4,466 research outputs found
Dynamical Alignment in Three Species Tokamak Edge Turbulence
Three dimensional computations of self consistent three species gyrofluid
turbulence are carried out for tokamak edge conditions. Profiles as well as
disturbances in dependent variables are followed, running the dynamical system
to transport equilibrium. The third species density shows a significant
correlation with that of the electrons, regardless of initial conditions and
drive mechanisms. For decaying systems the densities evolve toward each other.
Companion tests with a simple two dimensional drift wave model show this
persists even if the third species is a passively advected test field.
Similarity in the transport character of electrons and the trace species does
not imply that the electrons themselves have a test particle transport
character.Comment: RevTeX 4, 21 pages, 15 figures, submitted to Physics of Plasma
Zonal Flows and Electromagnetic Drift Wave Turbulence
Detailed computations of tokamak edge turbulence in three dimensional,
globally consistent flux tube geometry show an inhibition of the standard
scenario in which zonal ExB flows generated by the turbulence should lead to
transport barrier formation. It is found by comparison to slab geometry and by
analysis of the energetics that the zonal flow energy is depleted by toroidal
coupling to the pressure through the geodesic curvature. Edge transport
barriers would then depend on the physics of the neoclassical equilibrium.Comment: 14 pages including 5 figures, submitted to Physics Letters
Derivation via free energy conservation constraints of gyrofluid equations with finite-gyroradius electromagnetic nonlinearities
The derivation of electromagnetic gyrofluid equations is made systematic by
using the Hermite polynomial form of the underlying delta-f gyrokinetic
distribution function. The gyrokinetic free-energy functional is explicitly
used to set up the model. The gyrofluid free energy follows directly. The
interaction term in the gyrokinetic Lagrangian is used to obtain the gyrofluid
counterpart, from which the polarisation equation follows. One closure rule is
decided for taking moments over the kinetic gyroaveraging operator. These steps
fix the rest of the derivation of the conservative part of the gyrofluid
equations. Dissipation is then added in a form to obtain positive definite
dissipation and to obtain the collisional fluid equations in their appropriate
limit. Existing results are recovered, with the addition of a completely
consistent model for finite gyroradius effects in the nonlinearities
responsible for magnetic reconnection.Comment: RevTeX 4, 39 pages, no figures, submitted to Physics of Plasmas. From
version 1, corrected minor errors in equations, re-did some explanations,
added some references, From version 2, added a section on correspondence to
fluid/MHD models as asked by the referee. This version was accepted by
Physics of Plasma
Flux surface shaping effects on tokamak edge turbulence and flows
Shaping of magnetic flux surfaces is found to have a strong impact on
turbulence and transport in tokamak edge plasmas. A series of axisymmetric
equilibria with varying elongation and triangularity, and a divertor
configuration are implemented into a computational gyrofluid turbulence model.
The mechanisms of shaping effects on turbulence and flows are identified.
Transport is mainly reduced by local magnetic shearing and an enhancement of
zonal shear flows induced by elongation and X-point shaping.Comment: 10 pages, 11 figures. Submitted to Physics of Plasma
Science for Place-based Socioecological Management: Lessons from the Maya Forest (Chiapas and Petén)
The role humans should play in conservation is a pervasive issue of debate in environmental thinking. Two long-established poles of this debate can be identified on a preservation-sustainable use continuum. At one extreme are use bans and natural science-based, top-down management for preservation. At the other extreme is community-based, multidisciplinary management for sustainable resource use and livelihoods. In this paper, we discuss and illustrate how these two strategies have competed and conflicted in conservation initiatives in the Maya forest (MF) of the Middle Usumacinta River watershed (Guatemala and Mexico). We further argue that both extremes have produced unconvincing results in terms of the region’s sustainability. An alternative consists of sustainability initiatives based on place-based and integrated-knowledge approaches. These approaches imply a flexible combination of disciplines and types of knowledge in the context of nature-human interactions occurring in a place. They can be operationalized within the framework of sustainability science in three steps: 1) characterize the contextual circumstances that are most relevant for sustainability in a place; 2) identify the disciplines and knowledge(s) that need to be combined to appropriately address these contextual circumstances; and 3) decide how these disciplines and knowledge can be effectively combined and integrated. Epistemological flexibility in the design of analytic and implementation frameworks is key. Place-based and integrative-knowledge approaches strive to deal with local context and complexity, including that of human individuals and cultures. The success of any sustainability initiative will ultimately depend on its structural coupling with the context in which it is applied
Nonlinear polarisation and dissipative correspondence between low frequency fluid and gyrofluid equations
The correspondence between gyrofluid and low frequency fluid equations is
examined. The lowest order conservative effects in ExB advection, parallel
dynamics, and curvature match trivially. The principal concerns are
polarisation fluxes, and dissipative parallel viscosity and parallel heat
fluxes. The emergence of the polarisation heat flux in the fluid model and its
contribution to the energy theorem is reviewed. It is shown that gyroviscosity
and the polarisation fluxes are matched by the finite gyroradius corrections to
advection in the long wavelength limit, provided that the differences between
gyrocenter and particle representations is taken into account. The dissipative
parallel viscosity is matched by the residual thermal anisotropy in the
gyrofluid model in the collision dominated limit. The dissipative parallel heat
flux is matched by the gyrofluid parallel heat flux variables in the collision
dominated limit. Hence, the gyrofluid equations are a complete superset of the
low frequency fluid equations.Comment: RevTeX 4, 28 pages, no figures, final revised version for Physics of
Plasmas prior to proof stag
Practical applications of data mining in plant monitoring and diagnostics
Using available expert knowledge in conjunction with a structured process of data mining, characteristics observed in captured condition monitoring data, representing characteristics of plant operation may be understood, explained and quantified. Knowledge and understanding of satisfactory and unsatisfactory plant condition can be gained and made explicit from the analysis of data observations and subsequently used to form the basis of condition assessment and diagnostic rules/models implemented in decision support systems supporting plant maintenance. This paper proposes a data mining method for the analysis of condition monitoring data, and demonstrates this method in its discovery of useful knowledge from trip coil data captured from a population of in-service distribution circuit breakers and empirical UHF data captured from laboratory experiments simulating partial discharge defects typically found in HV transformers. This discovered knowledge then forms the basis of two separate decision support systems for the condition assessment/defect clasification of these respective plant items
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