B-1 Light Sources and FELs
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SAPAG03 Mode-Analysis Methods for the Study of Collective Instabilities in Electron-Storage Rings 30
  • M. Venturini
    LBNL, Berkeley, California, USA
  We report on recent progress on the application of mode analysis to the study of collective instabilities in electron storage rings including Higher Harmonic RF Cavities (HHCs). The focus is on transverse instabilities in the presence of a dominant resistive-wall impedance, a problem of particular relevance to the new generation of diffraction-limited light sources. The secular equation for the system eigenvalues is solved after applying a regularizing transformation, a key step to obtaining numerically accurate solutions. We provide a demonstration that for vanishing chromaticity and in the absence of radiation damping the beam motion is always unstable. This is in contrast to the more conventional Transverse-Mode-Coupling Instability (TMCI) without HHCs, which is known to exhibit a well defined instability threshold.  
slides icon Slides SAPAG03 [2.261 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-SAPAG03  
About • paper received ※ 18 October 2018       paper accepted ※ 24 October 2018       issue date ※ 26 January 2019  
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Machine Learning for X-Ray Free-Electron Lasers  
  • D.F. Ratner
    SLAC, Menlo Park, California, USA
  X-ray Free Electron Lasers (XFELs) are among the most complex accelerator projects in the world today. With large parameter spaces, sensitive dependence on beam quality, huge data rates, and challenging machine protection, there are expanding opportunities to apply machine learning (ML) to XFEL operation. In this talk I will summarize some promising ML methods for XFELs, and highlight recent examples of successful applications.  
slides icon Slides SUPAG08 [2.695 MB]  
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Quantum Statistical Properties of Free Electron Laser With a Planar Wiggler and Ion-Channel Guiding  
  • M. Alimohamadi
    Farhangian University, Tehran, Iran
  Funding: [4] A. Bambini and A. Renieri. Lett. Nuovo Cimento 21, 399 (1978). [5] F. Ciocci, G. Dattoli, A. Renieri and A. Torre, Physics Reports, 141(1), 1-50(1986).
An analysis of the free-electron lasers (FELs) with a planar wiggler and in the presence of ion-channel guiding, has been carried out using a Hamiltonian quantum field theory. The quantum Hamiltonian of single a particle has been derived in the Bambini-Renieri (BR) frame [1-5]. The equations are valid in a reference frame, moving with a relativistic velocity with respect to the laboratory frame, chosen in such a way that the carrier frequency of the pulse equals the pseudoradiation (wiggler) field frequency. In this reference frame, the equations assume a simple non-relativistic form. Time-dependent wave function and three constants of motion are obtained. The Wei-Norman [2] Lie algebraic approach has been employed to solve exactly the spherical Raman-Nath equation (SRNE) [3-5]. A quantum approach has been used to get photon gain, photon statistics and squeezing properties of a FEL. The quantum statistical properties have also been studied numerically.
[1]H. Mehdian, M. Alimohamadi, etal, J.Plasma. Phys. 78 (5), 537-544(2012). [2] J. Wei, E. Norman, J. Math. Phys. A 4,575 (1963).[3] M. Alimohamadi, et al, J. Fus. Energy 31 (5), 463-466(2012).
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TUPAF16 Analysis of the Beam Loss Mechanism During the Energy Ramp-Up at the SAGA-LS 227
  • Y. Iwasaki
    SAGA, Tosu, Japan
  The accelerator of the SAGA Light Source consists of 255 MeV injector linac and 1.4 GeV storage ring. The accumulated electron beam current of the storage ring is about 300 mA. The energy of the electrons are raised up to 1.4 GeV in 4 minutes in the storage ring. At the moment of the beam acceleration (the beam energy is lower than 300 MeV), the electron beam is lost like the step function. The lost beam current is normally about 5 mA to 30 mA. The beam loss at the energy ramp-up is not observed, when the beam current is lower than 200 mA. To understand the beam loss mechanism, which depend on the beam current, we developed high-speed logging system of 100 kHz for monitoring the beam current and the magnets power supplies using National Instruments PXI. We investigated the relationship between the beam loss and the betatron tune shifts. The tune shifts during the beam acceleration were analyzed from the measured data of the output current of the magnets power supplies by using beam tracking code of TRACY2. By adopting the new high-speed logging system, the time structure of the beam loss process was clearly observed. We will present the high-speed logging system developed for monitoring the beam current and the power supplies at this meeting. The results of the investigation to find the relationship of the beam loss and the tune shifts will be also shown.  
slides icon Slides TUPAF16 [1.286 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF16  
About • paper received ※ 19 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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TUPAF22 FEL Simulation Using the Lie Method 240
  • K. Hwang, J. Qiang
    LBNL, Berkeley, California, USA
  Funding: U.S. Department of Energy under Contract No. DE-AC02-05CH11231
Advances in numerical methods for free-electron-laser~(FEL) simulation under wiggler period averaging~(WPA) are presented. First, WPA is generalized using perturbation Lie map method. The conventional WPA is identified as the leading order contribution. Next, a widely used shot-noise modeling method is improved along with a particle migration scheme across the numerical mesh. The artificial shot noise arising from particle migration is suppressed. The improved model also allows using arbitrary mesh size, slippage resolution, and integration step size. These advances will improve modeling of longitudinal beam profile evolution for fast FEL simulation.
