870 research outputs found
Química e cidadania : uma abordagem a partir do desenvolvimento de atividades experimentais investigativas
Este trabalho teve por objetivo analisar a contribuição da abordagem investigativa para a resolução de problemas visando o desenvolvimento da cidadania por alunos do primeiro ano do Ensino Médio da rede pública de ensino brasileira, quando envolvidos em atividades experimentais investigativas que versaram sobre situações sociocientíficas controversas relacionadas ao tema “combustíveis”. A coleta de dados se deu por meio da aplicação de um minicurso de quarenta horas para uma turma de oito alunos. A abordagem proposta auxiliou os alunos no processo de tomada de decisão e contribuiu também para o desenvolvimento e aprendizagem de conteúdos conceituais, procedimentais e atitudinais, proporcionando aos mesmos uma visão mais adequada da ciência, ou seja, uma atividade humana em permanente construção
Designing high efficiency glow discharge cleaning systems
In this paper we present our studies about the choices of anode design and operational regime in order to get high efficiency glow discharge cleaning of the first wall of a fusion device. We analyzed a database of toroidal and poloidal profiles of the ion current density at the wall, measured by electrostatic probes embedded in RFX-mod first wall tiles, taken in different configurations. The ion current at the wall, both global and local, is in fact strictly connected to the cleaning efficiency, since during glow discharge the wall is physically sputtered by the ions. We found that small size anodes and high in-vessel pressure lead to the peaking of the current profile around the anodes locations, and we experimentally characterized this effect. Instead, we found that anode radial position in the poloidal section has negligible effect on current density profile, even when the anodes are placed at the first wall. Finally, the most convenient operational regime, in terms of pressure and current, has been proposed. Keywords: RFX-mod, Glow discharge, Wall cleaning, Ion current profile, Anode desig
Microturbulence studies in RFX-mod
Present-days Reversed Field Pinches (RFPs) are characterized by quasi-laminar
magnetic configurations in their core, whose boundaries feature sharp internal
transport barriers, in analogy with tokamaks and stellarators. The abatement of
magnetic chaos leads to the reduction of associated particle and heat transport
along wandering field lines. At the same time, the growth of steep temperature
gradients may trigger drift microinstabilities. In this work we summarize the
work recently done in the RFP RFX-mod in order to assess the existence and the
impact upon transport of such electrostatic and electromagnetic
microinstabilities as Ion Temperature Gradient (ITG), Trapped Electron Modes
(TEM) and microtearing modes.Comment: Work presented at the 2010 Varenna workshop "Theory of Fusion
Plasmas". To appear in Journal of Physics Conference Serie
Resistive g-modes in a reversed field pinch plasma
First direct experimental evidence of high frequency, high toroidal mode
number (n>20), magnetic fluctuations due to unstable resistive interchange
modes (g-modes) resonant in the edge region of a reversed field pinch (RFP)
plasma is presented. Experimental characterization of time and space
periodicities of the modes is provided by means of highly resolved in-vessel
edge and insertable magnetic diagnostics. It is found that the spectral mode
properties are in good agreement with the predictions of the theoretical linear
resistive magnetohydrodynamic stability analysis. A simple model is proposed
for the observed saturation levels of the modes.Comment: Submitted to Physical Review Letter
Electromagnetic filaments and edge modifications induced by electrode biasing in the RFX-mod tokamak
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