Recent Developments at the Brookhaven Source Development Laboratory - PowerPoint PPT Presentation

Recent Developments at the Brookhaven Source Development Laboratory Brian Sheehy National Synchrotron Light Source Brookhaven National Laboratory Beam Physics Seminar Jefferson Laboratory October 15, 2004

The SDL Team G. L. Carr, E. D. Johnson, S. Krinsky, H. Loos , J. B. Murphy, J. Rose, T. Shaftan, B. Sheehy, Y. Shen, X.-J. Wang, Z. Wu, L. H. Yu National Synchrotron Light Source; Brookhaven National Laboratory • Facility Overview •Diagnostics/Control • High Gain Harmonic Generation (HGHG) • Cascading • Tunability •Optical Compression and and Shaping coherent FEL output • SPIDER and CPA •Other Sources • MV/cm peak field THz source

Facility Overview FEL seed at 800 nm Normal incidence 177 Modulator Nisus Wiggler 77 MeV Undulator MeV Adjustable Ion Pair Imaging CTR Monitor Dispersion NISUS pop-in Photoinjector Chicane Experiment Magnet RF zeroPhasing monitors Trim Chicane at 88 nm 30 mJ Ti:Sapphire s Amplifier FEL Measurement Energy, Spectrum, Synchronization and Pulse Length Measurements at 266 nm • BNL Gun IV photoinjector, S-band, 4.5 MeV • 4 stage Linac up to 200 MeV • upgrade to 250-300 MeV near completion • Magnetic Chicane Compressor R 56 = 5 cm • Seed at λ s = 800 nm in 1 m undulator K=1.67 , followed by dispersive section • NISUS undulator, 10 m, 256 period, K = 1.1 • fundamental at λ s /3 = 266 nm, output 100 µ J • 1 µ J at third harmonic λ s /9 = 89 nm

Diagnostics/Control Automated beam matching in NISUS Unmatched Unmatched • over 30 Ce:YAG pop-in beam 400 horizontal position monitors (BPM), including 17 RMS size (um) ± 0.42 µ m ε n 4.78 200 in the radiator 3.73 ± 0.38 m β α -0.95 ± 0.09 •Automated beam matching and 0 400 400 emittance measurements 4.12 ± 0.10 µ ε n m ± 0.15 m β 200 4.03 vertical ± 0.04 α 0.51 • Optical 0 0 2 4 6 8 10 Distance (m) Matched Matched •longitudinal electron beam 300 tomography 200 4.00 ± 0.19 µ ε n m • CSR instability question 3.26 ± 0.20 m β 100 0.09 ± 0.07 α 0 • temporal beam shaping 200 4.23 ± 0.15 µ ε n m 3.16 ± 0.16 m β 100 0.28 ± 0.05 α •electro-optic electron beam 0 0 2 4 6 8 10 Transverse beam parameters Transverse beam parameters measurements

Diagnostics/Control Layout of the two-photon absorption pump-probe autocorrelator Micrometer delay stage Photocathode Drive Laser: 250 fsec resolution cross – correlation with oscillator BBO Crystal • shaping: emittance, THz Reference Detector Detector 266 nm HGHG light 100 fs 250 fs blue Wedged beam splitter IR • two photon absorption autocorrelator for 5 ps 266 nm output UV Power meter BBO crystal 2 • picosecond resolution synchroscan 1.5 Signal 1 streak camera 0.5 0 40 30 • visible & XUV monochromators 20 10 Phase 0 -10 2 0 matching -20 • SPIDER: complete field measurement -2 -4 -30 -6 angle -8 -40 -10 Time (ps) of FEL output (mrad )

RF Zero Phase RF Zero Phase Uncompressed beam on pop14 Accelerate bunch at RF zero-crossing Bending magnet 40 Tail Head generates 60 dispersion 80 100 Positive 120 RF slope 140 100 150 200 250 300 Image at screen Zero RF depends on Mild compression slope energy spread Negative Tail Head 40 RF slope 60 80 100 120 Use linac phase to ‘streak’ the bunch on screen 140 160 180 100 150 200 250 300 350 Strong compression. But! Tail Head 20 40 60 This is really an energy measurement, 80 100 120 not a current measurement 140 160 180 200 50 100 150 200 250 300 350 400 Yikes! CSR Instability?

Longitudinal phase space tomography (H. Loos) 10 ∆ E (keV) E-t corr Each value of the chirp 0 manifests a different -10 projection of the phase Current (A) -6 -4 -2 0 2 4 6 t 50 current space. 25 0 E -6 -4 -2 0 2 4 6 0.3 Drive laser Intensity 0.2 0.1 0 -6 -4 -2 0 2 4 6 Time (ps) -400 0 400 -400 0 400 -400 0 400 -400 0 400 20 Energy (keV) 10 -400 0 400 -400 0 400 -400 0 400 -400 0 400 0 -10 -400 0 400 -400 0 400 -400 0 400 -400 0 400 -20 -4 -2 0 2 4 Time (ps) -400 0 400 -400 0 400 -400 0 400 -400 0 400 Spread (keV)

The energy projection can be very deceptive Huang & Shaftan NIMA 528, 345 (2004) Current and energy profiles of a chirped beam (a) without energy modulation, (b) with energy modulation.

