DF - GFP - Artículos de revistashttp://hdl.handle.net/10016/73982019-03-26T10:45:03Z2019-03-26T10:45:03ZThe Radial Propagation of Heat in Strongly Driven Non-Equilibrium Fusion PlasmasVan Milligen, BoudewijnCarreras Verdaguer, Benjamin A.García Gonzalo, LuisHernández Nicolau, Javierhttp://hdl.handle.net/10016/281642019-03-06T01:15:04Z2019-02-05T00:00:00ZThe Radial Propagation of Heat in Strongly Driven Non-Equilibrium Fusion Plasmas
Van Milligen, Boudewijn; Carreras Verdaguer, Benjamin A.; García Gonzalo, Luis; Hernández Nicolau, Javier
Heat transport is studied in strongly heated fusion plasmas, far from thermodynamic equilibrium. The radial propagation of perturbations is studied using a technique based on the transfer entropy. Three different magnetic confinement devices are studied, and similar results
are obtained. "Minor transport barriers" are detected that tend to form near rational magnetic
surfaces, thought to be associated with zonal flows. Occasionally, heat transport "jumps" over these
barriers, and this "jumping" behavior seems to increase in intensity when the heating power is raised,
suggesting an explanation for the ubiquitous phenomenon of "power degradation" observed in
magnetically confined plasmas. Reinterpreting the analysis results in terms of a continuous time
random walk, "fast" and "slow" transport channels can be discerned. The cited results can partially
be understood in the framework of a resistive Magneto-HydroDynamic model. The picture that
emerges shows that plasma self-organization and competing transport mechanisms are essential
ingredients for a fuller understanding of heat transport in fusion plasmas.
2019-02-05T00:00:00ZDoes size matter?Carreras, Benjamín A.Newman, D.E.Dobson, Ianhttp://hdl.handle.net/10016/188632018-09-08T09:51:11Z2014-04-01T00:00:00ZDoes size matter?
Carreras, Benjamín A.; Newman, D.E.; Dobson, Ian
Failures of the complex infrastructures society depends on having enormous human and economic cost that poses the question: Are there ways to optimize these systems to reduce the risks of failure? A dynamic model of one such system, the power transmission grid, is used to investigate the risk from failure as a function of the system size. It is found that there appears to be optimal sizes for such networks where the risk of failure is balanced by the benefit given by the size.
2014-04-01T00:00:00ZParallelization in time of numerical simulations of fully-developed plasma turbulence using the parareal algorithmSamaddar, D.Newman, D.E.Sánchez, Raúlhttp://hdl.handle.net/10016/89112018-09-08T09:51:02Z2010-09-01T00:00:00ZParallelization in time of numerical simulations of fully-developed plasma turbulence using the parareal algorithm
Samaddar, D.; Newman, D.E.; Sánchez, Raúl
It is shown that numerical simulations of fully-developed plasma turbulence can be successfully parallelized in time using the parareal algorithm. The result is far from trivial, and even unexpected, since the exponential divergence of Lagrangian trajectories as well as the extreme sensitivity to initial conditions characteristic of turbulence set these type of simulations apart from the much simpler systems to which the parareal algorithm has been applied to this day. It is also shown that the parallel gain obtainable with this method is very promising (close to an order of magnitude for the cases and implementations described), even when it scales with the number of processors quite differently to what is typical for spatial parallelization.
16 pages, 12 figures.
2010-09-01T00:00:00ZBCYCLIC: A parallel block tridiagonal matrix cyclic solverHirshman, S. P.Perumalla, K. S.Lynch, V. E.Sánchez Fernández, Luis Raúlhttp://hdl.handle.net/10016/89102019-03-05T10:18:50Z2010-09-01T00:00:00ZBCYCLIC: A parallel block tridiagonal matrix cyclic solver
Hirshman, S. P.; Perumalla, K. S.; Lynch, V. E.; Sánchez Fernández, Luis Raúl
A block tridiagonal matrix is factored with minimal fill-in using a cyclic reduction algorithm that is easily parallelized. Storage of the factored blocks allows the application of the inverse to multiple right-hand sides which may not be known at factorization time. Scalability with the number of block rows is achieved with cyclic reduction, while scalability with the block size is achieved using multithreaded routines (OpenMP, GotoBLAS) for block matrix manipulation. This dual scalability is a noteworthy feature of this new solver, as well as its ability to efficiently handle arbitrary (non-powers-of-2) block row and processor numbers. Comparison with a state-of-the art parallel sparse solver is presented. It is expected that this new solver will allow many physical applications to optimally use the parallel resources on current supercomputers. Example usage of the solver in magneto-hydrodynamic (MHD), three-dimensional equilibrium solvers for high-temperature fusion plasmas is cited.
13 pages, 6 figures.
2010-09-01T00:00:00Z