Simulations of the IR/THz source at PITZ (SASE FEL and CTR) Introduction Outline Simulations of SASE FEL Simulations of CTR Summary Issues for Discussion Mini-Workshop on THz Option at PITZ DESY, Zeuthen 22.09.2015
Proposal for IR/THz source at PITZ 2 Photo Injector Test Facility at DESY, Zeuthen site (PITZ) Considering Development of Intense and wide wavelength range IR/THz source at PITZ Motivations & Goals European - XFEL PITZ-like X-ray IR/THz Pump & Probe experiment PITZ is an ideal machine for development of the prototype IR/THz source (Reference: E.A.Schneidmiller et al., WEPD55, FEL2012 conf.) Photon diagnostics Radiation based e-bunch diagnostics Service for light users Case studies of radiation generation produced by the PITZ electron beam SASE FEL for λ rad 100 µm (f 3 THz) Coherent Transition Radiation (CTR) for λ rad 100 µm (f 3 THz)
PITZ Beamline Overview 3 CTR Station RF Gun CDS Booster Deflecting Cavity APPLEII Undulator 0 m Quadrupole magnet Proposal extension for SASE FEL Dipole magnet 4.385 m Screen 16.300 m 22.500 m PITZ Beamline layout including radiation stations for simulation studies Photocathode RF Gun Cut Disk Structure (CDS) Booster UV photocathode laser Cylindrical pulse shape (Gaussian, flat-top) 3D-ellipsoidal pulse shape Electron beam diagnostics stations Radiation stations for simulations studies CTR station Extension for SASE FEL Key Parameters Laser temporal length Bunch charge Maximum mean momentum <P z > 2-20 ps FWHM few pc 4 nc ~22 MeV/c
Simulations of SASE FEL 4 Consideration of undulator parameters Overview of FEL parameter space Beam dynamics simulations Radiation calculations Summary and outlook
SASE FEL: Consideration of undulator parameters 5 Important Equations The Peak magnetic field (B max ) : B max T = a 1 exp a 2 g λ u + a 3 g λ u 2, where a 1, a 2, and a 3 are coefficients and 0.1 < g λ u < 1. For APPLE-II in helical mode*: a 1 = 0. 39, a 2 = 0. 42, and a 3 = 0. 001 Sketch of APPLE- II Undulator* Undulator Parameter (K) K = 0. 934 B max T λ u cm Reference: * Conceptual Design Report ST/F-TN-07/12, Fermi@Elettra, 2007. ** P. Elleaume, NIM. A., 455(2000), 503-523. Radiation Wavelength (λ rad ) λ rad = λ u 2γ 2 1 + K 2 rms where γ is Lorentz factor.
SASE FEL: Consideration of undulator parameters 6 Plot of P z (g, λ rad, λ u ) Conditions : λ rad of 20 100 µm P z of 15 22 MeV/c g 10 mm λ u = 40 mm λ rad = 20 µm λ rad = 100 µm λ u = 35 mm λ u = 30 mm Selections : λ u of 40 mm 22 MeV/c for 20 µm 15 MeV/c for 100 µm λ u = 40 mm λ u = 35 mm λ u = 30 mm
I [A] I [A] SASE FEL: Overview of FEL Parameter Space (for λ rad = 100 µm) 7 The calculations have been performed with code FAST (Calculated by M.Yurkov & E. Schneidmiller). Generate SASE FEL radiation wavelength of 100 µm using: Helical undulator with period length of 40 mm Electron beam with 15 MeV/c momentum, 4 nc bunch charge, ~2 mm rms bunch length Saturation power [W] Saturation length [cm] 400 2E+08 400 300 1E+08 200 7E+07 5E+07 200 3E+07 600 500 400 2 4 6 8 10 12 14 16 18 20 n [mm-mrad] 2 4 6 8 10 12 14 16 18 20 n [mm-mrad] Transverse normalized emittance (ε n ) has almost no impact on saturation power. Higher ε n lower saturation length.
