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[en] The FACETS (Framework Application for Core-Edge Transport Simulations) project began in January 2007 with the goal of providing core to wall transport modeling of a tokamak fusion reactor. This involves coupling previously separate computations for the core, edge, and wall regions. Such a coupling is primarily through connection regions of lower dimensionality. The project has started developing a component-based coupling framework to bring together models for each of these regions. In the first year, the core model will be a 1 dimensional model (1D transport across flux surfaces coupled to a 2D equilibrium) with fixed equilibrium. The initial edge model will be the fluid model, UEDGE, but inclusion of kinetic models is planned for the out years. The project also has an embedded Scientific Application Partnership that is examining embedding a full-scale turbulence model for obtaining the crosssurface fluxes into a core transport code.
[en] Using analytical methods, the authors study the reasons for the formation of a magnetic-surface island structure in the central region of l=3 stellarator and torsatron magnetic configurations. Possible methods of substantially reducing the dimensions of this structure at minimum magnetic-configuration distortions are discussed. Magnetic configurations are considered both in vacuum and in the presence of a plasma. (author)
[en] The application of non-axisymmetric magnetic perturbations has been demonstrated to destabilize edge-localized modes (ELMs) in the National Spherical Torus Experiment. A model 3D equilibrium has been calculated for these experiments using the VMEC code, which assumes nested flux surfaces and therefore that resonant perturbations are shielded. First, a free-boundary equilibrium is calculated using the NSTX coil set, with pressure and current profiles matched to a standard 2D reconstruction, but with up-down symmetry enforced. A new equilibrium is then calculated with the n = 3 field applied at a level consistent with experiment. This equilibrium is then used as the basis of further calculations using codes developed for analysis of stellarator plasmas. The neoclassical transport due to the 3D fields is calculated to be small compared with the experimental transport rates. Initial stability analysis has been performed, and indicates a modest degradation in ballooning stability with 3D fields applied. A new 3D equilibrium is also calculated using the SIESTA code, which allows for the formation of islands and stochastic regions. A comparison of the field structure between the SIESTA calculation and the assumption of fully penetrated vacuum perturbation indicates smaller island sizes and very small stochastic transport in the SIESTA case.
[en] The problem of collisional transport for a non-axisymmetric and collision-dominated plasma is considered by assuming the existence of a family of closed, nested and slowly time-dependent, toroidal magnetic surfaces. Two possible collision-dominated regimes are considered which correspond to two physically meaningful asymptotic orderings related, respectively, to the existence of weak and strong diamagnetic particle drifts. (author)
[pt]O problema do transporte colisional para um plasma nao axisimetrico e dominado por colisoes e considerado, assumindo se a existencia de uma familia de superficies magneticas toroidais, fechadas, aninhadas e fracamente dependente do tempo. Dois possiveis regimes dominados por colisoes sao considerados, os quais correspondem a ordenamentos assimptoticos fisicamente significativos relacionados, respectivamente a existencia de flutuacoes de particulas diamagneticas fracas e fortes. (M.C.K.)
[en] A Taylor-relaxed plasma (j=kB with k a constant) under external magnetic helicity injection encounters resonances in spatial frequencies of its force-free eigenmodes. Such driven resonance underlies the physics of magnetic self-organization and determines the flux amplification in laboratory helicity injection applications. Here we show that for partially relaxed plasmas where the deviation from the fully relaxed Taylor state, for example, a flux-dependent k, is a function of the normalized flux χ/χa with χa the poloidal flux at the magnetic axis, a modified driven resonance persists even if k(χ) has an order-unity variation across the flux surfaces
[en] Outward electron orbits that extend to the inward part of a closed helical vacuum magnetic region are found in three-dimensional calculations, which take into account two experimental findings. The pitch angle of electrons in the stochastic magnetic region (SMR) is scattered considerably due to the presence of a shifted self-space potential φs. Eventually, the electron becomes a helically trapped particle, and starts an inward movement along one of the |Bmin| contours. Once penetrating into the helical magnetic region, the electron is never lost to the chamber wall, because the negative φs in the SMR acts as a potential barrier.