Beam Dynamics and EM Fields
Dynamics 05: Code Development and Simulation Techniques
Paper Title Page
MOOCS2 Numerical Verification of the Power Transfer and Wakefield Coupling in the CLIC Two-beam Accelerator 51
 
  • A.E. Candel, K. Ko, Z. Li, C.-K. Ng, V. Rawat, G.L. Schussman
    SLAC, Menlo Park, California, USA
  • A. Grudiev, I. Syratchev, W. Wuensch
    CERN, Geneva, Switzerland
 
  The Compact Linear Collider (CLIC) provides a path to a multi-TeV accelerator to explore the energy frontier of High Energy Physics. Its two-beam accelerator concept envisions large complex 3D structures, which must be modeled to high accuracy so that simulation results can be directly used to prepare CAD drawings for machining. The required simulations include not only the fundamental mode properties of the accelerating structures but also the Power Extraction and Transfer Structure (PETS), as well as the coupling between the two systems. Time-domain simulations will be performed to understand pulse formation, wakefield damping, fundamental power transfer and wakefield coupling in these structures. Applying SLAC's parallel finite element code suite, these large-scale problems will be solved on some of the largest supercomputers available. The results will help to identify potential issues and provide new insights on the design, leading to further improvements on the novel two-beam accelerator scheme.  
slides icon Slides MOOCS2 [286.042 MB]  
 
MOODS5 3D Electromagnetic Design and Beam Dynamics Simulations of a Radio-Frequency Quadrupole 97
 
  • B. Mustapha, A. Kolomiets, P.N. Ostroumov
    ANL, Argonne, USA
 
  Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.
During the design of the 60.635 MHz RFQ for the ATLAS efficiency and intensity upgrade*, we have established a new full 3D approach for the electromagnetic and beam dynamics simulations of a RFQ. A Detailed full 3D model (four meter long) including vane modulation was built and simulated using CST Microwave Studio, which is made possible by the ever advancing computing capabilities. The approach was validated using experimental measurements on a prototype 57.5 MHz RFQ**. The effects of the radial matchers, vane modulation and tuners on the resonant frequency and field flatness have been carefully studied. The full 3D field distribution was used for beam dynamics simulations using both CST Particle Studio and the beam dynamics code TRACK***. In the final design we have used trapezoidal modulation instead of the standard sinusoidal in the accelerating section of the RFQ to achieve more energy gain for the same length, following the leading work of the Protvino group****. In our case, the output energy increased from 260 keV/u to 295 keV/u with minimal change in the beam dynamics.
* P.N. Ostroumov et al, Proceedings of LINAC-2010
** P.N. Ostroumov et al, Proceedings of LINAC-2006
*** TRACK @ http://www.phy.anl.gov/atlas/TRACK
**** O.K. Belyaev et al, Proceedings of LINAC-2000
 
slides icon Slides MOODS5 [2.531 MB]  
 
TUOCN1 Accurate Computation of Transfer Maps for Realistic Beamline Elements from Surface Data 742
 
  • C.E. Mitchell
    NRL, Washington, DC, USA
  • A. Dragt
    UMD, College Park, Maryland, USA
 
  The behavior of orbits in charged-particle beam transport systems, including both linear and circular accelerators as well as final focus sections and spectrometers, can depend sensitively on nonlinear fringe-field and high-order-multipole effects in the various beam-line elements. The inclusion of these effects requires a detailed and realistic model of the interior and fringe fields, including their high spatial derivatives. A collection of surface fitting methods has been developed for extracting this information accurately from 3-dimensional field data on a grid, as provided by various 3-dimensional finite-element field codes. Based on these realistic field models, Lie or other methods may be used to compute accurate design orbits and accurate transfer maps about these orbits. This talk will provide a description of the methods along with example applications. An exactly-soluble but numerically challenging model field is used to provide a rigorous collection of performance benchmarks.  
slides icon Slides TUOCN1 [1.630 MB]  
 
TUODN2 Exploration of Parallel Optimization Techniques for Accelerator Design 787
 
  • Y. Wang, M. Borland, V. Sajaev
    ANL, Argonne, USA
 
  Funding: Work supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
Optimization through simulation is a time-consuming task in accelerator design, especially for high dimensional problems. We explored several parallel optimization techniques, including Parallel Genetic Algorithm (PGA), Hybrid Parallel Simplex (HPS), and Parallel Particle Swarm Optimization (PPSO), to solve some real world problems. The serial simplex method in elegant was used as a benchmark for newly-developed parallel optimization algorithms in Pelegant. PGA and HPS are not faster than the serial simplex method, but they more reliably find the global optimum. PPSO is well suited for parallel computing, allowing significantly faster turn-around given sufficient computing resources. Parallel optimization implementations in Pelegant thus promise to not only make optimization results more reliable, but also open the possibility of fast, "real time" optimization of complex problems for accelerator operation.
 
