• J. A. Holmes, S. M. Cousineau, V. V. Danilov, S. Henderson, D.-O. Jeon, M. A. Plum, A. P. Shishlo, Y. Zhang
  ORNL, Oak Ridge, Tennessee
• D. A. Bartkoski
  UTK, Knoxville, Tennessee

The computational approach is providing essential guidance and analysis for the commissioning and operation of SNS. Computational models are becoming sufficiently realistic that it is now possible to study detailed beam dynamics issues quantitatively. Increasingly, we are seeing that the biggest challenge in performing successful analyses is that of knowing and describing the machine and beam state accurately. Even so, successful benchmarks with both theoretical predictions and experimental results are leading to increased confidence in the capability of these models. With this confidence, computer codes are being employed in a predictive manner to guide the machine operations. We will illustrate these points with various examples taken from the SNS linac and ring.

• E. Gjonaj, X. Dong, R. Hampel, M. Kärkkäinen, T. Lau, W. F.O. Müller, T. Weiland
  TEMF, Darmstadt

The X-FEL project and the ILC require a high quality beam with ultra short electron bunches. In order to predict the beam quality in terms of both, single bunch energy spread and emittance, an accurate estimation of the short range wake fields in the TESLA crymodules, collimators and other geometrically complex accelerator components is necessary. We have presented earlier wake field computations for short bunches in rotationally symmetric components with the code ECHO. Most of the wake field effects in the accelerator, however, are due to geometrical discontinuities appearing in fully three dimensional structures. For the purpose of simulating such structures, we have developed the Parallel Beam Cavity Interaction (PBCI) code. The new code is based on the full field solution of Maxwell equations in the time domain, for ultra-relativistic current sources. Using a specialized directional-splitting technique, PBCI produces particularly accurate results in wake field computations, due to the dispersion free integration of the discrete equations in the direction of bunch motion. One of the major challenges to deal with, when simulating fully three dimensional accelerator components is the huge computational effort needed for resolving both, the geometrical details and the bunch extensions by the computational grid. For this reason, PBCI implements massive parallelization on a distributed memory environment, based on a flexible domain decomposition method. In addition, PBCI uses the moving window technique, which is particularly well suited for wake potential computations in very long structures. As a particular example of such a structure, the simulation results of a complete module of TESLA cavities with eight cells each for a um-bunch will be given.

• A. P. Shishlo, S. M. Cousineau, V. V. Danilov, J. Galambos, S. Henderson, J. A. Holmes, M. A. Plum
  ORNL, Oak Ridge, Tennessee

The contents, structure, implementation, benchmarking, and applications of ORBIT as an accelerator simulation code are described. Physics approaches, algorithms, and limitations for space charge, impedances, and electron cloud effects are discussed. The ORBIT code is a parallel computer code, and the scalabilities of the implementations of parallel algorithms for different physics modules are shown. ORBIT has a long history of benchmarking with analytical exactly solvable problems and experimental data. The results of this benchmarking and the current usage of ORBIT are presented.

• G. Rumolo, E. Métral
  CERN, Geneva

• S. Peggs, U. Iriso
  BNL, Upton, Long Island, New York

• A. Lehrach, B. Lorentz, R. Maier, D. Prasuhn, H. Stockhorst, R. Tölle, D. M. Welsch
  FZJ, Jülich
• O. Boine-Frankenheim, R. W. Hasse, S. Sorge
  GSI, Darmstadt
• F. Hinterberger
  Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, Bonn

The HESR is planned as an antiproton storage ring in the momentum range from 1.5 to 15 GeV/c. An important feature of this new facility is the combination of phase space cooled beams utilizing electron and stochastic cooling and dense internal targets (e.g. pellet targets). In this paper different beam dynamics issues like closed orbit correction, performance of cooled beams interacting with internal targets and luminosity considerations are discussed in respect of utilized simulation codes.

O. Boine-Frankenheim et al., Nucl. Inst. and Meth. A 560, 245 (2006).
A. Lehrach at al., Nucl. Instr. Meth. A 561, 289 (2006).
F. Hinterberger, Jül-Report No. 4206 (2006), ISSN 0944-2952.

• J. H. Timmer, P. A. Komorowski, H. Röcken
  ACCEL, Bergisch Gladbach

• M. Dehler
  PSI, Villigen

• B. S.C. Oswald, A. Adelmann, M. Bopp, R. Geus
  PSI, Villigen

* P. Arbenz, M. Becka, R. Geus, U. L. Hetmaniuk, and T. Mengotti,
"On a Parallel Multilevel Preconditioned Maxwell Eigensolver".
Parallel Computing, 32(2): 157-165 (2006).

