SLAC, Menlo Park, California
UNM, Albuquerque, New Mexico
The goal is to construct a symplectic evolution map for a large section of an accelerator, say a full turn of a large ring or a long wiggler. We start with an accurate tracking algorithm for single particles, which is allowed to be slightly non-symplectic. By tracking many particles for a distance S one acquires sufficient data to construct the mixed-variable generator of a symplectic map for evolution over S. Two ways to find the generator are considered: (i) Find its gradient from tracking data, then the generator itself as a line integral *. (ii) Compute Hamilton's principal function on many orbits. The generator is given finally as an interpolatory C2 function, say through B-splines or Shepard's meshless interpolation. A test of method (i) is given in a hard example: a full turn map for an electron ring with strong sextupoles. The method succeeds where Taylor maps fail, but there are technical difficulties near the dynamic aperture due to oddly shaped interpolation domains. Method (ii) looks more promising in strongly nonlinear cases. We also explore explicit maps from direct fits of tracking data, with symplecticity imposed on local interpolating functions.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
Precise and fast 3D space-charge calculations for bunches of charged particles are still of growing importance in recent accelerator designs. A widespread approach is the particle-mesh method computing the potential of a bunch in the rest frame by means of Poisson's equation. Whereas an adaptive discretization of a bunch is often required for efficient space charge calculations in practice, such a technique is not implemented in many computer codes. For instance, the FFT Poisson solver that is often applied allows only an equidistant mesh. An adaptive discretization following the particle density is implemented in the GPT tracking code (General Particle Tracer, Pulsar Physics). The disadvantage of this approach is that jumps in the distribution of particles are not taken into account. In this paper we present a new approach to an adaptive discretization which is based on the multigrid technique. The goal is that the error estimator needed for the adaptive distribution of mesh lines can be calculated directly from the multigrid procedure. The algorithm will be investigated for several particle distributions and compared to that adaptive discretization method implemented in GPT.
TU Darmstadt, Darmstadt
TEMF, TU Darmstadt, Darmstadt
The problem of self-consistent simulations of short relativistic particle bunches in long accelerator structures exhibits a pronounced multi-scale character. The adequate resolution of the THz space charge fields excited by short ultra-relativistic bunches requires mesh spacings in the micrometer range. On the other hand, the discretization of complete accelerator sections using such fine meshes results in a vast number of degrees of freedom. Due to the spatial concentration of the particles and the excited space charge fields, the application of time-adaptive mesh refinement is an emerging idea. We reported on the implementation of time-adaptive mesh refinement for the Finite Integration Technique (FIT)*. Based on this work, we implemented an hp-adaptive discontinuous Galerkin (DG) code. The twofold refinement mechanisms of the hp-adaptive DG method offer maximum modeling freedom. We present details of the h- and p-adaptations for the DG method on Cartesian grids. Special emphasis is put on the stability and efficiency of the adaptation techniques.
Muroran Institute of Technology, Department of Electrical and Electronic Engineering, Muroran
In addition to standard high performance computing technologies such as supercomputers and grid computers, a method of dedicated computers have been attempted to construct portable high performance computing environments in the vicinity of office PC. The method of dedicated computers have also been adopted into electromagnetic field simulations, which are mainly in a linear algebra equation solver for general electromagnetic field analysis and the FDTD solver for microwave simulations. In this paper, attempts of FDTD/FIT dedicated computer (FDTD/FIT machine) are introduced*. The basic scheme of the FDTD/FIT method itself is very simple and suitable for implementation as hardware circuits. In addition, it is also essential to realize many other functions such as imposing of boundary conditions, treatment of non-uniform materials, power input, etc. Moreover, to fully bring out the advantage of the method of dedicated computer, the computer architecture should be designed to achieve efficient computing of all of FDTD/FIT scheme including the boundary condition setting, etc. Especially various efforts of minimization of memory access overhead are discussed in this paper.
