Thermal wave studies of electron transport using modulated ECRH

Abstract

Modulated ECRH has been used to study electron thermal transport in DITE. In most cases the spatial structure of the thermal waves produced is consistent with a simple diffusive transport model in which the heat flux is proportional to the electron temperature gradient, q = -neχe ∇Te. At low density (ne ≈ 1019 m-3) the values of electron thermal diffusivity deduced from modulation experiments (χemod) are ≈ 2.5 m2.s-1, similar to the values deduced from power balance analysis (χePB and sawtooth heat pulse propagation (χest). At higher density (ne ≈ 3 × 1019 m-3) the interpretation of the modulation data is sensitive to details of the ECRH power deposition profile. The high density data are fitted best by assuming that approximately 30% of the ECRH power is deposited with a broad profile with the remainder more localized, in qualitative accordance with ray tracing code predictions. The values of χemod deduced are then ≈ 1.3 m2.s-1, again similar to the values of χePB and χest