• V.G. Khachatryan, V. Sahakyan, A. Tarloyan, V.M. Tsakanov
  CANDLE, Yerevan
• T. Garvey, S. Reiche
  PSI, Villigen

The study of radiation saturation length and saturation power sensitivity to beam main parameters (emittance, energy spread and peak current) at the entrance of the undulator section of PSI-XFEL project is presented. The comparative analysis of the SASE FEL performance with external and natural focusing in undulator section is given.

• E. Hemsing, A. Marinelli, P. Musumeci, J.B. Rosenzweig, R. Tikhoplav
  UCLA, Los Angeles, California
• A. Gover
  University of Tel-Aviv, Faculty of Engineering, Tel-Aviv
• S. Reiche
  PSI, Villigen

The resonant harmonic interaction of an electron beam (e-beam) with an EM input field in a helical undulator is explored. The e-beam is coupled to the input radiation field at frequency harmonics through transverse gradients in the EM field, and helical micro-bunching of the e-beam is shown to occur naturally at the higher harmonics with the injection of a simple gaussian laser mode onto a cylindrically symmetric e-beam. This approach is under investigation as a method to generate a strongly pre-bunched e-beam seed for superradiant emission of light that carries orbital angular momentum in a downstream free-electron laser.

• D. Schiller
  UCLA, Los Angeles, California
• S. Reiche
  PSI, Villigen

QUINDI has been developed to address the numerical challenge of calculating the radiation spectra from electron bunches in bending magnet systems. Since the introduction of QUINDI, many improvements and features have been added. QUINDI now supports a 3D model for bending magnets which includes fringing fields. A more modular approach has been achieved which allows better interoperability with other tracking and radiation codes. There have been many updates to the electric field calculation and spectrum processing, as well as to the post-processor, SpecGUI.

• M.P. Dunning, G. Andonian, A.M. Cook, E. Hemsing, A.Y. Murokh, S. Reiche, J.B. Rosenzweig, D. Schiller
  UCLA, Los Angeles, California
• M. Babzien, K. Kusche, V. Yakimenko
  BNL, Upton, Long Island, New York

Coherent radiation emitted by relativistic electron bunches traversing the edge regions of dipole magnets in a chicane bunch compressor was extracted and transported for measurement, using a dedicated terahertz beamline at the Accelerator Test Facility (ATF) at Brookhaven National Laboratory (BNL). Measurements include frequency spectrum and polarization of the radiation. The measurements are compared to predictions from QUINDI, a new simulation code developed at UCLA to model radiation emitted by charged particles in bending systems. Simulations and measurements indicate that because of interference of radiation from the two magnet edges, the edge radiation is suppressed at long wavelengths. In addition to being a source of broadband terahertz radiation, the system is also used as a non-invasive, single-shot, relative bunch length diagnostic to monitor compression in the chicane.

• G. Marcus, G. Andonian, A. Fukasawa, P. Musumeci, S. Reiche, J.B. Rosenzweig
  UCLA, Los Angeles, California
• M. Ferrario, L. Palumbo
  INFN/LNF, Frascati (Roma)
• L. Giannessi
  ENEA C.R. Frascati, Frascati (Roma)

It has been suggested that an ultra-short, very low charge beam be used to drive short wavelength single-spike operation at the SPARC FEL. This paper explores the development and construction of a longitudinal diagnostic capable of completely characterizing the radiation based on the Frequency-Resolved Optical Gating (FROG) technique. In particular, this paper explores a new geometry based on a Transient-Grating (TG) nonlinear interaction and includes studies of start to end simulations for pulses at the SPARC facility using GENESIS and reconstructed using the FROG algorithm. The experimental design, construction and initial testing of the diagnostic are also discussed.

• G. Andonian, M. Ruelas
  RadiaBeam, Marina del Rey
• S. Reiche
  UCLA, Los Angeles, California

The accelerator community has many codes that model beams and emitted radiation. Many of these codes are specialized and often, as in start-to-end simulations, multiple codes are employed in subsequent fashion. One of the most important goals of simulations is to accurately model beam parameters and compare results to those obtained from real laboratory diagnostics. This paper describes the development of a user-friendly code that models the coherent radiation of high brightness beams, with a heavy emphasis on simulation of observables via laboratory diagnostics.