P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 LCLS Diagnostics and Commissioning Workshop Injector, Linac and Undulator Diagnostics and Beam Position Monitors P. Krejcik

LCLS Diagnostics and Commissioning September 22-23, 2004 Context of Diagnostics in Commissioning Review scope of proposed diagnostics Emphasize that diagnostics themselves need commissioning Consider if full features (resolution, automation) are needed at beginning of commissioning Implicit sequence of commissioning: e.g. feedbacks after BPMs commissioned; slice parameters need prof. monitors and TCAVs

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Readiness of diagnostic systems Which SLC diagnostics should be preserved? Technology choices still being made on some new systems BPM modules – trying to attain desired resolution Prof monitor cameras – resolution, controls integration, data rate Some diagnostics are turnkey systems, others are R&D projects R&D still required for ultrafast diagnostics CSR THz power bunch length monitors EO bunch profiling

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Dynamic Aspects of Commissioning Initially diagnose a wildly mis-tuned and unstable machine Yet the same diagnostics should ultimately have finesse to optimize SASE operation Deal with imperfect and uncalibrated settings Detective work for finding hardware faults Quantify magnitude and sources of jitter

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Diagnostics Roadmap for electrons Trajectory resolution Position Angle Energy Beam size resolution Emittance Energy spread Bunch length &  T development Longit. profile Single shot rms Slice parameters resolution Emittance Energy spread Bunch charge FEEDBACKFEEDBACK Stabilization response Jitter characterization Noninvasive Invasive Setup Tuning 120 Hz

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Accelerator System Diagnostics* 180 BPMs at quadrupoles and in each bend system upstream linac L0 RF gun L3L1 X L2 8 Energy (BPM), energy spread (Prof) measurements : 8 Energy (BPM)  E , energy spread (Prof)  E measurements : 2 Transverse RF deflecting Cavities for slice measurements BC1 BC2 DL2 DL1 undulator LTU 5 Bunch length monitors Dump E,  E 5 Emittance measurements (Profs, Wire Scanners) : 5 Emittance  x,y measurements (Profs, Wire Scanners) : 3 prof. mon.’s (  x,y = 60°) * See also P. Emma talk how optics is optimized for diagnostics

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Beam Position Monitoring requirements

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Beam Position Monitors Stripline BPMs in the injector and linac (existing) and in the LTU Differencing large numbers Mechanical precision Fabrication by printing electrodes on ceramic tubes Drift in electronics Digital signal processing Cavity BPMs in the undulator, LTU launch Signal inherently zero at geometric center C-band (inexpensive) signal needs to be mixed down in the tunnel

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Stripline versus Cavity BPM Signals P f 700 MHz 500 MHz BP filter ADC x4 119 MHz Clock 24 th harmonic Digital processing RF in Control system /4 Stripline Mixer LO sync’ed to RF IF noise (resolution) minimized by removing analog devices in front of ADC that cause attenuation drift minimized by removing active devices in front of ADC noise (resolution) minimized by removing analog devices in front of ADC that cause attenuation drift minimized by removing active devices in front of ADC C-band cavity Dipole mode coupler ~5 GHz

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Simplistic View of Digital BPMs Is the purely digital approach the best way to go? Must always maximize signal to noise for best resolution So eliminate any cause of attenuation: couplers, hybrids, active devices etc. This also eliminates drift which causes offsets Other approaches also try to do this: e.g. AM to PM conversion with a hybrid and then digitize Might as well digitize first, eliminate the middle men, and do the conversions digitally Ultimately left with calibrating the drift in the BPM cables, because ADCs are now very stable.

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Linac stripline BPMs Need to replace old BPM electronics Commercially available processing units look promising Beam testing of module as soon as funding available Test new BPM fabrication techniques

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Analysis of Test Signals in the “Libera” module – S. Smith Measured signal to noise ratio implies resolution of 7  m in a 10 mm radius BPM Identified fixable artifacts in data processing

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Cavity beam position monitors for the undulator and LTU Coordinate measuring machine verification of cavity interior X-band cavity shown Dipole-mode couplers X-band cavity shown Dipole-mode couplers R&D at SLAC – S. Smith X-band cavity shown Dipole-mode couplers X-band cavity shown Dipole-mode couplers NLC studies of cavity BPMs, S. Smith et al

