Tokamak research at University of S�o Paulo

Nascimento, I. C.; Caldas, Iberê L.; Galvão, R. M. O.

doi:10.1007/bf01079673

Cited by 12 publications

(9 citation statements)

References 17 publications

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“…1 presents experimental data on ionic conductivity of 48 binary sodium silicate glasses ranging from 20°C to 400°C that follows Eq. 1 [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25]. Conductivity data of Wrigth and Shelby [25] were estimated from experimental values of E A and r measured at 500 K. As will be detailed below, Eq.…”

Section: Resultsmentioning

confidence: 99%

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Test of the Anderson–Stuart model and correlation between free volume and the ‘universal’ conductivity in sodium silicate glasses

Nascimento

2007

J Mater Sci

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Experimental ionic conductivity r and activation energy E A data in the binary sodium silicate system are reviewed. Analysis and brief discussion based on 48 glasses in a wide compositional range (between 4 and 45 Na 2 O mol%) are presented. Emphasis is placed on the application of the Anderson-Stuart model to describe the variation of activation energy E A with sodium concentration. In this analysis were considered experimental parameters such as shear modulus G and relative dielectric permittivity e, also in wide compositional range. A 'universal' finding is obtained using log 10 r vs. E A /k B T in 47 of the 48 glasses investigated, where E A is the activation energy for conduction, k B is the Boltzmann constant and T is the absolute temperature. Using conductivity and molar volume from density data, both measured at 20°C in the same glasses, it was found a remarkable common cubic scaling relation between conductivity enhancement of the free volume due to increase in alkali content. The drastic drop in conductivity by 16 orders of magnitude for so many ionconducting binary sodium silicate glasses is then caused by structure and ion content. The effects of shear modulus, relative dielectric permittivity and free volume are taken into account, as also the problem of phase separation. In particular, it is suggested that the glass network expansion, which is related to the available free volume, is a parameter that could partially explain the increase in ionic conductivity for this binary system.

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Section: Resultsmentioning

confidence: 99%

“…These glasses were chosen because, unlike most glasses reported in the literature, data on both density and ionic conductivity were available for the same batch. More details can be found elsewhere [7].…”

Section: Methodsmentioning

confidence: 99%

Test of the Anderson–Stuart model and correlation between free volume and the ‘universal’ conductivity in sodium silicate glasses

Nascimento

2007

J Mater Sci

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“…Plasmas 15, 112304 ͑2008͒ transport considered in this work is lower than the small structure contribution. For the small tokamak TBR, 46 measurements obtained with electrostatic probes show that the potential at the plasma edge is almost linear. Experimental power spectrum analysis of TBR data 47 suggests a frequency of 30 kHz for the first wave and 18 kHz for the second.…”

Section: -4 Marcus Et Almentioning

confidence: 96%

Reduction of chaotic particle transport driven by drift waves in sheared flows

et al. 2008

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Investigations of chaotic particle transport by drift waves propagating in the edge plasma of tokamaks with poloidal zonal flow are described. For large aspect ratio tokamaks, the influence of radial electric field profiles on convective cells and transport barriers, created by the nonlinear interaction between the poloidal flow and resonant waves, is investigated. For equilibria with edge shear flow, particle transport is seen to be reduced when the electric field shear is reversed. The transport reduction is attributed to the robust invariant tori that occur in nontwist Hamiltonian systems. This mechanism is proposed as an explanation for the transport reduction in Tokamak Chauffage Alfvén Brésilien [R. M. O. Galvão et al., Plasma Phys. Controlled Fusion 43, 1181 (2001)] for discharges with a biased electrode at the plasma edge.

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“…(28) We stress that, although the mapping between two successive kicks is exact (within the limitations of our model) the part that treats a kick is obtained through a kind of approximation. Hence, this second part of the map contains higher-order terms that introduce a small dissipative effect.…”

Section: Impulsive Excitation Mapmentioning

confidence: 99%

“…= 0.50T (toroidal field at magnetic axis); 1, = 2~7/5 (rotational transform at plasma edge); 1. = 27r (rotational transform at plasma centre) [28].…”

Section: Phase Portraitsmentioning

confidence: 99%

Magnetic field line mappings for a tokamak with ergodic limiters

Caldas

Pereira

Ullmann

et al. 1996

Chaos, Solitons & Fractals

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Abstract-An ergodic magnetic limiter is a device whose main effect in a tokamak is to create a cold boundary layer of chaotic magnetic field lines. In order to study its effect we have used two approaches. The first is a description of magnetic island formation through an analytical method to describe its dimensions, results being in accordance with numerical Poincare maps for magnetic field lines. The second is a model which simulates the ergodic limiter action as a sequence of impulsive perturbations, enabling the derivation of analytical formulae for the Poincare maps.

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Tokamak research at University of S�o Paulo

Cited by 12 publications

References 17 publications

Test of the Anderson–Stuart model and correlation between free volume and the ‘universal’ conductivity in sodium silicate glasses

Test of the Anderson–Stuart model and correlation between free volume and the ‘universal’ conductivity in sodium silicate glasses

Reduction of chaotic particle transport driven by drift waves in sheared flows

Magnetic field line mappings for a tokamak with ergodic limiters

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