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Fusion Research Center

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https://hdl.handle.net/1853/70733

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George W. Woodruff School of Mechanical Engineering

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Publication Search Results

Now showing 1 - 10 of 17

Investigation of background edge thermal transport in ELMing and ELM-suppressed H-modes in DIII-D

(Georgia Institute of Technology, 2006-11-17) Stacey, Weston M. ; Evans, T. E.

Thermal diffusivities are inferred in the plasma edge of a matched pair of DIII-D [J. Luxon, Nucl. Fusion 42, 614 (2002)] high confinement mode discharges, one with edge localized modes (ELMs) present and the other with ELMs suppressed by resonant magnetic perturbations. These experimentally inferred thermal diffusivity profiles are compared with the predictions of a variety of thermal transport theories.
Higher Order Approximations of the TEP Method for Neutral Particle Transport in Edge Plasmas

(Georgia Institute of Technology, 2006) Stacey, Weston M. ; Zhang, Dingkang ; Mandrekas, John

Higher 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.
Thermal 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.
Nuclear 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.
A neoclassical calculation of toroidal rotation profiles and comparison with DIII-D measurements

(Georgia Institute of Technology, 2006) Stacey, Weston M. ; Johnson, R. W. ; Mandrekas, John

Momentum 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.
Application of a particle, momentum and energy balance model to calculate the structure of the edge pedestal in DIII-D

(Georgia Institute of Technology, 2005-04) Stacey, Weston M. ; Groebner, Rich J.

A calculation of edge density and temperature profiles based on "classical" physics - particle, momentum and energy balance, heat conduction closure relations, neutral particle transport - yielded a pedestal structure that is qualitatively and quantitatively similar to that found experimentally in five DIII-D [J. Luxon, Nucl. Fusion,42, 614 (2002)] discharges, when experimental radial electric field and rotation profiles and experimentally inferred heat transport coefficients were used. The principal cause of the density pedestal was a peaking of the inward pinch velocity just inside the separatrix caused by the negative well in the experimental electric field, and the secondary cause was a peaking of the radial particle flux caused by the ionization of incoming neutrals. There is some evidence that this peaking of the radial particle flux just inside the separatrix may also be responsible in part for the negative electric field in that location.
Sub-critical Transmutation Reactors with Tokamak Fusion Neutron Sources

(Georgia Institute of Technology, 2005) Stacey, Weston M. ; Mandrekas, John ; Hoffman, E. A. (Elisha Albright)

The principal results of a series of design scoping studies of sub-critical fast transmutation reactors (based on the nuclear and processing technology being developed in the USDoE Generation IV, Advanced Fuel Cycle and Next Generation Nuclear Plant programs) coupled with a tokamak fusion neutron source (based on the ITER design basis physics and technology) are presented.
Transmutation 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.
Edge Pedestal Structure

(Georgia Institute of Technology, 2004-12) Stacey, Weston M.

The hypothesis is advanced and investigated that, in between or in the absence of ELMs (edge-localized-modes), the structure of the edge pedestal is determined by the transport requirements of plasma particle, momentum and energy balance and recycling neutral atoms. "Pedestal equations" following from this hypothesis are presented and applied to calculate the edge density, temperature, rotation velocity and radial electric field profiles in a DIII-D H (high)-mode plasma. A distinct pedestal structure in the density and temperature profiles and sharp negative peaks in the radial electric field and poloidal velocity just inside the separatrix are predicted, in qualitative and quantitative agreement with measured values. Details of the calculation are discussed.
Structure of the edge density pedestal in tokamaks

(Georgia Institute of Technology, 2004-09) Stacey, Weston M.

A 'first-principles' model for the structure of the edge density pedestal in tokamaks between or in the absence of edge localized magnetohyrodynamic instabilities is derived from ion momentum and particle conservation and from the transport theory of recycling neutral atoms. A calculation for (high) H-mode tokamak discharge parameters indicates that the equations have a self-consistent solution which has an edge pedestal in the ion density profile and sharp negative spikes in the poloidal velocity and radial electric field profiles in the edge pedestal, features characteristic of H-mode edge profiles. These sharp negative spikes in radial electric field and poloidal rotation produce a peak in the inward ion pinch velocity in the sharp gradient (pedestal) region which produces an edge particle transport barrier. The calculated magnitude of the density at the top of the pedestal and the density gradient scale length and radial electric field in the pedestal region are comparable to measured values.