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The origin of density profile peaking due to impurity puffing and the anomalous particle pinch are explored by computer simulations with special versions of the 1.5-D BALDUR predictive transport code. Transport analysis of high density H mode plasmas with strong neon puffing and density profile peaking yields a new scaling law for the anomalous inward drift velocity. This scaling implies that the anomalous inward drift velocity divided by the diffusion coefficient is directly proportional to Z(eff) and thus the anomalous inward drift velocity is directly proportional to Z(eff), since the diffusion coefficient is found to be independent of this parameter. The strong density profile peaking is caused by the increase in Z(eff) and by an enhanced factor F discovered during neon puffing. The time evolution of F correlates with the neon influx rate, but not with the content and the power losses due to line radiation and ionization. The factor F rises with growing influx rate and depends nonlocally on the region where inelastic collisions prevail. One plausible mechanism for the enhancement of F is that inelastic collisions between fluctuating electrons and impurity ions change the dissipative part of the fluctuating electron distribution.

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Authors: BECKER G, Max-Planck-Institut für Plasmaphysik, Garching bei München (DE)
Bibliographic Reference: Article: Nuclear Fusion, Vol. 36 (1996) No. 12, pp. 1751-1758
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