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On Projecting Discretized Electromagnetic Fields with Unstructured Grids

Description: A new method for projecting discretized electromagnetic fields on one unstructured grid to another grid is presented in this paper. Two examples are used for studying the errors of different projection methods. The analysis shows that the new method is very effective on balancing both the error of the electric field and that of the magnetic field (or curl of the electric field).
Date: August 13, 2008
Creator: Lee, Lie-Quan; Candel, Arno; Kabel, Andrea; Li, Zenghai & /SLAC
Partner: UNT Libraries Government Documents Department

Omega3P: A Parallel Finite-Element Eigenmode Analysis Code for Accelerator Cavities

Description: Omega3P is a parallel eigenmode calculation code for accelerator cavities in frequency domain analysis using finite-element methods. In this report, we will present detailed finite-element formulations and resulting eigenvalue problems for lossless cavities, cavities with lossy materials, cavities with imperfectly conducting surfaces, and cavities with waveguide coupling. We will discuss the parallel algorithms for solving those eigenvalue problems and demonstrate modeling of accelerator cavities through different examples.
Date: March 4, 2009
Creator: Lee, Lie-Quan; Li, Zenghai; Ng, Cho; Ko, Kwok & /SLAC
Partner: UNT Libraries Government Documents Department

A Two-Dimensional Fem Code for Impedance Calculation in High Frequency Domain

Description: A new method, using the parabolic equation (PE), for the calculation of both high-frequency impedances of small-angle taper (or collimator) is developed in [1]. One of the most important advantages of the PE approach is that it eliminates the spatial scale of the small wavelength from the problem. As a result, only coarser spatial meshes are needed in calculating the numerical solution of the PE. We developed a new code based on Finite Element Method (FEM) which can handle arbitrary profile of a transition and speed up the calculation by orders of magnitude. As a first step, we completed and benchmarked a two-dimensional code. It can be upgraded to three-dimensional geometry.
Date: August 25, 2010
Creator: Wang, Lanfa; /SLAC; Lee, Lie-Quan; /SLAC; Stupakov, Gennady & /SLAC
Partner: UNT Libraries Government Documents Department

A Moving Window Technique in Parallel Finite Element Time Domain Electromagnetic Simulation

Description: A moving window technique for the finite element time domain (FETD) method is developed to simulate the propagation of electromagnetic waves induced by the transit of a charged particle beam inside large and long structures. The window moving along with the beam in the computational domain adopts high-order finite-element basis functions through p refinement and/or a high-resolution mesh through h refinement so that a sufficient accuracy is attained with substantially reduced computational costs. Algorithms to transfer discretized fields from one mesh to another, which are the key to implementing a moving window in a finite-element unstructured mesh, are presented. Numerical experiments are carried out using the moving window technique to compute short-range wakefields in long accelerator structures. The results are compared with those obtained from the normal FETD method and the advantages of using the moving window technique are discussed.
Date: June 7, 2010
Creator: Lee, Lie-Quan; Candel, Arno; Ng, Cho; Ko, Kwok; /SLAC & ,
Partner: UNT Libraries Government Documents Department

Solving Large Scale Nonlinear Eigenvalue Problem in Next-Generation Accelerator Design

Description: A number of numerical methods, including inverse iteration, method of successive linear problem and nonlinear Arnoldi algorithm, are studied in this paper to solve a large scale nonlinear eigenvalue problem arising from finite element analysis of resonant frequencies and external Q{sub e} values of a waveguide loaded cavity in the next-generation accelerator design. They present a nonlinear Rayleigh-Ritz iterative projection algorithm, NRRIT in short and demonstrate that it is the most promising approach for a model scale cavity design. The NRRIT algorithm is an extension of the nonlinear Arnoldi algorithm due to Voss. Computational challenges of solving such a nonlinear eigenvalue problem for a full scale cavity design are outlined.
Date: September 28, 2006
Creator: Liao, Ben-Shan; Bai, Zhaojun; /UC, Davis; Lee, Lie-Quan; Ko, Kwok & /SLAC
Partner: UNT Libraries Government Documents Department

Shape Determination for Deformed Electromagnetic Cavities

Description: The measured physical parameters of a superconducting cavity differ from those of the designed ideal cavity. This is due to shape deviations caused by both loose machine tolerances during fabrication and by the tuning process for the accelerating mode. We present a shape determination algorithm to solve for the unknown deviations from the ideal cavity using experimentally measured cavity data. The objective is to match the results of the deformed cavity model to experimental data through least-squares minimization. The inversion variables are unknown shape deformation parameters that describe perturbations of the ideal cavity. The constraint is the Maxwell eigenvalue problem. We solve the nonlinear optimization problem using a line-search based reduced space Gauss-Newton method where we compute shape sensitivities with a discrete adjoint approach. We present two shape determination examples, one from synthetic and the other from experimental data. The results demonstrate that the proposed algorithm is very effective in determining the deformed cavity shape.
Date: December 10, 2007
Creator: Akcelik, Volkan; Ko, Kwok; Lee, Lie-Quan; Li, Zhenghai; Ng, Cho-Kuen; Xiao, Liling et al.
Partner: UNT Libraries Government Documents Department

