Bunch Length Measurements at SPEAR3 Jeff Corbett for the SPEAR3 - PowerPoint PPT Presentation

Bunch Length Measurements at SPEAR3 Jeff Corbett for the SPEAR3 Accelerator Group Outline 1. SLAC, LCLS, SPEAR3 and short bunch operation (low- ) 2. Streak camera measurements 3. Cross-correlation measurements 4. Summary Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

SLAC Project M circa 1962 Stanford Linear Accelerator Center Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

SLAC 2-mile accelerator and SPEAR storage ring SLAC with LCLS Early view of SLAC PEP-II LCLS SPEAR circa 1972 SPEAR3 circa 2009 LCLS SPEAR3 Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Free-Electron Lasers - short pulse, high power, coherence FELS Rings Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Electron and Photon Pulse Structure: SASE Electron START MIDDLE END Photon …the (LCLS) X -ray pulse duration appears much shorter than the nominal 80 fs (bunch) …the 80fs mode of operation actually produces X -ray pulses of ~20-40fs (L. Young, et al, Nature 446,1 July 2010) Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Back to the SPEAR3 Light Source SPEAR3 3 GeV, 10nm-rad 18 DBA cells Visible Diagnostic Beam Line Injector Circa 2002 Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

SPEAR3 Accelerator Optics ¼ ring Double-bend Achromat 18 cell racetrack lattice || =20ps rms reduce alpha  2ps rms Single cell optics Achromat Low Alpha (short bunch) Low Emittance x ~10m y ~5m x >0 x =0 x >0 Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Typical streak camera data R2 synchroscan 100 200 300 400 ~50ps fwhm 500 600 700 800 900 1000 200 400 600 800 1000 1200 screen height ps/px 2 1 z z I z I I exp 1 o 2 1 A sgn( z z ) R1: 157.45ps 0.1538ps/px R2: 704.41ps 0.6879ps/px R3: 1214.60ps 1.1861ps/px asymmetry term R4: 1686.50ps 1.6470ps/px ~5 pixel focus Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Low-emittance optics: bunch length vs. current filter Longitudinal bunch profile change time (ps) Bunch current (au) Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Current scan and ring impedance note distortion Bunch length Amplitude Z/n=0.20, L=25nH Bunch current (mA) Asymmetry Synchronous Phase Shift 7.5 V/pC, R = 600 Ohm Bunch current (mA) Bunch current (mA) Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Bunch length measurements in low-alpha mode ( /340) Amplitude Amplitude R2 range R1 range Low beam current (~10-20pc , SR emission) filter change?? Streak camera resolution limit ~2.4ps rms Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Bunch length scaling in low- mode (cont’d) Current dependence - single-bunch alpha/59 Current increase BESSY-II SPEAR3 10.0 kHz 10 3.95 kHz bunch length [ps, rms] 3.16 kHz 2.16 kHz Streak camera limit 1.50 kHz ~2.4ps rms 1 0.50 kHz 0.1 0.0001 0.001 0.01 0.1 1 10 single bunch current [ma]

Streak camera resolution issues computer sweep mcp barrel plates head bunch electrons photons CCD camera head tail tail display/analysis phosphor photocathode Trigger or 119MHz Hamamatsu c5680 Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

System Calibration Focus mode Glass Etalon Use 2L/c echo to determine px/ps 5-6 pixel FWHM Chromatic dispersion screen height ps/px 450550 650 700nm 600 R1: 157.45ps 0.1538ps/px R3 R2 R1 R2: 704.41ps 0.6879ps/px R3: 1214.60ps 1.1861ps/px R4: 1686.50ps 1.6470ps/px Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Synchroscan, dual-scan, triggered-scan operation Triggered-scan isolates but has noise Synchroscan integrates but has ripple 50ms horizontal 20ms dual-scan triggered 500 A, low- 500 A, low- 10ms 5ms fit Gaussians, histogram statistics deconvolve ripple, ~1ps phase noise Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Statistical evaluation of triggered-scan data Histograms Single-shot fits Centriod, Sigma and Sum Nominal optics Centriod Sigma Low-alpha optics Sum Bursting in tail Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Bursting as seen on the streak camera 200 VerSweep (px) 400 600 800 1000 100 200 300 400 500 600 700 800 900 1000 HorSweep (px) Fitted sigma p5*px2ps, (ps) 23 22 21 20 0 5 10 15 20 25 30 35 40 45 50 time (ms) Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Bursting as seen on fast-gated camera /21 4.7mA Gate trigger freq: ~10kHz Horizontal single turn profile Gaussian fit (4.7mA, Alpha/21 bursting) 100 gates per exposure 100 200 pixels 300 400 500 100 200 300 400 500 600 700 800 900 1000 pixels (13um*13um pixel size) 800 Fitted amp (a.u.) 600 400 200 0 10 20 30 40 50 60 70 80 90 100 Fitted sigma x at source point(um) 2000 1500 1000 500 0 10 20 30 40 50 60 70 80 90 100 Gate number (~100us per gate) Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Injection damping transients – longitudinal plane 500us per frame 50us, from start 100us, delayed 1ms 200us, from start De Santis/Byrd De Santis/Byrd

x-y projection and x-t projection of injected beam turns Fast Gated Camera Streak Camera Fast Gated Camera Streak Camera x-y x-t x-y x-t turn #4 turn #1 turn #2 turn #5 turn #3 turn #6 Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Laser/SR cross-correlation bunch length measurements Goal is to produce ps x-ray pulses at MHz rates for pump/probe SLAC/Stanford PULSE Institute LCLS SPEAR3 Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Short Bunch Measurements with SR IR/THz beam line FIR interferometer/form factor Fr Ö hlich CSR component/electro-optic Steffen/M ü ller/Peier ‘optical sampling’ in the visible ( Zolotorev, et al, ALS ) Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Laser/ SR Cross-correlation Geometry Spatial/temporal overlap Lock-in photodiode ps SR pulse SR beam 400nm 800nm BBO 50fs Ti:Sa pulse delay line computer scope Ti:Sa oscillator Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Second-Harmonic in a BBO BBO Crystal APD Ti:Sa SR Beam visible, few ps, 1 fJ 800nm 1.28MHz SR 2 Ti:Sa Laser RF Lock-in Amp 0.5 J, 60fs 5.06MHz 1.28MHz overlap integral Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Plan View of Optical Bench APD BBO crystal White light Streak camera Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Laser timing and Lock-in Measurement computer diode pico-motor 1.28MHz 476MHz diode 5.1MHz laser pulse 1.28MHz SR pulse Lock-in to 1.28MHz signal 400nm component … time Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Bunch Profile in Low- Optics 1.5mA, 8.7 ps LE 1mA, 21.8 ps 86uA, 5.9 ps LA 1.5 mA, 8.7 ps 10.0 kHz 10 3.95 kHz Comparison with SC data bunch length [ps, rms] 3.16 kHz 2.16 kHz 1.50 kHz 1 0.50 kHz 0.1 0.0001 0.001 0.01 0.1 1 10 single bunch current [ma] Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Profile Measurements in Low-Emittance Optics Streak Camera Data 14mA, 31 ps 1mA 21.8 ps Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010

Summary and Future Improvements  Low- operation for short-pulse, high rep-rate x-ray beam  Streak camera measurements of bunch length scaling law  Streak camera limited by low flux, ~2.4ps synchroscan resolution  Developing laser/SR cross-correlation measurements (no IR port)  Testing different EO crystals, fiber laser  Use visible diagnostic beam to provide timing for pump/probe stations Thank you! Second DITANET Topical Workshop: Longitudinal Diagnostics 12-13 July 2010