Measurement of iron transport in the TFTR tokamak by charge exchange recombination spectroscopy

Abstract
Transport of iron in TFTR discharges heated by 6.7 MW of co-injected neutral beam power has been studied by spatially resolved charge exchange recombination spectroscopy in the visible region of the spectrum. The time evolutions of the densities of Fe24+ and Fe23+ ions following injection of iron are modelled by the neoclassical flux plus a moderately hollow diffusivity, increasing linearly from 1.3 m2/s on axis to 2.4 m2/s at the plasma edge. For r/a > 0.5, the iron diffusivity is significantly smaller than the helium diffusivity measured in identical discharges, while it is larger in the region immediately surrounding the plasma axis.