THz Pump Beam for LCLS. Henrik Loos. LCLS Hard X-Ray Upgrade Workshop July 29-31, 2009

Transcription

1 Beam for LCLS Henrik Loos Workshop July 29-31, Henrik Loos

2 Overview Coherent Radiation Sources Timing THz Source Performance 2 2 Henrik Loos

3 LCLS Layout 6 MeV 135 MeV 25 MeV 4.3 GeV 13.6 GeV σ z.83 mm σ z.83 mm σ z.19 mm σ z.22 mm σ z.22 mm σ δ.5 % σ δ.1 % σ δ 1.6 % σ δ.71 % σ δ.1 % Linac- Linac-X L =6 m L =.6 m rf ϕ rf = 16 gun Linac-1 Linac-2 Linac-3 L 9 9 m L 33 m L 55 m ϕ rf 25 ϕ rf 41 ϕ rf...existing b 25-1a X undulator linac b,c,d 24-6d 3-8c BC1 BC2 L =13 m DL1 L 6 6 m L 22 m undulator L 12 m R mm R mm DL2 R 56 L =275 m R 56 SLAC linac tunnel research yard L-a,b FEE NEH Use LCLS electron beam to generate synchronized THz pulses for x-ray experiments 3 3 Henrik Loos

4 THz Sources Ultra-short electron beam carries broadband electro-magnetic field from DC to ~1um Extract coherent radiation at any beam obstruction Foil -> Transition Radiation (CTR) Annular mirror -> Diffraction Radiation (CDR) Bend magnet -> Edge Radiation (CER) THz pulse with radial polarization 4 4 Henrik Loos

5 THz Timing Pump THz pulse needs to be ahead of x-rays THz from same electron bunch requires delay of x-rays Generate THz from different electron bunch In present accelerator layout use 2 nd bunch 1s to 1s ns ahead of lasing bunch within same accelerator RF pulse Spoil beam quality of pre-bunch to prevent lasing THz pulse well synchronized with x-ray («5 fs) due to same drive laser pulse & RF pulse Generate THz from different accelerator If first 2 km of SLAC linac are used for LCLS RF timing can be set independently from existing LCLS accelerator Still good synchronization with x-ray due to same RF master clock 5 5 Henrik Loos

6 Location of THz Generation 6 MeV 135 MeV 25 MeV 4.3 GeV 13.6 GeV σ z.83 mm σ z.83 mm σ z.19 mm σ z.22 mm σ z.22 mm σ δ.5 % σ δ.1 % σ δ 1.6 % σ δ.71 % σ δ.1 % Linac- Linac-X L =6 m L =.6 m rf ϕ rf = 16 gun Linac-1 Linac-2 Linac-3 L 9 9 m L 33 m L 55 m ϕ rf 25 ϕ rf 41 ϕ rf b 25-1a LCLS II X undulator b,c,d 24-6d 3-8c BC1 BC2 L =13 m L 6 6 m L 22 m undulator R mm R mm DL2 L =275 m R 56 SLAC linac tunnel research yard L-a,b THz FEE NEH Use spend beam downstream of undulator in dump area 6 6 Henrik Loos

7 THz Generation after Undulator THz frequency range 1 1 THz Spectral range 3 3 cm -1 Radiation source Diffraction radiation has high frequency cutoff Transition radiation needs thin foil Edge radiation from dipole non-interceptive Energy 13.6 GeV, γ = 267 Radiation source size clipped by beam pipe Near field calculation for λ > 1 nm 7 7 Henrik Loos

8 Layout Options for THz Extraction Undulator Focusing Mirror 4mm 7.5 m CER to NEH Annular Mirror or Be-foil Profile Monitor YAGS:DMP1:5 3-Feb-29 15:38:13 Dump Magnets Diagnostics Can 3 < d < 1 mm y (mm) 1 5 Visible CER CTR to NEH -5 4 mm Plane Mirror Dump x (mm) 8 8 Henrik Loos

9 CER & Annular Mirror Option Peak of radiation at radius proportional to wavelength 1 For 1 decade spectral range need mirror aspect ratio of 3:1 1 8 λ = 3 μm 8 λ = 1 μm Mirror Aperture Radius (mm) 6 4 Radius (mm) 6 4 Mirror Hole Dist (mm) Dist (mm) 9 9 Henrik Loos

10 CER THz Pulse Energy Transmission Pulse Energy (mj) 1.5 Q = 1 nc Q = 1 nc E = 13.6 GeV Wavenumber (cm -1 ) Bunch Length (μm) 1 1 Henrik Loos

11 THz Beam Transport Transport from Dump area to Near Hall ~1 m Periodic focusing with 1 m drifts, 8 optics Transmission > 6% above 1 THz (only from diffraction) Radius (mm) 1 5 λ = 3 μm Distance (m) Radius (mm) 1 5 λ = 5 μm Distance (m) Henrik Loos

12 CTR THz Pulse Field & Energy Simulation for 1 nc, 6 fs, focus after 5 m lens THz pulse resembles e- bunch profile after ~1 ps low pass filter Peak electric field proportional to peak current With stronger focusing > 1 MV/cm Pulse energy > 1mJ At shortest bunch operation half cycle < 1 fs THz pulse possible Radius (mm) Current (norm.) Time (ps) -1 1 Time (ps) Electric Field (MV/cm) Formfactor (%) Time (ps) Wavenumber (cm -1 ) Henrik Loos

13 Summary Main issue is generation of THz pulse ahead of x-rays THz Pulse synchronized to x-ray beam Half cycle e-beam length (~25 fs) THz pulse with > 1MV/cm field possible Henrik Loos