Author: Garcia, B.W.
Paper Title Page
Towards the Demonstration of Soft X-Ray Echo-Enabled Harmonic Generation at Fermi  
  • E. Allaria, R. Bracco, D. Castronovo, I. Cudin, M.B. Danailov, G. De Ninno, S. Di Mitri, B. Diviacco, W.M. Fawley, M. Ferianis, L. Giannessi, M. Lonza, G. Penco, P. Rebernik Ribič, E. Roussel, S. Spampinati, C. Spezzani, L. Sturari, M. Svandrlik, M. Veronese, R. Visintini, M. Zaccaria, D. Zangrando
    Elettra-Sincrotrone Trieste S.C.p.A., Basovizza, Italy
  • H.-H. Braun, E. Prat, S. Reiche
    PSI, Villigen PSI, Switzerland
  • G. De Ninno
    University of Nova Gorica, Nova Gorica, Slovenia
  • B.W. Garcia, J.B. Hastings, E. Hemsing, T.O. Raubenheimer, G. Stupakov, J.J. Welch
    SLAC, Menlo Park, California, USA
  • G. Penn
    LBNL, Berkeley, California, USA
  • E. Roussel
    SOLEIL, Gif-sur-Yvette, France
  • A. Zholents
    ANL, Argonne, Illinois, USA
  The echo-enabled harmonic generation seeding scheme is based on an echo mechanism that develops in the electron beam phase-space interacting with two seed lasers before and after a strong dispersive region. It has been proposed for extending the capabilities of externally seeded free electron lasers to reach short wavelengths. After the original proposal, a few experiments have confirmed the capabilities of efficient bunching generation at very high harmonics. However, up to now none of the experiments demonstrated FEL amplification from high harmonic bunching produced at 10 nm wavelengths or shorter. In this work, we report about our plans for performing an EEHG experiment at FERMI. The experiment will be done at the FEL-2 line normally operated in the double stage high-gain harmonic generation configuration in the wavelength range 20-4 nm. After the modification of a few hardware components planned for the first semester of 2018, the FEL-2 layout will be suitable for EEHG at wavelengths down to approximately 6 nm.  
MOP010 Constraints on Pulse Duration Produced by Echo-Enabled Harmonic Generation 1
  • G. Penn
    LBNL, Berkeley, California, USA
  • B.W. Garcia, E. Hemsing, G. Marcus
    SLAC, Menlo Park, California, USA
  Funding: This work was supported by the Director, Office of Science, Office of Basic Energy Sciences, of the U.S. Department of Energy under Contract Nos. DE-AC02-05CH11231 and DE-AC02-76SF00515.
Echo-enabled harmonic generation (EEHG) is well-suited for producing long, coherent pulses at high harmonics of seeding lasers. There have also been schemes proposed to adapt EEHG to output extremely short, sub-fs pulses by beam manipulations or through extremely short seed lasers, but the photon flux is generally lower than that produced by other schemes. For the standard EEHG layout, it is still interesting to consider different parameter regimes and evaluate how short a pulse can be generated. EEHG at high harmonics uses a large dispersive chicane which can change the relative distance of electrons by substantial distances, even longer than a typical FEL coherence length. We evaluate the ability to produce short pulses (in the femtosecond to 10-fs range) using a combination of theory and simulations.
poster icon Poster MOP010 [0.446 MB]  
MOP016 Comparing FEL Codes for Advanced Configurations 1
  • B.W. Garcia, G. Marcus
    SLAC, Menlo Park, California, USA
  • L.T. Campbell
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
  • B.W.J. MᶜNeil
    USTRAT/SUPA, Glasgow, United Kingdom
  • S. Reiche
    PSI, Villigen PSI, Switzerland
  Various FEL codes employ different approximations and strategies to model the FEL radiation generation process. Many codes perform averaging procedures over various length scales in order to simplify the underlying dynamics. As FELs are developed in more advanced configurations beyond simple SASE, the assumptions of some codes may be called into question. We compare the unaveraged code Puffin to averaged FEL codes including a new version of GENESIS in a variety of situations. In particular, we study a harmonic lasing setup, a High-Gain Harmonic Generation (HGHG) configuration modeled after the FERMI setup, and a potential Echo-Enabled Harmonic Generation (EEHG) configuration also at FERMI. We find the codes are in good agreement, although small discrepancies do exist.  
MOP017 Echo-Enabled Harmonic Generation Results with Energy Chirp 1
  • B.W. Garcia, M.P. Dunning, C. Hast, E. Hemsing, T.O. Raubenheimer, G. Stupakov
    SLAC, Menlo Park, California, USA
  • D. Xiang
    Shanghai Jiao Tong University, Shanghai, People's Republic of China
  We report here on several experimental results from the NLCTA at SLAC involving chirped Echo-Enabled Harmonic Generation (EEHG) beams. We directly observe the sensitivity of the different n EEHG modes to a linear beam chirp. This differential sensitivity results in a multi-color EEHG signal which can be fine tuned through the EEHG parameters and beam chirp. We also generate a beam which, due to a timing delay between the two seed lasers, contains both regions of EEHG and High-Gain Harmonic Generation (HGHG) bunching. The two regions are clearly separated on the resulting radiation spectrum due to a linear energy chirp, and one can simultaneously monitor their sensitivities.  
TUB01 Seeding Experiments and Seeding Options for LCLS II 1
  • E. Hemsing, R.N. Coffee, W.M. Fawley, Y. Feng, B.W. Garcia, J.B. Hastings, Z. Huang, G. Marcus, D.F. Ratner, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • G. Penn, R.W. Schoenlein
    LBNL, Berkeley, California, USA
  We discuss the present status of FEL seeding experiments toward the soft x-ray regime and on-going studies on possible seeding options for the high repetition soft x-ray line at LCLS-II. The seeding schemes include self-seeding, cascaded HGHG, and EEHG to reach the 1-2 nm regime with the highest possible brightness and minimal spectral pedestal. We describe relevant figures of merit, performance expectations, and potential issues.  
TUP024 Stochastic Effects from Classical 3D Synchrotron Radiation 1
  • B.W. Garcia, T.O. Raubenheimer
    SLAC, Menlo Park, California, USA
  • R.D. Ryne
    LBNL, Berkeley, California, USA
  In most cases, the one-dimensional coherent synchrotron radiation wakefield gives an excellent approximation to the total coherent effect due to classical synchrotron radiation in bend magnets. However, full particle Liénard-Wiechert simulations have revealed that there is non-numerical, stochastic noise which generates fluctuations about the approximate 1D solution. We present a model for this stochastic term in which this noise is due to long-range interaction with a discrete number of synchrotron radiation cones. The nature of this noise and how it depends on the 3D dimensions of the beam are explored.