121 research outputs found
Extension of the SIESTA MHD equilibrium code to free-plasma-boundary problems
is a recently developed MHD equilibrium code designed to perform fast and accurate calculations of ideal MHD equilibria for three-dimensional magnetic configurations. Since SIESTA does not assume closed magnetic surfaces, the solution can exhibit magnetic islands and stochastic regions. In its original implementation SIESTA addressed only fixed-boundary problems. That is, the shape of the plasma edge, assumed to be a magnetic surface, was kept fixed as the solution iteratively converges to equilibrium. This condition somewhat restricts the possible applications of SIESTA. In this paper, we discuss an extension that will enable SIESTA to address free-plasma-boundary problems, opening up the possibility of investigating problems in which the plasma boundary is perturbed either externally or internally. As an illustration, SIESTA is applied to a configuration of the W7-X stellarator.This research was funded in part by the Ministerio de Economía, Industria y Competitividad of Spain, Grant No. ENE2015-68265. This research was carried out in part at the Max-Planck-Institute for Plasma Physics in Greifswald (Germany), whose hospitality is gratefully acknowledged. This research was supported in part by the U.S. Department of Energy, Office of Fusion Energy Sciences under Award DE-AC05-00OR22725. SIESTA runs have been carred out in Uranus, a supercomputer cluster located at Universidad Carlos III de Madrid and funded jointly by the European Regional Development Funds (EU-FEDER) Project No. UNC313-4E-2361, and by the Ministerio de Economía, Industria y Competitividad via the National Project Nos. ENE2009-12213-C03-03, ENE2012-33219, and ENE2012-31753
Influencia de la cizalla en el comportamiento reológico, estructural y estabilidad física de Emulsiones formuladas con aerosil 200, Pluronic pe9400 y aceite esencial de Romero
Se prepararon emulsiones que contenían aceite esencial de romero, un conservante de
alimentos natural, mediante la técnica de microfluidización. Se obtuvieron emulgeles
añadiendo Aerosil 200.
Se examinó la influencia de la presión de homogeneización en el tamaño de gota. Las
emulsiones preparadas a 5000 psi en el Microfluidizer mostraron un menor diámetro de
Sauter y fueron seleccionadas para llevar a cabo los estudios posteriores.
Se ha estudiado la influencia de la cizalla en las propiedades reológicas, estabilidad
física y en la microestructura de las emulsiones y emulgeles formados. La emulsión
seleccionada mostraba re-coalescencia inducida por cizalla mientras que los emulgeles
presentaban un alineamiento de la red-3D.
Los emulgeles preparados mostraron un comportamiento dependiente del tiempo. A
pesar de que las propiedades viscoelásticas decrecían en el emulgel debido a la acción
de cizalla, se detectó una significante mejora en la estabilidad física con la técnica de
Multiple Light ScatteringUniversidad de Sevilla. Doble Grado en Física e Ingeniería de Materiale
Electron Bernstein waves emission in the TJ-II Stellarator
Taking advantage of the electron Bernstein waves heating (EBWH) system of the
TJ-II stellarator, an electron Bernstein emission (EBE) diagnostic was
installed. Its purpose is to investigate the B-X-O radiation properties in the
zone where optimum theoretical EBW coupling is predicted. An internal movable
mirror shared by both systems allows us to collect the EBE radiation along the
same line of sight that is used for EBW heating. The theoretical EBE has been
calculated for different orientations of the internal mirror using the TRUBA
code as ray tracer. A comparison with experimental data obtained in NBI
discharges is carried out. The results provide a valuable information regarding
the experimental O-X mode conversion window expected in the EBW heating
experiments. Furthermore, the characterization of the radiation polarization
shows evidence of the underlying B-X-O conversion process.Comment: 21 pages, 14 figure
The monoenergetic approximation in stellarator neoclassical calculations
In the standard "monoenergetic" approach to numerical calculation of
stellarator neoclassical transport, to expedite computation, ad-hoc changes are
made to the kinetic equation so speed enters only as a parameter. Here we
examine the validity of this approach by considering the effective particle
trajectories in a model magnetic field. We find monoenergetic codes
systematically under-predict the true trapped particle fraction, with the error
in the trapped ion fraction being of order unity when the electric field is
large, suggesting some results of these codes may be unreliable in this regime.
This inaccuracy is independent of any errors introduced by approximation of the
collision operator.Comment: 8 pages, 2 figures, submitted to Plasma Phys. Controlled Fusio
Characterization of Energy Confinement Using Extended International Stellarator Confinement Database
Environmental changes and violent conflict
This letter reviews the scientific literature on whether and how environmental changes affect the risk of violent conflict. The available evidence from qualitative case studies indicates that environmental stress can contribute to violent conflict in some specific cases. Results from quantitative large-N studies, however, strongly suggest that we should be careful in drawing general conclusions. Those large-N studies that we regard as the most sophisticated ones obtain results that are not robust to alternative model specifications and, thus, have been debated. This suggests that environmental changes may, under specific circumstances, increase the risk of violent conflict, but not necessarily in a systematic way and unconditionally. Hence there is, to date, no scientific consensus on the impact of environmental changes on violent conflict. This letter also highlights the most important challenges for further research on the subject. One of the key issues is that the effects of environmental changes on violent conflict are likely to be contingent on a set of economic and political conditions that determine adaptation capacity. In the authors' view, the most important indirect effects are likely to lead from environmental changes via economic performance and migration to violent conflict. © 2012 IOP Publishing Ltd
Co-production of knowledge and sustainability transformations: a strategic compass for global research networks
An increasing number of voices highlight the need for science itself to transform and to engage in the co-production of knowledge and action, in order to enable the fundamental transformations needed to advance towards sustainable futures. But how can global sustainability-oriented research networks engage in co-production of knowledge and action? The present article introduces a strategic tool called the ‘network compass’ which highlights four generic, interrelated fields of action through which networks can strive to foster co-production. It is based on the networks’ particular functions and how these can be engaged for co-production processes. This tool aims to foster self-reflection and learning within and between networks in the process of (re)developing strategies and activity plans and effectively contributing to sustainability transformations
Study of the neoclassical radial electric field of the TJ-II flexible heliac
Calculations of the monoenergetic radial diffusion coefficients are presented
for several configurations of the TJ-II stellarator usually explored in
operation. The neoclassical radial fluxes and the ambipolar electric field for
the standard configuration are then studied for three different collisionality
regimes, obtaining precise results in all cases
Pathways to Impact of Transdisciplinary Research: The Role of Contexts, Goals, and Epistemological Assumptions
- …