P. Emma, SLACICFA XFEL 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 , 2004

P. Emma, SLACICFA XFEL July 29, 2004 Previous Talks/Publications R. Miller, IEEE Trans. Nucl. Sci., June X.-J. Wang, PAC’99, March J. Frisch, BNL/LCLS Diag. Workshop, March P. Emma et al., LCLS-TN-00-12, Aug R. Akre et al., PAC’01, June R. Akre et al., EPAC’02, June H. Schlarb: (Aug. 2003).

P. Emma, SLACICFA XFEL July 29, 2004 Transverse RF Deflector in the SLAC Linac V 0  20 MV  z  50  m, E  28 GeV eeee zzzz 2.44 m cccc pppp   90° V(t)V(t)V(t)V(t) yyyyRF‘streak’ S-band built in 1960’s (G. Loew…) f rf = 2856 MHz

P. Emma, SLACICFA XFEL 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 % 28.5 GeV 80 fs FWHM 30 kA RF Deflector

P. Emma, SLACICFA XFEL 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

P. Emma, SLACICFA XFEL July 29, 2004 Measurements RF Deflector OFF RF Deflector ON

P. Emma, SLACICFA XFEL July 29, 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 y2y2y2y2 RF deflector phase (deg)

P. Emma, SLACICFA XFEL 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

P. Emma, SLACICFA XFEL 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

P. Emma, SLACICFA XFEL 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 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)

P. Emma, SLACICFA XFEL July 29, 2004 Screen Pixel Calibration (from H. Schlarb’s 2003 talk) 100% klys. drive: mm/deg 50% klys. drive: mm/deg 50% klys. drive: 4.92 pix/deg less sensitive to timing jitter screen y-position (pix) BPM y-position (mm)

P. Emma, SLACICFA XFEL 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

P. Emma, SLACICFA XFEL 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 EEEE EEEE EEEE EEEE 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 EEEE EEEE EEEE EEEE EEEE EEEE T-cav. T-cav.  x,y ?

P. Emma, SLACICFA XFEL July 29, 2004 Slice-Emittance Measurement Simulation RF-deflector at 1 MV slice OTR 10 times  y  bunch length scannedquad scanned quad

P. Emma, SLACICFA XFEL 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)

P. Emma, SLACICFA XFEL 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