SASE FEL: Beam Dynamics Simulations (for λ rad = 100 µm) 8 Simulation Tool: ASTRA code Goals of the beam transport: <P z > ~ 15 MeV/c at the undulator entrance Symmetric transverse beam sizes and emittances at the undulator entrance Laser pulse shape Laser temporal length Rms laser spot size Bunch charge Z start to Z end Gun peak E-field Booster peak E-field Gun phase Booster phase Solenoid fields Input for ASTRA Flattop 20 ps FWHM 1.25 mm 4 nc 0 (cathode) to 22.500 m 60 MV/m 10 MV/m (for <P z > ~ 15 MeV/c) Optimized for: High peak current Low energy spread Evolutions of transverse beam sizes and emittances rms sizes emittances The longitudinal profiles at undulator entrance Slice emittances Long. phase space ~200 A ~6 mm FWHM Current profile Momentum spread
SASE FEL: Radiation Calculations (for λ rad = 100 µm) 9 GENESIS 1.3 code (Version 2) was used for numerical calculations of SASE FEL. Input for GENESIS: Time-dependent mode, space-charge calculation included. Helical undulator with period length of 40 mm SASE FEL, Radiation wavelength of 100 µm (3 THz) Temporal profile of radiation pulse at the saturation ~200 MW Energy in the radiation pulse as a function of Undulator length Spectral profile of radiation pulse at the saturation ~1 mj
SASE FEL: Summary & Outlook 10 Summary The saturation length is ~3 m (75 periods) The radiation has high energy (~1 mj) and long temporal length (~20 ps). Outlook for Simulation Studies Studies for radiation wavelength of 20 µm. Use hybrid undulator instead of APPLE-II (PPM)? Boundary conditions in the GENESIS1.3 code Radiation profiles & transport
Simulations of CTR 11 Parameters of CTR station Beam dynamics simulations Radiation calculations Summary & outlook
CTR: Preliminary Design of CTR station 12 Deflecting Cavity CTR Station APPLEII Undulator Proposal extension for SASE FEL 0 m 4.385 m 16.300 m 22.500 m 15 mm θ max = tan 10 mm 0.25 40 mm Expected acceptance angle: θ max = 6 γ γ = 6 θ max = 6 0.25 = 24 P z 12 15 MeV/c Transm. coef. Vs λ for 0.5 mm thick window* * Casalbuoni et al., TESLA 2006-04
CTR: Beam Dynamics Simulations 13 Simulation Tool: ASTRA code The bunch compressed by velocity bunching in the booster. Minimum <P z > is limited to ~15 MeV/c Laser pulse shape Laser temporal time Rms laser spot size Bunch charge Z start to Z end Gun peak field Booster peak field Input Parameters for ASTRA Gaussian 2.43 ps (FWHM) 1 mm 20 pc to 1 nc 0 (cathode) to 16.30 m 60 MV/m 18 MV/m Gun phase* 0 Evolutions of simulated rms bunch length Rms momentum spread and peak current VS bunch charges at the CTR station 1 nc 500 pc 200 pc 100 pc 20 pc Long. phase spaces at the CTR station (2) (1) (3) (4) (5) (1) 1 nc (2) 500 pc (3) 200 pc (4) 100 pc (5) 20 pc Booster phase* -60 *with respect to maximum momentum gain phase
CTR: Radiation Calculations 14 CTR calculations were performed by using Generalized Ginzburg-Frank Formula [Casalbuoni et al., TESLA 2005-15]. Assume: The radiation screen is a finite circular metallic screen with the radius a. Electron beam with transverse radius of r b impinges normally on the screen. The spectral and spatial radiation energy in the far-field regime for backward CTR are given by d 2 U bunch dωdω = e2 4π 3 ε 0 c β 2 sin 2 θ 1 β 2 cos 2 θ 2 N2 F long ω 2 2c ωr b sin θ J 0 ωr b sin θ c 2cβγ ωr b I 0 ωr b cβγ T γ, ωa, θ 2 Longitudinal Form factor of the e-beam + F long ω = ρ long t e iωt dt T γ, ωa, θ = ωa cβγ J 0 ωa sin θ c K 1 ωa cβγ + ωa sin θ cβ 2 γ 2 sin θ J 1 ωa sin θ c K 0 ωa cβγ
