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The Continuous Time Random Walk (CTRW) provides a mathematical framework for the study of transport in heterogenous media. It is much more general than usual transport models based on (local) Ordinary Differential Equations, and in particular can handle transport in systems without characteristic scales (such as systems in a state of [[Self-Organised Criticality]] or SOC). | The Continuous Time Random Walk (CTRW) provides a mathematical framework for the study of transport in heterogenous media. It is much more general than usual transport models based on (local) Ordinary Differential Equations, and in particular can handle transport in systems without characteristic scales (such as systems in a state of [[Self-Organised Criticality]] or SOC). | ||
== Motivation == | |||
Interestingly, the absence of local characteristic scales means that ''effective'' transport coefficients (the diffusivity etc.) become dependent on the system size, as is indeed suggested by experimental scaling laws for plasma confinement. | |||
In the framework of transport in plasmas, it is believed that the presence of ''trapping regions'' (such as turbulent eddies, magnetic islands, internal transport barriers) may lead to [[Non-diffusive transport|sub-diffusion]], whereas the occurrence of ''streamers'' and profile self-regulation (via [[TJ-II:Turbulence|turbulence]]) may lead to [[Non-diffusive transport|super-diffusion]]. | In the framework of transport in plasmas, it is believed that the presence of ''trapping regions'' (such as turbulent eddies, magnetic islands, internal transport barriers) may lead to [[Non-diffusive transport|sub-diffusion]], whereas the occurrence of ''streamers'' and profile self-regulation (via [[TJ-II:Turbulence|turbulence]]) may lead to [[Non-diffusive transport|super-diffusion]]. | ||