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Non-diffusive transport: Difference between revisions
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It has long been known that the standard model for transport in magnetically confined plasmas ([[Neoclassical transport]]) often fails to provide an accurate description of experimental results: it tends to underestimate transport by one order of magnitude or more, typically. This is a very disappointing situation with a view to constructing a fusion reactor, since worse confinement means that an eventual reactor will need to be bigger and more expensive. Therefore, the search for the cause of this failure (and for methods to restore transport to its Neoclassical value) is one of the main issues of fusion research. | It has long been known that the standard model for transport in magnetically confined plasmas ([[Neoclassical transport]]) often fails to provide an accurate description of experimental results: it tends to underestimate transport by one order of magnitude or more, typically; the non-Neoclassical component of transport is called "[[Anomalous transport|anomalous]]". This is a very disappointing situation with a view to constructing a fusion reactor, since worse confinement means that an eventual reactor will need to be bigger and more expensive. Therefore, the search for the cause of this failure (and for methods to restore transport to its Neoclassical value) is one of the main issues of fusion research. | ||
The standard Neoclassical model is a collisional (diffusive) model, which means that transport is characterised by ''typical scale lengths'', both for space and time, so that the effective diffusion coefficient is essentially the ''mixing length'' value: <math>D = \Delta r^2 / \Delta t</math>, where <math>\Delta r</math> is the typical step size and <math>\Delta t</math> the typical waiting time. | The standard Neoclassical model is a collisional (diffusive) model, which means that transport is characterised by ''typical scale lengths'', both for space and time, so that the effective diffusion coefficient is essentially the ''mixing length'' value: <math>D = \Delta r^2 / \Delta t</math>, where <math>\Delta r</math> is the typical step size and <math>\Delta t</math> the typical waiting time. | ||