LBNL, Berkeley, California
LLNL, Livermore, California
It was shown recently that it may be computationally advantageous to perform computer simulations in a Lorentz boosted frame for a certain class of particle acceleration devices or problems such as: free electron laser, laser-plasma accelerator, and particle beams interacting with electron clouds*. However, even if the computer model relies on a covariant set of equations, it was pointed out that algorithmic difficulties related to discretization errors may have to be overcome in order to take full advantage of the potential speedup**. Further complications arise from the need to transform input and output data between the laboratory frame and the frame of calculation, but can be overcome at low additional computational cost***. We will present the theory behind the speed-up of numerical simulation in a boosted frame, our latest developments of numerical methods, and examples of application to the modeling of the above-cited problems and others if applicable.
SLAC, Menlo Park, California
SLAC's Advanced Computations Department (ACD) has developed the parallel Finite Element 3D electromagnetic code suite ACE3P for modeling of complex accelerator structures. The Particle-In-Cell module Pic3P was designed for simulations of beam-cavity interactions dominated by space charge effects. Pic3P solves the complete set of Maxwell-Lorentz equations self-consistently and includes space-charge, retardation and boundary effects from first principles. In addition to using conformal, unstructured meshes in combination with higher-order Finite Element methods, Pic3P also uses causal moving window techniques and dynamic load balancing for highly efficient use of computational resources. Operating on workstations and on leadership-class supercomputing facilities, Pic3P allows large-scale modeling of photoinjectors with unprecedented accuracy, aiding the design and operation of next-generation accelerator facilities. Applications include the LCLS RF gun and the BNL polarized SRF gun.
The University of Liverpool, Liverpool
UNM, Albuquerque, New Mexico
We consider a 2D bunch represented by \mathcal N simulation particles moving on arbitrary planar orbits. The mean field of the bunch is computed from Maxwell's equations in the lab frame with a smoothed charge/current density, using retarded potentials. The particles are tracked in beam frame, thus requiring a transformation of densities from lab to beam frame. We seek improvements in speed and practicality in two directions: (a) choice of integration variables and quadrature rules for the field calculation; and (b) finding smooth densities from scattered data. For item (a) we compare a singularity-free formula with the retarded time as integration variable, which we used previously, with a formula based on Frenet-Serret coordinates. The latter suggests good approximations in different regions of the retardation distance, for instance a multipole expansion which could save both time and storage. For item (b) we compare various ideas from mathematical statistics and numerical analysis, e.g., quasi-random vs. pseudo-random sampling, Fourier vs. kernel smoothing, etc. Implementations in a parallel code with \mathcal N up to a billion will be given, for a chicane bunch compressor.
ANL, Argonne
Beam scattering effects, including intra-beam scattering (IBS) and Touschek scattering, may become an issue for linac-based 4th-generation light sources, such as X-ray free-electron lasers (FELs) and energy recovery linacs (ERLs), as the electron density inside the bunch is very high. In this paper, we describe simulation tools for modeling beam-scattering effects that were recently developed at the Advanced Photon Source (APS). We also demonstrate their application to a possible ERL-based APS upgrade. The beam loss issue due to the Touschek scattering effect is addressed through momentum aperture optimization. The consequences of IBS for brightness, FEL gain, and other figures of merit are also discussed. Calculations are performed using a particle distribution generated by an optimized high-brightness injector simulation.
IHEP Beijing, Beijing
Electron Cloud Instability (ECI) may take place in any positively charged particle circular accelerator especially in positron and proton storage ring. This instability has been confirmed to be a serious restriction to the beam stabilities. The physical model on the formation of electron cloud in various kinds of magnetic fields was introduced in the first section of the paper. The transverse and longitudinal wake field model to present the interaction between electron cloud and beam were introduced in another section of the paper. As an example, in positron storage of BEPCII and RCS of CSNS, the densities of electron cloud and beam instabilities caused by the accumulated electrons were simulated.
ORNL, Oak Ridge, Tennessee
The laser assisted hydrogen stripping becomes a widely discussed alternative for the existing stripping foil approach. The simulation tool for this new approach is presented. The created application is implemented in form of extension module to Python ORBIT parallel code that is under development at the SNS. The physical model of the application deals with quantum theory and allows calculating evolution and ionization of hydrogen atoms and ions affected by superposition of electromagnetic and laser fields. The algorithm, structure, benchmark cases, and results of simulations for several future and existing accelerators are discussed.
