Eur. Phys. J. D 54, 399-407 (2009)
https://doi.org/10.1140/epjd/e2009-00123-8

Simulations of anomalous ion diffusion in experimentally measured turbulent potential

¹ Faculty of Mathematics and Physics, Charles University in Prague, Ke Karlovu 3, 12116 Prague, Czech Republic
² Institute of Plasma Physics AS CR, v.v.i., Za Slovankou 1782/3, 18200 Prague, Czech Republic
³ Faculty of Nuclear Engineering, Czech Technical University, Brehova 7, 11519 Prague, Czech Republic

Corresponding author: ^a jakub.seidl@email.cz

Received: 14 September 2008
Revised: 2 March 2009
Published online: 17 April 2009

Abstract

The diffusion of plasma impurities in tokamak-edge-plasma turbulence is investigated numerically. The time-dependent potential governing particle motion was measured by 2D array of 8×8 Langmuir probes in edge region of CASTOR tokamak. The diffusion of particles is found to be classical in the radial direction, but it can be of an anomalous Lévy-walk type in the poloidal direction. The diffusion is found to be dependent on the ratio of particles' mass and charge. When this ratio grows, the diffusion coefficient in radial direction grows as well, whereas poloidal diffusion coefficient drops down. Moreover, movement of particles in the time-frozen snapshot of this potential is investigated showing that also the time-independent potential is much more favorable for the particle diffusion in poloidal direction than in radial one. In the case of single ionized carbon ions the poloidal diffusion in time-independent potential transits to the Lévy-walk type for temperatures greater than 25 eV, for radial diffusion Lévy-walk was not observed even for 500 eV.