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 C-band beam tests of the cavity BPM – S. Smith 25  m 200 nm Raw digitizer records from beam measurements at ATF cavity BPM signal versus predicted position at bunch charge 1.6 nC plot of residual deviation from linear response << 1  m LCLS resolution requirement plot of residual deviation from linear response << 1  m LCLS resolution requirement C-band chosen for compatibility with wireless communications technology

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 LCLS BPM Testing Testing is planned at the “Controls Test Stand” to be located at the FFTB, Evaluation of processor electronics Resolution determined by comparing several adjacet BPMs Possibility to test new striplines Copy the design of NLC C-band cavity BPMS

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Beam Size Measurement Wire scanners, based on existing SLAC systems Measures average projected emittance But is minimally invasive and can be automated for regular monitoring Profile monitors Single shot, full transverse profile YAG screen in the injector for greater intensity OTR screens in the linac and LTU for high resolution 1  m foils successfully tested in the SPPS: Small emittance increase disrupts FEL, but no beam loss -1:1 imaging optics => ~ 9  m resolution Used in combination with TCAV for slice energy spread and emittance CTR for bunch length measurement OTR image taken in the SPPS Courtesy M. Hogan, P. Muggli et al OTR image taken in the SPPS Courtesy M. Hogan, P. Muggli et al

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Profile Monitor Camera Specification Digital camera technology Not TV camera that subsequently needs a frame grabber External trigger supplied to the camera by control system 30 fps at 1280x960 pixels, 10 bit resolution Digital image read out over ethernet or firewire Inexpensive, commercially available ~$1k – Z. Salata.

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Profile Monitor Camera Dynamic Range How many bits are necessary to see the tails? saturation 3  needs 10 bits 4  needs 12 bits

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Profile monitor commissioning Can be tested off the beamline at the Controls Test Stand Evaluate data acquisition and integration into the control system test a complete optical setup and measure optical resolution and wavelength response

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Bunch length diagnostic comparison Device TypeInvasive measurement Single shot measurement Abs. or rel. measurement Timing measurement Detect  bunching RF Transverse Deflecting Cavity Yes: Steal 3 pulses No: 3 pulsesAbsoluteNo Coherent Radiation Spectral power No for CSR Yes for CTR YesRelativeNoYes Coherent Radiation Autocorrelation No for CSR Yes for CTR NoAbsolute (2 nd moment only) No Electro Optic Sampling NoYesAbsoluteYesNo Energy Wake-loss YesNoRelativeNo

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Bunch Length Measurements with the RF Transverse Deflecting Cavity   y y  Asymmetric parabola indicates incoming tilt to beam Cavity on Cavity off Cavity on - 180° Bunch length reconstruction Measure streak at 3 different phases  z = 90  m (Streak size) m 30 MW

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Commissioning of the Transverse Cavities Calibration of the deflection strength in units of pixels on the profile monitor Also requires beam trajectory feedback to stabilize the RF phase of the deflecting cavity Prof monitor image acquisition fully integrated into the control system

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Calibration scan for RF transverse deflecting cavity Beam centroid [pixels] Cavity phase [deg. S-Band] Bunch length calibrated in units of the wavelength of the S-band RF Further requirements for LCLS: High resolution OTR screen Wide angle, linear view optics

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 OTR Profile Monitor in combination with RF Transverse Deflecting Cavity - detailed applications in P. Emma talk Simulated digitized video image Injector DL1 beam line is shown Best resolution for slice energy spread measurement would be in adjacent spectrometer beam line.

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Coherent radiation from the electron bunch Frequency domain Spectral power in a fixed bandwidth SpectrometryAutocorrelation Time domain Electro optic sampling Measured directly near the bunch Or transported out of the beam line

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Diagnosing Coherent Radiation 1. spectral power Smooth Gaussian bunch spectrum from BC1 With 5% microbunching Measure bunch length Detect microbunching Measure bunch length Detect microbunching Fixed BW detector Signal prop. 1/  z Bunch length signal for RF feedback  - J. Wu

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, THz main peak BC2 Bunch length monitor spectrum - based on coherent spectral power detection BC2 bunch length feedback requires THz CSR detector Demonstrated with CTR at SPPS Spikes in the distribution now have same spectral signature as microbunching

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Transition radiation is coherent at wavelengths longer than the bunch length, >(2  ) 1/2  z SLAC SPPS measurement: P. Muggli, M. Hogan Limited by long wavelength cutoff and absorption resonances  z  9  m Diagnosing Coherent Radiation 2. autocorrelation

