Introducing FACETS, the Framework Application for Core-Edge Transport Simulations

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 1/2 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

First results from core-edge parallel composition in the FACETS project

FACETS (Framework Application for Core-Edge Transport Simulations), now in its second year, has achieved its first coupled core-edge transport simulations. In the process, a number of accompanying accomplishments were achieved. These include a new parallel core component, a new wall component, improvements in edge and source components, and the framework for coupling all of this together. These accomplishments were a result of an interdisciplinary collaboration among computational physics, computer scientists, and applied mathematicians on the team

An enhanced record of MIS 9 environments, geochronology and geoarchaeology: data from construction of the High Speed 1 (London–Channel Tunnel) rail-link and other recent investigations at Purfleet, Essex, UK

New data from the complex Lower Thames locality at Purfleet, Essex, reinforce the correlation of interglacial deposits there with Marine Isotope Stage (MIS) 9, the second of four post-Anglian (MIS 12) interglacials recorded in the river-terrace sequence east of London. Arising from various developer-funded archaeologically driven projects, and primarily the construction of ‘High Speed 1’ (HS1: formerly the Channel Tunnel Rail Link), the new evidence includes additions to palaeontological knowledge of this interglacial, notably from ostracods and vertebrates, results from isotopic analyses of shell and concretionary carbonates, and the first application of numerical dating techniques at Purfleet. These analyses, combined with palaeotemperature estimates from the Mutual Ostracod Temperate Range method, confirm that deposition of the fossiliferous deposits coincided with interglacial conditions, with similar-to- or warmer-than-present summer temperatures and colder winters, providing a suggestion of greater continentality. OSL and amino-acid racemisation support correlation of the interglacial with MIS 9, whereas the climatic and sedimentological evidence points to correlation with the earliest and warmest substage (MIS 9e). There is also evidence that a greater part of the Purfleet sequence might date from the interglacial, although whether these also represent MIS 9e or later parts of the complex stage cannot be determined. The additional archaeological material is consistent with previous interpretations of a tripartite stratigraphical sequence of lithic traditions: basal Clactonian, above which is Acheulian (handaxe manufacture), followed by one of the earliest British appearances of Levallois technique. However, given the revised interpretation of the climatic affinity of the upper parts of the sequence, Levallois technique might have been used at Purfleet before the end of MIS 9

Perturbative momentum transport in MAST L-mode plasmas

Non-axisymmetric magnetic fields are used to perturbatively probe momentum transport physics in MAST L-mode plasmas. The low beta L-mode target was chosen to complement previous experiments conducted in high beta NSTX H-mode plasmas (β N = 3.5-4.6) where an inward momentum pinch was measured. In those cases quasi-linear gyrokinetic simulations of unstable ballooning micro-instabilities predict weak or outward momentum convection, in contrast to the measurements. The weak pinch was predicted to be due to both electromagnetic effects at high beta and low aspect ratio minimizing the symmetry-breaking of the instabilities responsible for momentum transport. In an attempt to lessen these electromagnetic effects at low aspect ratio, perturbative experiments were run in MAST L-mode discharges at lower beta (β N = 2). The perturbative transport analysis used the time-dependent response following the termination of applied 3D fields that briefly brake the plasma rotation (similar to the NSTX H-mode experiments). Assuming time-invariant diffusive (χ ℓ) and convective (V ℓ) transport coefficients, an inward pinch is inferred with magnitudes, (RV ℓ/χ ℓ) = (-1)-(-9), similar to those found in NSTX H-modes and in conventional tokamaks. However, if experimental uncertainties due to non-stationary conditions during and after the applied 3D field are considered, a weak pinch or even outward convection is inferred, (RV ℓ/χ ℓ) = (-1)-(+5). Linear gyrokinetic simulations indicate that for these lower beta L-modes, the predicted momentum pinch is predicted to be relatively small, (RV ℓ/χ ℓ) sim ≈ -1. While this falls within the experimentally inferred range, the uncertainties are practically too large to quantitatively validate the predictions. Challenges and implications for this particular experimental technique are discussed, as well as additional possible physical mechanisms that may be important in understanding momentum transport in these low aspect ratio plasmas. </p