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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Electron Bunch Measurements with a Transverse RF Deflector P. Emma ICFA XFEL 2004 Workshop July 29, 2004 ICFA Future Light Sources Sub-panel Mini-workshop on XFEL Short Bunch Measurement and Timing Stanford Linear Accelerator Center, July 26 - 30, 2004
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Previous Talks/Publications R. Miller, IEEE Trans. Nucl. Sci., June 1965. X.-J. Wang, PAC’99, March 1999. J. Frisch, BNL/LCLS Diag. Workshop, March 2000. P. Emma et al., LCLS-TN-00-12, Aug. 2000. R. Akre et al., PAC’01, June 2001. R. Akre et al., EPAC’02, June 2002. H. Schlarb: http://www.desy.de/s2e/ (Aug. 2003). http://www.desy.de/s2e/
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Transverse RF Deflector in the SLAC Linac V 0 20 MV z 50 m, E 28 GeV eeee zzzz 2.44 m cccc pppp 90° V(t)V(t)V(t)V(t) yyyyRF‘streak’ S-band built in 1960’s (G. Loew…) f rf = 2856 MHz
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Short Bunch Generation in the SLAC Linac 1-GeV Damping Ring z 1.1 mm z 50 m z 12 m z 6 mm SLAC Linac 30 GeV 30 GeV FFTB Existing bends compress to 80 fsec Existing bends compress to 80 fsec 1.5 Å compression by factor of 500 1.5% 28.5 GeV 80 fs FWHM 30 kA RF Deflector
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Linac Installation SPPS: L = 2.4 m f = 2856 MHz TTF-2: L = 3.6 m f = 2856 MHz LCLS: L = 0.5 & 2.4 m f = 2856 MHz P. Krejcik
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Measurements RF Deflector OFF RF Deflector ON
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 3-Point Bunch Length Measurement Asymmetric parabola indicates incoming beamtilt Asymmetric parabola indicates incoming beam tilt Bunch length reconstruction: measure streak at 3 different RF phases Cavity on + 180° Cavity off Cavity on 180° z = 90 m y2y2y2y2 RF deflector phase (deg)
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Practical Issues Extracting rms beam size from non-Gaussian, noisy screen image Screen calibration Limited field of view on screen RF phase drift during measurement Inadequate RF voltage Clumsy software Data acquisition time vs. beam drift time
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Voltage/Screen Calibration BPM y-position after deflector (mm) RF deflector phase (deg) BPM calibration is only accurate to ~10% level: …better to calibrate amplitude on screen and get pixels/deg (P. Krejcik) RF phase setting is highly accurate
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Screen Pixel Calibration Errors Errors on x-axis produce bias in standard linear regression techniques… T. Lohse, P. Emma, SLAC-CN-371, Feb 1989. no noise on x-axis: slope = 3.5 exactly Simulated beam position RF phase noise on x-axis: fitted-slope = 2.6 (true = 3.5) Simulated beam position RF phase (from H. Schlarb’s 2003 talk)
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Screen Pixel Calibration (from H. Schlarb’s 2003 talk) 100% klys. drive: 0.427 mm/deg 50% klys. drive: 0.0415 mm/deg 50% klys. drive: 4.92 pix/deg less sensitive to timing jitter screen y-position (pix) BPM y-position (mm)
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 RF Deflector as Arrival Time Monitor At 14 GeV, a 10- m BPM resolution can resolve <10 fsec timing error – but must also consider RF phase jitter. E 0 28 GeV, V 0 24 MV, y 50 m
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Location of Main Linac Diagnostics 5+ energy spread meas. stations (optimized with small )...existing linac L0 rfgun L3L1 X L2 x,y EEEE EEEE EEEE EEEE 5+ emittance meas. stations designed into optics ( x,y ) slice measurements possible with transverse RF (L0 & L3) BPMs at or near most quadrupoles and in each bend syst. RF deflectors for slice and E measurements EEEE EEEE EEEE EEEE EEEE EEEE T-cav. T-cav. x,y ?
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Slice-Emittance Measurement Simulation RF-deflector at 1 MV slice OTR 10 times y bunch length scannedquad scanned quad
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Slice-Emittance Measurement Simulation slice-5 Injector at 135 MeV with S-band RF-deflector at 1 MV = meas. sim. = calc. = y distribution = actual (same SLAC slice- code used at BNL/SDL) (slice- y -emittance also simulated in BC1-center)
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P. Emma, SLACICFA XFEL 2004 - July 29, 2004 Slice Energy Spread Measurements in LTU LTU at 14 GeV with S-band RF-deflector at 24 MV FEL goal E /E E /E 10 4 x 12 m
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