slides icon Slides TUPAF22 [2.245 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAF22  
About • paper received ※ 17 October 2018       paper accepted ※ 28 January 2019       issue date ※ 26 January 2019  
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Numerical Simulations for Generating Fully Coherent Soft X-Ray Free Electron Lasers With Ultra-Short Wavelength  
  • K.S. Zhou
    SINAP, Shanghai, People’s Republic of China
  Funding: Shanghai Institute of Applied Physics, Chinese Academy of Sciences
For the fully coherent, ultra-short and high power soft x-rays are becoming key instruments in different research fields, such as biology, chemistry or physics. However it’s not easy to generate this kind of advantaged light source by conventional lasers, especially for the soft x-rays with ultra-short wavelength. The external seeded free electron laser (FEL) is considered as one feasible method. Here, we give an example to generate fully coherent soft x-rays with the wavelength 1nm by the two-stage cascaded FELs. The EEHG scheme is used in the first-stage while the HGHG scheme is used in the second-stage.
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TUPAG17 Beamline Map Computation for Paraxial Optics 297
  • B. Nash, J.P. Edelen, N.B. Goldring, S.D. Webb
    RadiaSoft LLC, Boulder, Colorado, USA
  Funding: Department of Energy office of Basic energy sciences, DE-SC0018571
Modeling of radiation transport is an important topic tightly coupled to many charged particle dynamics simulations for synchrotron light sources and FEL facilities. The radiation is determined by the electron beam and magnetic field source, and then passes through beamlines with focusing elements, apertures and monochromators, in which one may typically apply the paraxial approximation of small angular deviations from the optical axis. The radiation is then used in a wide range of spectroscopic experiments, or else may be recirculated back to the electron beam source, in the case of an FEL oscillator. The Wigner function representation of electromagnetic wavefronts has been described in the literature and allows a phase space description of the radiation, similar to that used in charged particle dynamics. It can encompass both fully and partially coherent cases, as well as polarization. Here, we describe the calculation of a beamline map that can be applied to the radiation Wigner function, reducing the computation time. We discuss the use of ray tracing and wave optics codes for the map computation and benchmarking. We construct a four crystal 1:1 imaging beamline that could be used for recirculation in an XFEL oscillator, and benchmark the map based results with SRW wavefront simulations.
slides icon Slides TUPAG17 [2.289 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG17  
About • paper received ※ 19 October 2018       paper accepted ※ 18 December 2018       issue date ※ 26 January 2019  
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Bragg Diffraction Modeling Between X-Ray Free-Electron Laser and Crystals  
  • H.X. Deng, N. S. Huang, K. Li
    SINAP, Shanghai, People’s Republic of China
  In pursuit of fully coherent X-ray free-electron laser (FEL), high reflective Bragg crystals have being and will be used as high selective spectral filter in the hard X-ray self-seeding FELs and X-ray FEL oscillators (XFELO), respectively. However, currently in the self-seeding FEL and XFELO simulations, the three-dimensional effect of Bragg diffraction is not fully considered. In this paper, we derive comprehensive solution for the response function of crystal in Bragg diffraction. And a three-dimensional X-ray crystal Bragg diffraction code named BRIGHT is introduced, which could collaborate closely with other FEL related code, e.g., GENESIS and OPC. The performance and feasibility are evaluated by two numerical examples, i.e., self-seeding experiment for LCLS and XFELO options for Shanghai high repetition rate XFEL and extreme light facility (SHINE). The results indicate BRIGHT provides a new and useful tool for three-dimensional FEL simulation.  
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TUPAG21 Novel, Fast, Open-Source Code for Synchrotron Radiation Computation on Arbitrary 3D Geometries 309
  • D.A. Hidas
    BNL, Upton, Long Island, New York, USA
  Open Source Code for Advanced Radiation Simulation (OSCARS) is an open-source project (https://oscars.bnl.gov) developed at Brookhaven National Laboratory for the computation of synchrotron radiation from arbitrary charged particle beams in arbitrary and time-dependent mag- netic and electric fields on arbitrary geometries in 3D. Computational speed is significantly increased with the use of built-in multi-GPU and multi-threaded techniques which are suitable for both small scale and large scale computing infrastructures. OSCARS is capable of computing spectra, flux, and power densities on simple surfaces as well as on objects imported from common CAD software. It is additionally applicable in the regime of high-field acceleration. The methodology behind OSCARS cal- culations will be discussed along with practical examples and applications to modern accelerators and light sources.  
slides icon Slides TUPAG21 [1.712 MB]  
DOI • reference for this paper ※ https://doi.org/10.18429/JACoW-ICAP2018-TUPAG21  
About • paper received ※ 20 October 2018       paper accepted ※ 18 December 2018       issue date ※ 26 January 2019  
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