CTR: Radiation Calculations 15 CTR calculations were performed by using Generalized Ginzburg-Frank Formula [Casalbuoni et al., TESLA 2005-15]. Form factors of the compressed bunch at the CTR station Assumptions and input: Perfect conductor and circular screen with radius of 15 mm. Backward radiation, far-field regime calculation E-beam with radius of 0.5 mm is normal incident to the screen. Total radiation energy VS bunch charge 2 µj@1 nc Normalized radiation energy VS frequency (f) and the emission angle (θ) 20 pc 1 nc 4 nj@20 pc
CTR: Summary & Outlook 16 Summary FWHM bunch length reaches only ~0.5 mm (1.6 ps) when compressed by velocity bunching using the booster. The radiation has low energy (nj - µj) and low frequency (0.01-0.5 THz). Outlook Bunch compressor is needed. New bunch compressor? Try to use HEDA2 section Simulations: an oblique screen, Near-field regime Radiation profiles & transport The first CTR experiment is foreseen to take place in 2016.
Summary 17 Preliminary S2E simulations for the SASE FEL and the CTR using the PITZ accelerator were studied. Comparison to the other IR/THz sources (the radiation from the PITZ sources are just estimation) Pulse energy VS FWHM of the generating bunch for the various sources PITZ SASE FEL (10 3 µj) Spectral peak power density VS frequency PITZ SASE FEL PITZ CTR (1 nc) PITZ CTR (1 nc) PITZ CTR (20 pc) PITZ CTR (20 pc) Reference: Anke-Susanne Müller, Rev. Accl. Sci. Tech., 03, 165 (2010)
Issues for Discussion 18 Comments from DESY Beschleuniger Ideenmarkt September 2015 Interesting and remarkable experiments those can be done at PITZ within time frame of 1 year from now. CTR SASE FEL Etc., In this starting step, research activities at PITZ concerning this proposal should be focused on Optimization of e-beam parameters?? quality of generated radiations Radiation based e-bunch diagnostics
Acknowledgement 19 PITZ Team M. Yurkov, Y. Schneidmiller, B. Marchetti C. Thongbai, S. Rimjaem DESY, Hamburg CMU, Thailand Thank you for your attention!
20 BACKUP SLIDES
SASE FEL: APPLE-II undulator 21 APPLE-II Type Undulator* B max T = a 1 exp a 2 g λ u + a 3 g λ u 2, g λ u Polarization a 1 a 2 a 3 Horizontal 1.76-2.77-0.37 Circular 1.54-4.46 0.43 Vertical 2.22-5.19 0.88 Sketch of APPLE- II Undulator *Reference: Conceptual Design Report ST/F-TN- 07/12, Fermi@Elettra, 2007 Example of APPLE-II Parameters gap (magnetic) gap (vacuum) period length undulator length UE40** 6.5 25 mm 5.0 mm 40 mm 4 m **T.Schmidt, Undulators for SwissFEL, FEL2009, Liverpool B max from Various Polarization Mode
SASE FEL: Sensitivities to the electron beam parameters 22 Parameter Fixed Varied Value Initial Iteration α x, α y 0-10 +2 σ x, σ y [mm] 0.5 0.1 +0.1 ε x, ε y [um] 2 1 +1 I peak [A] 160 200-10 P z,rms / P z,avg [%] 0.2 0.1 +0.1 100 µm
SASE FEL using a model beamline* 23 * P.Boonpornprasert et al., MOP055. FEL2013
SASE FEL: Parameter Optimizations 24 Fixed gun phase to -20 The optimized parameters are: Gun phase = -20 Booster phase = -10 Main solenoid current = 356 A rms momentum [kev/c] Peak current [A] Normalized emittance [mm.mrad] 50 195 250 203
CTR: Other approach for RF compression 25