slides icon Slides TUODN2 [0.218 MB]  
 
WEP063 Tracking Particles Through A General Magnetic Field 1591
 
  • A. Xiao, M. Borland, L. Emery, Y. Wang
    ANL, Argonne, USA
 
  Funding: Work supported by the U. S. Department of Energy, Office of Science, Office of Basic Energy Sciences, under Contract No. DE-AC02-06CH11357.
A method that tracks particles directly through a general magnetic field described in a 3D field table was added to the code elegant recently. It was realized by converting an arbitrary particle's motion to a combination of free-drift motion and centripetal motion through the coordinate system rotation and using a general linear interpolation tool developed at the Advanced Photon Source (APS). This method has been tested by tracking particles through conventional magnetic elements (dipole, sextupole, etc.) to verify reference coordinate system conversions, tracking accuracy, and long-term tracking stability. Results show a very good agreement between this new method and the traditional method. This method is not designed to replace mature traditional methods that have been used in most tracking codes. Rather, it is useful for magnets with complicated field profiles or for studying edge effects.
 
 
WEP066 Tracking Code Developement for Beam Dynamics Optimization 1600
 
  • L. Yang
    BNL, Upton, Long Island, New York, USA
 
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
Dynamic aperture (DA) optimization with direct particle tracking is a straight forward approach when the computing power is permitted. It can have various realistic errors included and is more close than theoretical estimations. In this approach, a fast and parallel tracking code could be very helpful. In this presentation, we describe an implementation of storage ring particle tracking code TESLA for beam dynamics optimization. It supports MPI based parallel computing and is robust as DA calculation engine. This code has been used in the NSLS-II dynamics optimizations and obtained promising performance.
 
 
WEP080 Spin Tracking with GPUs to 250 GeV in RHIC Lattice 1624
 
  • V.H. Ranjbar
    Tech-X, Boulder, Colorado, USA
  • M. Bai, F. Méot
    BNL, Upton, Long Island, New York, USA
 
  Funding: Supported by DOE NP grant DE-SC0004432
We have benchmarked UAL-SPINK against Zgoubi and a list of well understood spin physics results. Along the way we addressed issues relating to longitudinal dynamics and orbit bump and distortion handling as well as appropriate slicing necessary for the TEAPOT-SPINK spin orbit integrator. We have also ported this TEAPOT-SPINK algorithm to the GPU’s. We present the challenges associated with this work.
 
 
WEP110 Electron Cloud Modeling for the ILC Damping Rings 1686
 
  • J.A. Crittenden, D. Sagan
    CLASSE, Ithaca, New York, USA
  • K.G. Sonnad
    Cornell University, Ithaca, New York, USA
 
  Funding: Support by DOE contract DE-FC02-08ER41538 and NSF contract PHY-0734867
Electron cloud buildup is a primary concern for the performance of the damping rings under development for the International Linear Collider. We have performed synchrotron radiation profile calculations for the 6.4-km DC04 and 3.2-km DSB3 lattice designs using the SYNRAD utility in the Bmad accelerator software library. These results are then used to supply input parameters to the electron cloud modeling package ECLOUD. Contributions to coherent tune shifts from the field-free sections and from the dipole and quadrupole magnets have been calculated, as well as the effect of installing solenoid windings in the field-free regions. For each element type, SYNRAD provides ring occupancy, average beam sizes, beta function values, and beta-weighted photon rates for the coherent tune shift calculation. An approximation to the antechamber design has been implemented in ECLOUD as well, moving the photoelectron source point to the edges of the antechamber entrance and removing cloud particles which enter the antechamber.
 
 
WEP130 Simulation Study of Transverse Spectrum in HIRFL-CSR 1722
 
  • P. Li, L.J. Mao, J.W. Xia, J.C. Yang, D.Y. Yin, Y.J. Yuan
    IMP, Lanzhou, People's Republic of China
 
  Funding: Work supported by HIRFL-CSR project
Particles in a storage ring oscillate in the longitudinal and transverse dimensions. Therefore, the beam parameters, such as tune, momentum spread, emittance and their evolution can be obtained by analyzing the beam signals in frequency domain. In this paper, the simulation result of transverse beam spectrum in HIRFL-CSR is reported, including the influence of electron cooling, power supply ripple and the misalignment between ion and electron beams. Transverse coupling would occur if the longitudinal magnetic field of electron cooling device can not be compensated. And the distribution of ion beam in transverse space is a circle due to the misalignment between ion and electron beams. In this paper, main interest is focused on the effect of power supply ripple. The tune ripple form is the sine ware with the frequency of 50Hz which is equal to that of the industrial frequency in the simulation firstly. And then different forms of current ripple of power supply are simulated for comparative analysis. Tune shift will be induced by the power supply ripple. In this paper, those factors which may affect the accumulation of HIRFL-CSR are simulated in transverse beam spectrum.
 
