Diagnostics Overview for the LCLS Presented by Josef Frisch For the LCLS ANL / LBNL / LLNL / SLAC

250 MeV4.3 GeV GeV OTR or YAG screen BPM in dispersive location Wire Scanner Pyroelectric bunch length monitor Laser Heater Tune-up Stopper Beam arrival time cavity X-ray Gas Detector RF structure - S- band RF structure – X band Transverse Cavity Quad scanned for emittance measurements 135 MeV 500 eV-10 KeV X-ray Gas Attenuator Primary LCLS Diagnostics BPMs distributed throughout machine not shown Undulator

3 Stripline Beam Position Monitors 4.8 micron resolution at 200pC S. Smith et. al.

4 Cavity Beam Position Monitors ~300nm Resolution 250pC Expect ~2 micron resolution at 20pC Note: good resolution has been demonstrated in high Q cavity bpms for multi-bunch beams (ATF Japan)

5 Beam Orbit (stripline BPMs) Undulator BC2 LINAC Orbit too Small to see

6 Undulator Orbit (cavity BPMs)

7 Transverse Orbit Feedbacks Gun Launch Injector launch X-band launch L2 Launch L3 Launch Sector 28 Launch BSY Launch DL2A DL2B LTUUndulator Launch Orbit Feedbacks operate independantly at ~10 Hz. Provide stabilization, not jitter supression Time slot control (120Hz) in near future. Possible cascading for better bandwidth

8 Electron Beam Transverse Screens Ce:YAG Cathode Emission Image at 6 MeV Ce:YAG in 135 MeV spectrometer TCAV on OTR in 135 MeV bend, TCAV on 135 MeV OTR image COTR makes OTR screens useless above 250 MeV 10,000X enhanced COTR

9 Wire Scanners No Jitter Correction With Jitter Correction

10 TCAV Bunch Length Measurement Can't measure bunch lengths <~20 femtoseconds RMS with S-band X-band TCAV 4X F, 2X V Resolution to ~2fs RMS X-band with SLED? TCAV with wire scanner

11 Relative Bunch Length Monitor Pyroelectric detector good from 100GHz to light (response is not flat) Si transmits from mm-wave to ~20 um and 7um to 1um

12 Precision Timing System Phase Cavity Fiber System Experiment Laser System Phase cavity measures electron beam timing Noise ~10fs, drift ~100fsec Note that X-ray timing may not exactly match electron beam timing Fiber system (LBNL) transmits time information ~100M to Near Hall laser. ~20 fs stability Laser system locking ~25fs stability

13 Phase Cavity System Standard Deviation of single cavity ~100fs RMS Time Difference between Cavities ~100 fs drift over 1 day Standard deviation of difference between cavities ~15 fs RMS Phase Cavity Adjustable Attenuator Mixer 2805 MHz X6 Multiplier 476 MHz Reference 51 MHz ¼ Divider Digitizer 16 Bit 2856 MHz 119 MHz Phase Measurement Software Trigger

14 Master Source MDL PLL Injec tor L2L3 BC1 DL2 Undulato r PCA V AM O PLL Optical / RF phase Detector Optical transmitt er Optical / RF phase Detector ΔΦ X6 Pha se Det Pha se Det PCA V BP Filte r BP Filte r BP Filte r BP Filte r ΔΦ Feedback Lengths Matched Laser BP Filte r Lase r Diod e Feedback 476 Out (unused) High Pow er RF High Pow er RF High Pow er RF BLD Full timing sytsem ~50 fs timing (offline reconstruction) When discussing timing systems, need to ask “stability relative to WHAT reference?“

Longitudinal Feedbacks GeV 135 MeV Undulator Energy → amplitude Energy and bunch length → Amplitude and phase Energy and bunch length → Amplitude and phase Energy → amplitude (phases of 2 sectors) Longitudinal feedbacks operate independently at ~5Hz (MATLAB) In L2 and L3 amplitude is controlled by moving phases in opposite directions

1.5 ÅEt over- compressedEt under- compressed E t f fully compressed peak current Monitor (CSR) gasdetector Ultra-short Bunch Operation Operate at 20pc near full compression, estimate 5 femtosecond FWHM bunch length Challenge for diagnostics – low charge, better timing precision desired

GeV Undulator Quick-change Diagnostic (ST0) Port 1: Test samples for wavelenth filters, diffraction slits, visible light blocking filter, X-ray attenautors Port 2: Ce:YAG screen, thermal sensor (future) Port 3: B4C Stopper to protect downstream safety stoppers Designed for rapid changes

GeV Undulator X-ray YAG: YAGXRAY 100um Ce:YAG Screen YAGXRAY 10KeV Saturation Curve YAG saturates At high intensity or Long wavelength

19 Primary FEE Diagnostics Gas Detector Gas Attenuator Direct Imager (Scintillator) FEL Offset Mirror Systems Beam Direction Solid Attenuators K-Monochromator Thermal Sensor Slit Collimators Pop-in cameras Reticule C0 collimator (in e- beam dump Fixed Mask Gas Detector Originally designed to help find lasing R. Bionta

20 Direct Imager YAG Screen Scintillators YAG::Ce NFOV Camera (12 x 12 mm) WFOV Camera (60 x 60 mm) UV and visible light sources ND filter wheels

GeV Undulator X-ray YAGs: Direct Imager Direct Imager Multiple Ce:YAG screens 5um, 100um, Wide and narrow field of view Direct Imager WFOV 20pc at 800eV NFOV Gas and solid attenuators allow adjustment of intensity to avoid saturation Speckle from Be Attenuator Pop-in monitors

22 Gas Detector FEL Primary photoelectrons cause N 2 molecules to fluoresce in the near UV N 2 gas inlet Photo detector Magnet coils Removable aperture Vital for user operations: Provides non-invasive shot by shot pulse energy to users and accelerator operations

23 Gas Detector Calibration Energy loss scan, vary steering measure energy loss from DL2 to dump 10 MeV 2.5mJ Calibration of gas detector against energy loss (linearity check)

24 Monocromator Datum Axis Set to pass 8.17 KeV Scan of K-mono transmission vs beam energy Can use harmonics for calibration at longer wavelengths Would like a Spectrometer

25 Total Energy Monitor Raw signal from total energy sensor Calibration of TE sensor against energy loss Cryogenic pulsed temperature rise sensor By the time this was operational we were trusting calibration from the e-beam energy loss

26 Critical Diagnostics for Operations BPMs: High stability low noise BPMs critical to machine operation Relative bunch length monitor Wire Scanners: For us these are the ONLY option for electron beam size measurements Single shot beam time monitor X-ray YAG screens: Versatile diagnostic. Gas Detector: Non-invasive pulse energy diagnostics.

27 What we need: Near Term Calibrated thermal X-ray pulse energy monitor Needs to be compact and inexpensive for installation after each X-ray mirror X-ray spectral measurement Can probably use the SXR experiment spectrometer with K-edge foils for absolute calibration Electron bunch length measurement for ultra- short bunches Multi-bunch diagnostics

28 What we need: Longer Term Non-invasive X-ray bunch length measurement Non-invasive, single shot X-ray to Laser relative time measurement with 1fs resolution Non-invasive single shot X-ray spectral measurement Above measurements need to work over full operation range (500eV to 10 KeV) Difficult Problems – Will keep us busy!

29 Comments Diagnostics are critical: Tolerances in XFELs are too tight for operation "as built". Need resources to build diagnostics after operation begins. New machines are likely to produce surprises. Some surprises are good! Close integration with experiments is important: XFELS have more flexibility and more variability than synchrotron sources. Experimenters need extensive online beam instrumentation.