LLNL, Livermore, California
The Finite Difference Time Domain (FDTD) method and the related Time Domain Finite Element Method (TDFEM) are routinely used for simulation of RF and microwave structures. In traditional FDTD and TDFEM algorithms the electric field E is associated with the mesh edges, and the magnetic flux density B is associated with mesh faces. It can be shown that when using this traditional discretization , projection of an arbitrary current density J(x,t) onto the computational mesh can be problematic. We developed and tested a new discretization that uses electric flux density D and magnetic field H as the fundamental quantities, with the D-field on mesh faces and the H-field on mesh edges. The electric current density J is associated with mesh faces, and charge is associated with mesh elements. When combined with the Particle In Cell (PIC) approach of representing J(x,t) by discrete macroparticles that transport through the mesh, the resulting algorithm conserves charge in the discrete sense, exactly, independent of the mesh resolution h. This new algorithm has been applied to unstructured mesh simulations of charged particle transport in laser target chambers with great success.
DESY Zeuthen, Zeuthen
INRNE, Sofia
The production of electron beams suitable for the successful operation of the European XFEL is studied at the Photo-Injector Test Facility at DESY, Zeuthen site (PITZ). The PITZ beamline is equipped with three dedicated stations for transverse emittance measurements and in the forthcoming shutdown period a section for transverse phase-space tomography diagnostics will be installed. The module contains four observation screens and therefore only four projections can be used in order to reconstruct an underlying phase-space density distribution. This work presents the performance of a number of reconstruction algorithms on limited projection sets using numerical data applied to the PITZ operating conditions. Different concepts for comparison between an original phantom and the reconstructed distribution are presented.
NSCL, East Lansing, Michigan
The cyclotron gas stopper is a newly proposed device to stop energetic ions in a high pressure helium gas and to transport them in a singly charged state with a gas jet to a vacuum region. Ions are injected into the region with vertical magnetic field, where they first meet a degrader and then move in helium gas. Due to multiple scattering, radioactive ions lose their energy, and the process is accompanied by ionization of helium. Externally applied voltage remove electrons and single-charged helium ions from the box. Under a certain incoming particle rate, the amount of ionized charge becomes large and cannot be removed completely. As a result, a neutralized plasma is accumulated in the center of the box and new incoming particles cannot be ejected from the field-shielded area. The present study focuses on a detailed understanding of space charge effects in the central ion extraction region. Particle-in-cell simulations of electron-helium plasma are based on self-consistent particle tracking in a field obtained from solution of Poisson’s equation for particle interacting via Coulomb forces. The paper analyzes the process and estimates the maximum possible incoming particle rate.
TRIUMF, Vancouver
DAE/VECC, Calcutta
SFU, Burnaby, BC
The TRIUMF-VECC Electron Linac is a device for gamma-ray induced fission of actinide targets, with applications in nuclear physics and material science. A phased construction and commissioning scheme will eventually lead to a 50 MeV, 10 mA CW linac based on superconducting RF technology. Using this linac to deliver high intensity electron beams for applications such as an energy-recovered light source is a possibility integrated in the design study. The multitude of design and tuning parameters, diverse objectives and constraints require a comprehensive and efficient optimization scheme. For this purpose we adopted the genetic optimization program developed at Cornell University* as a prototype. Feature extensions were developed to accommodate specifics of the Electron Linac design, provide framework for more generic and integrated design process, and perform robustness/acceptance analyses. In this report we will discuss the method and its application to the design optimization of the Electron Linac. [1]. I. Bazarov and C. Sinclair, PRST-AB 8, 034202 (2005), and references therein.
LBNL, Berkeley, California
Tech-X, Boulder, Colorado
Laser plasma generated wakefields sustain accelerating gradient a thousand times higher than conventional accelerators, allowing acceleration of electron beams to high energy over short distances. Recently, experiments have demonstrated the production of high quality electron bunches at 1GeV within only a few centimeters. We present simulations, with the VORPAL framework, of the next generation of experiments, likely to use externally injected beams and accelerate them in a meter long 10 GeV laser plasma accelerator stage, which will operate in the quasi-linear regime where the acceleration of electrons and positrons is nearly symmetric. We will show that by using scaling of the physical parameters it is possible to perform fully consistent particle-in-cell simulations at a reasonable cost. These simulations are used to design efficient stages. In particular, we will show that we can use higher order laser modes to tailor the focusing forces, which play an important role in determining the beam quality. This makes it possible to increase the matched electron beam radius and hence the total charge in the bunch while preserving the low bunch emittance required for applications.
