Field line separation and particle-field line decorrelation in a stochastic magnetic fieldFunded under: FP3-FUSION 11C
The separation of neighbouring field lines in a stochastic magnetic field is studied by using, for the latter, correlation functions consistent with all relevant constraints. Significant differences are found with respect to earlier studies that did not fully take into account the latter constraints. In particular, exponentiation lengths of both signs are found, describing in particular a decay (on the average) of any initial anisotropy. The vanishing sum of these exponentiation lengths ensures the existence of an invariant which was overlooked in previous works. Next, the separation of a particle's trajectory from the magnetic field line to which it was initially attached is studied by a similar method. Here too, an initial phase of exponential separation appears. Assuming the existence of a final diffusive phase, anomalous diffusion coefficients are determined. In the strongly collisional regime, this result is identical with the well-known Rechester-Rosenbluth coefficient, which is obtained here by a more quantitative (though not entirely deductive) treatment. In the weakly collisional case, a new expression for the diffusion coefficient is found. The limit of a collisionless plasma is discussed in detail.
Bibliographic Reference: Report: EUR-CEA-FC-1516 EN (1995) 36 pp.
Availability: Available from CEA, Département de Recherches sur la Fusion Contrôlée, Saint-Paul-lez-Durance (FR)
Record Number: 199510533 / Last updated on: 1995-04-11
Original language: en
Available languages: en