COMBINED ANALYSIS OF STEADY-STATE AND TRANSIENT TRANSPORT BY THE MAXIMUM-ENTROPY METHOD

A new maximum entropy approach has been applied to analyse three types of transient transport experiments. For sawtooth propagation experime nts in the ASDEX Upgrade and ECRH power modulation and power-switching experiments in the Wendelstein 7-AS Stellarator, either the time evol ution of the temperature perturbation or the phase and amplitude of th e modulated temperature perturbation are used as non-linear constraint s to the chi(e) profile to be fitted. Simultaneously, the constraints given by the equilibrium temperature profile for steady-state power ba lance are fitted. In the maximum entropy formulation, the flattest chi (e) profile consistent with the constraints is found. It was found tha t chi(e) determined from sawtooth propagation was greater than the pow er balance value by a factor of five in the ASDEX Upgrade. From power modulation experiments, employing the measurements of four modulation frequencies simultaneously, the power deposition profile as well as th e chi(e) profile could be determined. A comparison of the predictions of a time-independent chi(e) model and a power-dependent chi(e) model is made. The power-switching experiments show that the chi(e) profile must change within a millisecond to a new value consistent with the po wer balance value at the new input power. Neither power deposition bro adening due to suprathermal electrons nor temperature or temperature g radient dependences of chi(e) can explain this observation.