Electron thermal transport barriers in RTP: experiment and modelling

Experiments in which very localized electron cyclotron heating (ECH) is scanned through the RTP plasma show sharp transitions, in which the electron temperature profile abruptly changes shape. The phenomenology - the profiles shapes, the sharp transitions - can be reproduced with a transport model which features electron transport barriers near all (half-) integer q values. This model is tested against ECH deposition scans in seven series of typically 60 discharges. Between the series qa and were varied: 4x1019 m-3<4.5. For a single scan, the model parameters are fixed. The model is capable of reproducing all data sets. A sensitivity analysis shows that the determination of the strength of the barriers at integer q values is very stable. These barriers show a trend χe(barrier)∼-1, while the dependence on qa is weak. The model reproduces the and qa components of L-mode scaling of global confinement. (author)