Analysis of ECRH switch on/off events in ASDEX Upgrade

In this paper transient phenomena related to the electron heat transport when electron cyclotron resonance heating (ECRH) power is switched on or off are investigated by predictive and interpretative transport analysis. In the latter two numerical approaches-one based on the transport code ASTRA and the other by COBRA code-are compared. The transport simulations were done in the ASTRA code based on a critical del T-e/T-e model. The results for the evolution of the electron temperature in steady state and transient phases are compared with the experiment. The changes of the heat diffusivity with the ECRH power are compared with the results of the transport calculations from the interpretative analysis. The critical del T-e/T-e model reproduces well both the heat diffusivity and the electron temperature evolution in the region outside the ECRH deposition, and the results show good agreement with the experimental data there. The model cannot recover the electron temperature changes inside the ECRH deposition region with accuracy due to the simple assumption made in transport below the threshold.