A model for electron transport barriers in tokamaks, tested against experimental data from RTP

Abstract

Recent experiments in the RTP tokamak have shown that the electron temperature, Te, profile in EC heated L mode discharges can have only a small number of distinct profile shapes, depending on the location of the additional heating. The sharp transitions between the profile shapes are associated with the loss or gain of a low rational q surface. These observations suggest that the electron thermal diffusivity χe is a direct function of the safety factor q, with alternating layers of low and high χe. It is shown that such a model not only excellently describes the distinct profile shapes but also predicts other, observed but so far unexplained, phenomena, such as sharp off-axis maxima of Te observed with off-axis heating at specific radii.