Resolving Apparent Differences between Heat and Density Pulse-Propagation in Jet and Text

Sawtooth induced heat and density pulse measurements reported in the literature for the JET and TEXT experiments are discussed. In JET the heat pulse travels ten times faster than the density pulse, but in TEXT both pulses travel at the same speed. The measurements are analysed using coupled transport equations for energy and particles. It is shown that the different behaviour of the density pulse in the two experiments can be attributed to differences in the off-diagonal elements of the transport matrix. If the perturbed fluxes of heat and particles are expressed as linear combinations of the thermodynamic forces del p and del T (rather than del n and del T), the corresponding transport matrices are remarkably similar. However, minor differences in this transport matrix between JET and TEXT account for the qualitative difference in the density pulses.