Anomalous Diffusivity Research Articles

Theory of anomalous tearing mode growth and the major tokamak disruption

An analytic theory of turbulence in reduced resistive magnetohydrodynamics is developed and applied to the major disruption in tokamaks. The renormalized equations for a long-wavelength tearing instability are derived. The theory predicts two principal nonlinear effects: an anomalous flux diffusivity due to turbulent fluid convection in Ohm’s law and a vorticity damping term due to turbulent magnetic stresses in the equation of motion. In the final phase of the disruption, when fine-scale fluid turbulence has been generated, detailed considerations show that anomalous diffusivity has the dominant effect at long wavelengths. For a low-m tearing mode, the solution of the renormalized equations during the turbulent phase yields a growth rate analogous to the classical case but increased by turbulent resistivity: γ∼(∑k′ k′2θ‖φk′‖2)3/8 ×(Δ′)1/2. This analytical prediction is in good accord with computational results.

Thermodynamic and kinetic properties of indium-implanted silicon I: Moderate temperature recovery of the implant damage and metastability effects

Rutherford backscattering analysis and junction depth and sheet conductivity measurements were used to investigate the recrystallization of indium-implanted Si(100) substrates and their electrical behaviour after annealings up to 800 °C. The data show an initial fast recovery of the implant damage and a high anomalous indium diffusivity. A strong correlation between the substitutionality of indium and the sheet conductivity is found. The observed conductivity decrease with increasing annealing temperature is attributed to the loss of substitutionality by the indium.

Anomalous transport effects in magnetically-confined plasma columns

The evolution of density structure in a magnetized plasma column is analyzed accounting for anomalous diffusion due to the lower hybrid drift instability. The plasma column is found to be divided into regions of classical, anomalous, and intermediate diffusivity. The bulk behavior, described in terms of radial confinement time, depends most sensitively upon the particle line density (ion/cm). For broad plasmas (large line density), the transport is characteristic of classical diffusion, and for slender plasmas (small line density) the transport is characteristic of anomalous diffusion. For intermediate line densities, the transport undertakes a rapid transition from classical to anomalous. Correlations between the theoretical results and past experiments are described.

Sorption of tritium by nickel during plastic deformation

The effect of plastic deformation on the amount of tritium absorbed, the surface concentration, and the apparent diffusivity was determined by comparing elastically and plastically deformed sections of nickel tensile tubes that were filled with tritium during deformation. Plastic deformation increased the amount of tritium absorbed by the metal and adsorbed on the surface, but decreased the apparent diffusivity. These data for nickel can be explained by the trapping theory developed primarily to explain anomalous hydrogen diffusivity and solubility in iron, where the dislocations created during deformation are postulated to trap the tritium, thereby producing higher values for interior and surface tritium concentrations and lower values for tritium diffusivity.

Diffusion of Nickel in Amorphous Silicon Dioxide and Silicon Nitride Films

Nickel-59 radiotracer has been used to determine nickel diffusion coefficients in amorphous silicon dioxide and silicon nitride films between 1100° and 1490°K. Nickel distribution has been found to be Fickian with the calculated diffusivities obeying Arrhenius equation. Long diffusion times have been found to produce anomalous diffusivities in silicon nitride.