 
WEP131 A New Approach to Calculate the Transport Matrix in RF cavities 1725
 
  • Y.I. Eidelman
    BINP SB RAS, Novosibirsk, Russia
  • N.V. Mokhov, S. Nagaitsev, N. Solyak
    Fermilab, Batavia, USA
 
  Funding: Work supported by USDoE
A realistic approach to calculate the transport matrix in RF cavities is developed. It is based on joint solution of equations of longitudinal and transverse motion of a charged particle in an electromagnetic field of the linac. This field is a given by distribution (measured or calculated) of the component of the longitudinal electric field on the axis of the linac. New approach is compared with other matrix methods to solve the same problem. The comparison with code ASTRA has been carried out. Complete agreement for tracking results for a TESLA-type cavity is achieved. A corresponding algorithm has been implemented into the MARS15 code.
 
 
WEP133 Adaptive Space-charge Meshing in the General Particle Tracer Code 1728
 
  • S.B. van der Geer
    Pulsar Physics, Eindhoven, The Netherlands
  • O.J. Luiten, M.J. de Loos
    TUE, Eindhoven, The Netherlands
  • G. Pöplau, U. van Rienen
    Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock, Germany
 
  Efficient and accurate space-charge calculations are essential for the design of high-brightness charged particle sources. Space-charge calculations in the General Particle Tracer (GPT) code make use of an efficient multigrid Poisson solver developed for non-equidistant meshes at Rostock University. GPT uses aggressive mesh-adaptation with highly non-equidistant spacing to speed up calcula- tion time, where the mesh line positions are based upon the projected charge density. Here we present a new meshing scheme where the solution of an intermediate step in the multigrid algorithm is used to define optimal mesh line positions. An analytical test case and comparison with a molecular dynamics calculation of an ultrafast electron diffraction experiment demonstrate the capabilities of this new algorithm in the GPT code.  
 
WEP134 Depolarization and Beam-beam Effects at Future e+e Colliders 1731
 
  • A.F. Hartin
    DESY, Hamburg, Germany
  • I.R. Bailey, C. Pidcott
    Lancaster University, Lancaster, United Kingdom
  • G.A. Moortgat-Pick
    University of Hamburg, Hamburg, Germany
 
  In order to exploit the full potential of proposed future high-energy electron-positron linear colliders, precise knowledge of the polarization state of the beams is required. In this paper we present an updated analysis of the depolarization effects caused by the intense beam-beam interaction, which is expected to be the dominant source of depolarization. The impact of higher-order effects are considered and numerical results from the Guinea-Pig and CAIN simulations are presented for the latest International Linear Collider (ILC) and Compact LInear Collider (CLIC) parameters.  
 
WEP136 Modelling of the EMMA ns-FFAG Ring Using GPT 1734
 
  • R.T.P. D'Arcy
    UCL, London, United Kingdom
  • J.K. Jones, B.D. Muratori
    STFC/DL/ASTeC, Daresbury, Warrington, Cheshire, United Kingdom
 
  EMMA (Electron Machine with Many Applications) is a prototype non-scaling Fixed-Field Alternating Gradient (ns-FFAG) accelerator whose construction at Daresbury Laboratory, UK, was completed in Aug 2010. The energy recovery linac ALICE will serve as an injector for EMMA, within an energy range of 10-20 MeV. The injection line consists of a dogleg to extract the beam from ALICE, a matching section, and tomography section for transverse emittance measurements. This is followed by a transport section to the injection point of the EMMA ring. The ring is composed of forty two cells, each containing one focusing and one defocusing quadrupole. Commissioning of the EMMA ring started in late 2010. A number of different injection energy and bunch charge regimes are planned; for some of the regimes the effects of space charge may be significant. It is therefore necessary to model the electron beam transport in the injection line and the ring using a code capable of both calculating the effect of and compensating for space charge. Therefore the General Particle Tracer (GPT) code has been used. A range of injection beam parameters have been modelled for comparison with experimental results.  
 
WEP137 Performance Analysis on the IBM Blue Gene/P for Wakefield Calculations 1737
 
  • M. Min, P.F. Fischer
    ANL, Argonne, USA
 
  Accurate and efficient simulations will significantly reduce the cost and the risk in the design process for various applications in accelerator design. We improved capability of the Argonne-developed high-fidelity wakefield simulation code, NekCEM, by upgrading pre-setup and communication subroutines for high-performance simulations beyond petascale. We present a detailed study of parallel performance of NekCEM on the IBM Blue Gene/P at Argonne. We demonstrate strong scaling up to P=131,072 cores using up to more than 1.1 billion grid points with the total number of elements up to E=273,000 and N=15 which gives 75% efficiency at 8,530 grid points per core compared to the base case of P =16,384 cores.  
 
