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Non-diffusive transport: Difference between revisions
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In recent years, it has been suggested that the plasma may contain phenomena that invalidate this picture. | In recent years, it has been suggested that the plasma may contain phenomena that invalidate this picture. | ||
There may ''turbulent eddies'' in which particles become trapped for some time, and there certainly are ''transport barriers'', associated with rational magnetic surfaces, and ''stochastic regions'' of the magnetic field. This could cause the waiting time distribution to become non-exponential; and thus the motion would be non-Markovian. Likewise, the phenomenon of ''streamers'', appearing in many models of plasma turbulence, could carry particles across long distances in the radial direction, and the distribution of particle steps could then also be deformed and develop ''long tails''. Consequently, the transport would then be non-local. Nobody knows exactly how important these phenomena are in the global transport picture. | There may ''turbulent eddies'' in which particles become trapped for some time, and there certainly are ''transport barriers'', associated with rational magnetic surfaces, and ''stochastic regions'' of the magnetic field. | ||
<ref>[http://dx.doi.org/10.1088/0741-3335/44/7/101 J.H. Misguich at el., Plasma Phys. Controlled Fusion, '''44''', L29 (2002)]</ref> | |||
This could cause the waiting time distribution to become non-exponential; and thus the motion would be non-Markovian. Likewise, the phenomenon of ''streamers'', appearing in many models of plasma turbulence, could carry particles across long distances in the radial direction, and the distribution of particle steps could then also be deformed and develop ''long tails''. Consequently, the transport would then be non-local. Nobody knows exactly how important these phenomena are in the global transport picture. | |||
Whatever the case, a well-established methodology exists to describe this deviation from standard diffusive transport (with characteristic scales): the Continuous Time Random Walk (CTRW) model. | Whatever the case, a well-established methodology exists to describe this deviation from standard diffusive transport (with characteristic scales): the Continuous Time Random Walk (CTRW) model. | ||