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An important point for turbulent transport consists in determining the scaling law for the diffusion coefficient D due to electrostatic turbulence as function of the control parameter A, where A is approximately equal to E divided by (omega x B). It is well known that for weak amplitudes or large frequencies, the reduced diffusion coefficient ID (approximately equal to D divided by omega or A{gamma}) has a quasilinear like (or gyro-Bohm like) scaling (gamma=2), while for large amplitudes or small frequencies it has been traditionally believed that the scaling is Bohm-like (gamma=1). Recently a percolation critical exponent (gamma=0.7) has been predicted by Isichenko. This aims to test this prediction for a given realistic model. The problem is studied by direct simulation of particle trajectories. Guiding centre diffusion in a spectrum of electrostatic turbulence is computed for test particles in a model spectrum. The spectrum involves only one frequency but a large number of randomly phased electrostatic plane waves, propagating isotropically in the plane perpendicular to the confining strong magnetic field, their amplitudes depending on wavelength in order to reproduce the K{-3} domain of the observed spectrum in Tokamaks. The results indicate compatibility with the Isichenko percolation prediction.

Additional information

Authors: REUSS J-D, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR);MISGUICH J H, CEA, CEN Cadarache, Saint-Paul-lez-Durance (FR)
Bibliographic Reference: Report: 1564 EN (1996) 24pp.
Availability: Available from Association Euratom-CEA, CEN Cadarache, 13108 Saint-Paul-lez-Durance (FR)
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