Diagnostics overview Beam profile monitors Cherenkov radiators Summary Injector Diagnostics DOE Review of the LCLS Project February 7-9, 2006 Henrik Loos Diagnostics overview Beam profile monitors Cherenkov radiators Summary

Injector Diagnostics Locations Cherenkov YAG, FC YAG Toroid T-Cavity Phase Monitor Wire Scanner Toroid OTR Toroid OTR YAG

Injector Diagnostics Tasks Charge Toroid (6 MeV) Faraday cups (6 MeV & 135 MeV) Trajectory & energy Stripline BPMs Profile monitors, compare position with alignment laser Transverse emittance & energy spread Wire scanners YAG screen (6 MeV) OTR screens (135 MeV) Bunch length Cherenkov radiators + streak camera (6 MeV) Transverse cavity + OTR (135 MeV) Slice measurements Horizontal emittance T-cavity + quad + OTR Vertical Emittance OTR in spectrometer beam line + quad Energy spread T-cavity + OTR in spectrometer beam line

LINAC Diagnostics SLAC linac tunnel research yard 6 MeV 135 MeV 4.30 GeV 13.6 GeV rf gun Linac-X L =0.6 m L0-A,B Linac-1 L 9 m BC-1 L 6 m Linac-2 L 330 m BC-2 L 22 m Linac-3 L 550 m Linac-0 L =6 m LTU L =275 m T-Cav 21-1b 21-1d X 21-3b 24-6d 25-1a 30-8c undulator T-Cav Spect. WS OTR OTR WS Dump BLM OTR WS - Wire Scanner BLM - Bunch Length Monitor SLAC linac tunnel research yard

Diagnostics Documentation PRD 1.1-314 LCLS Beam Position Measurement System Requirements PRD 1.1-323 Linac Wire Scanner System Requirements PRD 1.2-003 Requirements for Injector Transverse RF Deflector PRD 1.2-006 Physics Requirements for Straight Ahead Spectrometer Beamline PRD 1.2-021 Physics Specifications for the Injector Profile Monitors (OTR and YAG) PRD 1.2-023 Beam Phase Monitor PRD 1.2-024 Physics Specifications for the Injector Cherenkov Radiators (CR01 & CRG1) PRD 1.2-025 Physics Specifications for the Injector Alignment Laser System ESD 1.2-105 Design Specifications for the Injector Faraday Cup / YAG Screens PRD 1.3-018 Single-Shot Relative Bunch Length Monitor Requirements ESD 1.3-105 LCLS Linac Wire Scanner Specification ESD 1.3-107 LCLS Injector-Linac Toroids Engineering Specification ESD 1.3-109 LCLS Linac-Injector Profile Monitors Mechanical Systems Engineering Specification

Requirements for YAG & OTR Monitors Name Location Hor. Beam Size (mm) Ver. Beam Size (mm) Resol. (µm) YAG01 GTL 1.400 [7.0] [6.0] 15 YAG02 0.460 YAG03 L0 0.410 YAGG1 3.340 [45.0] 1.500 [8.0] 30 YAGS1 SAB 0.030 0.060 YAGS2 [10.0] 0.100 [12.0] OTRH1 DL1 0.180 0.380 40 OTRH2 0.200 0.280 OTR1,3 0.125 0.130 OTR2 0.065 OTR4 0.160 [1.5] 0.120 [14.0] 25 OTRS1 7 Name Location Hor. Beam Size (mm) Ver. Beam Size (mm) Resol. (µm) OTR11 BC1 3.800 0.100 30 OTR12 0.040 1.000 13 OTR21 BC2 2.600 0.050 16 OTRTCAV L3 0.070 [1.0] OTR30 DL2 0.010 [0.2] 0.025 3 OTR33 OTRDMP Dump 0.075 0.060 [0.6] 20 Large 50mm crystal required for gun spectrometer. Special optics shared with Cherenkov radiator. Requires foil with and angle of 15 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.

Beam Profile Monitors (YAG & OTR) Resolution based on 5% accuracy of beam size measurement Common design of optics for YAG & OTR YAG requirements Use 100µm thick crystals to meet resolution GTF measurements show feasibility OTR requirements Optimize yield to enable beam profile measurement at 0.2nC Provide sufficient depth of field for imaging of 45° foil Simulation shows 1mm DOF for f/# of 5 within 20µm resolution Match direction of reflection with axis of dispersion or T-CAV deflection Foil is aluminum to optimize TR yield and 1µm thick to minimize radiation OTR yield for 100mrad angular acceptance Energy (MeV) QE (%), 450-650 nm QE (%), 400-750 nm 135 0.44 0.75 4300 0.98 1.68 13500 1.17 1.99

Optics Layout Used for all standard YAG/OTR screens Telecentric lens 55mm focal length >100 line pairs/mm Magnification up to 1:1 Filter wheel with neutral density filters Beam splitter and reticule for in situ calibration Megapixel CCD with 12bit and 4.6µm pixel Radiation shielding required in main linac tunnel CCD Lens Filters Vacuum OTR Beam splitter Reticule YAG e-beam Illumination

OTR/YAG Optics Design Courtesy D. Martin

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

OTR Diagnostics Behind Bend Bend magnet generates synchrotron radiation (SR) and edge radiation (ER). Presents non-uniform background on transition radiation (TR) screen downstream of bend magnet. Affects horizontal and vertical beam profiles. Simulation of SR, ER, and TR distribution on OTR screen as seen by camera. Simulation for BC1 hor. pol. vert. pol. Beam profile Energy 250 MeV — TR+SR+ER — TR — Vertical cut, ± 5σ

SR & ER Background Mitigation Simulation shows significant background from SR & ER on OTR screens in both doglegs and bunch compressors. Polarization filter Cuts most of SR Does not remove significant ER at GeV energies Reduces TR signal by 50% Image processing Cut vertical lobes of SR & ER in software Fit Gaussian to vertical beam profile

Cherenkov Radiators* Located in gun region for temporal diagnostics of 6 MeV beam from gun Cherenkov light transported to streak camera in laser room (~12m away) Design requirements Match time resolution of radiator to streak camera (Hamamatsu FESCA-200, < 300fs) Generate and transport a sufficient # of photons to camera for 200pC beam Image transverse electron beam distribution onto streak camera for transverse resolved measurement *Courtesy D. Dowell

Cherenkov Radiator Locations in GTL Beam size σx x σy (mm) CR01 0.46 x 0.46 CRG1 3.34 x 1.5

Cherenkov Radiator Design Fused silica n = 1.458, θCR = 46.7° Total internal reflection Frosting of back surface NΦ = 7.5/e/mm/50nm @400nm Temporal and spatial resolution Thickness of 100µm Δt = 375fs Δx = 190μm

Optical Transport Layout 1:1 relay imaging from radiator to streak camera Assume 1% efficiency from frosting to scatter into 100mrad 6% acceptance through tube for source of 5mm x 100mrad 1.5·105 photons on slit of streak camera for 200 pC Laser Room Streak Camera 10m long optics tube 50 mm clear aperture 20 surfaces with 95% transmission/surface mirror reflectivity 75% 100 micron thick radiator

Parameters for Cherenkov radiators determined. Summary YAG/OTR beam profile monitor requirements specified for injector and linac. Optics layout for injector YAG/OTR defined and studied to meet requirements for resolution and yield. Effect of SR&ER on beam profile monitor studied. Parameters for Cherenkov radiators determined. Design for optics to streak camera in progress.