An investigation of coupled energy and particle transport in tokamak plasmas

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Abstract
This paper examines some experimental evidence for coupling between particle and energy transport in tokamak plasmas and presents analytical and numerical investigations of this type of transport. This coupling generally leads to discrepancies between the effective thermal diffusivities inferred from analyses of power balance and perturbation measurements. Such discrepancies have been observed experimentally. Comparisons are presented between the results from the numerical solution of a coupled transport model and data from experiments with modulated heating carried out on the DITE machine. The salient features of coupled transport have been assessed and demonstrated to be fully consistent with experimental data: it has been shown that transport matrices with relatively large off-diagonal components can lead to small apparent perturbations of the density, when the energy balance is perturbed, whilst still affecting the thermal transport considerably. Furthermore, perturbation measurements, used in conjunction with predictive transport codes, have emerged as a useful technique for validating transport models.