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ItemNon-Diffusive Transport in the Tokamak Edge Pedestal(Georgia Institute of Technology, 2012) Stacey, Weston M. ; Groebner, Rich J. ; Evans, T. E.There are (at least) two classical mechanisms for non-diffusive transport in the edge plasma: i) particle “pinch” velocities due to forces such as VxB, and Er; and ii) outward drifts due to ion-orbit loss and X-transport. A theoretical development for the treatment of these non-diffusive transport mechanisms within the context of fluid theory is assembled and applied to several DIII-D discharges in order to investigate the importance of these non-diffusive transport mechanisms in the edge pedestal. Several interesting insights emerge from this investigation.
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ItemEvolution of the H-mode edge pedestal between ELMs(Georgia Institute of Technology, 2010-08) Stacey, Weston M. ; Groebner, Rich J.The evolution of edge pedestal parameters between edge-localized modes (ELMs) is analyzed for an H-mode DIII-D [J Luxon, Nucl. Fusion 42, 612 (2002)] discharge. Experimental data are averaged over the same sub-intervals between successive ELMs to develop data that characterize the evolution of density, temperature, rotation velocities, etc. over the interval between ELMs. These data are interpreted within the context of the constraints imposed by particle, momentum and energy balance, in particular in terms of the pinch-diffusion relation for radial particle flux that is required by momentum balance. It is found that in the edge pedestal there is an increase of both inward (pinch) electromagnetic and outward (diffusive) pressure gradient forces over the inter-ELM interval.
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ItemHigher Order Approximations of the TEP Method for Neutral Particle Transport in Edge Plasmas(Georgia Institute of Technology, 2006) Stacey, Weston M. ; Zhang, Dingkang ; Mandrekas, JohnHigher order approximations, which take into account the effects of angular anisotropy, spatial non-uniformity and energy dependence of the distribution of neutral particles, have been developed and implemented to extend the range of validity of the Transmission and Escape Probabilities (TEP) method for the calculation of neutral particle transport in plasmas. Comparisons with Monte Carlo calculations of model test problems and DIII-D L- and H- mode discharges show that these new extensions significantly improve the accuracy and extend the range of validity of the TEP methodology.
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ItemThermal Transport in the DIII-D Edge Pedestal(Georgia Institute of Technology, 2006) Stacey, Weston M. ; Groebner, Rich J.A new procedure for inferring χ[subscript i,e] in the plasma edge from experimental data and integrated modeling code calculations has been developed which takes into account atomic physics and radiation effects and convective as well as conductive heat flux profiles. Application to DIII-D shots indicates that the sharp temperature gradient pedestal region may be caused as much, if not more, by an increase (with radius) of the conductive heat flux as by a decrease of the thermal transport coefficient. Inferred χ[subscript i,e][superscript exp] are compared with theoretical predictions.
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ItemNuclear Mission for Fusion (Transmutation, fissle breeding and Pu dispostion)(Georgia Institute of Technology, 2006) Stacey, Weston M.There are potential applications of fusion neutron sources to 'drive' sub-critical fission reactors to perform one or more possible 'nuclear' missions. Since only a fraction of the neutrons in these applications would be fusion neutrons, the requirements are modest relative to the requirements for pure fusion electrical power (e.g. for the transmutation mission-- fusion power P[subscript fus] ≤ 250 MW, fusion power density β [subscript N] ≤ 2.5, 14 MeV neutron wall load Γ[subscript n] < 1 MW/m² and power amplification Q[subscript p] ≤ 2). A sub-critical, source-driven reactor almost certainly would be more expensive and initially would have lower availability than a conventional critical reactor, because of the additional cost and lower initial availability of the fusion or accelerator neutron source. In order to be competitive with a critical reactor for a given mission, a sub-critical reactor must introduce certain advantages that allow the mission to be carried out more efficiently, and there appear to be such advantages. Making use of ITER physics and technology, using ITER as a prototype, and adopting the reactor and processing technology being developed in the nuclear program could lead to a fusion-driven sub-critical reactor for the transmutation of spent nuclear fuel, fissile breeding or disposition of weapons-grade plutonium being on-line by 2040, as compared to the plans for putting critical and accelerator-driven sub-critical reactors on-line for such missions by 2030. All of the R and D needed to develop the fusion neutron source for such a facility is directly on the path to fusion power (in fact is needed for an electric power DEMO); and the operation of a fusion-driven sub-critical reactor could also serve the purposes envisioned for a ‘volume neutron source’, thus taking the place of such a device in the development path to fusion power.
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ItemA neoclassical calculation of toroidal rotation profiles and comparison with DIII-D measurements(Georgia Institute of Technology, 2006) Stacey, Weston M. ; Johnson, R. W. ; Mandrekas, JohnMomentum and particle balance and neoclassical viscosity were applied to calculate the radial profile of toroidal rotation velocity in several DIII-D [J. Luxon, Nucl. Fusion, 42, 614 (2002)] discharges in a variety of energy confinement regimes (Lowmode, Low-mode with Internal Transport Barrier, High-mode, and High-mode with Quiescent Double Barrier). Calculated toroidal rotation velocities generally were found to (over-) predict measured values to well within a factor of 2.
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ItemTransmutation missions for fusion neutron sources(Georgia Institute of Technology, 2005) Stacey, Weston M.There are a number of potential neutron transmutation missions (destruction of long-lived radioisotopes in spent nuclear fuel, ‘disposal’ of surplus weapons grade plutonium, ‘breeding’ of fissile nuclear fuel) that perhaps best can be performed in sub-critical nuclear reactors driven by a neutron source. The requirements on a tokamak fusion neutron source for such transmutation missions are significantly less demanding than for commercial electrical power production. A tokamak fusion neutron source based on the current physics and technology database (ITER design base) would meet the needs of the spent nuclear fuel transmutation mission; the technical issue would be achieving ≥ 50% availability, which would require advances in component reliability and in steady-state physics operation.