WEP138 Developing Software Packages for Electromagnetic Simulations 1740
 
  • J. Xu, M. Min, B. Mustapha
    ANL, Argonne, USA
 
  Funding: This work was supported by the U.S. Department of Energy, Office of Nuclear Physics, under Contract No. DE-AC02-06CH11357.
In addition to previous developments on parallel beam dynamics software packages, our efforts have been extended to electromagnetic simulations. These efforts include developing new software packages solving the Maxwell equations in 2D and 3D. Scalable algorithms have been used for use of ALCF supercomputers. These new solvers are based on high order numerical methods. Comparative studies of structured and unstructured grids, continuous and discontinuous Galerkin methods will be discussed. The effects of bases will also be presented. Efficiency and challenges of new software packages will be presented. Some benchmarking and simulation results will be shown.
 
 
WEP139 Comparison of 1D and 2D CSR Models with Application to the Fermi@Elettra Bunch Compressors 1743
 
  • G. Bassi
    BNL, Upton, New York, USA
  • J.A. Ellison, K.A. Heinemann
    UNM, Albuquerque, New Mexico, USA
 
  Funding: Work partially supported by DOE grant DE-FG02-99ER41104
We compare our 2D mean field (Vlasov-Maxwell) treatment of coherent synchrotron radiation (CSR) effects with 1D approximations of the CSR force which are commonly implemented in CSR codes. In our model we track particles in 4D phase space and calculate 2D forces*. The major cost in our calculation is the computation of the 2D force. To speed up the computation and improve 1D models we also investigate approximations to our exact 2D force. Preliminary results are encouraging**. As an application, we present numerical results for the LCLS bunch compressors, where recently detailed measurements of the CSR-induced energy loss and transverse emittance growth have been performed and compared with numerical calculations***.
* Phys. Rev. ST Accel. Beams 12, 080704 (2009)
** http://www.lnf.infn.it/conference/uBI10/
*** Phys. Rev. ST Accel. Beams 12, 030704 (2009)
 
 
WEP140 Benchmarking Stepwise Ray-Tracing in Rings in Presence of Radiation Damping 1746
 
  • F. Méot
    BNL, Upton, Long Island, New York, USA
 
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A number of recent machine designs, including ‘‘nano-beams'', sub-millimeter ‘‘low-beta'' IRs, etc., require high accuracy on beam orbit and beam size, reliable evaluation of machine parameters, dynamic apertures, etc. This can only be achieved using high precision simulation tools. Stepwise ray-tracing methods are in this category of tools, stochastic synchrotron radiation and its effects on an electron beam in a storage ring are simulated here in that manner. Benchmarking of the method against analytical model expectations, using a Chasman-Green cell, is presented.
 
 
WEP141 Development of a Stepwise Ray-Tracing Based on-Line Model at AGS 1749
 
  • F. Méot, L. A. Ahrens, K.A. Brown, J.W. Glenn, H. Huang, T. Roser, V. Schoefer, N. Tsoupas
    BNL, Upton, Long Island, New York, USA
 
  Funding: Work supported by Brookhaven Science Associates, LLC under Contract No. DE-AC02-98CH10886 with the U.S. Department of Energy.
A model of the Alternating Gradient Synchrotron is being developed based on stepwise ray-tracing numerical tools. It provides a realistic representation of the lattice, and accounts for the two helical partial Siberian snake insertions. The aim is to make this stepwise ray-tracing based model an aid for the understanding of the AGS, in matter of both beam dynamics and polarization transmission.
 
 
WEP142 Electron Cloud Modeling Results for Time-resolved Shielded Pickup Measurements at CesrTA 1752
 
  • J.A. Crittenden, Y. Li, X. Liu, M.A. Palmer, J.P. Sikora
    CLASSE, Ithaca, New York, USA
  • S. Calatroni, G. Rumolo
    CERN, Geneva, Switzerland
 
  Funding: Support by DOE contract DE-FC02-08ER41538 and NSF contract PHY-0734867
The Cornell Electron Storage Ring Test Accelerator (CesrTA) program includes investigations into electron cloud buildup, applying various mitigation techniques in custom vacuum chambers. Among these are two 1.1 meter long sections located symmetrically in the east and west arc regions. These chambers are equipped with pickup detectors shielded against the direct beam-induced signal. Here we report on results from the ECLOUD modeling code which highlight the sensitivity of these measurements to model parameters such as the photoelectron energy distributions, and the secondary elastic yield value.
 