• G. Pöplau
  Rostock University, Faculty of Engineering, Rostock
• K. Floettmann
  DESY, Hamburg
• U. van Rienen
  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. Recently new algorithms for solving Poisson's equation have been implemented in the tracking code Astra. These Poisson solvers are iterative algorithms solving a linear system of equations that results from the finite difference discretization of the Poisson equation. The implementation is based on the software package MOEVE (Multigrid Poisson Solver for Non-Equidistant Tensor Product Meshes) developed by G. Pöplau. The package contains a state-of-the-art multigrid Poisson solver adapted to space charge calculations. In this paper the basic concept of iterative Poisson solvers is described. It is compared to the established 3D FFT Poisson solver which is a widely-used method for space charge calculations and also implemented in Astra. Advantages and disadvantages are discussed. Further the similarities and differences of both approaches are demonstrated with numerical examples.

• T. Lau, E. Gjonaj, T. Weiland
  TEMF, Darmstadt

For devices in which the bunch dimensions are much smaller than the dimensions of the structure the numerical field solution is typically hampered by spurious oscillations. The reason for this oscillations is the large numerical dispersion error of conventional schemes along the beam axis. Recently, several numerical schemes have been proposed which apply operator splitting to optimize and under certain circumstances eliminate the dispersion error in the direction of the bunch motion. However, in comparison to the standard Yee scheme the methods based on operator splitting do not conserve the standard discrete Gauss law. This contribution is dedicated to the construction of conserved discrete Gauss laws and conservative current interpolation for some of the split operator methods. Finally, the application of the methods in a PIC simulations is shown.

• F. Hamme, U. Becker, P. Hammes
  CST, Darmstadt

• M. Dohlus
  DESY, Hamburg

• I. V. Pogorelov, J. Qiang, R. D. Ryne, M. Venturini, A. Zholents
  LBNL, Berkeley, California
• R. L. Warnock
  SLAC, Menlo Park, California

• G. Asova, S. Khodyachykh, M. Krasilnikov, F. Stephan
  DESY Zeuthen, Zeuthen
• P. Castro, F. Loehl
  DESY, Hamburg

A high phase-space density of the electron beam is obligatory for the successful operation of a Self Amplified Spontaneous Emission - Free Elector Laser (SASE-FEL). Detailed knowledge of the phase-space density distribution is thus very important for characterizing the performance of the used electron sources. The Photo Injector Test Facility at DESY in Zeuthen (PITZ) is built to develop, operate and optimize electron sources for FELs. Currently a tomography module for PITZ is under design as part of the ongoing upgrade of the facility. This contribution studies the performance of the tomography module. Errors in the beam size measurements and their contribution to the calculated emittance will be studied using simulated data. As a practical application the Maximum Entropy Algorithm (MENT) will be used to reconstruct the data generated by an ASTRA simulation.

• A. Dolinskii, V. Gostishchev, M. Steck
  GSI, Darmstadt
• O. A. Bezshyyko
  National Taras Shevchenko University of Kyiv, The Faculty of Physics, Kyiv

• A. Markovik, G. Pöplau, U. van Rienen
  Rostock University, Faculty of Computer Science and Electrical Engineering, Rostock
• R. Wanzenberg
  DESY, Hamburg

The determination of electron cloud instability thresholds is a task with high priority in the ILC damping rings research and development objectives. Simulations of electron cloud instabilities are therefore essential. In this paper a new particle tracking program is presented which includes the Poisson solver MOEVE for space charge calculations. Recently, perfectly electric conducting beam pipes with arbitrary elliptical shapes have been implemented as boundary conditions in the Poisson solver package MOEVE. The 3D space charge algorithm taking into account a beam pipe of elliptical shape will be presented along with numerical test cases. The routine is also implemented in the program code ASTRA, in addition we compare the tracking with both routines.

• D. L. Bruhwiler, J. R. Cary, D. A. Dimitrov, P. Messmer
  Tech-X, Boulder, Colorado
• E. Esarey, C. G.R. Geddes
  LBNL, Berkeley, California
• E. Kashdan
  Brown University, Providence, Rhode Island

Electromagnetic particle-in-cell (PIC) simulations of laser wakefield accelerator (LWFA) experiments have shown great success recently, qualitatively capturing many exciting features, like the production of ~1 GeV electron beams with significant charge, moderate energy spread and remarkably small emittance. Such simulations require large clusters or supercomputers for full-scale 3D runs, and all state-of-the art codes are using similar algorithms, with 2nd-order accuracy in space and time. Very high grid resolution and, hence, a very large number of time steps are required to obtain converged results. We present preliminary results from the implementation and testing of 4th-order algorithms, which hold promise for dramatically improving the accuracy of future LWFA simulations.

