Diagnostic Systems for High Brightness Electron Injectors Henrik Loos 48 th ICFA Advanced Beam Dynamics Workshop on Future Light Sources SLAC 2010 1 1 Henrik Loos
LCLS Injector Injector Diagnostics Characterize high brightness low energy electron beam generated by RF gun Characterize parameters of mid range energy electron beam prior to bunch compression 2 2 Henrik Loos
Outline Gun Beam Diagnostics Cathode imaging Spectrometer Longitudinal phase space Emittance Injector Beam Diagnostics Transverse beam profile Temporal profile Slice emittance Longitudinal phase space Coherence diagnostics limits 3 3 Henrik Loos
LCLS OTR/YAG Diagnostics Common design 100um YAG crystal 1um OTR foil (Al) Fixed magnification ~10 20 mm FOV 10 um resolution (OTR) CCD Camera Mega pixel 12 bit Insertable filters Actuator Screen Optics Box 4 4 Henrik Loos
Profile Monitor YAGS:IN20:241 27-Jun-2008 11:38:30 Gun Emission Imaging 5 y (mm) 0-5 Daily cathode imaging check with Automated routine Profile Monitor YAGS:IN20:241 28-Nov-2009 11:12:02-10 -5 0 5 10 x (mm) High resolution of quantum efficiency structure on cathode Extreme example after Laser Cleaning Few pc charge Laser spot 2mm iris y (mm) 4 2 0-2 -4-2 0 2 4 6 x (mm) 5 5 Henrik Loos
Gun Spectrometer Diagnostics 6.05 BXG @ 0.00596 0.5 nc 31-Jul-2008 22:39:36 50 BXG @ 0.00596 0.5 nc 31-Jul-2008 22:39:36 Energy (MeV) 6 5.95 5.9 5.85 5.8 Q ~ 250 pc -35-30 -25-20 -15 Laser Phase (degree) Energy Spread (kev) 40 30 20 10-35 -30-25 -20-15 Laser Phase (degree) y (mm) Profile Monitor YAGS:IN20:841 31-Jul-2008 22:26:40 5 0-5 10 x 50 mm YAG crystal -20-10 0 10 20 x (mm) 6 6 Henrik Loos
Longitudinal Phase Space Energy scale from beam in spectrometer Signal from Cherenkov radiator Time scale with streak camera Technique requires light transport to streak camera Dispersion effects need to be considered PITZ Test Facility J. Rönsch, DIPAC 09 7 7 Henrik Loos
Slit Mask Emittance Measurement Q = 100 pc, 5.6 MeV Low energy beam space charge dominated Quad scan measurement of entire beam not accurate Measure emittance of beamlets Obtain phase space directly SPARC Emittance Meter A. Cianchi, EPAC 06 8 8 Henrik Loos
Injector Transverse Deflector Cavity RF Cavity Screen e S-band 0.67 m V(t) RF streak σ y V 0 > 1.2 MV f RF = 2856 MHz E S = 130 MeV σ z β d ψ 90 β s σ 2 y k ev 2 2 RF 0 = σ y0 + βd βsσ z sin ψ cosφ Es 2 from 1960 s Map time axis onto transverse coordinate Simple calibration by scan of cavity phase Typical calibration factor ~1 from z y 9 9 Henrik Loos
Injector TCAV Bunch Length Transverse deflector provides enough resolution for 10s of slices Beam Size (µm) TCAV bunch length on OTRS:IN20:571 27-Jul-2009 21:18:21 Super 800 600 400 200 0 σ y = 54.01±13.12 µm σ z = 636.473±8.518 µm cal = -1.338±0.010 µm/µm Q = 250 pc -90 off 90 TCAV Phase (degree) Counts () 2000 1500 1000 Counts () 500 0-500 -5000 0 5000 4 x 104 Profile OTRS:IN20:571 27-Jul-2009 21:18:21 Position Super (µm) at 0 3 2 1 Profile 27-Jul-2009 21:18:21 Super at 1 850 um rms 60 um rms 0-100 0 100 200 300 400 Profile OTRS:IN20:571 27-Jul-2009 21:18:21 Position Super (µm) at -1 2000 Counts () 1500 1000 500 850 um rms 0-500 -4000-2000 0 2000 4000 6000 OTRS:IN20:571 Position (µm) 10 10 Henrik Loos
Injector Longitudinal Phase Space YAGS2 RF deflector ON energy time Laser OFF σ E /E < 12 kev YAGS2 Dec. 10, 2008 YAGS2 Laser heater effect on slice energy spread can be studied Laser: 40 µj σ E /E 45 kev Timing between heater laser & electron beam adjusted Laser: 230 µj σ E /E 120 kev 11 11 Henrik Loos
Low Charge Time Slice Emittance Individual Slice Fit Lower limit on OTR slice emittance ~10pC Q E σ z I γε x = 20 pc = 135 MeV = 400 μm = 5 A = 0.14 μm Norm. Emittance ( µm) 0.6 0.5 0.4 0.3 0.2 0.1 0 Emittance Current Laser Spot Ø 0.6 mm -3-2 -1 0 1 2 3 Time (ps) 12 12 12 Henrik Loos
OTRS:IN20:541 OTRS:IN20:541 Laser Heater Effect on Diagnostics Heater induced microbunching should become energy spread Observe peak at 760 nm in OTR spectrum at first screen after heater chicane Beam replica visible in first order of grating Spectrum not measured on DS screens, but small effect on intensity noticible y (Pixel) 300 400 500 600 700 800 900 400 500 600 x (Pixel) 400 500 600 x (Pixel) OTRS:IN20:541 LH off LH < 1uJ LH 37uJ OTR1 400 500 600 x (Pixel) 13 13 Henrik Loos
COTR Mitigation COTR affects intensity and observed beam size in visible range Effect appears after bend magnet, uncompressed Still present if range limited to 380 400 nm x Beam Size (µm) 100 90 80 70 60 50 Correlation Plot 14-Nov-2008 23:03:39 OTRS:LI21:291:XRMS Q = 250 pc 40 10.2 10.4 10.6 10.8 11 11.2 Dogleg Quad Strength (kg) OTR12 L0 L1X gun L1S wire scanner DL1 BC1 L 135 MeV 250 MeV 14 14 Henrik Loos
YAG Screen Saturation YAG screen not suitable for focused high brightness beam Saturation limits beam size 250 um @ 1 nc 125 um at 250 pc Injector emittance screens have ~ 60 120 um beam size CCD Counts x 10 6 4.2 4 3.8 3.6 3.4 3.2 3 2.8 Correlation Plot 14-Nov-2008 20:26:46 YAGS:IN20:921:TMIT 1 1.5 2 2.5 3 3.5 4 4.5 5 Electron density (1/µm 2 ) x 10 4 15 15 Henrik Loos
Summary Well established suite of diagnostics available for gun & injector beam parameters Provides projected and time resolved measurements with deflector cavity Semi-invasive wire scanners for routine measurements and as a reference to compare with YAG/OTR screens. YAG screens good for large beam size, saturation effect limits to non-focused beams OTR useful prior to any R56, coherence observed in visible and UV w/o compression 16 16 Henrik Loos