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Transport in Nontwist Hamiltonian systems

Grant number: 10/00740-6
Support Opportunities:Scholarships in Brazil - Doctorate
Effective date (Start): November 01, 2011
Effective date (End): September 30, 2013
Field of knowledge:Physical Sciences and Mathematics - Physics - Physics of Fluids, Plasma Physics and Electrical Discharge
Principal Investigator:Iberê Luiz Caldas
Grantee:Celso Vieira Abud
Host Institution: Instituto de Física (IF). Universidade de São Paulo (USP). São Paulo , SP, Brazil
Associated research grant:07/54000-0 - Non-linear dynamics, AP.TEM


The physics of plasmas has been developed since the 50's encouraged by the prospect of generating energy from controlled thermonuclear fusion. A promising mechanism for magnetic confinement is the tokamak, which consists of a toroidal machine of magnetic confinement of plasma, controlled from magnetic fields generated by currents in the coils and the plasma current. For the success of the experiment, it is necessary to overcome some difficulties that limit plasma confinement. Among other issues, the main problems are: the emergence of instability in the plasma and the anomalous transport of particles leaving the confined plasma and goes toward the wall of the tokamak, which causes the plasma lose energy and cool. This project aims to investigate the effects of spatial profiles of electric and magnetic fields on the transport of particles in the confined plasma edge in Tokamaks. In this context are used Hamiltonian dynamic models that have been proposed to describe the field lines at the edge of the plasma. We will consider these fields with non-monotonic radial profiles, which will lead us to a standard non-twist map. One consequence of the variation of parameters in dynamic systems is the possibility of bifurcations occur - sudden topological changes - such as loss of stability of a fixed point. One of these changes is the transition to global chaos (opposed to the chaos present only in narrow bands in phase space). The transition to global chaos is important because it leads to an increase in transport. In the proposed project we will investigate the transition to global chaos in maps obtained from non-twists models with reversed shear. In these models the transport is strongly affected by this transition. A particularity of the transition in non-twists is the robustness of the barrier in the region without shear, and the influence of this barrier on the transport, which persists after the break. In this scenario there are issues that still require further investigation. In particular the sequence of bifurcations that occur with a change of control parameter and that affect the transport through the broken barrier. An important application of this research is to predict the consequences of this scenario for the chaotic transport in tokamaks (AU)

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Scientific publications
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
VIEIRA ABUD, C.; CALDAS, I. L.. Onset of shearless magnetic surfaces in tokamaks. NUCLEAR FUSION, v. 54, n. 6, . (10/00740-6)
Academic Publications
(References retrieved automatically from State of São Paulo Research Institutions)
ABUD, Celso Vieira. Trnasport in nontwiast hamiltonian systems. 2013. Doctoral Thesis - Universidade de São Paulo (USP). Instituto de Física (IF/SBI) São Paulo.

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