1. Free Electron Laser driven by Laser Plasma Acceleration FACET-II Science Opportunities Workshop, October 15 th 2015 Jeroen van Tilborg, Carl Schroeder, and Wim Leemans BELLA Center, LBNL

2. Maturing laser plasma accelerator technology behind push for applications: LPA FEL 2 Last decade: LPAs have matured High peak-current (>kA) Ultra-short (few-fs) Excellent emittance Hyper-spectral synchronization Stability improvements (commercial laser systems, laser shaping, active alignment, injection methods)  Compact LPA-driven Free Electron Laser λ u =1-2 cm E=200-500 MeV  λ photon =7-70 nm

3. Efforts across the globe underway 3 Shanghai (CAS/ Inst. Appl. Phys.) DESY / LAOLA ELI - Beamlines MPQ LUNEX5 (SOLEIL / LOA) Alpha-X: U. Strathclyde INFN: SPARC / FLAME C. B. Schroeder et al., FEL (2006) D. Jaroszynski et al., Phil. Trans. R. Soc. (2006) F. Grüner et al., Appl. Phys. B (2007) Nakajima et al., Nat. Phys (2008) Cuprie et al., J. Phys. B (2014) Nakajima et al., Nat. Phys (2008) IMPACT (Spring8)

4. BELLA Center secured funding from the Moore Foundation to realize compact LPA-FEL 4 Laser ~ 23’ x 32’ LPA + FEL ~ 50’ x 15’ Install new 100TW laser kHz 3mJ front-end, 5 Hz 4J final One laser room  stable Use existing LPA & undulator cave Building 71

5. LPA electron beam subject to stringent requirements 5 Key requirements - Sub-% ΔE/E required for lasing - Decompress electron beam - Charge 2-3 pC/MeV - Beam size: ~10-μm-level over several meters (low emittance & additional transport)

6. Interplay between energy spread, charge/MeV and emittance drives optimum decompression & FEL gain 6 E-beam 5 fs flat-top e-beam 250 MeV 10% (rms) energy spread Example: 2 pC/MeV  125 pC D=x33  I decomp =760 A Undulator: VISA-like undulator parameters (λ u =1.8 cm period, 220 periods, β av ~1 m) Schroeder et al. FEL (2013) 4m saturation: >2 pC/MeV ε N <0.4 mm mrad x 100 saturation E=250 MeV σ E /E=10% (rms) ε N =0.1 mm mrad

7. Two regimes interesting for LPA FEL beamline (stable LPA & high charge density LPA) 7 Jet-based LPA: stable, damage-free Transport, Diagnostics, UV undulator radiation Capillary LPA: high energy, high pC/MeV Soft X-ray FEL

8. Preliminary LPA transport tested (quadrupole implementation, plasma lens) 8 Quadrupole doublet Asymmetric focusing Future: triplet (sym. focusing) Active Plasma Lens Introduced 1950s (ion beams) Symmetric focusing Tunable Gradients >3000 T/m Rely on negligible wakefields Panofski et al. RSI 1950 van Tilborg et al. PRL (in press)

9. Plasma lens offers strong advantages for compact focusing geometries 9 van Tilborg et al. PRL (in press) Applications Rapid e-beam capture (cm) Compact staged acceleration

10. Successful demonstration of staged acceleration. Two independent LPAs coupled with plasma lens & tape 10 Steinke et al. (submitted)

11. LPA emittance measurements confirm sub-micron source size 11 Emittance = Size x Divergence (sub-μm x few mrad) Betatron X-ray spectrum ~ size Source size ~ 0.1 - 0.5 micron Electron beam Weingartner et al. PRSTAB (2012) Measure e-beam size at image plane Source size ~ 0.5 – 1 micron Plateau et al. PRL (2012) Photon beam

12. LPA-driven undulator radiation observed 12 MCP image Shaw et al. AAC Proceedings 2012 Incoherent X-rays (no designed e-beam transport) from ~400 MeV e-beams van Tilborg et al. Opt. Lett. 2013 Laser harmonics (<20 th ) from VHS tape Seeding  CWE harmonics  Gas-based

13. Simulations support LPA transport 13 Two triplets deliver ΔE=1 MeV through undulator Simulations by Center for Beam Physics Quadrupoles Plasma lens

14. GENESIS simulations predict strong gain for LPA beams 14 GENESIS predicts strong gain, to 100 MW (>10 11 ϕ /pulse/slice) E-beam: ε=0.1 μm, σ=10 μm, 3.4 pC/MeV, 250 MeV (σ E =10%), D=x64, I peak =400 A VISA Undulator: λ u =1.8 cm, K=1.26  λ r =67.45 nm

15. What are the upcoming challenges? 15 Have an LPA that meets all standards (>300 MeV, low emittance, stability & high charge/MeV) Tunable transport (dipole edge- focusing, undulator focusing, multiple lenses, CSR mitigation) Develop new diagnostics [duration e-beam after chicane (CTR), duration X-rays (THz streaking)]