 
WEP146 A Quasi-3D Model of Electron Cyclotron Resonance Ion Source (ECRIS) 1755
 
  • L. Zhao, B. Cluggish, J.S. Kim
    Far-Tech, Inc., San Diego, California, USA
 
  Funding: Grant supported by DOE office of Nuclear Physics
FAR-TECH, Inc is developing a hybrid, quasi-3D model to model charge breeding of an ion beam in an electron cyclotron resonance ion source. The model is a combination of 3D mapping of the plasma background calculated by GEM1D* and 3D tracking of the ion trajectories with MCBC**. The 3D electron distribution function and electric field of the background plasma are calculated self-consistently. The test beam ions are then tracked in it using MCBC which includes Coulomb, ionization and charge exchange collisions. The exact ion trajectories in the plasma and steady state 3D ion distribution at the extraction aperture are predicted and compared with previous simulations and experiments.
* D. H. Edgell et al., Rev. Sci. Instrum. 73, 641, 2002.
** J. S. Kim et al., Rev. Sci. Instrum. 79, 02B906, 2008.
 
 
WEP147 The Effect of Space-charge and Wake Fields in the Fermilab Booster 1758
 
  • A. Macridin, J.F. Amundson, P. Spentzouris
    Fermilab, Batavia, USA
  • D.O. McCarron
    IIT, Chicago, Illinois, USA
  • L.K. Spentzouris
    Illinois Institute of Technology, Chicago, Illinois, USA
 
  Funding: This work was supported by the DOE contracts DE-AC02-07CH11359, DE-AC02-05CH11231 and DE-AC02-06CH11357 and the ComPASS project funded through the SciDAC.
We calculate the impedance and the wake functions for laminated structures with parallel-planes and circular geometries. We critically examine the approximations used in the literature for the coupling impedance in laminated chambers and find that most of them are not justified because the wall surface impedance is large. A comparison between the flat and the circular geometry impedance is presented. We use the wake fields calculated for the Fermilab Booster laminated magnets in realistic beam simulations using the Synergia code. We find good agreement between our calculation of the coherent tune shift at injection energy and the experimental measurements.
 
 
WEP149 Beam Measurement by a Wall Gap Monitor in ALPHA 1761
 
  • T.H. Luo, P.D. McChesney, P.E. Sokol
    IUCF, Bloomington, Indiana, USA
  • S.-Y. Lee
    IUCEEM, Bloomington, Indiana, USA
 
  In this report, we present our electron beam measurements with a wall gap monitor (WGM) in ALPHA injection and extraction beam lines. The WGM is first bench mark tested, and then installed in the ALPHA injection line to measure both the macro andμpulse of the injected beam and calibrate the beam current. By scanning the bending magnet before the WGM, and applying a demodulation signal processing scheme, we measured the tomography of the longitudinal phase space of the injected beam. We moved the WGM to extraction beam line and measured the properties of the extracted beam. By comparing the frequency spectrum of injected and extracted beam, we have confirmed the debunching performance of ALPHA.  
 
WEP150 GPU Computing for Particle Tracking 1764
 
  • H. Nishimura, S. James, K. Muriki, Y. Qin, K. Song, C. Sun
    LBNL, Berkeley, California, USA
 
  Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
This is a feasibility study of using a modern Graphics Processing Unit (GPU) to parallelize the accelerator particle tracking code. To demonstrate the massive parallelization features provided by GPU computing, a simplified TracyGPU program is developed for dynamic aperture calculation. Performances, issues, and challenges from introducing GPU are also discussed.
 
 
WEP151 HPC Cloud Applied to Lattice Optimization 1767
 
  • C. Sun, S. James, K. Muriki, H. Nishimura, Y. Qin, K. Song
    LBNL, Berkeley, California, USA
 
  Funding: Work supported by the U.S. Department of Energy under Contract No. DE-AC02-05CH11231
As Cloud services gain in popularity for enterprise use, vendors are now turning their focus towards providing cloud services suitable for scientific computing. Recently, Amazon Elastic Compute Cloud (EC2) introduced the new Cluster Compute Instances (CCI), a new instance type specifically designed for High Performance Computing (HPC) applications. At Berkeley Lab, the physicists at the Advanced Light Source (ALS) have been running Lattice Optimization on a local cluster, but the queue wait time and the flexibility to request compute resources when needed are not ideal for rapid development work. To explore alternatives, for the first time we investigate running the Lattice Optimization application on Amazon’s new CCI to demonstrate the feasibility and trade-offs of using public cloud services for science.

 
 
WEP152 Parallel Optimization of Beam-Beam Effects in High Energy Colliders 1770
 
  • J. Qiang, R.D. Ryne
    LBNL, Berkeley, California, USA
 
  Funding: Work supported by the Director of the Office of Science of the US Department of Energy under Contract no. DEAC02-05CH11231.
Beam-beam effects limit luminosity in high energy colliders. Parallel beam-beam simulation codes were developed to study those beam-beam effects and to help the collider design. In this paper, we will present a parallel optimization algorithm integrating together with the parallel beam-beam simulation to optimize the luminosity of the colliding beams. This algorithm is based on a differential evolutionary global optimization method and takes advantage of the two-level parallelization in both parallel search and parallel objective function evaluation. This significantly increases the scalability of the simulation on peta-scale supercomputers and reduces the time for finding the optimal working point.
 