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Mylar resonances Simple model: Gaussian,  z =20 µm, d=12.7 µm, n=3 Mylar window+splitter Transport issues for THz radiation Smaller measured width:  Autocorrelation <  bunch ! Modulation/dips in the interferogram Fabry-Perot resonance: =2d/m, m=1,2,… Signal attenuated by Mylar: (RT) 2 per sheet Fabry-Perot resonance: =2d/m, m=1,2,… Signal attenuated by Mylar: (RT) 2 per sheet P. Muggli, M. Hogan

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Developments in autocorrelation techniques Investigate other detector types for wavelength dependance Golay cell Beam splitters without wavelength dependance Single shot autocorrelator Camera records fringes on single shot Use CSR from chicane bed

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Bunch length scan performed while observing spectral power with THz detector Coherent transition radiation wavelength comparable to bunch length LINAC FFTB Comparison of bunch length minimized according to wakefield loss and THz power Pyroelectric detector foil GADC Linac phase Wake energy loss THz power

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Dither feedback control of bunch length minimization at SPPS - L. Hendrickson Dither time steps of 10 seconds Bunch length monitor response Feedback correction signal Linac phase “ping” optimum Jitter in bunch length signal over 10 seconds ~10% rms

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Diagnosing Longitudinal phase space: Energy spectrum versus Bunch length signal - Muggli, Hogan et al Jitter in the compressor phase: Resuting energy profileCorresponding bunch length signal Single shot measurements jitter signal

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 L B =1.80 m B=1.60 T L B =1.80 m B=1.60 T SPPS Four Dipole Chicane s L T =14.3 m 9 GeV BPM - energy Prof. Monitor -  E Momentum compaction R 56 = –75 mm  z 50  m   1.6%  z0 1.2 mm Correlated energy spread Linac chirp Measured energy spread SR background

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Measured and predicted energy spread from wakefield chirp in SPPS Special setup to give 100  m bunch length with more charge at the head of the bunch Measured at end of linac

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Wakefields change not only the energy spread in the bunch But also the centroid energy of the bunch Fast means of determining relative bunch length Wakefields change not only the energy spread in the bunch But also the centroid energy of the bunch Fast means of determining relative bunch length

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Relative bunch length measurement based on wakefield energy loss scan Energy change measured at the end of the linac as a function of the linac phase (chirp) upstream of the compressor chicane Shortest bunch has greatest energy loss Predicted wakeloss___ For bunch length  z __ Predicted shape due to wakeloss plus RF curvature P. Emma, K. Bane

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Coherent radiation from the electron bunch Frequency domain Spectral power Spectrometry Autocorrelation Time domain Electro optic sampling Measured directly near the bunch Or transported out of the beam line

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 SPPS Electro Optic Bunch Length Measurement with in-vacuum crystal Probe laser Defining aperture Beam axis M1 M2 EO xtal Geometry chosen to measure direct electric field from bunch, not wakefield Modelled by H. Schlarb electrons

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Features of the SPPS Electro Optic Setup Compressed pulse from the users pump-probe Ti:Sa laser oscillator Transported low power pulse over ~150 m fiber to the electron beam line OTR provides coarse timing Ti:Sa oscillator StretcherShaper Fiber launch e- EO xtl polarizing beamsplitter s p imaging optics ~150 m fiber OTR

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Features of the SPPS Electro Optic Setup Fiber incorporated in pulse compression setup including compensating fiber dispersion with a spatial light modulator Cavalieri et al, FOCUS Group U. Michigan Fiber incorporated in pulse compression setup including compensating fiber dispersion with a spatial light modulator Cavalieri et al, FOCUS Group U. Michigan SLM 640-pixel To fiber Grating pair From stretcher

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Features of the SPPS Electro Optic Setup Crystal mounted close to electron beam Avoid wakefields from smaller apertures ZnTe crystal: 200 um thick EO coefficient, phase match, phonon resonances Crystal mounted close to electron beam Avoid wakefields from smaller apertures ZnTe crystal: 200 um thick EO coefficient, phase match, phonon resonances

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Electro-Optical Sampling at SPPS – A. Cavalieri et al. Single-Shot <300 fs 170 fs rms Timing Jitter ErEr Line image camera polarizer analyzer Pol. Laser pulse Electron bunch EO crystal Bunch length scan

