ECRH power deposition studies in ASDEX Upgrade

In this paper the calculated ECRH power deposition profiles pECRH(rho) are compared with the experimentally derived ones in ASDEX Upgrade. ECRH power deposition is calculated by the beamtracing code and with its help the pECRH(rho) behaviour at different ECRH scenarios is investigated. Experimentally, power deposition can be obtained from electron temperature differences dT(e) after switching on/off ECRH or from the perturbed electron temperature (T) over tilde (e) when modulated ECRH is applied. The complete experimental recovery of the pECRH(rho) requires the determination of its maximum, centre rho(0) and width w(0). The centre of the deposition rho(0) is determined experimentally from the temperature response, from dT(e) after switching on/off ECRH or alternatively from (T) over tilde (e) in modulated ECRH experiments. The measured width is broadened quickly by perpendicular heat transport, which makes the experimental determination of w(0) very difficult. A scheme in which off- axis cw ECRH is applied in order to reduce the transport in the core plasma, where the modulated ECRH is deposited, is used in the determination of w(0). We estimate the ECRH deposition width w(0) in an indirect way, in which (T) over tilde (e)(rho) profiles determined experimentally from FFT are compared to those calculated with the transport code ASTRA. Finally, the total absorbed ECRH power is obtained experimentally by using a self-consistent power balance scheme