Heat pulse propagation: Diffusive models checked against full transport calculations

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Abstract
The problem of deducing χe from heat pulse propagation measurements is addressed. An extended diffusive model is described, which takes into account perturbed sources and sinks. χe is expressed as a function of two observables, the heat pulse velocity vHP and the radial damping rate α. A simple expression is derived in the typical heat pulse measuring region, i.e. 0.1 to 0.2 a outside of the sawtooth mixing radius: χe = 4.3 a vHP/α. Here, vHP and α are defined for cylindrical geometry, hence corrected for Shafranov shift and possible elongation of the plasma. This expression is checked against full transport simulations and found to be accurate. It is also shown that the thus inferred χe is a local value, not affected by the χe profile outside the measuring region.