Emittance-exchange-based high harmonic generation scheme for FEL JIANG Bocheng SINAP 2012 July 18~20 Lanzhou China 2012 Deflecting/Crabbing Cavity Applications in Accelerators Mini-Workshop

Lay out Introduction of short wavelength FEL scheme Introduction of EEX EEX-HHG scheme for short wavelength FEL Simulations results Stable telescope beam line

Introduction of short wavelength FEL scheme FEL can be divided into two branches 1 、 SASE (self-amplified spontaneous emission) FEL 2 、 Seeded FEL SASE is a mature scheme to reach hard X ray. However less temporal coherence bigger shot-to-shot fluctuations needs long undulator (~10 2 m) Seeded FEL, lack of short wavelength seeding laser, great challenges to push to X ray region.

Introduction of short wavelength FEL scheme Seeding FEL 1.HHG seeding, (High-order Harmonic Generation) through laser interact with gas, as seeding laser for the FEL. 2.HGHG, Using high order harmonics (limited to 4~5th order) 3.Casecade, Using high order harmonics as seeding laser for next stage FEL. 4.EEHG, (echo-enabled harmonic generation), modulate electron beam density creates higher harmonics. 5.EEX-HHG(Emittance-exchange-based high harmonic generation),modulate electron beam density creates higher harmonics.

Emittance exchange X Z doglegDeflect Cavity dogleg Dipole P. Emma et al., Phys. Rev. ST Accel. Beams 9, (2006). ηk+1=0 k=2πeV rf /λE e In the original proposal for the EEX beam line was used to approximately exchange a smaller longitudinal emittance with a larger transverse one to improve the FEL.

Emittance exchange 6 X Z dogleg Deflect Cavity dogleg E Z Mask E A0 Yin-e Sun, HBEB2009, MAUI

Laser Modulator Chicane Dipole Deflect Cavity Beam Masker radiation EEX-HHG FEL x’(rad)

EEX-HHG FEL

 Comparing to EEHG Disadvantages: Less charge. Pendings: CSR, ISR(pending on detailed design) Advantages: 1.transverse emittance can be reduced together with Energy band creation. 2.Higher correlation in longitudinal phase space. 3.EEX and the second modulator can be separated by additional accelerator tube. EEX done at lower energy, second modulator at higher energy. Laser Chicane Masker radiation

EEX-HHG FEL

Deflect Cavity f2ff ηk=1 ηk=1/N N=f 2 /f 1 Deflect Cavity f1+f2 f2-f1 Chicane EEX beam line Telescope EEX beam line Dao Xiang and Alex Chao, Phys. Rev. ST Accel. Beams 14, (2011)

EEX-HHG FEL Telescope EEX beam line transport matrix Set N=1, a=0, b=0, degenerate to dogleg beam line

Simulations Dogleg beam line ε x_in =1.5mmmrad, ε z_in =3.7mmmrad K=-2.9(17.5MV) ， L cavity =0.2m, θ bend =22 ◦, η=0.343m β x =147m, α x =51 Elegant ε x_out =3.7mmmrad ， σ t =95fs PARMELA(space charge) ε x_out =5.0mmmrad ， σ t =200fs

Simulations Z in /E in ≈ - ξ ε out X ≈ ε in Z ≈3.7 mm mrad Choice of β is to produce enough beam size, place less challenges for mask fabrications. At the optimized α, ε out Z ≈ ε in X ≈ 1.5mm mrad, energy bands smeared out. The to get clear energy bend, α is away from optimized one. ε out Z ≈5.4 mm mrad

Simulations GINGER By using a 400-nm seed laser, radiation power at the 24th harmonic (16.67-nm wavelength) saturated at 16.5m undulator

Simulations Chicane beam line ε x_in =1.51mmmrad, ε z_in =3.7mmmrad β x =64.2m, α x =4.5,, β y =50m, α y = -5 K=2.9 ， L cavity =0.2m, θ bend =22 ◦, η=-0.343m V 0 =17.5MV ε x_out =4.08mmmrad ， σ t =91fs(after suppression) Telescope beam line ε x_in =1.77mmmrad, ε z_in =3.7mmmrad β x =314m, α x =194, β y =98m, α y =48 ??? K=2.9 ， L cavity =0.2m, θ bend =12.66 ◦, η*=-0.343m η=0.114m ε x_out =3.8mmmrad ， σ t =154fs(after suppression) N=3

Simulations Beam size y 1cm

Simulations (CSR) CSRtrack 2DElegant 1D

Simulations (CSR+ISR) Elegant CSR+ISR

Deflect Cavity Dipole f2-f1 Less Y focus problem

Thanks