 
WEP153 Simulation Results of a Feedback Control System to Damp Electron Cloud Single-Bunch Transverse Instabilities in the CERN SPS 1773
 
  • R. Secondo, J.-L. Vay, M. Venturini
    LBNL, Berkeley, California, USA
  • J.D. Fox, C.H. Rivetta
    SLAC, Menlo Park, California, USA
  • W. Höfle
    CERN, Geneva, Switzerland
 
  Funding: Work supported by the US-DOE under Contract DE-AC02-05CH11231 and the US-LHC Accelerator Research Program (LARP).
Transverse Single-Bunch Instabilities due to Electron Cloud effect are limiting the operation at high current of the SPS at CERN. Recently a high-bandwidth Feedback System has been proposed as a possible solution to stabilize the beam and is currently under study. We analyze the dynamics of the bunch actively damped with a simple model of the Feedback in the macro-particle code WARP, in order to investigate the limitations of the System such as the minimum amount of power required to maintain stability. We discuss the feedback model, report on simulation results and present our plans for further development of the numerical model.
 
 
WEP154 Direct Numerical Modeling of E-Cloud Driven Instability of a Bunch Train in the CERN SPS 1776
 
  • J.-L. Vay, M.A. Furman, M. Venturini
    LBNL, Berkeley, California, USA
 
  Funding: Supported by the US-DOE under Contract DE-AC02-05CH11231, the SciDAC program ComPASS and the US-LHC Accelerator Research Program (LARP). Used resources of NERSC and the Lawrencium cluster at LBNL.
Electron clouds impose limitations on current accelerators that may be more severe for future machines, unless adequate measures of mitigation are taken. It has been proposed recently to use feedback systems operating in the GHz range to damp single-bunch transverse coherent electron cloud driven instabilities that may occur in relatively long, ns scale, proton bunches such as those in the CERN SPS. The simulation package WARP-POSINST was recently upgraded for handling multiple bunches and modeling concurrently the electron cloud buildup and its effect on the beam, allowing for direct self-consistent simulation of bunch trains generating, and interacting with, electron clouds. We have used the WARP-POSINST package on massively parallel supercomputers to study the growth rate and frequency patterns in space-time of the electron cloud driven transverse instability for a proton bunch train in the CERN SPS accelerator with, or without, feedback models (with various levels of idealization) for damping the instability. We will present our latest simulation results, contrast them with actual measurements and discuss the implications for the design of the actual feedback system.
 
 
WEP156 GPU-Accelerated 3D Time-Domain Simulation of RF Fields and Particle Interactions 1779
 
  • S.J. Cooke, B. Levush, A.N. Vlasov
    NRL, Washington, DC, USA
  • T.M. Antonsen
    UMD, College Park, Maryland, USA
  • I.A. Chernyavskiy
    SAIC, McLean, USA
 
  Funding: This work is supported by the U.S. Office of Naval Research.
The numerical simulation of electromagnetic fields and particle interactions in accelerator components can consume considerable computational resources. By performing the same computation on fast, highly parallel GPU hardware instead of conventional CPUs it is possible to achieve a 20x reduction in simulation time for the traditional 3D FDTD algorithm. For structures that are small compared to the RF wavelength, however, or that require fine grids to resolve, the FDTD technique is constrained by the Courant condition to use very small time steps compared to the RF period. To avoid this constraint we have implemented an implicit, complex-envelope 3D ADI-FDTD algorithm for the GPU and demonstrate a further 5x reduction in simulation time, now two orders of magnitude faster than conventional FDTD codes. Recently, a GPU-based particle interaction model has been introduced, for which results will be reported. These algorithms form the basis of a new code, NEPTUNE, being developed to perform self-consistent 3D nonlinear simulations of vacuum electron devices.
 
 
WEP157 An Implementation of the Fast Multipole Method for High Accuracy Particle Tracking of Intense Beams 1782
 
  • E.W. Nissen, B. Erdelyi
    Northern Illinois University, DeKalb, Illinois, USA
 
  We implement a single level version of the fast multipole method in the software package COSY Infinity. This algorithm has been used in other physics fields to determine high accuracy electrostatic potentials, and is implemented here for charged particle beams. The method scales like NlogN with the particle number and has a priori error estimates, which can be reduced to essentially machine precision if multipole expansions of high enough order are employed, resulting in a highly accurate algorithm for simulation of intense beams without averaging such as encountered in PIC methods. In order to further speed up the algorithm we use COSY Infinity’s innate differential algebraic methods to help with the expansions inherent in this system. Differential algebras allow for fast and exact numerical differentiation of functions that carries through any mathematical transformations performed, and can be used to quickly create the expansions used in the fast multipole method. This can then be combined with moment method techniques to extract transfer maps which include space charge within distributions that are difficult to approximate.  
 
