Heat-Pulse Propagation in Tokamaks and the Role of Density Perturbations

Studies of the propagation of heat pulses, launched by a sawtooth collapse or by modulated auxiliary heating, yield information on transport properties in the tokamak. Corresponding values of the thermal conductivity are often found to be significantly larger than values obtained from power balance calculations. A full treatment of the heat-pulse must, however, include possible coupling to an associated density pulse. Such effects are discussed in the context both of neoclassical transport theory and of a model of anomalous transport due to drift waves. It is found that the discrepancies between heat-pulse and power balance measurements could arise from coupling between density and temperature perturbations due to the presence of off-diagonal terms in the transport matrix.