The spectral line emissions from impurities injected using the laser ablation technique have been modelled in order to deduce impurity transport coefficients in the Advanced Toroidal Facility (ATF). The transport is found to be mainly diffusive, with little or no convective component. To reproduce the observed line emission it is necessary to postulate a radially dependent diffusion coefficient. For plasmas heated by electron cyclotron frequency waves the impurity transport is best fitted with a diffusion coefficient of 1000 cm2/s in the centre, increasing to 5000 cm2/s at the plasma edge. The global impurity particle confinement time for these plasmas is 65 ms and is considerably larger than the corresponding energy confinement time. Plasmas heated by high energy neutral particle beams display different impurity transport, with the best fit being a diffusion coefficient that is peaked on axis (5000 cm2/s) and that decreases towards larger minor radii (500 cm2/s at the plasma boundary). These transport coefficients have been successfully used to simulate the evolution of intrinsic impurities as well as laser ablated impurities in ATF
Impurity injection experiments on the Alcator C tokamak