Investigation of coupled energy and particle transport

Most theoretical models of coupled transport predict particle and thermal fluxes that are each driven by both density and temperature gradients; one would therefore expect some form of coupling between the energy and particle transport. This contrasts with the assumptions usually made when analysing tokamak thermal transport by equilibrium and dynamical techniques, namely that the thermal flux is driven solely by a temperature gradient and that the thermal diffusivity is a function of radius only. Coupled transport has been invoked as an explanation of the discrepancies between χeff values deduced from perturbation and power balance measurements (the former typically being higher than the latter) observed on several tokamaks. The present investigation into coupled transport is motivated by results from the ECRH modulation experiments carried out on the DITE tokamak. Here, in contrast with other experiments, the values of χeff inferred from modulation experiments and from power balance and sawtooth heat pulse propagation were all in good agreement, provided that allowance was made for the broadening of the ECRH deposition profile at the higher densities. This paper addresses whether coupled transport can be present even when the various values of χeff are in agreement, as in the DITE experiments. (author) 4 refs., 3 figs., 1 tab