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The standard definition of the diffusion coefficient D uses the limit of the mean square excursion; in a finite (bounded) domain this definition is not relevant. But most physical problems deal with bounded systems. A generalization of D, useful to describe transport in a finite region which is a subset of a bounded system can be obtained from the exit times tau(i) of test particles. This paper gives an analytical relation between D and the tau(i) for diffusive processes. The method is applied to compute an averaged diffusion coefficient for collisional particles in a domain between overlapping islands such as exist in a tokamak magnetic configuration, and a discussion given as to whether this process is of a purely diffusive nature.

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Authors: SABOT R, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);DUBOIS M A, CEA, CEN Saclay, Gif-sur-Yvette (FR)
Bibliographic Reference: Article: Physics Letters A, Vol. 212 (1996) p. 201
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