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Advanced Accelerator Concepts Workshop, August 2018

Emittance measurements of laser plasma accelerated electron beams for advanced accelerator applications. S. K. Barber * , J. van Tilborg , C. B. Schroeder, F. Isono , R. Lehe , H.-E Tsai, K. K. Swanson, S. Steinke, K. Nakamura, C. G. R. Geddes, C. Benedetti, E. Esarey , and W.P. Leemans

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Advanced Accelerator Concepts Workshop, August 2018

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  1. Emittance measurements of laser plasma accelerated electron beams for advanced accelerator applications S. K. Barber*, J. van Tilborg, C. B. Schroeder, F. Isono, R. Lehe, H.-E Tsai, K. K. Swanson, S. Steinke, K. Nakamura, C. G. R. Geddes, C. Benedetti, E. Esarey, and W.P. Leemans Lawrence Berkeley National Laboratory, California, USA G. Andonian, N. Majernik, J. B. Rosenzweig Department of Physics, University of California, Los Angeles, USA Advanced Accelerator Concepts Workshop, August 2018

  2. Beam brightness is dependent on LPA injection method • Most advanced accelerator based applications require high brightness electron beams. • Shock induced density down-ramp injection: trapped electrons originate from a more selective area in the background electron’s phase space. • Ionization injection: trapped electrons receive transverse ponderomotive kick and residual transverse momentum in polarization plane.

  3. “Quadrupole-energy scan” technique implemented on our beamline for single shot emittance diagnostic : energy dependent transport elements , : fitting parameters RadiaBeam built PMQ triplet , , R. Weingartneret al. Phys. Rev. ST Accel. Beams 15, 111302 (2012) • Focusing element is permanent magnet quadrupole (PMQ) triplet • Optimized for 57 MeV electrons: produces symmetric focusing in horizontal and vertical planes

  4. Higher order transport terms can influence the emittance measurements • Lattice for experiment was optimized to mitigate second order optics contributions Second order transport element Spectrometer resolution, δ(E) Simulated σy(E) and δ(E) curves for the optimal lattice configuration and with the PMQ triplet shifted downstream by 1 cm (dashed).

  5. Down-ramp injection produces smaller emittance than ionization injection, at significant charge densities • Down Ramp Injection: εn<1 μm at 2 pC/MeV • Ionization Injection: factor ~2 larger S. K. Barber et al. Phys. Rev. Lett. 119, 104801 (2017) K. Swanson et al. Phys. Rev. Accel. Beams 20, 051301 (2017) H. Tsai et al. Phys. of Plasmas 25, 043107 (2018) Both injection schemes are tuned to produce electron beams at ~57 MeV, with comparable spectral charge density (charge/MeV)

  6. Simulations were used to identify signatures of space charge effects • With 10’s of pC in ~micron scale volume and sub 60 MeV energies, need to consider space charge Space charge defocusing term proportional to beam current S. K. Barber et al. Plasma Phys. Control. Fusion 60 054015 (2018)

  7. Beamline is designed to optimize FEL performance and scale e-beam energy Key components of the beamline: First focusing element: active plasma lens (APL) or permanent magnet quadrupole (PMQ) triplet Chicane to stretch e-beam and reduce slice energy spread EM Triplet to deliver matched e-beam at undulator entrance 4m VISA undulator

  8. VISA undulator designed for demonstration of SASE saturation in short distance, perfect for LPA driven FEL VISA segment 1Tremaine, A. et al. 2001. 2Murokh, A. et al. 2003 • Experiments at ATF were among the first to reach FEL saturation in only 4m1,2 • Unique feature: embedded quadrupole focusing (FODO lattice) with 33 T/m gradient • Maximizes beam density over length of the undulator

  9. Details of transport are important to understand performance goals Simulations are performed using a suite of tools: • Elegant for lattice optimization and matching routines • Full particle tracking with collective effects, CSR modeled in elegant, space charge with Astra • Final particle distribution ported to Genesis, 10 time dependent simulations with different shot noise seeds are run Slice emittance growth due to collective effects Peak power vs. distance in VISA undulator Matching to VISA FODO lattice S. Reiche. NIMA, 429, 1999. http://www.desy.de/~mpyflo/ M. Borland LS-287. , 2000.

  10. BELLA Center FEL project: Demonstrate FEL gain at 100 MeV, ramp up to ~300 MeV Radiation spectrum at exit Peak power along undulator LPA source: • 100 MeV • 25 pC • =420 nm Peak power along undulator Radiation spectrum at exit LPA source: • 275 MeV • 25 pC • =55 nm x104 gain x103gain Longitudinal stretching factor

  11. Summary • Direct emittance comparison ionization and down-ramp injected LPA beams • Measurements inform performance studies for FEL line indicating gain is within reach Acknowledgements: This material is based upon work supported by the U.S. Department of Energy, Office of Science, Office of Workforce Development for Teachers and Scientists, Office of Science Graduate Student Research (SCGSR) program. The SCGSR program is administered by the Oak Ridge Institute for Science and Education for the DOE under contract number DE‐SC0014664. This work was also supported by US DOE contracts DE-SC0009914 and DE-AC02-05CH11231, by the National Science Foundation under Grants No. PHY-1632796, and by the Gordon and Betty Moore Foundation under Grant ID GBMF489

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