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Curved Mesh Correction And Adaptation Tool to Improve COMPASS Electromagnetic Analyses

Description: SLAC performs large-scale simulations for the next-generation accelerator design using higher-order finite elements. This method requires using valid curved meshes and adaptive mesh refinement in complex 3D curved domains to achieve its fast rate of convergence. ITAPS has developed a procedure to address those mesh requirements to enable petascale electromagnetic accelerator simulations by SLAC. The results demonstrate that those correct valid curvilinear meshes can not only make the simulation more reliable but also improve computational efficiency up to 30%. This paper presents a procedure to track moving adaptive mesh refinement in curved domains. The procedure is capable of generating suitable curvilinear meshes to enable large-scale accelerator simulations. The procedure can generate valid curved meshes with substantially fewer elements to improve the computational efficiency and reliability of the COMPASS electromagnetic analyses. Future work will focus on the scalable parallelization of all steps for petascale simulations.
Date: November 14, 2011
Creator: Luo, X.; Shephard, M.; Poly., /Rensselaer; Lee, L.Q.; Ng, C.; Ge, L. et al.
Partner: UNT Libraries Government Documents Department

Simulation of HOM Leakage in the PEP-II Bellows

Description: An important factor that limits the PEP-II from operating at high currents is higher-order-mode (HOM) heating of the bellows. One source of HOM heating is the formation of trapped modes at the bellows as a result of geometry variation in the vacuum chamber, for example, the masking near the central vertex chamber. Another source comes from HOMs generated upstream that leak through the gaps between the bellows fingers. Modeling the fine details of the bellows and the surrounding geometry requires the resolution and accuracy only possible with a large number of mesh points on an unstructured grid. We use the parallel finite element eigensolver Omega3P for trapped mode calculations and the S-matrix solver S3P for transmission analysis. The damping of the HOMs by the use of absorbers inside the bellows will be investigated.
Date: June 7, 2005
Creator: Ng, C.-K.; Folwell, N.; Ge, L.; Langton, J.; Lee, L.-Q.; Novokhatski, A. et al.
Partner: UNT Libraries Government Documents Department

Thermal Analysis of SRF Cavity Couplers Using Parallel Multiphysics Tool TEM3P

Description: SLAC has developed a multi-physics simulation code TEM3P for simulating integrated effects of electromagnetic, thermal and structural loads. TEM3P shares the same software infrastructure with SLAC’s paralell finite element electromagnetic codes, thus enabling all physics simulations within a single framework. The finite-element approach allows high fidelity, high-accuracy simulations and the parallel implementation facilitates large-scale computation with fast turnaround times. In this paper, TEM3P is used to analyze thermal loading at coupler end of the JLAB SRF cavity.
Date: May 1, 2009
Creator: Akcelik, V, Lee, L.-Q., Li, Z., Ng, C.-K., Ko, K.,Cheng, G., Rimmer, R., Wang, H.
Partner: UNT Libraries Government Documents Department

Parallel Computation of Intergrated Electronmagnetic, Thermal and Structural Effects for Accelerator Cavities

Description: The successful operation of accelerator cavities has to satisfy both rf and mechanical requirements. It is highly desirable that electromagnetic, thermal and structural effects such as cavity wall heating and Lorentz force detuning in superconducting rf cavities can be addressed in an integrated analysis. Based on the SLAC parallel finite-element code infrastructure for electromagnetic modeling, a novel multi-physics analysis tool has been developed to include additional thermal and mechanical effects. The parallel computation enables virtual prototyping of accelerator cavities on computers, which would substantially reduce the cost and time of a design cycle. The multi-physics tool is applied to the LCLS rf gun for electromagnetic, thermal and structural analyses.
Date: July 2, 2008
Creator: Akcelik, V.; Candel, A.; Kabel, A.; Lee, L-Q.; Li, Z.; Ng, C-K. et al.
Partner: UNT Libraries Government Documents Department

Simulating Dark Current in NLC Structures

Description: Dark current generation and capture are of great importance in high gradient accelerating structure R&D especially for the NLC which aims to operate at 65 MV/m with specific limits on dark current and RF breakdown rates. Although considerable effort has been devoted to building and testing various types of structures to meet these requirements, few theoretical studies have been done to understand these effects in actual structures. This paper focuses on the simulation of dark current in a NLC test structure for which experimental data are available. The parallel time-domain field solver Tau3P and the parallel particle tracking code Track3P are used together to simulate, for the first time, a dark current pulse to compare with the data measured downstream. Results from SLAC X-band 30-cell constant impedance structure for RF drive pulses with different rise times are presented and discussed.
Date: October 11, 2007
Creator: Ng, C. K.; Folwell, N.; Guetz, A.; Ivanov, V.; Lee, L. Q.; Li, Z. H. et al.
Partner: UNT Libraries Government Documents Department

Thermal Analysis of SRF Cavity Couplers Using Parallel Multiphysics Tool TEM3P

Description: SLAC has developed a multi-physics simulation code TEM3P for simulating integrated effects of electromagnetic, thermal and structural loads. TEM3P shares the same software infrastructure with SLAC's parallel finite element electromagnetic codes, thus enabling all physics simulations within a single framework. The finite-element approach allows high-fidelity, high-accuracy simulations and the parallel implementation facilitates large-scale computation with fast turnaround times. In this paper, TEM3P is used to analyze thermal loading at coupler end of the JLAB SRF cavity.
Date: May 20, 2009
Creator: Akcelik, V; Lee, L.-Q.; Li, Z.; Ng, C.-K.; Ko, K.; /SLAC et al.
Partner: UNT Libraries Government Documents Department