WEP159 Improved Algorithms for Multipacting Simulation in the Analyst Code 1785
 
  • J.F. DeFord, B.L. Held, K.J. Willis
    STAAR/AWR Corporation, Mequon, USA
 
  Funding: Work funded by the U.S. Dept. of Energy, Office of Science, SBIR Contract No. DE-FG02-05ER84373.
Electron multipacting is often deleterious in RF structures and must be controlled via modifications to the geometry, materials, or external fields. Recent improvements to the capabilities for modeling multipacting in the Analyst software package are presented in this paper. A backward difference scheme*, coupled with Newton-Raphson iteration, is used to integrate particle position/momentum, with integrations interrupted at element faces to minimize errors and lost particles. Support for the Furman-Pivi secondary emission model** has been implemented, with separate representations for low energy, re-diffused, and backscattered secondary particles, and multiple emissions per impact based upon a probability distribution. We have also developed a method to prune the tree of secondary particles resulting from an impact that minimizes particle count growth while maintaining important statistical information about the resonance. Finally, we have added support for volumetric sourcing of primaries, wherein the model volume is seeded with a population of particles with random positions and initial velocities. These improvements, along with benchmark calculations, will be presented.
* D. Darmofal, et al., Jour. Comp. Phys., 123, 1996, pp. 182-195.
** M. Furman, et al., LBNL-52807, June, 2003.
 
 
WEP160 Inclusion of Surface Roughness Effects in Emission Modeling With the MICHELLE Code 1788
 
  • J.F. DeFord
    STAAR/AWR Corporation, Mequon, USA
  • N.J. Dionne, S.G. Ovtchinnikov, J.J. Petillo
    SAIC, Burlington, Massachusetts, USA
 
  High-brightness electron beams are needed in millimeter-wave tubes and other high-power RF applications. Cathode surface roughness at the micron scale, commonly due to machining or other effects, can lead to broadening of the velocity distribution of electrons downstream, increasing emittance and lowering beam brightness. In this paper we investigate methods of including surface roughness effects in the MICHELLE code*. Modeling of typical surface imperfections over an entire cathode is not feasible, since it requires representation of features that are 3 to 5 orders of magnitude smaller than the cathode. Moreover, the actual surface imperfections for a given cathode are unknown without a prohibitive microscopic investigation of the surface, and these details vary between cathodes with the same machining history. To avoid these problems we investigated modifications to emission models that can account for these effects in an average sense, allowing the use of a smooth emission surface in a model while retaining the essential effects of the rough surface on the beam. We present the results of this investigation, along with representative solutions for sample structures.
*John Petillo, et al., “Recent Developments in the MICHELLE 2D/3D Electron Gun and Collector Modeling Code”, IEEE Trans. Electron Devices Sci., vol. 52, no. 5, May 2005, pp. 742-748.
 
 
WEP161 Modeling and Simulations of Electron Emission from Diamond-Amplified Cathodes 1791
 
  • D.A. Dimitrov, R. Busby, J.R. Cary, D.N. Smithe
    Tech-X, Boulder, Colorado, USA
  • I. Ben-Zvi, X. Chang, T. Rao, J. Smedley, E. Wang, Q. Wu
    BNL, Upton, Long Island, New York, USA
 
  Funding: This work is supported by the U. S. Department of Energy under the DE-SC0004431 grant.
Emission of electrons from a diamond-amplified cathode was recently demonstrated*. This experiment was based on a promising new concept** for generation of high-current, high-brightness, and low thermal emittance electron beams. The measurements from transmission and emission experiments have shown the potential to realize the diamond-amplified cathode concept. However, the results indicate that the involved physical properties should be understood in greater detail to build diamond cathodes with optical properties. We have already made progress in understanding the secondary electron generation and charge transport in diamond with the models we implemented in the VORPAL computational framework. We have been implementing models for electron emission from diamond and will present results from 3D VORPAL simulations with the integrated capabilities on generating electrons and holes, initiated by energetic primary electrons, propagation of the charge clouds, and then the emission of electrons into diamond. We will discuss simulation results on the dependence of the electron emission on diamond surface properties.
* X. Chang et al., Electron Beam Emission from a Diamond-Amplified Cathodes, to appear in Phys. Rev. Lett. (2010).
** I. Ben-Zvi et al., Secondary emission enhanced photoinjector, Rep. C-A/AP/149, BNL (2004).
 
