Bulletin of the American Physical Society
2007 APS April Meeting
Volume 52, Number 3
Saturday–Tuesday, April 14–17, 2007; Jacksonville, Florida
Session M9: Computational Methods in Beam Physics |
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Sponsoring Units: DPB Chair: Joseph Bisognano, University of Wisconsin-Madison Room: Hyatt Regency Jacksonville Riverfront City Terrace 5 |
Sunday, April 15, 2007 3:15PM - 3:51PM |
M9.00001: Parallel n-body algorithms for charged particles in external fields, with applications to accelerator physics Invited Speaker: In an effort to increase the luminosity of Brookhaven National Lab's Relativistic Heavy Ion Collider (RHIC), a novel electron cooling system has been proposed. Although the ions and electrons are highly relativistic in the lab frame, their motion is non-relativistic in the beam frame. The dynamics shares similarities with the classical n-body problem of astrophysics, but with charged particles interacting through Coulomb forces, rather than (for example) the stars of a globular cluster interacting through gravitation. In arbitrary external fields, the dynamical friction force on ions (and, hence, the cooling rate) is difficult to estimate. We present two numerical algorithms that simulate the friction force from first principles. The first algorithm is a Hermite n-body scheme adapted from astrophysics, while the second is a new algorithm where the interaction between pairs of particles is calculated exactly. We compare the two algorithms, and present results relevant to the RHIC cooling system. [Preview Abstract] |
Sunday, April 15, 2007 3:51PM - 4:27PM |
M9.00002: Recent Innovations in Simulating Space-Charge-Dominated Ion Beams Invited Speaker: Driven primarily by the needs of the Heavy Ion Fusion Sciences (HIFS) program, many new capabilities have been added to the Warp code to simulate the broader range of ion beam experiments that are now being carried out. These capabilities have attracted the interest of other programs, such as LHC, ILC, and of private industry, such as Cyberquest. The two thrusts are the innovations are the development of the models used to simulate a rich set of physical processes, such as the presence of electrons and background gas and ions, and improvement of the overall efficiency of the code, for example, by refining time and space only where needed. Some of the innovations that will be discussed include: a suite of models describing electron and ion interactions with walls, gas, etc.; inter- and intraspecies collisions; a new large-timestep particle mover that captures both the drift orbits and the gyroradius correctly; adaptive mesh refinement for electro- and magneto-statics or electromagnetics, and time-centered subcycling with individual particle step sizes based on the local Courant condition; parallelization of all of these methods. [Preview Abstract] |
Sunday, April 15, 2007 4:27PM - 5:03PM |
M9.00003: A New Approach to Adaptive Control of Multiple Scales in Plasma Simulations Invited Speaker: A new approach to temporal refinement of kinetic (Particle-in-Cell, Vlasov) and fluid (MHD, two-fluid) simulations of plasmas is presented: Discrete-Event Simulation (DES). DES adaptively distributes CPU resources in accordance with local time scales and enables asynchronous integration of inhomogeneous nonlinear systems with multiple time scales on meshes of arbitrary topologies. This removes computational penalties usually incurred in explicit codes due to the global Courant-Friedrich-Levy (CFL) restriction on a time-step size. DES stands apart from multiple time-stepping algorithms in that it requires neither selecting a global synchronization time step nor pre-determining a sequence of time-integration operations for individual parts of the system (local time increments need not bear any integer multiple relations). Instead, elements of a mesh-distributed solution self-adaptively predict and synchronize their temporal trajectories by directly enforcing local causality (accuracy) constraints, which are formulated in terms of incremental changes to the evolving solution. Together with flux-conservative propagation of information, this new paradigm ensures stable and fast asynchronous runs, where idle computation is automatically eliminated. DES is parallelized via a novel Preemptive Event Processing (PEP) technique, which automatically synchronizes elements with similar update rates. In this mode, events with close execution times are projected onto time levels, which are adaptively determined by the program. PEP allows reuse of standard message-passing algorithms on distributed architectures. For optimum accuracy, DES can be combined with adaptive mesh refinement (AMR) techniques for structured and unstructured meshes. Current examples of event-driven models range from electrostatic, hybrid particle-in-cell plasma systems to reactive fluid dynamics simulations. They demonstrate the superior performance of DES in terms of accuracy, speed and robustness. [Preview Abstract] |
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