Evidence of coupling of thermal and particle transport from heat and density pulse measurements in JET

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Abstract
The evolution of electron temperature and density perturbations in a Tokamak following a sawtooth collapse is considered. An integrated numerical analysis of such perturbations is presented, which uses the complete time evolution after the collapse. The method takes into account coupling between heat and particle transport, the effects of the inward propagating density pulse due to a change of recycling at the edge when the heat pulse reaches the limiter, as well as the observed damping of the heat pulse, mainly due to electron-ion energy exchange. Heat and density pulses in JET have been simulated with the method, yielding the four elements of the linearized transport matrix. Certain features of the measurements, notably an initial decrease in the local density, can be explained by the presence of nonzero off-diagonal terms in the matrix.