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

Transcription

1 Diagnostics overview Transverse Beam Properties Longitudinal Beam Properties

2 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 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

3 YAG, FC Toroid YAG Phase Monitor T-Cavity Wire Scanner Toroid OTR OTR Toroid YAG

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

5 Transverse Diagnostics YAG scintillator OTR Wire Scanners

6 Requirements for YAG & OTR Monitors Name Location Hor. Beam Size (mm) Ver. Beam Size (mm) Resol. (µm) Name Location Hor. Beam Size (mm) Ver. Beam Size (mm) Resol. (µm) YAG01 YAG02 YAG03 YAGG1 YAGS1 GTL GTL L0 GTL SAB [7.0] [45.0] [6.0] [8.0] OTR11 OTR12 OTR21 OTRTCAV OTR30 BC1 BC1 BC2 L3 DL [0.2] [1.0] YAGS2 OTRH1 SAB DL [10.0] [12.0] OTR33 OTRDMP DL2 Dump [0.6] OTRH2 DL OTR1,3 DL OTR2 OTR4 OTRS1 DL1 DL1 SAB [1.5] [10.0] [8.0] [14.0] [12.0] 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 YAG Beam Profile Monitor Yellow scintillator crystal, emits green light when charged particle passes through Fluorescence decay time 70ns High photon yield N φ = 3.5 /e - For 1 nc charge: N φ = ~10 8 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/µm 2 Equals 65 µm beam size at 1 nc Combined with Faraday cup in GTL -> camera shielding Thin mirror (1mm) at higher energies e - YAG θ Mirror Lens CCD

8 Transition Radiation Radiation of a charged particle at relativistic speed moving from one medium into another. Relativistic speeds -> Coulomb field is quasielectro-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 Electron Beam θ 2 γ Metal Foil

9 Small quantum efficiency About 1 photon/100 electrons OTR Profile Monitor Aluminum foil 1µm Mitigates radiation issue Foil damage is concern OTR yield for 100mrad angular acceptance Energy (MeV) QE (%), nm Logarithmic dependence on energy and solid angle Limited z-space Foil at 45 degree Depth of field ~1mm Match reflection direction with TCAV or dispersion direction

10 Optics Layout 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 Vacuum e-beam OTR YAG Lens CCD Filters Beam splitter Reticule Illumination

11 OTR/YAG Optics Design Actuator Optics Box CCD Screen Lens Beam Splitter Filters 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 Ver. Position (pixel) Counts Uniq Vision CCD Dark Image Test Counts Single image Diff image Hor. Position (pixel) Periodic BG structure removed with background subtraction Background noise 2 bits rms Dynamic range > 100 TECM55 lens with ruler (scale 1/64 ) x Position (µm) Resolution: B/W transition < 20um

14 Profile Monitor Controls y 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 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 Rows x 10 4 CCD Image YAG Crystal Mock-up x x

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 Area IN20 LI21 LI24 LI27 LI28 LTU Total Scanners

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 Transverse Cavity Bunch Length Measurement TCAV in 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 Horizontal Kicker Vertical Deflecting Cavity Electron Beam Off-axis Screen

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, nondedicated optics, screen resolution Beam size (pixel) Mock-up σ x = 49.50± 2.85 pixel σ t = 2.02± 0.05 degree Mock-up TCAV amplitude (norm.)

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) ( ) 2 2 dw1 ω i = ω f ( ω) f ( ω) n( t) e ω t W N d dω e, = dω 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 Current (ka) Form Factor Time (fs) BC Time (fs) Wave Number (cm -1 ) BC2 BC1 FF BC2 FF BC1 Exp BC2 Exp

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. Efficiency (%) um 54 um 82 um 111 um 141 um 170 um 200 um Detector Signal (µj) no hp10 hp20 lp10 lp Wavenumber (cm -1 ) Bunch Length (µm)

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