal, emits green light when charged particle passes through Fluorescence decay time 70ns High photon yield Nφ = 3.5 /e- For 1 nC charge: Nφ = 2 1010 ~108 Photons at 5pC Plenty of photons to detect with a CCD 100µm thickness to meet resolution Saturation at high charge densities Saturation limit 0.04 pC/µm2 Equals 65 µm beam size at 1 nC Combined with Faraday cup in GTL -> camera shielding Thin mirror (1mm) at higher energies YAG Beam Profile Monitor Mirror e- θ YAG Lens CCD

8. θ 2 γ Electron Beam Metal Foil Transition Radiation • Radiation of a charged particle at relativistic speed moving from one medium into another. • Relativistic speeds-> Coulomb field is quasi-electro-magnetic wave. • Vacuum-metal boundary-> Field is reflected and emitted in 1/γ angle • Light intensity linear to bunch charge • Emission is instantaneous and free of saturation effects

9. Small quantum efficiency About 1 photon/100 electrons Logarithmic dependence on energy and solid angle 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 Profile Monitor

10. Used for all standard YAG/OTR screens Telecentric lens 55mm focal length >100 line pairs/mm Magnification up to 1:1 with extender Mounting of camera enables field of view from 5 to 20 mm 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 CCD Lens Filters Vacuum OTR Beam splitter Reticule YAG e-beam Illumination Optics Layout

11. OTR/YAG Optics Design Actuator Optics Box CCD Lens Filters Screen Beam Splitter Reticle

12. OTR Imager for 135 MeV 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 • 12um resolution tested • Device ready to install • No actuator, rate limit required for beam into spectrometer line

13. CCD Camera and Lens Test Uniq Vision CCD Dark Image Test TECM55 lens with ruler (scale 1/64”) Periodic BG structure removed with background subtraction Background noise 2 bits rms Dynamic range > 100 Resolution: B/W transition < 20um

14. y CCD Image x Rows YAG Crystal Profile Monitor Controls • Rate limit electron beam • Single bunch & burst mode • Prevent foil damage and limit camera irradiation • Profile monitor hardware control • Chassis for actuator, filters, illumination • EPICS driver ready • Camera control (EPICS) • Cameralink and EPICS IOC • Buffered acquisition@10Hz • Screen update @1Hz • Image processing (Matlab) • Flip image to match image coordinates with beam • Background subtraction • Automated image cropping • Beam size calculation • Different algorithms implemented • Gaussian fit • Baseline cut, etc. Mock-up

15. Software Development Matlab EPICS

16. 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. Wire Scanner Status • Requirements • Step size 5um • Accuracy 2um, reproducibility 10um • Tungsten wire 20um to 60um, matched to beam size • Hardware status • Wire scanners for injector tested to meet specs and calibrated • Photomultipliers with charge integrating ADCs tested • Software • Low level EPICS • Calibration tool • Scan user interface to select 1 or more wires • Buffered acquisition linked to timing system • High level Matlab • Software for normalization with toroid and jitter correction with BPM • Profile analysis and emittance calculation same as for profile monitors

18. Requirements

19. Design - Mechanical Distance Measurement (LVDT or similar) Motor Beam Limit Switches

20. User Interface - Operations

21. Bunch Length Monitoring • Transverse Cavities are the Gold standard • Provide single shot energy vs. time, with excellent resolution (<5 micron bunches measured at TTF2/FLASH) • Invasive – can only measure at a low repetition rate • Used to calibrate other measurements • Coherent mm-wave radiation power detectors • Used a full rate for uncalibrated feedback measurement. • Other systems may be used to reduce need for transverse cavity based calibration – but not baseline • Electro-optical measurement • Optical spectrum statistical measurement

22. 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 in ‘08 Max field of 25 MV Parasitic measurement with horizontal kicker and off-axis OTR Vertical Deflecting Cavity Horizontal Kicker Electron Beam Off-axis Screen Transverse Cavity Bunch Length Measurement

23. Injector TCAV • TCAV tested successfully at full gradient in klystron lab • 3MW, 120Hz, 3us pulse • 2MW, 120Hz, 3us pulse was requirement

24. 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 Mock-up

25. Software Development

26. 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 W1(ω) depends on radiation source • Bunch length determined bylong wavelengths λ » 2πσrms • BC1: 1cm – 1mm • BC2: 1mm - .1mm BC1 BC2

27. Millimeter Wave Gap Radiation • Single Shot (assuming single shot spectrometer, or multiple detectors) • Non-Invasive • Simple high rate readout – can use signal from single detector • Very simple, low cost • Low noise readout <1% RMS demonstrated • Diode detectors work to ~300GHz -> ~200 micron bunch length • Possibly can be extended to ~ 1THz, ~70 micron bunch length • Provides only relative measure of bunch length • To be installed after BC1.

28. Layout of Gap Radiation Measurement

29. Millimeter-wave gap monitor tests in End Station A • Output of 100GHz detectors as phase (bunch length) is adjusted M. Woods SLAC • Comparison of 2, 100GHz detectors for a range of operating conditions • RMS difference 1.4% for 10,000 pulses

30. Millimeter Wave Coherent Synchrotron Radiation • Single Shot (assuming single shot spectrometer, or multiple detectors) • Non-Invasive • Measures from arbitrarily short to ~mm bunches (with appropriate filters). • Simple high rate readout – can use signal from single detector with input filter • Measures power spectrum (no phase information) – cannot reconstruct bunch shape • Variations on spectral response must be calibrated using external bunch length measurement – not practical to provide a calibrated signal • To be installed after BC1 and BC2.

31. BL11 Millimeter-wave CER bunch length monitor • Mirror with hole after bend to collect synchrotron radiation stripe • Reflective optics (off-axis parabolas) to collect and transport light • Beam splitting filter for high pass / low pass to 2 mm-wave detectors • Different filters available • Compare power on detectors for (uncalibrated) bunch length measurement • Similar in concept to gap monitor, but bend and collecting optics give larger (>X10) signal, at cost of increased complexity • Need higher signal for short bunch measurements where diode detector do not work

32. Layout of CER Bunch Length Monitor

33. Detector Setup for BL11

34. 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.

35. 1.5ps 4.5ps 1.5ps. 200-500pC, 44MeV beam using a spectrometer with a resolution of 0.05nm/pixel P. Catravas et al, Physical Review Letters 82 (1999) 5261 Optical Synchrotron Radiation Noise Measurement • RMS distribution measurement does not require calibration • Non-invasive • Not single shot • Will test after BC1 • Can upgrade to (near?) single shot measurement using optical spectrometer