Muons, Inc, Batavia
Many measurements in particle and accelerator physics are limited by the time resolution. This includes particle identification via time-of-flight in major experiments like CDF at Fermilab, Atlas and CMS at the LHC. Large-scale systems could be significantly improved by large-area photo-detectors. The invention of a new method of making MCPs that promises to yield better resolution and be considerably less expensive than current techniques. Two different models for MCP simulations are suggested. Semi-analytical approach is a powerful tool for the design of static image amplifiers. Monte Carlo simulations can be successfully used for large area photo detectors with micron and Pico-second resolution range. Both approaches were implemented in the codes MCPS and MCS. The results of computer modeling are presented. References. 1. V.Ivanov, Z.Insepov, Pico-Second Workshop VII, The Development of Large-Area Pico-second Photo-Devices, Feb. 26-28, 2009; ANL. 2. V.Ivanov. The Code “Micro Channel Plate Simulator”, User’s Guide, Muons, Inc., 2009
Fermilab, Batavia
The beam-beam simulation code (BBSIMC) is a incoherent multiparticle tracking code for modeling the nonlinear effects arising from beam-beam interactions and the compensation of them using an electromagnetic lens. It implements short range transverse and longitudinal wakefield, dipole noise to mimic emittance growth from gas scattering, beam transfer function, and wire compensation models. In this paper, we report on recent improvements of the BBSIMC including a beam-beam compensation model using a low energy electron beam and an interpolation scheme of beam-beam forces. Some applications are presented for the Relativistic Heavy Ion Collider (RHIC) electron lens.
SLAC, Menlo Park, California
An x-ray Free-Electron Laser (FEL) calls for a high brightness electron beam. Generically, such a beam needs to be accelerated to high energy on the GeV level and compressed down to tens of microns, if not a few microns. The very bright electron beam required for the FEL has to be stable and the high quality of the electron beam has to be preserved during the acceleration and bunch compression. With a newly developed model independent global optimizer [*], here we report study for the control and error diagnostics of such a generic machine: magnetic elements, and RF cavities, and the electron beam parameters: the peak current, centroid energy, and trajectory. Collective effects, such as coherent synchrotron radiation, space charge, and various wakefields are incorporated in a parametric approach. Applicability and verification are detailed for the LINAC Coherent Light Source, an x-ray FEL project being commissioned at SLAC.
Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
A single bunch instability caused by an electron cloud has been studied using analytical and semi-analytical methods with the wake field. The wake field in these cases was computed in the classical sense as excited electromagnetic field that transversally distorts those parts of the bunch trailing certain transversal offset in the leading part of the same bunch. The transversal wake force in this case is only depending on the longitudinal distance between the leading part of the bunch producing the wake force and the trailing parts of the bunch feeling the wake force. However during the passage of the bunch through the electron cloud the density of the electron cloud near the beam axis changes rapidly which does not allow the single variable approximation for the wake field. In this paper pursuing the idea of K. Ohmi we compute numerically the wake forces as two variable function of the position of the leading part of the bunch and the position of the bunch parts trailing the leading offset in the bunch.
Northern Illinois University, DeKalb, Illinois
This research involves the development of a model of the small circumference (11.5 m) accelerator in which the earth’s field has a strong effect, and in which image charge forces are also included. The code used for this simulation was COSY Infinity 9.0 which uses differential algebras to determine high order map elements, as well as quantities such as chromaticity. COSY also uses Normal Form algorithms to determine the betatron tune and any amplitude dependent tune shifts which may result. The power of COSY is that it can derive the required quantities directly form the map without costly integration and tracking. Thus determining the map for both the default elements of the ring, plus the effects of image charge forces, and the earth’s magnetic field is both non-trivial, and important. This research uses the Baker Campbell Hausdorf method to determine the map of the ring with the external fields included. Furthermore COSY has the ability to directly implement misalignments within the beamline itself allowing for a study of their effects on beam dynamics. The presentation will include both coding development and applications to the University of Maryland Electron Ring.