Transmission and Propagation of an Accelerating Mode in a Photonic Bandgap Fiber

Description: A hollow core photonic bandgap (PBG) lattice in a dielectric fiber can provide high gradient acceleration in the optical regime, where the accelerating mode resulting from a defect in the PBG fiber can be excited by high-power lasers. Efficient methods of coupling laser power into the PBG fiber are an area of active research. In this paper, we develop a simulation method using the parallel finite-element electromagnetic suite ACE3P to study the propagation of the accelerating mode in the PBG fiber and determine the radiation pattern into free space at the end of the PBG fiber. The far-field radiation will be calculated and the mechanism of coupling power from an experimental laser setup will be discussed.
Date: August 26, 2010
Creator: Ng, C.-K.; England, R.J.; Lee, L.-Q.; Noble, R.; Rawat, V.; Spencer, J. et al.
Partner: UNT Libraries Government Documents Department

PEP-X IMPEDANCE AND INSTABILITY CALCULATIONS

Description: PEP-X, a next generation, ring-based light source is designed to run with beams of high current and low emittance. Important parameters are: energy 4.5 GeV, circumference 2.2 km, beam current 1.5 A, and horizontal and vertical emittances, 185 pm by 8 pm. In such a machine it is important that impedance driven instabilities not degrade the beam quality. In this report they study the strength of the impedance and its effects in PEP-X. For the present, lacking a detailed knowledge of the vacuum chamber shape, they create a straw man design comprising important vacuum chamber objects to be found in the ring, for which they then compute the wake functions. From the wake functions they generate an impedance budget and a pseudo-Green function wake representing the entire ring, which they, in turn, use for performing microwave instability calculations. In this report they, in addition, consider in PEP-X the transverse mode-coupling, multi-bunch transverse, and beam-ion instabilities.
Date: August 25, 2010
Creator: Bane, K.L.F.; Lee, L.-Q.; Ng, C.; Stupakov, G.; au Wang, L.; Xiao, L. 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, they 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: June 30, 2006
Creator: Yang, C.; Gao, W.G.; Bai, Z.J.; Li, X.Y.S.; Lee, L.Q.; Husbands, P. et al.
Partner: UNT Libraries Government Documents Department

Computational Science Research in Support of Petascale Electromagnetic Modeling

Description: Computational science research components were vital parts of the SciDAC-1 accelerator project and are continuing to play a critical role in newly-funded SciDAC-2 accelerator project, the Community Petascale Project for Accelerator Science and Simulation (ComPASS). Recent advances and achievements in the area of computational science research in support of petascale electromagnetic modeling for accelerator design analysis are presented, which include shape determination of superconducting RF cavities, mesh-based multilevel preconditioner in solving highly-indefinite linear systems, moving window using h- or p- refinement for time-domain short-range wakefield calculations, and improved scalable application I/O.
Date: June 20, 2008
Creator: Lee, L.-Q.; Akcelik, V; Ge, L; Chen, S; Schussman, G; Candel, A et al.
Partner: UNT Libraries Government Documents Department

State of the Art in EM Field Computation

Description: This paper presents the advances in electromagnetic (EM) field computation that have been enabled by the US DOE SciDAC Accelerator Science and Technology project which supports the development and application of a suite of electromagnetic codes based on the higher-order finite element method. Implemented on distributed memory supercomputers, this state of the art simulation capability has produced results which are of great interest to accelerator designers and with realism previously not possible with standard codes. Examples from work on the International Linear Collider (ILC) project are described.
Date: September 25, 2006
Creator: Ng, C.; Akcelik, V.; Candel, A.; Chen, S.; Folwell, N.; Ge, L. et al.
Partner: UNT Libraries Government Documents Department

High-Performance Computing in Accelerating Structure Design And Analysis

Description: Future high-energy accelerators such as the Next Linear Collider (NLC) will accelerate multi-bunch beams of high current and low emittance to obtain high luminosity, which put stringent requirements on the accelerating structures for efficiency and beam stability. While numerical modeling has been quite standard in accelerator R&D, designing the NLC accelerating structure required a new simulation capability because of the geometric complexity and level of accuracy involved. Under the US DOE Advanced Computing initiatives (first the Grand Challenge and now SciDAC), SLAC has developed a suite of electromagnetic codes based on unstructured grids and utilizing high performance computing to provide an advanced tool for modeling structures at accuracies and scales previously not possible. This paper will discuss the code development and computational science research (e.g. domain decomposition, scalable eigensolvers, adaptive mesh refinement) that have enabled the large-scale simulations needed for meeting the computational challenges posed by the NLC as well as projects such as the PEP-II and RIA. Numerical results will be presented to show how high performance computing has made a qualitative improvement in accelerator structure modeling for these accelerators, either at the component level (single cell optimization), or on the scale of an entire structure (beam heating and long range wakefields).
Date: June 27, 2006
Creator: Li, Z.H.; Folwell, N.; Ge, Li-Xin; Guetz, A.; Ivanov, V.; Kowalski, M. et al.
Partner: UNT Libraries Government Documents Department