• Degree of modulation observed inconsistent with CSR models • S. Heifets, G. Stupakov and S. Krinsky PRST-AB 5, 064401 (2002) • Z. Huang & H.-J.Kim PRST-AB 5, 074401 (2002) • Z. Huang T. Shaftan SLAC-PUB-9788, 329. • Longitudinal Space Charge model: • small modulation in photocathode drive laser • small current modulations due to drive laser modulations at photocathode • longitudinal space charge forces result in enhanced energy modulations in the bunch • these dominate the horizontal distribution in zero-phase measurements • experimental confirmation • lack of coherent enhancement of the IR in coherent transition radiation • modulation behavior with chicane strength, trans beam size, energy, etc Theory: Huang & Shaftan NIM A 528, 345 (2004) • phase space tomography Experiment: Shaftan et al NIM A 528, 397 (2004) potential threat for short pulse short wavelength FEL’s • can convert to current modulation; larger energy spresd • goes away for perfectly uniform laser temporal profile

Temporal Shaping (in progress) 800 nm At SDL in collaboration with SPARC Ti:Sapph Oscillator 9 nJ and SLAC 100 fsec Dazzler Amplified and compressed IR pulse 5 nJ Stretcher Intensity (arb units) 200-400 psec 25 mJ Amplifier 170-350 psec 15 mJ Compressor 0.1 - 30 psec Time (psec) 266 nm ω− tripler 1.8 mJ

Power Mon Monument e d o h t a c o Optical Relay, 14 meters t o h P Power Atten Spatial Filter ω Variable + 3 ω ω = 2 Regenerative Amplifier Power Divider ω ω + 2 r r e e ω = s s a a Spot L L 2-pass Amplifier G G Imaging A A Y Y 0 0 5 7 r 1 1 e n 2-pass Amplifier - - w e R R t o t C C A P Autocor- G G rellator Compressor 1 Compressor 2 Stretcher Optical Seeding Optical Relay, ~35 meters Isolator And Diagnostics r o m r Dazzler t e a u z l - r y e o t l r c t a r e u n o p A A c S Millennia Laser Tsunami Laser Photodiode

Electro-Optic e-beam meaurements Laser Spectro- Fiber Electrons meter Analyzer λ /4 Plate Accelerator Modulator Trim ZnTe to NISUS Trim Dipole Polarizer (800 nm) Seed Laser Monitor Delay or chirp Retardation induced by e-bunch field E vac π 3 2 n r E l ∆ ϕ = 0 41 vac ( ) λ + ε 1 Asymmetry in transmitted/reflected gives ∆ϕ − T R sin( ϕ ∆ ) = Jitter 150 fsec rms over 20 + T R seconds Chirp seed and spectrally resolve the asymmetry – single shot measurement (800 fsec resolution).

High Gain Harmonic Generation (HGHG) 3 Energy Fluctuations σ = 41% 2 e - p(E) SASE 1 0 10 0 1 2 3 σ = 7% p(E) 5 HGHG • Self amplified Spontaneous Emission (SASE) Spontaneous emission � microbunching �� enhanced emission • Noisy 0 0 1 2 3 E/<E> • Broad Bandwidth • Not longitudinally coherent Spectrum • HGHG Seed modulates e - energy � coherent microbunching �� emission • Short wavelength : tune radiator to harmonic of seed • Stable • Narrow bandwidth, higher brightness • Longitudinal coherence

Cascading HGHG to soft X-ray wavelengths (L.H Yu) 1-ST STAGE 2-ND STAGE 3-RD STAGE FINAL AMPLIFIER MODULATOR AMPLIFIER AMPLIFIER MODULATOR AMPLIFIER MODULATOR AMPLIFIER λ w = 6.5 cm λ w = 4.2 cm λ w = 2.8 cm λ w = 11 cm λ w = 6.5 cm λ w = 4.2 cm λ w = 2.8 cm Length = 2 m Length = 2 m Length = 8 m Length = 4 m Length = 12 m Length = 6 m Length = 2 m Lg = 1.3 m Lg = 1.4 m Lg = 1.75 m Lg = 1.6 m Lg = 1.3 m Lg = 1.4 m Lg = 1.75 m DISPERSION DISPERSION DISPERSION d ψ/ d γ = 1 d ψ/ d γ = 1 d ψ/ d γ = 0.5 e- e- “Spent” DELAY LASER DELAY “Fresh” DELAY 1.7 electrons PULSE electrons “Fresh” “Spent” electrons electrons “FRESH BUNCH” GW e- e- CONCEPT 500 70 800 MW 400 MW MW MW 2.128 ÷ 5 ÷ 5 ÷ 5 53.2 nm nm 10.64 nm 266 nm SEED e-beam 750Amp 1mm-mrad LASER 2.6GeV σ γ / γ =2×10 – 4 total L w =36m

A proposed 2 stage cascade for the SDL P in =1.5 MW 56 MW P out =140 MW 266nm 133nm 66.5 nm 0.8m MINI 6 m NISUS 2m VISA e-beam 600Amp 250 MeV 2.7 mm-mrad σ γ / γ = 1.×10 - 4 Pulse length ~ 0.5ps � 70 µ J

A Novel Tunability scheme for HGHG (T. Shaftan) Seed with fixed λ . Radiator DS Modulator 175.5 175.5 175.5 . . E [MeV] E [MeV] E [MeV] . 175 175 175 t [ps] 174.5 174.5 174.5 1 0 1 1 0 1 1 0 1 after Modulator after DS before FEL (Dispersive Section) • Dispersive Section (DS) converts energy modulation into bunching • DS also compresses the energy modulation wavelength • a small but measureable effect in our machine, but could be optimized to yield a tuning range of 20%

Optimal tunability configuration 1 1 1 1 1 energy 0 0 0 0 0 time . . . . . 1 1 1 1 1 1 0 1 1 0 1 1 0 1 1 0 1 1 0 1 Seed with Radiator XRF DS XRF Modulator HGHG fixed λ Klystron Compression or stretching in the dispersive section can be used to modify the period of the microbunching. This is ordinarily a small effect, but it could be optimized to yield ~20% tunability.