 
WEP162 Modeling of Diamond Based Devices for Beam Diagnostics 1794
 
  • D.A. Dimitrov, R. Busby
    Tech-X, Boulder, Colorado, USA
  • I. Ben-Zvi, J.W. Keister, T. Rao, J. Smedley
    BNL, Upton, Long Island, New York, USA
  • E.M. Muller
    Stony Brook University, Stony Brook, USA
 
  Funding: The authors wish to acknowledge the support of the U.S. Department of Energy (DOE) under grants DE-SC0004584 (Tech-X Corp.) and DE-FG02-08ER41547 (BNL).
Beamlines at new light sources, such as the National Synchrotron Light Source II will operate at flux levels beyond the saturation level of existing diagnostics, necessitating the development of new devices. Currently, there is no detector which can span the entire flux range that is possible even in a second generation light source and will become crucial for next generation light sources. One new approach* is a diamond-based detector that will be able to monitor beam position, flux and timing to much better resolution. Furthermore, this detector also has linear response to flux over 11 orders of magnitude. However, the successful development of the detector requires thorough understanding and optimization of the physical processes involved. We will discuss the new modeling capabilities we have been implementing in the VORPAL 3D code to investigate the effects of charge generation due to absorption of x-ray photons, transport, and charge trapping. We will report results from VORPAL simulations on charge collection and how it depends on applied field, charge trapping, and the energy of absorbed photons.
*J. W. Keister, J. Smedley, D. A. Dimitrov, and R. Busby, Charge Collection and Propagation in Diamond X-ray Detectors, IEEE Transactions on Nuclear Science, 57, 2400 (2010).
 
 
WEP163 RF Cavity Characterization with VORPAL 1797
 
  • C. Nieter, P.J. Mullowney, C. Roark, P. Stoltz, C.D. Zhou
    Tech-X, Boulder, Colorado, USA
  • F. Marhauser
    JLAB, Newport News, Virginia, USA
 
  When designing a radio frequency (RF) accelerating cavity structure various figures of merit are considered before coming to a final cavity design. These figures of merit include specific field and geometry based quantities such as the ratio of the shunt impedance to the quality factor (R/Q) or the normalized peak fields in the cavity. Other important measures of cavity performance include the peak surface fields as well as possible multipacting resonances in the cavity. High fidelity simulations of these structures can provide a good estimate of these important quantities before any cavity prototypes are built. We will present VORPAL simulations of a simple pillbox structure where these quantities can be calculated analytically and compare them to the results from the VORPAL simulations. We will then use VORPAL to calculate these figures of merit and potential multipacting resonances for two cavity designs under development at Jefferson National Lab for Project X.  
 
WEP164 Accelerating Beam Dynamics Simulations with GPUs 1800
 
  • I.V. Pogorelov, K. Amyx, P. Messmer
    Tech-X, Boulder, Colorado, USA
 
  Funding: This work is funded by the DOE/BES Grant No. DE-SC0004585, and by Tech-X Corp.
We present recent results of prototyping general-purpose particle tracking on GPUs, discussing our CUDA implementation of transfer maps for single-particle dynamics and collective effects. Our goal being incorporation of the GPU-accelerated tracking into ANL's accelerator code ELEGANT, we used the code's quadrupole and drift-with-LSC elements as test cases. We discuss the use of data-parallel and hardware-assisted approaches (segmented scan and atomic updates) for resolving memory contention issues at the charge deposition stage of algorithms for modeling collective effects.
 
 
WEP165 Advanced Modeling of TE Microwave Diagnostics of Electron Clouds 1803
 
  • S.A. Veitzer, D.N. Smithe, P. Stoltz
    Tech-X, Boulder, Colorado, USA
 
  Funding: Part of this work is being performed under the auspices of the U.S. Department of Energy as part of the ComPASS SciDAC project, #DE-FC02-07ER41499.
Numerical simulations of electron cloud buildup and in particular rf microwave diagnostics provide important insights into the dynamics of particle accelerators and the potential for mitigation of destabilizing effects of electron clouds on particle beams. Typical Particle-In-Cell (PIC) simulations may accurately model cloud dynamics; however, due to the large range of temporal scales needed to model side band production due to ecloud modulation, typical PIC models may not be the best choice. We present here preliminary results for advance numerical modeling of rf electron cloud diagnostics, where we replace kinetic particles with an equivalent plasma dielectric model. This model provides significant speedup and increased numerical stability, while still providing accurate models of rf phase shifts induced by electron cloud plasmas over long time scales.
 
 
WEP167 Searching for the Optimal Working Point of the MEIC at JLab Using an Evolutionary Algorithm 1805
 
  • B. Terzić
    JLAB, Newport News, Virginia, USA
  • C. Jarvis
    Macalester, St. Paul, Minnesota, USA
  • M. Kramer
    UCB, Berkeley, California, USA
 
  Funding: Authored by Jefferson Science Associates, LLC under U.S. DOE Contract No. DE-AC05-06OR23177. Supported in part by SciDAC collaboration.
The Medium-energy Electron Ion Collider (MEIC), a proposed medium-energy ring-ring electron-ion collider based on CEBAF at Jefferson Lab. The collider luminosity and stability are sensitive to the choice of a working point – the betatron and synchrotron tunes of the two colliding beams. Therefore, a careful selection of the working point is essential for stable operation of the collider, as well as for achieving high luminosity. Here we describe a novel approach for locating an optimal working point based on evolutionary algorithm techniques.