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Electro optic resolution limits Spatial imaging resolution limits time resolution Crossing angle determines width of time window and temporal resolution Resolution limit then set by crystal thickness and the phase velocity mismatch Crystal material chosen to minimize phase mismatch Spatial imaging resolution limits time resolution Crossing angle determines width of time window and temporal resolution Resolution limit then set by crystal thickness and the phase velocity mismatch Crystal material chosen to minimize phase mismatch

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Electro optic resolution limits Future experiments Smaller crossing angle Smaller angle magnifies time coordinate on spatial axis But reduces the time window to accommodate beam jitter EO polymer films Strong EO coefficient May not last long Higher laser power cross correlation techniques (Jamison et al) Laser amplifier located near beamline Future experiments Smaller crossing angle Smaller angle magnifies time coordinate on spatial axis But reduces the time window to accommodate beam jitter EO polymer films Strong EO coefficient May not last long Higher laser power cross correlation techniques (Jamison et al) Laser amplifier located near beamline Ti:Sapphire laser 200  m thick ZnTe crystal eeee New chamber T. Montagne

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Synchronization of the Laser timing Jitter in the laser timing effects Electro optic bunch timing measurement Pump-probe timing for the users Enhancement schemes using short pulse lasers Jitter in the laser timing effects Electro optic bunch timing measurement Pump-probe timing for the users Enhancement schemes using short pulse lasers

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 SPPS Laser Phase Noise Measurements – R. Akre 476 MHz M.O. x MHz to linac MDL 3 km fiber ~1 km VCO Ti:Sa laser osc diode EO scope Phase detector 2856 MHz

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Energy and Bunch Length Feedback Loops L0 L1 DL1 Spectr. BC1 BC2 L2L3 BSY 50B1 DL2 V rf (L0) Φ rf (L2) V rf (L1) Φ rf (L3) EEE Φ rf (L2) zz Φ rf (L1) zz E 4 energy feedback loops 2 bunch length feedback loops 120 Hz nominal operation, <1 pulse delay Progressive commissioning schedule

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Undulator trajectory launch loop to operate at 120 Hz, <1 pulse delay Damps jitter below 10 Hz i.e. need stability above 10 Hz! At lower rep. rates, less damping Linac orbit loops to operate at 10 Hz because of corrector response time Antidamp Damp Gain bandwidth shown for different loop delays - L. Hendrickson Closed Loop Response of Orbit Feedback

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Remaining intra-undulator diagnostics – from Bingxin Yang, Lehman Review August ‘04 Location: every long break (905 mm) Diagnostics chamber length: 425 mm Functional components RF BPM, Cherenkov detector, OTR profiler, wire scanner, x-ray (intensity) diagnostics

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 FY04 accomplishments – from Bingxin Yang, Lehman Review August ‘04 Layout of diagnostics chamber OTR profiler Camera module designed Wire scanner Scanner design in progress Wire card adapt SLAC design X-ray diagnostics design Beam intensity: double crystal Beam profile: imaging detector

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Major issues at UCLA workshop – from Bingxin Yang, Lehman Review August ‘04 Beam damage of optical components Example from Marc Ross’ coupon test, LINAC 2000 Saturated FEL beam deposit higher energy density Desirable information Trajectory accuracy (  x~1  m) Effective K (  K/K ~ 1.5×10 -4 ) Relative phase (  ~10º) Intensity gain (  E/E~0.1%, z-) Undulator field quality

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Rethink x-ray diagnostics (Galayda) – from Bingxin Yang, Lehman Review August ‘04 Intra-undulator diagnostics Electron beam position monitor (BPM) Electron beam profiler (OTR & wire scanner) Low power x-ray Intensity measurements (R&D) Beam loss Monitor Far-field low-power x-ray diagnostics (R&D) Clean signature from spontaneous radiation Space for larger optics / detectors Single set advantage (consistency, lower cost) Goal = obtain “desirable information”

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Final Beam Dump Sensitive measurement of beam energy Optimized for energy spread resolution of 4*10 -5 (P.Emma) Bends smear out microbunching Dispersion hides emittance measurement Might be possible in the vertical plane

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Summary Diagnostics integrated into the LCLS design All systems require commissioning time to achieve LCLS resolution requirements New diagnostics still require R&D for bunch length and timing Developmental work at SPPS is critical Diagnostics being developed hand-in-hand with controls and feedbacks

P. Krejcik LCLS Diagnostics and Commissioning September 22-23, 2004 Appendix