• J. A. Holmes, S. M. Cousineau, V. V. Danilov, J. Galambos, S. Henderson, M. A. Plum, A. P. Shishlo
  ORNL, Oak Ridge, Tennessee

• D. L. Bruhwiler
  Tech-X, Boulder, Colorado

High-energy electron cooling requires co-propagation of relativistic electrons over many meters with the recirculating bunches of an ion collider ring. The expected increase of ion beam luminosity makes such systems a key component for proposed efforts like the RHIC luminosity upgrade* and the FAIR project**. Correctly simulating the dynamical friction of heavy ions, during brief interactions with low-density electron populations, in the presence of arbitrary electric and magnetic fields, requires a molecular dynamics approach that resolves close Coulomb collisions. Effective use of clusters and supercomputers is required to make such computations practical. Previous work*** will be reviewed. Recent algorithmic developments**** and future plans will be emphasized.

* http://www.bnl.gov/cad/ecooling
** http://www.gsi.de/GSI-Future/cdr
*** A. V. Fedotov et al., Phys. Rev. ST/AB (2006), in press.
**** G. I. Bell et al., AIP Conf. Proc. 821 (2006), p. 329.

• J.-L. Vay
  LBNL, Berkeley, California
• A. Friedman, D. P. Grote
  LLNL, Livermore, California

We have developed a new, comprehensive set of simulation tools aimed at modeling the interaction of intense ion beams and electron clouds (e-clouds). The set contains the 3-D accelerator PIC code WARP and the 2-D "slice" e-cloud code POSINST, as well as a merger of the two, augmented by new modules for impact ionization and neutral gas generation. The new capability runs on workstations or parallel supercomputers and contains advanced features such as mesh refinement, disparate adaptive time stepping, and a new "drift-Lorentz" particle mover for tracking charged particles in magnetic fields using large time steps. It is being applied to the modeling of ion beams (1 MeV, 180 mA, K+) for heavy ion inertial fusion and warm dense matter studies, as they interact with electron clouds in the High-Current Experiment (HCX). We describe the capabilities and present recent simulation results with detailed comparisons against the HCX experiment, as well as their application (in a different regime) to the modeling of e-clouds in the Large Hadron Collider (LHC).

• R. A. Kishek, G. Bai, B. L. Beaudoin, S. Bernal, D. W. Feldman, R. B. Fiorito, T. F. Godlove, I. Haber, P. G. O'Shea, C. Papadopoulos, B. Quinn, M. Reiser, D. Stratakis, D. F. Sutter, J. C.T. Thangaraj, K. Tian, M. Walter, C. Wu
  IREAP, College Park, Maryland

The University of Maryland Electron Ring (UMER) is a scaled electron recirculator using low-energy, 10 keV electrons, to maximize the space charge forces for beam dynamics studies. We have recently circulated in UMER the highest-space-charge beam in a ring to date, achieving a breakthrough both in the number of turns and in the amount of current propagated. As of the time of submission, we have propagated 5 mA for at least 10 turns, and, with some loss, for over 50 turns, meaning about 0.5 nC of electrons survive for 10 microseconds. This makes UMER an attractive candidate for benchmarking space charge codes in regimes of extreme space charge. This talk will review the UMER design and available diagnostics, and will provide examples of benchmarking the particle-in-cell code WARP on UMER data, as well as an overview of the detailed information on our website. An open dialogue with interested coded developers is solicited.

• F. Wolfheimer, E. Gjonaj, T. Weiland
  TEMF, Darmstadt

Particle-In-Cell (PIC) simulations are commonly used in the field of computational accelerator physics for modelling the interaction of electromagnetic fields and charged particle beams in complex accelerator geometries. However, the practicability of the method for real world simulations, is often limited by the huge size of accelerator devices and by the large number of computational particles needed for obtaining accurate simulation results. Thus, the parallelization of the computations becomes necessary to permit the solution of such problems in a reasonable time. Different algorithms allowing for an efficient parallel simulation by preserving an equal distribution of the computational workload on the processes while minimizing the interprocess communication are presented. This includes some already known approaches based on a domain decomposition technique as well as novel schemes. The performance of the algorithms is studied in different computational environments with simulation examples including a full 3D simulation of the PITZ-Injector [*].

*A. Oppelt et al Status and First Results from the Upgraded PITZ Facility, Proc. FEL 2005

• P. Spentzouris
  Fermilab, Batavia, Illinois