Plasma Accelerator Driven XFELs: Simulations of a PWFA-Based XFEL

1. SLAC, 2015-10-16 FACET-II Workshop: Plasma Accelerator Driven XFELs Start-to-end Simulations of a PWFA Based XFEL Bernhard Hidding et al. (special kudos F. Habib, G. Wittig, A. Knetsch, G. Hurtig et al.) Scottish Centre for the Application of Plasma-Based Accelerators SCAPA, Department of Physics, University of Strathclyde & Department of Experimental Physics, University of Hamburg

2. Underdense photocathode promises high-brightness bunches suitable for FEL

3. Underdense photocathode promises high-brightness bunches suitable for FEL 4.3 GeV, w/ Finndulator: LCLS performance after 20m

4. Underdense photocathode promises high-brightness bunches suitable for FEL

5. General schematic setup e.g. for FACET-II (collinear Trojan Horse)

6. Alternative: use LWFA-produced electron bunches as drivers for PWFA-TH stages

7. General schematic setup e.g. for FACET-II (collinear Trojan Horse) PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc.

8. General schematic setup e.g. for FACET-II (collinear Trojan Horse) PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc. model optically engineered downramp for emittance preservation, include into PIC

9. General schematic setup e.g. for FACET-II (collinear Trojan Horse) handshake between PIC (HDF5) and transport code PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc. model optically engineered downramp for emittance preservation, include into PIC

10. General schematic setup e.g. for FACET-II (collinear Trojan Horse) handshake between PIC (HDF5) and transport code PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc. catch beam from plasma modeled with Elegant model optically engineered downramp for emittance preservation, include into PIC

11. General schematic setup e.g. for FACET-II (collinear Trojan Horse) handshake between PIC (HDF5) and transport code PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc. catch beam from plasma modeled with Elegant model optically engineered downramp for emittance preservation, include into PIC match beam to undulator (Elegant)

12. General schematic setup e.g. for FACET-II (collinear Trojan Horse) handshake between PIC (HDF5) and transport code handshake transport code to FEL tools PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc. catch beam from plasma modeled with Elegant model optically engineered downramp for emittance preservation, include into PIC match beam to undulator (Elegant)

13. General schematic setup e.g. for FACET-II (collinear Trojan Horse) FEL simulations: • desXie • Genesis • Puffin handshake between PIC (HDF5) and transport code handshake transport code to FEL tools PIC simulation using Gaussian drive beam shapes or macroparticle input from full beam optics simulations such as ELEGANT etc. catch beam from plasma modeled with Elegant model optically engineered downramp for emittance preservation, include into PIC match beam to undulator (Elegant)

14. 3D PIC (here with laser envelope approximation, no ion motion) • Use FACET(II) scale drive beam to drive TH stage, aim at rather conservative witness bunch parameters (for TH standards) • To begin with, aim at 4 nm FEL wavelength (water window). desXie => ~1 GeV, ~15 cm acceleration length charge ~10 pC rms bunch length = 0.7 µm max bunch length = 6 µm projected energy spread < 0.0015 rms emittance y,z = 4.3e-08 m rad peak current = 2.1 kA driver witness longitudinal phase space current profile slice energy spread

15. Plasma downramp: the low peak E-fields (<100 GV/m) of PWFA allow for optical shaping of the plasma density profile • Use diffractive optics (e.g. axilens) to produce plasma supporting the PWFA (e.g. hydrogen) • Longitudinal: laser intensity downramp (for TH) and upramp (for staging) translated into plasma profile. • Nice: TH does require only one downramp (no upramp as w/ external injection, no staging as for HEP) longitudinal hydrogen downramp

16. Beam extraction and transport (here: w/o soft downramp) • Shape downramp to preserve beam quality, at the same time optimize Twiss parameters (goal α=0 and max. bunch radius) • Need PM quads due to large bunch divergence transport line transverse phase space at undulator entrance transverse phase space at plasma transport line entrance

17. Undulator: natural focusing not enough, needs external focusing horizontal and vertical beam sizes in undulator:

18. desXie for 4 nm, 𝛽a𝑣𝑒≈1.55 𝑚 FEL  0.0082 au = 1.1985 Lgain = 0.445 m u = 1.53 cm

19. desXie for 4 nm r = 4 nm au = 1.1985 Wbeam 1095 MeV 4 u = 1.53 cm 4

20. Genesis SASE results FWHM~1.66 fs 4 Lsat ~ 10.5 m Psat ~ 0.19 GW FWHM pulse duration ~ 1.66 fs max pulse duration ~ 7.5 fs 4

21. w/ B. McNeil, L. Campbell Puffin (currently 1D, soon 3d): energy spread important L. Campbell et al., Phys. Plasmas 19, 093119 (2012) Triple bunch TH using three plasma photocathode laser pulses (arXiv:1403.1109, 2014) massive dispersion in undulator, phase space rotation, compression and then stretching sets in Puffin great for many things, e.g. for plasma acc. because can deal with large energy spread (broadband emission), short pulses (quickly varying current profile), large dispersion in undulator Development is part of an ongoing project in the UK, in collaboration with Daresbury Lab, Tech-X and the Hartree Centre, which aims to build a s2e suite of accelerator simulation tools from already existing codes (Puffin, ELEGANT, VSim, ASTRA) with common analysis and build tools.

22. w/ B. McNeil, L. Campbell Puffin 1D check (dispersion, radiation) L. Campbell et al., Phys. Plasmas 19, 093119 (2012) • 1D gain as predicted by desXie can be reproduced • Dispersion: bunch compresses only slightly at 1 GeV and the reduced energy spread levels, slice energy spread increases by ~10%, only • Spectrum at saturation broad

23. Summary and Implications • Full start to end simulations of TH-PWFA-FEL are becoming feasible, initial results look very encouraging • Collinear TH important for FACET-II, demonstrate multi-bunch production (multi-color FEL), implement full control over TH laser pulse(s) parameters (wavelength, duration, intensity, shape, polarization, • Emittance and beam quality preservation: Optical shaping of plasma profile may allow for emittance preservation, also for high rep rates  use diffractive optics to shape longitudinal ramps • This is connected to narrow plasma channels bottleneck problem • Use TH beams as acid test for emittance preservation – shape electron beams (chirp, emittance etc.) • Diagnostics: Measure e.g. emittance at 1e-9 mrad levels (maybe ICS can be used to measure in plasma).. • Much room for optimization of FEL (optimize e-bunch: higher energies, better energy spread, better emittance, current, optimize undulators..