JLAB, Newport News, Virginia
In this paper, we present benchmarking results for high-class 3D electromagnetic (EM) codes in designing RF cavities today. These codes include Omega3P [1], VORPAL [2], CST Microwave Studio [3], Ansoft HFSS [4], and ANSYS [5]. Two spherical cavities are selected as the benchmark models. We have compared not only the accuracy of resonant frequencies, but also that of surface EM fields, which are critical for superconducting RF cavities. By removing degenerated modes, we calculate all the resonant modes up to 10 GHz with similar mesh densities, so that the geometry approximation and field interpolation error related to the wavelength can be observed.
LBNL, Berkeley, California
Numerical simulations to design high-energy particle accelerators give rise to large-scale ill-conditioned highly indefinite linear systems of equations that are becoming increasingly difficult to solve using either a direct solver or a preconditioned iterative solver alone. In this paper, we describe our current effort to develop a parallel hybrid linear solver that balances the robustness of a direct solver with the efficiency of a preconditioned iterative solver. We demonstrate that our hybrid solver is more robust and efficient than the existing state-of-the-art software to solve these linear systems on a large number of processors.
Tech-X, Boulder, Colorado
Even if common, self-described data formats are used, data organization (e.g. the structure and names of groups, datasets and attributes) differs between applications. This makes development of uniform visualization tools problematic and comparison of simulation results difficult. VizSchema is an effort to standardize metadata of HDF5 format so that the entities needed to visualize the data can be identified and interpreted by visualization tools. This approach allowed us to develop a standard powerful visualization tool, based on VisIt, for visualization of large data of various kinds (fields, particles, meshes) allowing 3D visualization of large-scale data from the COMPASS suite (VORPAL and Synergia) for SRF cavities and laser-plasma acceleration.
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.
PSI, Villigen
One possible electron source for the PSI-XFEL is the Low Emittance Gun (LEG), which is currently under development at PSI. It consists of a pulsed DC gun, which operates at 500 keV and has the option of using either a photo cathode or a field emitter array. The gun is followed by a pulsed in-vacuum solenoid and a two frequency cavity, not only used to accelerate the beam but also to create a highly linear energy correlation required for ballistic bunching. All components are rotationally symmetric, so a full particle-in-cell simulation of the setup using 2 1/2 D MAFIA, including space charge, wake fields and beam loading effects, shows the base line performance. The low emittance beam, which propagates in a large part of the setup at relatively small energies of around 500 kEV, is rather sensitive to small perturbations in the fields. So we also investigated the effect of mechanical misalignments on the beam quality using the 3D in-house code CAPONE.
TEMF, TU Darmstadt, Darmstadt
The Vlasov equation describes the evolution of a particle density under the effects of electromagnetic fields. It is derived from the fact that the volume occupied by a given number of particles in the 6D phase space remains constant when only long-range interaction as for example Coulomb forces are relevant and other particle collisions can be neglected. Because this is the case for typical charged particle beams in accelerators, the Vlasov equation can be used to describe their evolution within the whole beam line. This equation is a partial differential equation in 6D and thus it is very expensive to solve it via classical methods. A more efficient approach consists in representing the particle distribution function by a discrete set of characteristic moments. For each moment a time evolution equation can be stated. These ordinary differential equations can then be evaluated efficiently by means of time integration methods if all considered forces and a proper initial condition are known. The beam dynamics simulation tool V-Code implemented at TEMF utilizes this approach. In this paper the numerical model, main features and designated use cases of the V-Code will be presented.
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.
JLAB, Newport News, Virginia
Automation of DC photoinjector designs using a genetic algorithm (GA) based optimization is an accepted practice in accelerator physics. Allowing the gun cavity field profile shape to be varied can extend the utility of this optimization methodology to superconducting and normal conducting radio frequency (SRF/RF) gun based injectors. Finding optimal field and cavity geometry configurations can provide guidance for cavity design choices and verify existing designs. We have considered two approaches for varying the electric field profile. The first is to determine the optimal field profile shape that should be used independent of the cavity geometry, and the other is to vary the geometry of the gun cavity structure to produce an optimal field profile. The first method can provide a theoretical optimal and can illuminate where possible gains can be made in field shaping. The second method can produce more realistically achievable designs that can be compared to existing designs. In this paper, we discuss the design and implementation for these two methods for generating field profiles for SRF/RF guns in a GA based injector optimization scheme and provide preliminary results.
Fermilab, Batavia
In the paper the results are presented for calculation of the transverse wake and RF kick from the power and HOM couplers of the ILC acceleration structure. The RF kick was calculated by HFSS code while the wake was calculated by GdfidL. The calculation precision and convergence for both cases is discussed. The beam emittance dilution caused by the couplers is calculated for the main linac and bunch compressor of ILC.
ANL, Argonne
Use of SDDS, the Self-Describing Data Sets file protocol and toolkit, has been a great benefit to development of several accelerator simulation codes. However, the serial nature of SDDS was found to be a bottleneck for SDDS-compliant simulation programs such as parallel elegant. A parallel version of SDDS would be expected to yield significant dividends for runs involving large numbers of simulation particles. In this paper, we present a parallel interface for reading and writing SDDS files. This interface is derived from serial SDDS with minimal changes, but defines semantics for parallel access and is tailored for high performance. The underlying parallel IO is built on MPI-IO. The performance of parallel SDDS and parallel HDF5 are studied and compared. Our tests indicate better scalability of parallel SDDS compared to HDF5. We see significant I/O performance improvement with this parallel SDDS interface.
SLAC, Menlo Park, California
In a multi-bunch high current storage ring, beam generated fields couple strongly into the RF cavity coupler structure when beam arrival times are in resonance with cavity fields. In this study the integrated effect of beam fields over a several thousand RF periods is simulated for the complete cavity, coupler, window and waveguide system of the PEP-II B-factory storage ring collider. We show that the beam generated fields at frequencies corresponding to several bunch spacings for this case gives rise to high field strength near the ceramic window and could limit the performance of future high current storage rings such as PEP-X or Super B-factories.