State of the art in electromagnetic modeling for the Compact Linear Collider

Description: SLAC's Advanced Computations Department (ACD) has developed the parallel 3D electromagnetic time-domain code T3P for simulations of wakefields and transients in complex accelerator structures. T3P is based on state-of-the-art Finite Element methods on unstructured grids and features unconditional stability, quadratic surface approximation and up to 6th-order vector basis functions for unprecedented simulation accuracy. Optimized for large-scale parallel processing on leadership supercomputing facilities, T3P allows simulations of realistic 3D structures with fast turn-around times, aiding the design of the next generation of accelerator facilities. Applications include simulations of the proposed two-beam accelerator structures for the Compact Linear Collider (CLIC) - wakefield damping in the Power Extraction and Transfer Structure (PETS) and power transfer to the main beam accelerating structures are investigated.
Date: July 10, 2009
Creator: Candel, Arno; Kabel, Andreas; Lee, Lie-Quan; Li, Zenghai; Ng, Cho; Schussman, Greg et al.
Partner: UNT Libraries Government Documents Department

Shape Determination for Deformed Cavities

Description: A realistic superconducting RF cavity has its shape deformed comparing to its designed shape due to the loose tolerance in the fabrication process and the frequency tuning for its accelerating mode. A PDE-constrained optimization problem is proposed to determine the deformation of the cavity. A reduce space method is used to solve the PDE-constrained optimization problem where design sensitivities were computed using a continuous adjoint approach. A proof-of-concept example is given in which the deformation parameters of a single cavity-cell with two different types of deformation were computed.
Date: October 4, 2006
Creator: Lee, Lie-Quan; Akcelik, Volkan; Chen, Sheng; Ge, Lixin; Li, Zenghai; Ng, Cho et al.
Partner: UNT Libraries Government Documents Department

Enhancing Scalability of Sparse Direct Methods

Description: TOPS is providing high-performance, scalable sparse direct solvers, which have had significant impacts on the SciDAC applications, including fusion simulation (CEMM), accelerator modeling (COMPASS), as well as many other mission-critical applications in DOE and elsewhere. Our recent developments have been focusing on new techniques to overcome scalability bottleneck of direct methods, in both time and memory. These include parallelizing symbolic analysis phase and developing linear-complexity sparse factorization methods. The new techniques will make sparse direct methods more widely usable in large 3D simulations on highly-parallel petascale computers.
Date: July 23, 2007
Creator: Li, Xiaoye S.; Demmel, James; Grigori, Laura; Gu, Ming; Xia,Jianlin; Jardin, Steve et al.
Partner: UNT Libraries Government Documents Department

Algebraic sub-structuring for electromagnetic applications

Description: Algebraic sub-structuring refers to the process of applying matrix reordering and partitioning algorithms to divide a large sparse matrix into smaller submatrices from which a subset of spectral components are extracted and combined to form approximate solutions to the original problem. In this paper, we show that algebraic sub-structuring can be effectively used to solve generalized eigenvalue problems arising from the finite element analysis of an accelerator structure.
Date: September 14, 2004
Creator: Yang, Chao; Gao, Weiguo; Bai, Zhaojun; Li, Xiaoye; Lee, Lie-Quan; Husbands, Parry et al.
Partner: UNT Libraries Government Documents Department

Enabling Technologies for Petascale Electromagnetic Accelerator Simulation

Description: The SciDAC2 accelerator project at SLAC aims to simulate an entire three-cryomodule radio frequency (RF) unit of the International Linear Collider (ILC) main Linac. Petascale computing resources supported by advances in Applied Mathematics (AM) and Computer Science (CS) and INCITE Program are essential to enable such very large-scale electromagnetic accelerator simulations required by the ILC Global Design Effort. This poster presents the recent advances and achievements in the areas of CS/AM through collaborations.
Date: November 9, 2007
Creator: Lee, Lie-Quan; Akcelik, Volkan; Chen, Sheng; Ge, Li-Xin; Prudencio, Ernesto; Schussman, Greg et al.
Partner: UNT Libraries Government Documents Department

Design and Optimization of Large Accelerator Systems through High-Fidelity Electromagnetic Simulations

Description: SciDAC1, with its support for the 'Advanced Computing for 21st Century Accelerator Science and Technology' (AST) project, witnessed dramatic advances in electromagnetic (EM) simulations for the design and optimization of important accelerators across the Office of Science. In SciDAC2, EM simulations continue to play an important role in the 'Community Petascale Project for Accelerator Science and Simulation' (ComPASS), through close collaborations with SciDAC CETs/Institutes in computational science. Existing codes will be improved and new multi-physics tools will be developed to model large accelerator systems with unprecedented realism and high accuracy using computing resources at petascale. These tools aim at targeting the most challenging problems facing the ComPASS project. Supported by advances in computational science research, they have been successfully applied to the International Linear Collider (ILC) and the Large Hadron Collider (LHC) in High Energy Physics (HEP), the JLab 12-GeV Upgrade in Nuclear Physics (NP), as well as the Spallation Neutron Source (SNS) and the Linac Coherent Light Source (LCLS) in Basic Energy Sciences (BES).
Date: August 1, 2008
Creator: Ng, Cho; Akcelik, Volkan; Candel, Arno; Chen, Sheng; Ge, Lixin; Kabel, Andreas et al.
Partner: UNT Libraries Government Documents Department