arXiv subjects

Wayne Arter

Publications and source records attributed to Wayne Arter.

8 recordsLinked to original sources

arXiv2018

Stability of scrape-off layer plasma: a modified Rayleigh-Benard problem

We present a linear stability analysis of a two-dimensional fluid model used to study the plasma dynamics in the scrape-off layer of tokamaks. The model equations are based on the Braginskii fluid equations under the assumptions of drift ordering and an electrostatic plasma. The model also employs the common slab geometry approximation, whereby the magnetic field is assumed constant and straight, with the effects of curvature reintroduced as effective gravitational terms. We demonstrate that the governing plasma equations for the scrape-off layer can be viewed as describing a thermal convection problem with additional effects. The new features include a non-uniform basic state gradient, linear damping terms, and additional advective terms. We characterise the conditions at the onset of instability, and perform an extensive parameter scan to describe how the stability threshold varies as a function of plasma parameters.

physics.plasm-ph↗

arXiv2016

Beyond Linear Fields: the Lie-Taylor Expansion

The work extends the linear fields' solution of compressible nonlinear magnetohydrodynamics~(MHD) to the case where the magnetic field depends on superlinear powers of position vector, usually but not always, expressed in Cartesian components. Implications of the resulting Lie-Taylor series expansion for physical applicability of the Dolzhansky-Kirchhoff~(D-K) equations are found to be positive. It is demonstrated how resistivity may be included in the D-K model. Arguments are put forward that the D-K equations may be regarded as illustrating properties of nonlinear MHD in the same sense that the Lorenz equations inform about the onset of convective turbulence. It is suggested that the Lie-Taylor series approach may lead to valuable insights into other fluid models.

math-ph↗

arXiv2016

Ranking the importance of nuclear reactions for activation and transmutation events

Pathways-reduced analysis is one of the techniques used by the Fispact-II nuclear activation and transmutation software to study the sensitivity of the computed inventories to uncertainties in reaction cross-sections. Although deciding which pathways are most important is very helpful in for example determining which nuclear data would benefit from further refinement, pathways-reduced analysis need not necessarily define the most critical reaction, since one reaction may contribute to several different pathways. This work examines three different techniques for ranking reactions in their order of importance in determining the final inventory, comparing the pathways based metric (PBM), the direct method and one based on the Pearson correlation coefficient. Reasons why the PBM is to be preferred are presented.

physics.comp-ph↗

arXiv2016

Power Deposition on Tokamak Plasma-Facing Components

The SMARDDA software library is used to model plasma interaction with complex engineered surfaces. A simple flux-tube model of power deposition necessitates the following of magnetic fieldlines until they meet geometry taken from a CAD (Computer Aided Design) database. Application is made to 1) models of ITER tokamak limiter geometry and 2) MASTU tokamak divertor designs, illustrating the accuracy and effectiveness of SMARDDA, even in the presence of significant nonaxisymmetric ripple field. SMARDDA's ability to exchange data with CAD databases and its speed of execution also give it the potential for use directly in the design of tokamak plasma facing components.

physics.plasm-ph↗

arXiv2014

The SMARDDA Approach to Ray-Tracing and Particle Tracking

There is an increasing need to model plasma interaction with complex engineered surfaces, notably to verify that power deposition rates are acceptable. The SMARDDA algorithm has been developed to meet this requirement, with particular reference to the neutral beam ducts that feed into the vacuum vessels of tokamaks. Application to limiters and divertors is made in a companion paper. The algorithm is described in detail, highlighting key novel features, and illustrative duct calculations presented.

physics.plasm-ph↗

arXiv2014

An Anti-Perfect Dynamo Result

It is shown that if the flow vector is a coordinate basis vector, then perfect dynamo action is not possible, regardless of whether the steady flow is compressible. Criteria determining the basis vector property are found to be expressible in terms of Lie derivatives, and construction of basis vector sets is straightforward.

physics.plasm-ph↗

arXiv2014

Geometric Results for Compressible Magnetohydrodynamics

Recently, compressible magnetohydrodynamics (MHD) has been elegantly formulated in terms of Lie derivatives. This paper exploits the geometrical properties of the Lie bracket to give new insights into the properties of compressible MHD behaviour, both with and without feedback of the magnetic field on the flow. These results are expected to be useful for the solution of MHD equations in both tokamak fusion experiments and space plasmas.

physics.plasm-ph↗

arXiv2012

Potential Vorticity Formulation of Compressible Magnetohydrodynamics

Compressible ideal magnetohydrodynamics (MHD) is formulated in terms of the time evolution of potential vorticity and magnetic flux per unit mass using a compact Lie bracket notation. It is demonstrated that this simplifies analytic solution in at least one very important situation relevant to magnetic fusion experiments. Potentially important implications for analytic and numerical modelling of both laboratory and astrophysical plasmas are also discussed.

physics.plasm-ph↗